the arboviruses - paráiah.iec.pa.gov.br/.../thearbepidemiolecol1988v3p38...40 the arboviruses:...

Editor

Thomas P. Monath, M.D.Director

Division of Vector-Bome Viral DiseasesCenters for Disease Control

Public Health ServiceV.S. DepaI1ment of Health and Human Services

Fort Collins, Colorado

CRC Press, locoBoca Ratoo, Florida

~.

The Arboviruses:Epidemiologyand

Ecologyv o 1 urne III

LIBRARY OF CONGRESSLibrary of Congress Cataloging-in-Publication Data

The Arboviruses : epidemiology and ecology/editor, Thomas P. Monath.p. cm.

Includes bibliographies and indexes.ISBN 0-8493-4385-2 (v. 1)ISBN 0-8493-4386-0 (v. 2)ISBN 0-8493-4387-9 (v. 3)ISBN 0-8493-4388-7 (v. 4)ISBN 0-8493-4389-5 (v. 5)1. Arbovirus diseases. 2. Arbovirus diseases--Epidemiology.3. Arthropod-bome viroses. I. Monath, Thomas P.

[DNLM: I. Arbovirus Infections--occurrence. 2. ArbovirusInfections--transmission. 3. Arboviruses. WC 524 A6658]QR201.A72A69 1988

616'.0194--dcI9DNLM/DLCfor Library of Congress 87-29992

CIP

This book represents inforrnation obtained from authentic and highly regarded sources. Reprinted material isquoted with permission, and sources are indicated. A wide variety of references are listed. Every reasonable efforthas been made to give reliable data and inforrnation, but the author and the publisher cannot assume responsibilityfor the yalidity of aIl materiaIs or for the consequences of their use.

AlI rights reserved. This book, or anyparts thereof, may not be reproduced in any form without written consentfroro the -publisher.

Direct ali inquiries to CRC Press, Inc., 2<XM) Corporate Blvd., N.W., Boca Raton, Florida, 33431

C> 1988 by CRC Press. Inc.

Intemational Standard Book Number 0-8493-4385-2 (v. I)Intemational Standard Book Number 0-8493-4386-0 (v. 2)Intemational Standard Book Number 0-8493-4387-9 (v. 3)Intemational Standard Book Number 0-8493-4388-7 (v. 4)Intemational Standard Book Number 0-8493-4389-5 (v. 5)

Library of Congress Card Number 87-29992Printed in the United States

Volume llJ 37

Chapter 26

THE EPIOEMIOLOGY OF DISEASES CAUSEO BY VIRUSES IN GROUPS CANO GUAMA (BUNY A VIRIOAE)

Robert E. Shope, John P. Woodall, and Amelia Travassos da Rosa

T ABLE OF CONTENTS

I. Historical Background 38

11. TheViruses 38

111. Diseases Caused by Viroses of Groups C and Guama 40

IV. Epidemiology 41A. Distribution 41B. Incidence 41C. Season ; 41D. OtherRiskFactors 41E. Serological Epidemiology 41

V. TransmissionCycles 42A. Evidence from Field Studies 42B. Evidence from Experimental Infection Studies 46

VI. Ecological Dynamics: Mammal Recapture Programs in Brazilian andTrinidadian Forests 47A. Experimental Design 47B. Virus Isolations and Seroconversions in Rodents and

.Marsupiais... 47C. Influence of Host Species, Age, Habitat, Time of Day, and

Season on Prevalence of Vertebrate Infections 48D. Influence of Vector Associations on Prevalence of

Vertebrate Infections J 49

VII. Surveillance, Prevention, andControl 50

VIII. FutureResearch 51

Acknowledgments 5:

References 51

The Arboviruses: Epidemiology and Ecology38

I. HISTORICAL BACKGROUND

Viroses of group C and group Guama were among the first agents isolated in 1954 whenresearchers of the Special Service of Public Health of Brazil and the Rockefeller Foundation I

set out to find the causes of human fevers at Belém, Brazil, near the mouth of the AmazonRiver. They noted that the fevers occurred in workers imported from northeastern Brazil toclear forests for planting pepper and robber, and in Japanese colonists settling in forest-fringe communities. They also noted that lifelong residents of the city of Belém became illif they entered the forest. Initially, tive different group C viroses and one virus in groupGuama were isolated from seTa of nonimmune Cebus monkeys placed in the forest assentinels, and another, different group Guama virus was isolated from acute-phase serumof a febrile worker clearing forest at the Oriboca Plantation, 20 km east of Belém. Theproject director, Ottis Causey, had the idea (which he and his colleagues later proved to becorrect) that the viroses were being transmitted by forest and forest-fringe mosquitoes, thatthose persons who entered the forest were at highest risk, and that the viroses were uniqueto the Amazon forests, and therefore persons from Japan and northeastern Brazil were fullysusceptible because they had not previously been exposed.

The viroses were isolated by intracerebral inoculation of seTa into baby mice. The isolateswere sent for comparison with other arboviruses at the Rockefeller Foundation Virus Lab-oratories in New York. In the mid-1950s the New York laboratory was making rapid progressin grouping a large variety of newly isolated arboviruses from various parts of the world.Casais and Whitman2.3 found the new agents to be distinct and to form two serogroups. Thetive viroses from sentinel monkeys were classified as group C to differentiate them fromgroup A (alphaviruses) and group B (flaviviruses). The other two viroses were initially toconstitute group D, but because of the growing concern that there would be more groupsthan there were letters, it was decided to utilize the name Guama, which was the first virusof the group to be isolated.

In 1957, the Brazilian workers substituted mice for monkeys as sentinels; mice provedhighly efficient as a surveillance mechanism. This observation led others to try sentinel miceand hamsters in Trinidad, Peru, Mexico, Panama, Colombia, and Florida, with the resultthat group C and/or group Guama viroses were isolated in each of these locations.4 Thereare now known to be 13 viroses in group C and 12 in group Guama.4.s Ali are foundassociated with low-lying, usually swampy forests in the New World tropics and subtropics,and ali are transmitted by culicine mosquitoes to small rodents, primates, and marsupiais.

The primary public health impact of the viroses in the two groups is on persons whoseoccupation takes them into the forest, for instance, members of geological expeditions,harvesters of nuts, lumber, or rubber, and military personnel. These viroses do not causeepidemics or fatal disease, but they are commonly responsible for severe, self-limited,disabling febrile illnesses which at times have led to significant loss of productivity for thosein forest occupations.

11. THE VIROSES'

Group C and Guama viroses belong to the family Bunyaviridae.6 The particles are 90 to100 nm diameter spheres with lipid-containing envelopes. The genome is single-stranded,three-segmented, negative-sense RNA which can reassort genetically. This is an importantproperty reflected in the occurrence of strains in nature which have apparently reassorted toyield progeny with properties of each of two commonly encountered parent viruses.2 Thevirions contain a nucleocapsid protein and two surface glycoproteins. Replication occurs inthe cytoplasm, both in vertebrate and insect cells, in close association with the Golgiapparatus.

39Volume 111

Table 1DISTRIBUTION AND SOURCES OF VIR USES IN GROUPS C AND GUAMA

Antigenic relationships of the viroses within each group have been shown by complement-fixation (CF), neutralization (N), hemagglutination-inhibition (HI), immunofluorescence,and enzyme-linked immunosorbent assay (ELISA). There are four serologic complexes ingroup C and two in group Guama (Table I). The N and HI tests measure reactivity of thesurface glycoproteins; the major CF antigen is the nucleocapsid protein. Monkeys immunized

GeographicGroup Complex Type Subtype distribution Source

C Caraparu Caraparu Brazil, Trinidad, Pan- Mosquitoes, humans, ro-ama, French Guiana, dentsSuriname

assa Panama Mosquitoes, humans, ro- .dents

Apeu Brazil Mosquitoes, humans,

marsupiaisVinces Ecuador Mosquitoes, sentinel

hamstersBruconha Brazil Mosquitoes

Madrid Madrid Panama Mosquitoes, humans, ro-dents

Marituba Marituba Brazil, Peru Mosquitoes, humans,

marsupiaisMurutucu Brazil, French Guiana Mosquitoes, humans, ro-

dents, marsupiaIsRestan Trinidad, Surinam Mosquitoes, humans

Nepuyo Trinidad, Brazil, Hon- Mosquitoes, humans, ro-duras, Mexico, Pan- dents, batsama, Guatemala

Gumbo Limbo Florida (V.S.) Mosquitoes, rodentsOriboca Oriboca Brazil, Trinidad, Suri- Mosquitoes, humans, ro-

name, French Guiana dents, marsupiaisItaqui Brazil, Venezuela Mosquitoes, humans, ro-

dents, marsupiaIsGuama Guama Guama Brazil, Trinidad, French Mosquitoes, phlebotom-

Guiana, Peru, Suri- ines, humans, rodents,name, Panama marsupiaIs, bats

Moju Brazil Mosquitoes, rodents,

marsupiaIsAnanindeua Brazil Mosquitoes, rodents,

birds, marsupiaIsMohogany Hammock Florida (V.S.) Mosquitoes, rodentsBimiti Trinidad, Brazil, French Mosquitoes, rodents

Guiana, Suriname,Peru

Timboteua Brazil RodentsCato Brazil, Trinidad, French Mosquitoes, humans

GuianaMirim Mirim Brazil Mosquitoes, sentinel

miceBertioga Brazil Mosquitoes, sentinel

miceCananeia Brazil Mosquitoes, sentinel

miceGuaratuba Brazil Mosquitoes, birds, senti-

nel rodentsItimirim Brazil Rodents

40 The Arboviruses: Epidemiology and Ecology

with a group C virus resisted infection when challenged with a heterologous group C virus,7and therefore lhe antigenic classification has epidemiologic significance.

Some of lhe viroses in group C forro pairs which share CF reactivity, i.e., Caraparu andItaqui, Murutucu and Oriboca, and Apeu and Marituba. These same viroses forro differentpairs which are closely related by neutralization and HI, i.e., Itaqui and Oriboca, Caraparuand Apeu, and Murutucu and Marituba. These pairings of viroses which are found in lhesame Brazilian forest were useful for rapid identification,8 and may possibly be explainedon lhe basis of genetic reassortment of viroses which coinfect hosts and/or vectors in lheforest.

The group Guama viroses are closely related by lhe CF test, but most serotypes are quitedistinct by HI and N. It was originally thought that group C viroses were not related togroup Guama viruses,2,3 but subsequently HI cross-reactivity was noted at a low level,9consistent with lhe remarkably similar biological and ecological properties of viroses in both

groups.Serum of mice and hamsters infected with viroses of both groups agglutinate goose red

blood cells. The HI test has been used effectively as a type-specific survey method inecologic studies of rodents and marsupiais, and for serosurvey of monkey and humanpopulations in lhe American tropics.

111. DISEASES CAUSED BY VIR USES OF GROUPS C ANO GUAMA

Persons infected by group C and group Guama viroses develop rever of sudden onsetranging from 38 to 40°C. Patients with group Guama virus infections usually have lowergrade fevers than those with group C infections. Severe headache is the dominant complaint.Vertigo, backache, and/or muscle and joint paios are seco in nearly 2/3 of cases, and nauseaand photophobia in about 1/3. The rever lasts from 2 to 5 days and is sometimes biphasic.Rash is absent; however, conjunctival injection is sometimes noted. Leukopenia is recordedin some cases. Patients recover with weakness and anorexia lasting 1 or 2 weeks, but withoutsequelae. The initial observations were made in 1955 of Brazilian laborers in the OribocaForest, near Belém, Brazil.' These men earned hourly wages, were not paid when sick, andtherefore were assuredly incapacitated when they sought medical assistance. They commonlywere out of work for 3 to 7 days when infected with viroses of group C or group Guama.

The incubation period is not known, but is probably less than 10 days based on knownperiods of forest exposure. Patients gave a history of exposure in the forest or at the forestfringe, and often of exposure during the evening. One Brazilian member of a field epide-miology team had beco employed for 5 years during the daytime in the Utinga Forest withoutserious febrile illness. He was reassigned in 1964 to collect mosquitoes at dusk. Within a2-week period he developed rever, backache, weakness ofhis legs, and leukopenia. Caraparuvirus (group C) was isolated from bis blood. He retumed to work in the forest to continueevening mosquito collections, and within another 2 weeks bis rever recurred. This time Catovírus (group Guama) was isolated from bis blood.

Several field-acquired infections and one laboratory infection have had similar febrilecourses. The source of infection in the laboratory case of Apeu rever is not known, but theexposure was assumed to be aerosol1o assa and Madrid viroses were isolated from ento-mological field workers in Panama,11 Cato virus from a febrile patient in Trinidad,12 andNepuyo virus from febrile field workers in Guatemala.13 There have beco 10 of the 13 groupC serotypes and 2 of the 12 group Guama serotypes isolated from febrile cases (Table 1).The apparent-to-inapparent infection ratio is not known.

Volume /11

41

IV. EPIDEMIOLOGY

A. DistributionGroup C and group Guama viroses are found only in lhe American tropics and subtropics,

including Florida, Central America, northern South America, and southern Brazil. Theirdistribution is limited by their requirement for specific mosquitoes and vertebrate hosts.Most of lhe types and subtypes have focal distribution which coincides with forest or forest-fringe habitats, usually in 10w-Iying, swampy areas. Of lhe 25 types and subtypes listed inTable I, 15 are found only in one country and restricted to one known focus. Seven others,Caraparu, Murutucu, Oriboca, Itaqui, Guama, Bimiti, and Caiu, are found in northern Brazilplus Trinidad and/or French Guiana, Suriname, and Panama. Itaqui is found in Brazil andVenezuela, and Restan is found in Trinidad and Suriname. Nepuyo virus has lhe widestdistribution, possibly because it infects bats which fly long distances. In contrast, lhe viroseswhich infect less mobile animais, i.e., rodents and marsupiais, are limited to one focus.

B. lncidenceThe incidence of human infection depends directly on exposure. A study of 500 Dutch

military personnel stationed for 1 year in Suriname showed that seroconversion occurred 7.4times per 100 soldier years using three group C antigens.14 The cate in some units, however,was as high as 22%, indicating that these soldiers probably had been stationed at some timeduring the year in a focus of group C virus-infected mosquitoes. Bensabathl5 comparedantibody cates to group C viroses in persons living in the center of Belém with antibodycates in persons living at the periphery of the city, bordering the forest. People living near,.the forest had a higher prevalence of antibody.

C.

SeasonAn accurate tabulation of seasonality cannot be made since only small numbers of patients

with groups C and Guama vinIs infections have beco recorded. It can be taken as an articleoffaith, however, that human infections will occur at the time of greatest natural transmission,which is the rainy season in tropical raio forest climates.16

D. Other Risk FactorsThere is no reason to believe that susceptibility varies with sex or face. The group C and

Guama rever cases which have been recorded have been predominantly in young adult males.The major risk factor is occupation, which almost certainly explains the age and sex bias.Persons are at risk who enter the forest to collect nuts, tap rubber trees, or relI trees forlumber. Military forces engaged in jungle operations, especially if exposed at dusk anddawn, are also at higher risk of infection.

There are no epidemics, and the apparent-to-inapparent infection ratio is not recorded.

E. Serological EpidemiologyThe HI and N tests have been used to survey for antibody to group C viroses. Results of

HI tests (Shope and Travassos da Rosa, unpublished, Table 2) of human seca from lheBrazilian Amazon revealed widespread antibody to lhe Oriboca, Marituba (represented byMurutucu subtype), and Caraparu complexes. Oriboca antibody was localized mostly in ParáState, and Murutucu in Pará and Amazonas States. These were not common infections.Caraparu antibody, on lhe other hand, was widely distributed and common, especially inAmazonas, where over a third of lhe indigenous people of some communities reacted.

A survey in lhe Ribeira Valley of coastal São Paulo State, Brazil revealed that 4.6% of516 residents, and 14.5% of 83 road workers who camped close to lhe forest, had Caraparuantibody.17.18 Antibodies have been found to three group C viroses in Suriname14 and toNepuyo vírus in Honduras.19

Serological survey results of group Guama antibodies have not been reported except forthe finding ofneutralizing antibody to Bimiti viros in one ofsix persons sampled in Trinidad.20

V. TRANSMISSION CYCLES

A. Evidence from Field StudiesExtensive studies to determine the natural vectors and hosts of groups C and Guama

viroses were carried out as part of the Rockefeller Foundation arboviros program in colla-boration with the govemments of Brazil and Trinidad. The evidence for transmission ofgroup C viroses as reviewed by WoodaWI implicates culicine mosquitoes and small mam-mais. Similar cycles exist for group Guama viroses.

The potential arthropod vectors of viroses in groups C and Guama are listed in Tables 3and 4. The listing is based on isolation of viros from the arthropod, or in some cases thetransmission of the viros from naturally infected mosquitoes to laboratory mice or hamsters.Guama was transmitted three times by Culex portesi, and once each by Cx. taeniopus.vomerifer. and B17; Mirim once by Cx. taeniopus; Caraparo once by Culex spp.; assa fivetimes by Cx. vomerifer and once by Cx. taeniopus; Marituba once by Cx. portesi; Nepuyoonce by Culex spp.; and Oriboca once by Cx. portesi. Transmission by naturally infectedmosquitoes is the best evidence so far available that these species are involved. All of thesetransmissions were by mosquitoes of the Culex subgenus Melanoconion, which algo pre-dominate among the sources of viros isolations. The evidence favors transmission by Me-lanoconion mosquitoes of alI 'group C viroses with the possible exception of Apeu, whichhas been isolated algo from Aedes. Isolates from Diptera other than M elanoconion mar meanthat the insect had recently fed on a viremic animal and retained infected gut contents, orthat it mar be an occasional vector only.

The evidence algo points to Culex (Melanoconion) mosquitoes as vectors of group Guamaviroses, but Timboteua and Itimirim viroses have not yet been isolated from mosquitoes,and others have been isolated too infrequently to draw a conclusion.

The Melanoconion are noctumal forest mosquitoes of the Americas, most active at dusk

State or


Table 2GROUP C HI ANTIBODY IN HUMANS OF THE BRAZILIAN

AMAZON

% positive with antigen of

43Volume III

Table 3POTENTIAL ARTHROPOD VECTORS OF GROUP C VIRUSES4,5,21

Table 4POTENTIAL ARTHROPOD VECTORS OF GROUP GUAMA VIRUSES4,s,zl

Culex

(Melonoconion) Other DipteraOther Culex Aedes

Undesignated (10) Undesignated (I) Mansonia (I)Limatus (I)Psorophora (I)Trichoprosopon (I)Lutzomyia (sand fly) (I)

Guarna portesi (93)"vomerifer (9)taeniopus (1)

Table 3POTENTIAL ARTHROPOD VECTORS OF GROUP C VIRUSES4,s,21

CulexVírus (Melanoconion) Other Culex Aedes Other Diptera

Caraparu a;kenii complex (2)" (Cx.) coronator (I) L;matus durham;; (I)sp;ss;pes (2) (Cx.) n;gr;palpus (I) Wyeomy;a med;oal-

b;pes (I)portes (22) (Eubonnea) acceler- Undesignated Sabeth-

ans (3) in; (I)vomerifer (14) (Eu.) amazonens;s Mixed pool (I)

(I)

Undesignated (2) Undesignaled (5)Ossa taen;opus (I)

vomerifer (6)Apeu a;ken;; complex (4) arboreal;s (I)

Undesignated (I) septemstr;atus (I)Vinces vomerifer (3)Bruconha sacchettae (5)

Undesignated (I)Madrid vomerifer (5)Marituba a;ken;; complex (2) Mixed species (2)

portes; (I)Undesignated (2)

Murutucu portes; (5) Undesignated (2) Coqu;llett;d;aa;ken;; complex (4) venezuelens;s (I)vomerifer (I) Undesignated Sabeth-

;n; (I)Undesignated (I)

Restan portes; (2) Undesignated (I)Nepuyo ;olambd;s (I) (Eu.) accelerans (I)

Undesignated (5)Gumbo Limbo Undesignated (61) taen;orhynchus (2)Oriboca portes; (46) Undesignated (6) taen;orhynchus (4) Coq. venezuelens;s

(I)a;ken;; complex (6) Coq. arr;balzaga; (I)sp;ss;pes (I) Manson;a spp. (I)Undesignated (I) Psorophora ferox (I)

Sabeth;n; (2)Mixed species (I)

ltaqui sp;ss;pes (I) Undesignated (I) Mixed species (I)a;ken;; complex (I)

portes; (3)vomerifer (10)

" Numbers of isolations in parentheses (includes laboratory transmission from naturally infected vectors).


Table 4 (continued)POTENTIAL ARTHROPOD VECTORS OF GROUP GUAMA VIRUSES4,S,11

Culex(Melanoconion) Other DipteraVirus Other Culex Aedes

Moju portesi (I)vomerifer (8)Undesignated (2)

Ananindeua portesi (3) BI9 complex (14)taeniopus (2) B27 (5)vomerifer (I) Undesignated (I)Undesignated (2)

Mahogany Hammock Undesignated (44)Bimiti portesi (19) Undesignated (I)

taeniopus (I)spissipes (I)

Timboteua (No isolations from

arthropods)CaIu portesi (80) Undesignated (12)Mirim taeniopus (I) serratus (I)

Undesignated (I)Bertioga sacchettae (I)Cananeia sacchettae (I)Guaratuba taeniopus (I) serratus (I) An. cruzii (I)ltimirim (No isolations from I

arthropods).Numbers of isolations in parentheses (includes laboratory transmission from naturally infected vectors).

Coq.

venezuelensis (2)Mansonia (2)Sabethini (1)Coq.

venezuelensis (1)Culicoides paraensis (5)

I\nopheles

numbus (I)Psorophoraferox (I)

and dawn. They feed basically on rodents and marsupiaIs, but some species prefer birds,and alI listed in Tables 3 and 4 will also engorge on primates, including humans whenavailable.

The vertebrate hosts of viroses of groups C and Guama are listed in Tables 5 and 6. Themost extensive studies of vertebrate hosts have been conducted in Belém, Brazil and BushBush Forest in Trinidad. Groups C and Guama viroses have also been isolated from wildvertebrates in Florida, São Paulo State (Brazil), and Panama (Table I). The indigenousrodent and marsupial species differ in each of these areas, and therefore the viroses usedifferent sets of hosts. For instance, in the forests near Belém, Oryzomys capito and Proe-chimys guyanensis made up 92% of the animaIs entering traps at ground leveI. In Trinidad,Oryzomys laticeps and Zygodontomys were the predominant rodents at ground leveI. Theserespective sets of animaIs are hosts in the cycle of Caraparu vírus in each site. The BrazilianOryzomys and Proechimys are also hosts of Itaqui, Murutucu, Oriboca, Guama, Moju, andCatu; the analogous Oryzomys and Zygodontomys in Trinidad are hosts of Guama, Bimiti,and Catu viroses in Bush Bush Forest.

Two group C viroses, Apeu and Marituba, and a group Guama vírus, Ananindeua, probablyuse marsupiaIs as their principal hosts. These viroses have been isolated only from marsupiaIs,and marsupiaIs have the highest prevalence of Apeu and Marituba antibody of any animaIstested. In contrast, as suggested by Woodall,21 marsupiaIs may not be susceptible to Caraparuvírus. This vírus has Dever been isolated from a marsupial, although the mosquitoes whichtransmit C'ilfaparu feed on marsupiaIs and marsupiaIs have antibody at low Ievels.

Some cycles of transmission occur at the leveI of the forest floor while other cycles takeplace in the forest canopy. Sentinel mice exposed in the canopy were infected more oftenwith Apeu, Marituba, and Oriboca viroses, while those exposed at ground leveI were infectedmore often with Caraparu and Itaqui viruses.2o This finding correlates with the cycles ofApeu and Marituba viroses in marsupiais, which tend to be canopy dwellers, and the cyclesof Caraparu and Itaqui in forest-floor-dwelling rodents.

Volume /lI 45

Table 5VERTEBRA TE HOSTS OF GROUP C VIRUSES

SerologyVírusísolatíonsVirus Host

~

Caraparu77

4313

assaApeu

MadridMarituba

Murutucu

Gumbo LimboOriboca

Itaqui

Oryzomys capitoO. laticeps

Proechimys guyanensisNectomys squamipesZygodontomys brevicaudaHeteromys anomalusProechimys semispinosusCaluromys philanderMarmosa cinerea

Proechimys semispinosusDidelphis marsupialisCaluromys philanderOryzomys capitoProechimys guyanensisNectomys squamipesDidelphis marsupialisMarmosa cinerea

Bradypus tridactylusProechimys guyanensisNectomys squamipesArtibeus literatusA. jamaicensis

Sigmodon hispidusOryzomys capitoProechimys guyanensisMarmosa cinerea

Didelphis marsupialisOryzomys capitoProechimys guyanensisNectomys squamipesMarmosa murinaMetachirus nudicaudatus

Note: Vinces, Bruconha, and Restan have not been isolated from wild vertebrates.

Maximum monthly HI percent antibody prevalence in Utinga Forest. Brazil. 1962-1966.Maximum quarterly HI percent antibody prevalence in Bush Bush Forest. Trinidad.1960-1963.

Table 6VERTEBRA TE HOSTS OF GROUP GUAMA VIRUSES

Vírusísolatíons

SerologyBrazil'HostVirus

4246283015

Guama 3125

4

Oryzomys capitoProechimys guyanensisNectomys squamipesCaluromys philanderMarmosa cinereaOryzomys laticepsHeteromys anomalusZygodontomys brevicaudaCoendu spp.

Brazil8 Trinidadb

4271

76

16241

12111

I922211

1I

1227

244

311

60

5236

12

17

275

118

7

171236

33343317

.b

The Arboviruses: EpidemioLogy and EcoLogy46

Table 6 (continued)VERTEBRATE HOSTS OF GROUP GUAMA VIRUSES

Virusisolations

SerologyBrazilaHostVirus

Moju 28

508

Ananindeua

Mahogany HammockBimiti

TimboteuaCaIu 39

5367

Oryzomys spp.Proechimys guyanensisNectomys squamipesOecomysDidelphis marsupialisCaluromys philanderDidelphis marsupialisSigmadon hispidusOryzomys laticepsZygodontomys brevicaudaHeteromys anomalus

Proechimys guyanensisProechimys spp.Nectomys squamipesProechimys guyanensisOryzomys capitoOryzomys laticepsZygodontomys brevicaudaDidelphis marsupialisM%ssus obsurus (bat)Xanthomyias virescens

Oryzomys spp.GuaratubaItimirim

Note: Mirim, Bertioga, and Cananeia have not been isolated from wild vertebrates.

Maximum monthly HI percent antibody prevalence in Utinga Forest, Brazil,1962-1966.

B. Evidence from Experimental Infection StudiesEvidence from natural cycles is preferred to evidence from experimental infection because

viroses change on laboratory passage, and vectors and vertebrate hosts may be alteredphysiologically by laboratory conditions. Nevertheless, lhe results of laboratory experimentsreinforce conclusions when they agree with observations in nature. Jonkers and biscolleagues 16.22.23 working in Trinidad showed lhe susceptibility of rodents to groups C and

Guama viroses. Their results correlated closely with field observations. Three of lhe fourgroup C viroses of Trinidad were inoculated into nonimmune rodents and each circulatedviros to high titer. Oryzomys and Zygodontomys were susceptible generally to group Cviroses. Heteromys was tested with Caraparu viros and did not develop viremia. Heteromysalgo was uncommonly infected with Caraparu virus in nature.

The three Trinidadian group Guama viroses induced viremia when inoculated into Ory-zomys and Zygodontomys in lhe laboratory. The viremia titers were lower than those ofgroup C viroses, but again were comparable to titers found in nature. Heteromys was notsusceptible to Guama infection in the laboratory.

Infection of laboratory animaIs has algo been used to determine if immunity to one virosin groups G or Guama inhibits viremia with another viros of lhe same group. Rhesus morl.keyswere susceptible to subcutaneous inoculation of six Brazilian group C viroses, althoughviremia with Itaqui and Caraparu was not consistently observed.24 The monkeys were chal-lenged with heterologous group C viroses and were immune to challenge with seven differentcombinations of primary and challenge viroses.

Cross-immunity was algo demonstrated with group Guama viroses in Trinidadian rodents,although the inhibition of viremia varied with lhe viros combination.23 Catu viros stillcirculated, although at a lower leveI, in animaIs immunized with Bimiti or Guama, while

17184II

7II72III

31622

242I

II

.

Volume 111 47

Guama viremia was almost completely inhibited in animaIs immune to either Bimiti or CatuvIroses.

These cross-challenge experiments offer a plausible explanation why people and rodentsexposed in the forest are not found serially viremic with different viroses of the sameserogroup.

VI. ECOLOGIC OYNAMICS: MAMMAL RECAPTURE PROGRAMS INBRAZILIAN ANO TRINIDADIAN FORESTS

A. Experimental DesignThe interaction of groups C and Guama viroses with their rodent and marsupial hosts was

studied in Brazil and Trinidad. A mammal recapture program was instituted by workers ofthe Belém Virus Laboratory in the Utinga Forest near Belém. Wild rodents and marsupiaiswere captured, bled, marked, released, and periodically recaptured during the period July1962 to November 1964.24.25 Ali together, 1389 animaIs were sampled 8750 times. Ap-proximately half the animaIs were Proechimys guyanensis, the spiny rat, and a further thirdwere Oryzomys capito, the rice rato The remainder were water rats and marsupiaIs of fivegenera and species. AnimaIs were tested for viremia at each capture and, when possible,for HI antibody at 3-week intervals.

Additional biometric data were collected. The animaIs were weighed at each capture, andan age curve for each species was estimated by constructing a weight curve on the time axisand extrapolating the weight curve from birth weight to the weight at first capture. AnimaIswere observed for pregnancy and lactation status. Rectal temperature readings were recordedfor a number of the rodents as they were trapped and retrapped; a battery-operated ther-mometer with calibrated hypodermic thermistor probe was used.

The animaIs were captured in box traps baited with com and banana. The time of capturewas recorded by rigging a string from the trap treadle to the flywheel of an alarm clockwh~ch stopped when the trap closed. The traps were located in a 25-ha square at 150 to 200m intervals. During part of the study, additional traps were placed in an attempt to addprecision to home-range estimates. Other traps were placed on platforms which were elevatedto the tree canopy in order to sample the arboreal marsupiaIs. The home range of an animalwas estimated by recording which traps the animal entered and the distance between trapswhich the animal entered at different recapture events.

B. Virus Isolations and Seroconversions in Rodents and MarsupiaisIt was unusual at any given capture to find viremia. Only 46 or about 0.5% of the blood

samples contained viroses of groups C and Guama. Virus was never isolated in serial samples.The length of viremia is probably less than 5 days since several animaIs were recaptured atintervals of 3 to 5 days. The highest titer viremia was 4.5 log mouse LDsJmt', and onlyseven animaIs had titers greater than 2.7 log mouse LDso. It is probable that samples werenot taken at the peak of viremia, but even so, it can be inferred from the brief and low-titered viremia that the Culex (Melanoconion) mosquitoes must have a low threshold ofinfection for groups C and Guama viroses.

Antibody studies indicated that animaIs were frequently infected later in life with one ormore additional viroses in groups C and Guama. No second episode of viremia was detectedin any rodent or marsupial, either of the same virus or of any other virus in the two groups.This is in contrast to human infection in which group C followed by group Guama viremiahas been documented.

It should be noted that nearly ali the viremias detected in Utinga Forest rodents occurredin young animaIs. The experience with naturally infected P. guyanensis at initial capture isillustrated in Figure I. By the time rodents of this species were old enough to range in

FIGURE 1. Number of Proechimys guyanensis with group Guama antibody byage when flrst captured in Utinga Forest. The circles show the numbers of viremicanimaIs with and without antibody in each age group.

search of food and thus find baited traps, 70%, as deterrnined by antibody studies, hadalready been infected with one or more of the Guama group viruses present in the forest.At the time of viremia, 19 of the rats were negative for Guama group HI antibody; only 2viremic animaIs were positive for Guama group antibody, although a figure of 27 wouldhave been expected on the assumption that rodents with antibody are exposed in the samedegree as those without. These data thus teach the lesson that young, nonimmunized animaIswere the source of vírus. The data algo offer an explanation for the apparently very low cateof viremia in animais captured in the study. Most animaIs were older and already immunewhen flrst trapped; if the very young animais entered the traps, many more individuaIs withviremia would probably have been found.

C. Influence of Host Species, Age, Habitat, Time of Day, and Season on Prevalenceof Vertebrate Infections

The study in Utinga Forest clarified the many factors which influenced the prevalence ofvertebrate infections, and especially of vertebrate viremias. Only two rodent species werefound frequently enough at ground leveI to account for the majority of group C and groupGuama infections. These were the spiny rat (23/46 viremias) and the rice rat (18/46 viremias).Other animaIs such as Nectomys squamipes (the water rat) and marsupiais were viremic insmall numbers in proportion to the small numbers trapped. In Utinga Forest, the groups Cand Guama viruses utilized each of the available rodents and marsupiais, but the spiny andrice rats. were of greatest importance because of their larger numbers.

To be most effective in maintaining the transmission cycle, the spiny rat and rice rat mustbe active at the same hours as Culex (Melanoconion) mosquitoes. The time of maximumactivity of over 400 rodents and marsupiaIs in Utinga Forest, as deterrnined by the clocksattached to the traps, was between 6 and 10 p.m. (Figure 2). Spiny rats had a second lesserpeak at 3 a.m. This feeding activity correlated almost exactly with the Culex (Melanoconion)biting frequency.26

180CJ NO ANTIBODY

160 mm ANTIBODY

O VIREMIC ANIMALS

140(/)>-~~ 120 (f)

wa? 100a.LLO 80a:wlI!~ 60:)

z:: .:~r~~~::I.::I~~:. III I0-170 171-250 251-340 341-500 >500

AGE IN DAYS WHEN FIRST CAPTURED


FIGURE 2. Hour aI which animais enlered traps in Ulinga Foresl marnrnal

recapture programo

Animais were almost Dever caught during the day. Nylon strings were attached to the ratsto find their daytime resting sites. The rats were found to inhabit burrows, sometimes I mor more underground and thus inaccessible to daytime-biting mosquitoes.

Viruses of groups C and Guama are in general focally distributed, and restricted to tropicalrainforest swamp habitat. This is in part explained by the short home ranges of the hostrodents. P. guyanensis and O. capito ranged from 12 to 325 m. The spiny rat ranged fartherthan the rice rat, older animais ranged farther than younger animais, and males farther thanfemales. Since viremia was mostly in younger animais, the chance that a viremic animalwould range very far is small.

Groups C and Guama viroses were transmitted in the Utinga Forest of the BrazilianAmazon during periods in which many young, nonimmune rodents were entering the pop-ulation. Figure 3 shows the estimated date of birth of rice rats based on weight at firstcapture. The figure algo shows that within 2 or 3 months of birth of each new cohort, theprevalence of group C vírus HI antibody Tose rapidly. Antibody levels then fel I betweenNovember and January during each dry season as older animais died, as transmission slowed,and as HI antibody decayed.

D. Influence of Vector Associations on Prevalence of Vertebrate InfectionsInfections of vertebrate animais with groups C and Guama viroses correlated with high

15 -NIGHT HOURS --

12OTHER ANIMALS Includes:

9 Didelphis (26)Marmosa (10)

6 Metachirops (2)

3 Nectomys (18)

cwa: 36::>Il: 30 PROECHIMYS<{

() 24(/)-J

~ 18

~ 12Ll.O 6a:wro~::> 36z

30 ORYZOMYS

24

18

12

6

12 14 16 18 20 22 24 2 4 6 8 10 12

HOUR

I 5 -NIGHT HOURS --

12OTHER ANIMALS Includes:

9 Didelphis (26)Marmosa (10)

6 Metachirops (2)

3 Nectomys (18)

()wa: 36:Jh: 30 PROECHIMYS~() 24CJ).J~ 18~~ 12LLO 6a:wro~:J 36z

30 ORYZOMYS

24

I

I

6

12 14 16 18 20 22 24 2 4 6 8 10 12

HOUR

Volume 111 49


RGURE 3. Estimated birth dates of juvenile Oryzomys capito captured between June 1962 and November1964 in Utinga Forest. Prevalence of Caraparu HI antibody in the same population is shown by the brokenliDe.

population levels of Culex (Melanoconion) mosquitoes. In Utinga Forest these periods fol-lowed the onset of heavy rains and probably were in response to flooding of the swamp.High levels of transmission also coincided with the rapid influx of young, nonimmune

Oryzomys.In the Bush Bush Forest of Trinidad, as in Brazil, groups C and Guama viruses were

transmitted most frequently when populations of Culex (Melanoconion) portesi mosquitoeswere abundant.16 This subgenus of mosquito, in turn, was believed to depend on high levelsof water in the swamp for its breeding.26 A population crash of rodents during 1964 in BushBush Forest, however, left the viruses without vertebrate amplifying hosts, and transmission(as measured by infection of sentinel mice) ceased almost completely.16

WoodaWI has reviewed the host preferences, vector susceptibility, and abundance of theCulex (Melanoconion) mosquitoes involved in transmission of viruses in group C. Thosespecies of mosquitoes which had the highest infection cates fed preferentially on rodents.Bird-feeding species had low infection cates. It was noted, in addition, that closely relatedsubtypes of Carapam vírus in Brazil and Trinidad were transmitted by different M elanoconionspecies. Woodall postulated that there was either a difference in vector susceptibility or agenetic difference between the Brazilian and Trinidadian vírus subtypes.

Transmission cates as measured by infection of sentinel mice generally correlated withthe abundance of Culex (Melanoconion), but there were some unexplained discrepancieswhich may relate to infection cates of mosquitoes, and indirectly to age and parous rates.27

VII. SURVEILLANCE, PREVENTION, ANO CONTROL

Illnesses caused by viroses in groups C and Guama are not reportable, and surveillanceis not maintained. The true impact of these diseases is therefore not known. Nor is there avaccine or any other useful method of prevention or control other than personal measures.These include mosquito repellents, bed nets, and avoidance of the forest habitat of Culex(Melanoconion) mosquitoes, especially from dusk to dawn.

8 8 ,,-,8 5, ~'I, , ," I'8 " / '.' I, /, I I >-

20 I I" I Antibody O\ I I' 1..-

O\ 8 I, I-, .I / \ m\ I '/. 20 ~'8 " ,I

, Z\ ~ , ,,I, I " ct:,I, I, I -

(/)15 8 'I 11' :I:-l ' , I Ict: \ I I I' I :J~ ' " : I 15 a:-\ I I \ ct:

~ \ i : ~u. \ I I a:O 10 \/ ~

ffi ~ 10 ~m~ w:J UZ Z

W-lct:>Wa:c..

o o

51

REFERENCES

I. Causey, 1:). R., Causey, C. E., Maroja, O. M., and Macedo, D. G., The isolation of arthropod-bomeviroses including members of two hitherto undescribed serological groups, in the Amazon region of Brazil,Am. J. Trop. Med. Hyg.. 10,227, 1961.

2. CasaIs, J. and Whitman, L., Group C, a new serological group of hitherto undescribed arthropod-bomeviroses. Immunological studies, Am. J. Trop. Med. Hyg.. 10,250,1961.

3. Whitman, L. and CasaIs, J., The Guama group: a new serological group of hitherto undescribed viroses.Immunological studies, Am. J. Trop. Med. Hyg., 10, 159, 1961.

4. Karabatsos, N., Ed., /nternational Catalogue Df Arboviruses /985. American Society ofTropical Medicineand Hygiene, San Antonio, Tex., 1985.

5. Calisher, C. H., Coimbra, T. L., Lopez, O. de S., Muth, D. J., Sacchetta, L. de A., Francy, D. B.,Lazuick, J. S., and Cropp, C. B., Identification of new Guama aod Group C serogroup bunyavirusesand ao ungrouped virus from southem Brazil, Am. J. Trop. Med. Hyg., 32,424, 1983.

6. Bishop, D. H. L. and Shope, R. E., Bunyaviridae, in Comprehensive Virology, FraenkeI-Conrat, H. andWagner, R. R., Eds., Plenum Press, New York, 1979, I.

7. Allen, W. P., Belman, S. G., and Borman, E. R., Group C arbovirus infections in rhesus monkeys,Am. J. Trop. Med. Hyg.. 16, 196. 1967.

8. Shope, R. E. and Causey, O. R., Further studies on lhe serological relationships of group C arthropod-bome viroses and lhe association of these relationships to rapid identification of types, Am. J. Trop. Med.Hyg.. 11,283,1962.

9. Shope, R. E., quoted in CasaIs, J., New developments in lhe classification of arthropod-bome animalviroses, An. Microbiol.. 11,13,1963.

10. Gibbs, C. J., Jr., Bruckner, E. A., and Schenker, S., A case of Apeu virus (Casais' group C) infection,Am. J. Trop. Med. Hyg.. 13,108,1964.

51

Volume /lI

VIII. FUTURE RESEARCH

There are important practical and theoretical questions which need to be answered. First,what is the troe incidence of illness caused by viroses of groups C and Guama? Diseaseswhich cause disability and loss of time at work at often neglected unless they also kill orhave sequelae. Tropical fevers are an impediment to colonization and exploitation of muchof the earth, and as shown in the 1950s, those in the Amazon are closely linked to mosquito-bome viroses.

Second, are there generic approaches to prevention? It is not yet practical to developvaccines for each of scores of arboviroses, nor is it easy to contrai mosquitoes or interveneat the leveI of the small mammal in the forest. It might, however, be feasible to find anantiviral drog for human use which is active prophylactically against viroses in the familyBunyaviridae. Prevention by drog would be ideal because exposure to these viroses is usuallyover a short term, and the time of risk can be anticipated in those who enter the forest.

Third, the viroses of groups C and Guama are ideal models to study reassortment in anatural forest setting. They are transmitted in a compact ecosystem which may well favorcoinfection of mosquitoes and/or small mammals with two viroses of a group. There isalready evidence of natural reassortment in the form of group C viroses which share antigenswith other viroses in the same group.2

ACKNOWLEDGMENTS

Studies reported here were supported by lhe Rockefeller Foundation and lhe ServicoEspecial de Saude Publica of lhe Govemment of Brazil. Many scientists participated incollection and analysis of data involving lhe mammal recapture project in Utinga Forest,including O. R. Causey, C. E. Causey, G. Bensabath, and A. P. Souza.

.52 The Arboviruses: Epidemiology and Ecology

I 11. Oe Rodaniche, E., De Andrade, A. P., and Galindo, P., Isolation of two antigenically distinct arthropod-bome viroses of group C in Panama. Am. J. Trop. Med. Hyg.. 13,839, 1964.

12. Tikaslngh, E. S., Ardoln, P., and Williams, M. C., First isolationofCatu vírus from a human in Trinidad,Trop. Geogr. Med.. 26,414, 1974.

13. Scherer, W. F., Olckerman, R. W., and Ordonez, J. V., Enfermedad humana causada por el vírusNepuyo, un bunyavirus de Mesoamerica transmitido por mosquitoes, Boi. Of Sanit. Panam.. 95, 111,1983.

14. Jonkers, A. H., Spence, L., and Karbaat, J., Arbovirus infections in Dutch military personnel stationedin Surinam. Further studies, Trop. Geogr. Med., 20, 251, 1968.

15. Bensabath, G., personal communication, 1960.16. Jonkers, A. H" Spence, L., Downs, W. G., Aitken, T. H. G., and Worth, C. B., Arbovirus studies

in Bush Bush Forest, Trinidad, W. I., September 1959-December 1964. VI. Rodent-associated viroses(VEE and agents of groups C and Guama): isolations and further studies, Am. J. Trop. Med. Hyg., 17,

I 285,1968.~ 17. Iversson, L, B" Travassos da Rosa, A. P. A., and Travassos da Rosa, J, F., Estudos sorologicos para

pesquisa de anticorpos de arbovirus im populacao humana de regiao do Vale do Ribeira. 11. Inquerito empacientes do Hospital Regional de Pariquera-cu, 1980, Rev. Saude Pub.. 15,587,1981.

J 18. Iversson, L, B., Travassos da Rosa, A, p, A., Travassos da Rosa, J, F., Eleuterlo, G. C., and Prado,J. A., Estudos sorologicos para pesquisa de anticorpos de arbovirus na populacao humana da regiao doVale do Ribeira. I. Seguimento sorologico de grupo populacional residente em ambiente silvestre, inInternacional Simposium on Tropical Arboviruses and Haemorrhagic F evers, Pinheiro, F. P., Ed., AcademiaBrasileira de Ciencias, Rio de Janeiro, 1982, 229.

19. Calisher, C. H., ChappeIl, W. A., Maness, K. S, C., Lord, R. O., and Sudia, W, O" Isolations ofNepuyo vírus strains from Honduras, 1967, Am. J. Trop. Med. Hyg.. 20,331, 1971.

20. Spence, L., Anderson, C. R., Altken, T. H. G., and Oowns, W. G., Bimiti vírus, a new agent isolatedfrom Trinidadian mosquitoes, Am. J. Trop. Med. Hyg., 11,414,1962.

21. WoodaIl, J. P., Transmission of group C arboviruses (Bunyaviridae), in Arctic and Tropical Arboviruses,Kurstak, E., Ed., Academic Press, New York, 1979, 123.

22. Jonkers, A. H., Spence, L., Downs, W. G" and Worth, C. B., Laboratory studies with wild rodentsand viroses native to Trinidad. 11. Studies with lhe Trinidad Caraparu-like agent TRVL 34053-1, Am. J.Trop. Med. Hyg.. 13,728, 1964.

23. Jonkers, A, H., Spence, L., and Olivler, O" Laboratory studies with wild rodents and viroses native toTrinidad. 111. Studies with three Guama-group viroses, Am. J. Trop. Med. Hyg., 17,299, 1968.

24. Causey, C, E., The role of small mammals in maintenance of arboviruses in lhe Brazilian Amazon forests,An. Microbiol., I I (Parte A), 119, 1963.

\" 25. Shope, R. E., de Andrade, A. H. P., and Bensabath, G., The serological response of animaIs to virus

infection in Utinga Forest, Belém, Brazil, Atas do Simposio sobre a Biota Amazonica 6 (Pathologia), 225,1967.

26. Aitken, T. H, G., Worth, C, B., and Tlkaslngh, E. S., Arbovirus studies in Bush Bush Forest, Trinidad,W. I., September 1959-December 1964. 111. Entomologic studies, Am. J. Trop. Med. Hyg., 17,253,1968.

27. Oavles, J. B., Corbet, P. S., Gillies, M, T., an~ McCrae, A. W, R., Parous rales in some Amazonianmosquitoes collected by three different methods, Buli. Entomol. Res.. 61, 125, 1971.

11. De Rodanlche, E., De Andrade, A. P., and Galindo, P., Isolation of two antigenically distinct arthropod-bome viroses of group C in Panama, Am. J. Trop. Med. Hyg.. 13,839, 1964.

12. Tlkaslngh, E. S., Ardoln, P., and Wllllams, M. C., First isolationofCatu virus frum a human in Trinidad,Trop. Geogr. Med.. 26,414, 1974.

13. Scherer, W. F., Dlckerman, R. W., and Ordonez, J. V., Enfermedad humana causada por el virusNepuyo, un bunyavirus de Mesoamerica transmitido por mosquitoes, Boi. af. Sanit. Panam.. 95. 111,1983.

14. Jonkers, A. H., Spence, L., and Karbaat, J., Arbovirus infections in Dutch military personnel stationedin Surinam. Further studies, Trop. Geogr. Med.. 20,251, 1968.

15. Bensabath, G., personal communication, 1960.16. Jonkers, A. H., Spence, L., Downs, W. G., Altken, T. H. G., and Worth, C. B., Arbovirus studies

in Bush Bush Forest, Trinidad, W. I., September 1959-December 1964. VI. Rodent-associated viroses(VEE and agents of groups C and Guama): isolations and further studies, Am. J. Trop. Med. Hyg., 17.285,1968.

17. Iversson, L. B., Travassos da Rosa, A. P. A., and Travassos da Rosa, J. F., Estudos sorologicos parapesquisa de anticorpos de arbovirus im populacao humana de regiao do Vale do Ribeira. U. Inquerito empacientes do Hospital Regional de Pariquera-cu, 1980, Rev. Saude Pub.. 15,587, 1981.

18. Iversson, L. B., Travassos da Rosa, A. P. A., Travassos da Rosa, J. F., Eleuterio, G. C., and Prado,J. A., Estudos sorologicos para pesquisa de anticorpos de arbovirus na populacao humana da regiao doVale do Ribeira. I. Seguimento sorologico de grupo populacional residente em ambiente silvestre, inInternacional Simposium on Tropical Arboviruses and Haemorrhagic F evers, Pinheiro, F. P., Ed., AcademiaBrasileira de Ciencias, Rio de Janeiro, 1982, 229.

19. Calisher, C. H., Chappell, W. A., Maness, K. S. C., Lord, R. D., and Sudia, W. D., Isolations ofNepuyo virus strains from Honduras, 1967, Am. J. Trop. Med. Hyg., 20, 331,1971.

20. Spence, L., Anderson, C. R., Aitken, T. H. G., and Downs, W. G., Bimiti virus, a new agent isolatedfrom Trinidadian mosquitoes, Am. J. Trop. Med. Hyg.. 11,414,1962.

2 I. Woodall, J. P., Transmission of group C arboviruses (Bunyaviridae), in Arctic and Tropical Arboviruses.Kurstak, E., Ed., Academic Press, New York, 1979, 123.

22. Jonkers, A. H., Spence, L., Downs, W. G., and Worth, C. B., Laboratory studies with wild rodentsand viroses native to Trinidad. U. Studies with lhe Trinidad Caraparu-like agent TRVL 34053-1, Am. J.Trop. Med. Hyg.. 13,728, 1964.

23. Jonkers, A. H., Spence, L., and Olivler, O., Laboratory studies with wild rodents and viroses native toTrinidad. UI. Studies with three Guama-group viroses, Am. J. Trop. Med. Hyg.. 17,299, 1968.

24. Causey, C. E., The role of small mammals in maintenance of arboviruses in lhe Brazilian Amazon forests,An. Microbiol.. I I (Parte A), 119, 1963.

25. Shope, R. E., de Andrade, A. H. P., and Bensabath, G., The serological response of animais to vírusinfection in Utinga Forest, Belém, Brazil, Atas do Simposio sobre a Biota Amazonica 6 (Pathologia), 225,1967.

26. Aitken, T. H. G., Worth, C. B., and Tlkaslngh, E. S., Arbovirus studies in Bush Bush Forest, Trinidad,W. I., September 1959-December 1964. UI. Entomologic studies, Am. J. Trop. Med. Hyg.. 17,253,1968.

27. Davies, J. B., Corbet, P. S., Glllies, M. T., and McCrae, A. W. R., Parous rales in some Amazonianmosquitoes collected by three different methods, Buli. Entomol. Res.. 61. 125, 1971.


the arboviruses - paráiah.iec.pa.gov.br/.../thearbepidemiolecol1988v3p38...40 the arboviruses:...

Documents