lecture 4 - dengue fever
TRANSCRIPT
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LECTURE # 4
Dengue Fever
Mary Elizabeth Wilson, [email protected]
Collaborative Course on Infectious Diseases
January 2009
Harvard School of Public HealthCentro de Pesquisa Gonçalo Moniz, Fundação Oswaldo Cruz (Fiocruz)
Brazil Studies Program, DRCLAS, Harvard University
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References
• Required:– Siqueira JB Jr, Martelli CM, Coelho GE, et al.
Dengue and dengue hemorrhagic fever, Brazil, 1981-2002. Emerg Infect Dis 2005;11(1):48-53.
– Teixeira Mda G, Costa Mda C, Barreto ML, Mota E. Dengue and dengue hemorrhagic fever epidemics in Brazil: what research is needed based on trends, surveillance, and control experiences? Cad Saude Publica 2005;21(5):1307-15.
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Reference: General Overview
• Optional: – Wilder-Smith A, Gubler DJ. Geographic
expansion of dengue: the impact of international travel. Med Clin N Am 2008;92:1377-1390.
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Objectives
• Describe the epidemiology of dengue fever in Brazil
• Understand transmission cycles• Describe consequences of infection• Define factors that influence vector
populations – (e.g., location, abundance, extrinsic incubation)
• Understand receptivity of region to other vector-borne viruses
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Questions for discussion: dengue
• Why is dengue causing increasingly severe epidemics?
• How is the virus maintained?• Where do new serotypes come from?• Explain the seasonality and year-to-year
changes in epidemiology.• A dengue vaccine is under development.
Discuss factors critical in its evaluation.• Why does mortality vary by region?
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Dengue
• Mosquito-transmitted flavivirus
• Four major serotypes (den-1, den-2, den-3, den-4)
• >2.5 bil persons live in dengue-endemic areas
• 50-100 mil cases dengue/yr
• Increase in area, cases, severity
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Dengue since 1955
WHO Data
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Dengue Infections
• Incubation 4-7 days (3-14)
• Infection– Asymptomatic or mild– Acute febrile illness (dengue fever)– Dengue hemorrhagic fever (DHF)– Dengue shock syndrome (DSS)– No chronic carrier state
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Clinical Findings
• Headache, fever, myalgia
• Nausea, vomiting
• Rash (50%)
• Laboratory– Low WBC– Low platelets– Abnormal liver function
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Dengue Hemorrhagic Fever
• Mortality > 20% (<1% with good care)
• Risk for DHF increased ~100x with 2nd infection (different serotype)
• Thailand, 2 cohort studies– DHF rate 0 in primary infection– 1.8% and 12.5% with 2nd
• Virulence may also vary by genotype
Am J Epidemiol 1984;120:653AJTMH 1988;38:172
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Dengue: 2007, CDC
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Dengue Fever, 2002
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Aedes aegypti
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Aedes Aegypti
• Wide distribution in urban areas– Well adapted to contemporary urban
life
• Breeding sites– Discarded plastic containers, cans– Used tires, flowerpots, tree holes
• Enters homes; prefers human blood
• Nervous feeder; multiple hosts
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Aedes Aegypti
• Usually do not disperse beyond 100 m
• Most movement of dengue viruses occurs via movement of viremic hosts
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Vector DispersalHorizontal and Vertical
• Study site: Singapore• Ae aegypti & Ae albopictus fed rubidium-
laced blood; female offspring released• Female movement traced (oviposition sites)• Findings:
– Horizontal: radius of 320 m– Vertical: release on level 12 of 21-story apt;
dispersed to top and bottom
Liew C, Curtis CF. Med Vet Entomol 2004;18:351-60.
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Aedes aegypti Distribution in the Americas
19701930's 2002
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Environmental Influences on Vector
• Presence or absence• Abundance; longevity of adult• Time for development• Frequency of biting
– Blood feeding frequency increases with higher temperatures
• Extrinsic incubation period (time for virus to disseminate in mosquito)
• Seasonality of pathogen transmission
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Extrinsic Incubation Period
• Time between entry of organism into vector and time when vector can transmit pathogen
• Sensitive to environmental conditions
• If extrinsic incubation period exceeds lifespan of vector, it cannot transmit infection
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Extrinsic Incubation and Dengue
• Temperature: inverse relationship with EI period (<20 C Ae aegypti eggs do not hatch)– 12 days for mosquitoes at 30 C– 7 days at 32 and 35 C
• Temperature required for effective transmission depends on virus & vector
Watts et al. Am J Trop Med Hyg 1987;36:143-52.
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Vertical Transmission of Dengue Virus
• Transovarial transmission of virus can occur
• Ae aegypti eggs subjected to adverse hatching conditions can remain viable in the environment >100 days.
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Dengue/Mosquito Interaction
• Aedes aegypti needs viral titer 105-107 particles/ml of blood to become infected
• Vector serves to select viruses that produce high viremia in humans
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Aedes Albopictus Female
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Aedes Albopictus
• Competent vector for 22 arboviruses– Dengue– Yellow fever– Eastern equine encephalitis– La Crosse virus– West Nile virus
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Aedes Albopictus
• Main vector in Hawaii dengue outbreak, 2001-2002
• Introduced into North America in 1985 via used tires from Asia
• Within 12 yr, spread to 25 states (dispersal followed interstate highways)
• Recent introductions into many parts of Latin America
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Aedes albopictus before 1980 & invaded since
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Chronology of Dengue in Brazil
• 1981-1993: localized epidemics– 1981 outbreak den1 & den4 in NW– 1986 den1 in Rio de Janeiro State– 1990 intro den2 Rio State; first confirmed DHF
• 1994-2002: epidemic/endemic countrywide– 1994-1999 Ae aegypti dispersed countrywide– 1999 widespread outbreaks– 2000 intro den3 in Rio State– 2002 large outbreaks (dengue deaths>malaria
deaths) Siqueira et al. EID 2005;11:48
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Brazil: Reported Dengue Cases per Month, 1986-2003
Siqueira et al. EID 2005;11:49.
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Reported Cases & Hospitalizations: DF/DHF, Brazil, 1986-2002
Siqueira et al. EID 2005;11:50.
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Dengue Hospitalizations/State by Year, 1990-2002
Siqueira et al. EID 2005;11:52.
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Cases of Dengue Hemorrhagic Fever
Secretaria de Vigilancia em Saude 2005
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Regional Incidence rate of Dengue per 100,000 persons, 2006
Midwest 453 HighNorth 222 AverageNortheast 204 AverageSoutheast 178 AverageSouth 20 Low
Brazil 185 Average
Source: SVS/SES (data until week 52, subject to modifications)
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Incidence of Dengue by State (low, medium, high)
Ministry of health. 2006.
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Dengue Cases Notified by Week by Region, 2006
Secretarias de Estado da Saude
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Circulating Dengue Serotypes in Brazil, 2006
Data accumulated until Nov 2006
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Dengue Reported Cases and Hospitalizations due to Dengue/DHF, Brazil, 1986-2008*
Epidemic waves in localized areas
Endemic / Epidemicvirus circulation nationwide
Increase in severe cases in children
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08
Rep
ort
ed C
ases
0
10000
20000
30000
40000
50000
60000
70000
Ho
spit
aliz
atio
ns
Reported Cases Hospitalizations
DENV2DENV1
DENV3
*Preliminary data; Source:CGPNCD/MOH
DEN3DEN3 DEN2DEN2
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Reported Cases and Hospitalizations due to DF/DHF by Month, Brasil, 1998 – 2008*
* Dark bars represent January
0
50,000
100,000
150,000
200,000
250,000
300,000
98 99 00 01 02 03 04 05 06 07 08
Rep
ort
ed C
ases
0
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Ho
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Reported cases Hospitalizations
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Clinical Outcomes for Dengue with Complications, Brazil, 2007-2008Clinical outcomes
(Dengue with complications)2007N (%)
2008N (%)
Total
Neurological manifestations 401 (11.4) 316 (3.9) 717
Heart Failure / Respiratory Distress 77 (2.2) 61 (0.7) 138
Hepatic Failure 46 (1.3) 21 (0.2) 67
Platelets count <50,000 mm3 1406 (39.9) 4144 (51.4) 5550
GI Bleeding 145 (4.1) 235 (2.9) 380
Fluid Accumulation 276 (7.8) 461 (5.7) 737
Potential DHF (Missing criteria) 1162 (32.9) 2817 (34.3) 3979
Total 3525 8063 11588
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Risk Factors for Severe Disease
• Serotype and genotype
• Previous infection
• Age
• Genetics
• Other?
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PNAS 2004;101:15125.
Global Aviation Network (civil traffic, 500 largest airports, 100 countries)
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Receptivity to Introductions
• Physicochemical environment
• Intermediate and reservoir hosts; vectors
• Housing, sanitation, living conditions
• Nutrition, immunity, genetics
• Human behavior and activities
• Surveillance, access to care
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Increase in Dengue Fever
• Urbanization, especially in tropics
• Growing population– More urban areas large enough to sustain
ongoing viral circulation
• Poor housing, inadequate water supply
• Poor vector control and resistance
• Travel and migration
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Chikungunya Virus
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Chikungunya Virus
• Alphavirus, family Togaviridae (first identified in Tanzania, 1953)
• Emerged in Indian Ocean islands 2005• Has moved to India, other countries in
region; explosive outbreaks; high attack rates
• Spread by Aedes aegypti and Ae albopictus
• Will it spread to the Americas?
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Clinical Manifestations: Chikungunya
• Rash 39-50%
• Myalgia 50-60%
• Headache 50-70%
• Arthralgia 78-100%– Severe, incapacitating,
persistent
• Fever 100%
Lancet ID May 2007
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Monthly chikungunya cases, expected deaths, and reported deaths, Ahmedabad, India, 2006.Error bars show 99% confidence intervals. July through December showed a statistically significant difference between mortality rates.
Emerg Infect Dis March 2008
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Outbreak in Italy, 2007
• 4 July – 27 Sept: 205 human cases in two villages northeastern Italy (175 lab-confirmed)
• Clinical attack rate increased with age
• CHIKV found in Ae albopictus
• Index case visitor from India
Rezza et al. Lancet 2007;370:1840-6.
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Chikungunya Virus
• High viral concentration >109
• Early appearance IgM and IgG
• Potential risk for nosocomial transmission
Emerg Infect Dis March 2008
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Chikungunya Virus
• Point mutation of virus associated with enhanced replication of virus in mosquito midgut (Ae. albopictus)
• More rapid dissemination into mosquito salivary glands
• 100-fold higher virus concentration in mosquito saliva
• Mutation absent initially (Reunion outbreak); later found in >90% isolates
Tsetsarkin KA, et al. A single mutation in chikungunya virus affects vector specificity and epidemic potential. PLoS Path Dec 2007.
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Lancet ID 2008;8:5.
Synchronization of Aedes Activity
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Aedes Albopictus Female
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Distribution of Dengue, Yellow Fever, & Ae. aegypti
Pink: Ae. aegyptiBlue: Ae. aegypti and dengue epidemic activityLined: YF endemic
Monath T. NEJM 2007;357:2223.
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Questions for discussion: dengue
• Why is dengue causing increasingly severe epidemics?
• How is the virus maintained?• Where do new serotypes come from?• Explain the seasonality and year-to-year
changes in epidemiology.• A dengue vaccine is under development.
Discuss factors critical in its evaluation.• Why does mortality vary by region?