liwei li department of medical microbiology and parasitology college of medicine, zhejiang...
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Liwei LiDepartment of Medical Microbiology and
Parasitology College of Medicine, Zhejiang University
Human ParasitologyHuman Parasitology
(( 人体寄生虫学人体寄生虫学 ))
Introduction to Introduction to ParasitologyParasitology
• F. E. G. Cox. History of Human Parasitology. Clin Microbiol Rev. 2002 October; 15 (4): 595–612 http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=126866
• Olson & Guselle. Are pig parasite a human health risk? http://www.banffpork.ca/proc/2000pdf/Chap13-Olson.pdf
You need to know in the course of You need to know in the course of human parasitologyhuman parasitology
• What is parasitology? • What are parasitism, parasite and host ?• What is the life cycle of a parasite?• How is the host-parasite interplay ?• How do we diagnose the infections with
parasites?• What do we need to understand in the
epidemiology of parasitic infections? • What are principles of control of parasitic
diseases?
microbes parasites
Pathogens
bacteria viruses fungi protozoa helminthes arthropods
Pathogens
Infectious or communicable diseases!
MosquitoMosquito
Parasitology is a discipline dealing with the biology of
animal parasites, ecology of parasitism with emphasis on parasite--host and parasite--environmental interactions.
Human parasitology or Medical parasitology is restricted
in studying those parasites that are of importance in medicine
Protozoology, helminthology and entomology
Parasitology is usually in the scope of preventive medicine and the foundation of clinical parasitic diseases
Definition of Definition of ParasitologyParasitology
Subject outlineSubject outlineIn this course we will concentrate on 3 major groups
of parasites:
1. Medical protozoa - flagellates, amoebae, malarial organisms
2. Medical Helminthes - parasitic worms such as the flukes, tapeworms, and roundworms
3. Medical Arthropods - insects and arachnids that are ectoparasites and carriers (vectors) of diseases
Why do we study parasitology?Why do we study parasitology?
1. Parasites provide unique examples of biological phenomena not found in free-living organisms
2. _
• Medical importance
• Veterinary importance
• Economic importance
Medical Importance of ParasitesMedical Importance of Parasites
• Humans are hosts to over 100 species of parasites.
• Many of these parasites are causative agents of major public health problems of the world.
Ten major tropical diseases (UNDP/World bank/TDR, 2000)• Malaria( 疟疾 )
• Shistosomaiasis (血吸虫病)• Filariasis ( 丝虫病, Lymphatic filariasis and Onchocerciasis)
• Leishmaniasis (利什曼病)• Trypanosomiasis ( 锥虫病, African trypanosomiasis and chagas disease )
• Leprosy (麻风病)• Tuberculosis (结核病)• Dengue fever (登革热)
Medical Importance of ParasitesMedical Importance of Parasites
Major human parasitesMajor human parasites• Estimated World Prevalence of the Major
Parasitic Infection of Human:– Malaria 300-500 million – Schistosomiasis 200 million– Lymphatic filariasis 120 million– Onchocerciasis 85 million– Leishmaniasis 12 million– Trypanosoma cruzi (South America) 18 million– Ascaris infection 1300 million– Hookworm infection 1300 million – Amoebiasis 60 million – Trichuriasis 900 million– Gardiasis 200 million
(WHO,1999)(WHO,1999)
Examples of Medical Importance Examples of Medical Importance in the Worldin the World
Medical Importance in China Medical Importance in China • Five major parasitic diseases • Malaria• Schistosomiasis• Kala-azar ( 黑热病 )• Filariasis• Hookworm disease
Medical Importance in China Medical Importance in China
Medical Importance in ChinaMedical Importance in ChinaParasite infection Estimated number of
cases(2004)
Malaria (P.v & P.f infection) 60.2 thousand (2006)
Ascariasis (large roundworm infection) 85.9 million
Trichuriasis (whipworm infection) 29.1million
Hookworm disease(A. d and N. a infection) 39.3 million
Clonorchiasis (oriental liver fluke infection) 12.5 million
Fasciolopiasis (intestinal fluke infection) 2 million
Paragonimiasis(lung fluke infection) 2.95 million
Taeniasis (pork and beef tapeworm infection) 1.5 million
Schistosomiasis (blood fluke infection) 843 thousand (2003)
China’s parasite infection based on the nationwide parasite survey
Medical Importance in ChinaMedical Importance in ChinaFood-borne parasitic disease is still a big
problem.Prevalence of pet-borne parasitic disease has
increased.Prevalence of opportunistic parasitic disease has
increased.Material exchange and population migration has
widened the geographical scope of parasitic disease.
Medical professionals generally lack the knowledge of parasitology.
WHAT TYPES OF LIVING ORGANISMS ARE WHAT TYPES OF LIVING ORGANISMS ARE PARASITIC?PARASITIC?
Parasites occur in two of the five kingdoms of living organisms.
What are the 5 kingdoms?
KINGDOM ANIMALIA contains 32 phyla.
Parasites of importance are concentrated in 3 phyla.
• PHYLUM PLATYHELMINTHES – Class Trematoda; Cestoda
• PHYLUM NEMATODA – Class Nematoda
• PHYLUM ARTHROPODA – Class Insecta……
KINGDOM PROTISTA - contains the single-celled protozoans.
What are parasitism, parasite and host?What are parasitism, parasite and host?
Evolution of parasitism:Understanding start with basic concept of symbiosis
• Symbiosis was first coined by the German de Bary in 1879 - to mean “living together”. It was originally coined to refer to all cases where dissimilar organisms or species (e.g., heterogenetic associations) live together in an intimate association
Interactions of Symbionts In order to facilitate our understanding of symbiosis, 3
subordinate categories of symbiotic relationships are indicated. They are: commensalism (including phoresis), mutualism, and parasitism
Symbiosis (cont.)Symbiosis (cont.)
1. Mutualism(互利共生 )• This occurs when each member of the association
benefits the other
• The mutuals are metabolically dependent on one another. Sometimes, one cannot survive in the absence of the other
• eg. the flagellate cannot
survive outside the termite
Sea anemones and Sea anemones and anemonefishanemonefish
Symbiosis (cont.)Symbiosis (cont.)
2. Commensalism(偏利共生 ,共栖 )• Commensalism means “eating at the same table”
and in many commensalistic relationships one organism (the commensal) is feeding on food that was not consumed by the host
• Commensalism occurs when one member of the associating pair, usually the smaller, receives all the benefit and the other member is neither benefited nor harmed
• To carry -- phoresis• Example: Remora fish associated with sharks
feeds on leftover food
SymbiosisSymbiosis (cont.)(cont.)
3. Parasitism(寄生 )• A parasitos (para: beside; sitos: grain or food): Original
meaning from the Greek is a relationship in which "one eats at another's table or lives at another's expense."
• Parasitism is a relationship in which one of the participants, the parasite, either harms its host (the part that got harmed) or in some sense lives at the expense of the host.
Debate: The amoeba Entamoeba invadens is harmless in turtles but causes 100% mortality in snakes.
Is it then a commensal (when it’s in turtles) or is it a parasite (when it’s in snakes)?
The true nature of parasitism involves an ecological relationship between the parasite and its host. A parasite is metabolically dependent on its host.
Symbiosis (sum.)Symbiosis (sum.)
Overlap between the major categories of symbiosis
Parasitism
Commensalism and Phoresis
Mutualism
•The categories of symbiosis are man-made constructs introduced primarily for convenience (they allow us to categorize natural symbiosis associations). There can in fact be overlap between various categories.
Parasite — In the relationship known as parasitism, the partner lives in or on another from which it gains benefit, always smaller, is the parasite which to some degree injures its partner.
— Parasites (animal parasites) are invertebrates that can not live independently and should depend upon others to maintain their lives (live at the expense of others).
—Parasites may be classified according to different ways:
residing site---endoparasite / ectoparasite
ecology---obligatory/facultative; accidental or
opportunistic
duration of parasitism---permanent/intermittent
Kinds of ParasitesKinds of Parasites• An organism that does not absolutely depend on
the parasitic way of life, but is capable of adapting to it if placed in such a relationship is known as a facultative parasite
• If an organism is completely dependent on the host during a segment or all of its life cycle the parasite is known as an obligatory parasite
• Parasites that live within the body of their host (intestinal tract, liver, etc.) are called endoparasites
• Parasites that are attached to the outer surfaces of their hosts are called ectoparasites
HostHost
— Definition: In the parasitism, the partners which provide the food and shelter for parasites, and to some degree are injured by this association, are scientifically called as hosts.
larger, more complex and better regulated bodies
Types of the hostTypes of the host• A definitive host( 终宿主 ) is the host in which
the parasite become sexually mature (where the adult worm harbor or undergoing sexual reproduction).
• An intermediate host( 中间宿主 ) is host in which the parasite undergoes larval development but does not reach sexual maturity, parasites often can undergo asexual reproduction in this type of host.
Reservoir host( 保虫宿主 ) is referred to those animals that harbor an infection that can be transmitted to humans. Even if the animal is the normal host of the parasite, it is the reservoir for the zoonotic infection of people . Thus , the reservoir host shares the same stage of the parasite with humans.
Definitions of Hosts (cont.)Definitions of Hosts (cont.)
Zoonosis( 人兽共患病 ): a disease of animals that may be transmitted to humans under natural conditions.
A transport/paratenic/transfer host ( 转 续 宿主 ) : When parasite enters the body of an abnormal host and not undergoes any development but continues to stay alive and be infective to the normal host . The host is called the transport host .not necessary for the completion of the parasite’s life cycle
Definitions of Hosts (cont.)Definitions of Hosts (cont.)
Definitions of Hosts (cont.)Definitions of Hosts (cont.)
• Immune compromised hosts are persons who are considered to have reduced resistance to illness include: infants, hospital patients, pregnant women, frail, elderly people, malnourished individuals, people with controlled physical or metabolic disorders (e.g., diabetes or high blood pressure), people with AIDS.
Definitions of Hosts (cont.)Definitions of Hosts (cont.)
• Opportunistic parasitic infection: Any infection caused by a parasite that does not normally cause disease in humans; occurs in persons with abnormally functioning immune systems (as AIDS patients or transplant patients receiving immunosuppressive drugs). – For example: Toxoplasma gondii, Crypsosporidium
(Pneumocystis jeroveci (carinii) -----
Pneumocystis pneumonia, PCP)
Vector parasite infections may be carried from one host to another by means of arthropod vectors. A vector may also be a host if development of the parasite takes place with its body.(If the arthropod is simply an instrument of passive transfer, we refer to it as a mechanical vector)
Definitions of Hosts (cont.)Definitions of Hosts (cont.)
What is the Life CycleWhat is the Life CycleLife cycle described the ontogenesis, development
and reproduction of the parasite, tracking it through the various phases of its life history which will encompass both parasitic and non-parasitic stages.
The key to understanding the transmission of a parasite species and parasitic disease is its life-cycle
Generalized stages of a parasite’s life cycle
Stage in human host (linking to pathogenesis)
Stage to discharge (diagnostic stage)
Stage developing outside human host
( in external environment, intermediate host or
insect host)--- (linking to transmission)
Stage infecting men (infective stage)
Parasite Life Cycle—A generalized mode
Human residing stage
Invading OralSkinVectorcontact
Infective
stage
Epidemiology
Extra-Human development
(soil, water, animal host, insect)
Diagnosis
Stage to discharge
Via:fecesUrineSputumVectorblood
Pathogenesis
SiteNo.
The types of life cycle of parasites
Direct type: one host (definitive host)
---geo-helminth
Indirect type: more one hosts(intermediate host(s)
and definitive host)
---bio-helminth
Life cycle (cont.)Life cycle (cont.)• Simple or Direct Life Cycle (monoxenous) is
one in which there is only one host where the parasite often spends most of its life, usually as an adult, and where it reproduces.
Life cycle (cont.)Life cycle (cont.)• Many parasites have more complex cycles which
include 2 or more hosts and are classified as having indirect life cycles.
Adaptations to parasitism Profound morphological adaptation to their way of life
Organs not necessary to a parasitic existence are
frequently lost or degenerated
Reproductive system is very highly developed in
association with increased reproductive capacity
Specialized attachment organs in the form of suckers
and hooks have been developed
Physiological and biochemical adaptations
Immune evasion
host-parasite interactionshost-parasite interactions
The harmful effects on the hostThe harmful effects on the host• Depriving for nutrition• Mechanical damage• Toxic effects• Immune-pathological consequences
host-parasite interactionshost-parasite interactions
Ascaris in small intestineAscaris in small intestine
Hookworm and anemiaHookworm and anemia
Complete blockage of Complete blockage of intestine caused by Ascarisintestine caused by Ascaris
Allergy caused by mosquito bitesAllergy caused by mosquito bites
schistosomiasisschistosomiasis
Effects of the host to the parasite• Genetic constitution of the host may profoundly influence the host-parasite relationship (racial variations in resistance to certain strains of Plasmodium vivax; sickle cell trait increased resistance to infection with P. falciparum )
host-parasite interactionshost-parasite interactions
Effects of the host to the parasite•Anti-parasitic immune responses
Natural immunity– mucocutaneous barrier, blood brain
barrier, phagocyte, complement, defensins…
Acquired immunity
Sterilizing immunity (cutaneous leishmaniasis)
Non-sterilizing immunity– premunition ( 带 虫 免 疫 ), concomitant immunity ( 伴随免疫 )
host-parasite interactionshost-parasite interactions
• Colonized (“infected”), asymptomatic– Differences in host susceptibility
• Many people are asymptomatically infected with Toxoplasma gondii.
– Capable of spreading microbe• Amoeba carrier
• Colonized, infected, symptomatic • Infected, host death
host-parasite interactionshost-parasite interactions
Characteristics of parasitic Characteristics of parasitic disease (infection)disease (infection)
• Chronic infection, carrier• Suppressive infection( 隐性感染 ) • Polyparasitism • Eosinophilia (嗜酸性粒细胞增多)• IgE ↑• Larva migrans( 幼虫移行症 )• Ectopic parasitism( 异位寄生 )
DiagnosisDiagnosisDiagnostic techniques • Etiological techniques• Immunodiagnostic techniques • Other molecular diagnostics
Epidemiology & principles of Epidemiology & principles of controlcontrol
• Basic and essential links for parasitic diseases:– Source of infection: patients, carriers,
reservoir hosts– Route of infection– Susceptible population
Epidemiology & principles of Epidemiology & principles of control(cont.)control(cont.)
• Endemic factors– Natural factors
• One won’t get parasitic diseases in the polar area
– Social factors • Eating habits, hygienic habit…• Sexual transmitted diseases…
Epidemiology & principles of Epidemiology & principles of control(cont.)control(cont.)
• Principal of disease control– Control the source of infection– Cut off the route of transmission– Massive protection, esp. for the
susceptible population• no successful vaccine
Epidemiology & principles of Epidemiology & principles of control(cont.)control(cont.)
• Health Education
Round WormsRound Worms
IntroductionIntroduction
• Among the commonest of all parasites and responsible for diseases of major importance in humans
• Non-segmented roundworms belonging to the Phylum Nemathelminthes, Class Nematoda
• The sexes are usually separate (Dioecious), the male which is smaller than the female commonly has a curved posterior end
MorphologyMorphology• Cylindrical and slender • Bilaterally symmetrical • Sex-differentiated • Celomic cavity: protocoele • The supporting body wall consists of
cuticle layer, syncytial layer (subcutical layer) and longitudinal muscular layer
• The alimentary tract is a simple tube extending from the mouth to the anus
MorphologyMorphology
• No circulatory system • The reproductive system is in
tubular form with dioecious (sex-differentiation): – Male: testis, vas deferens, seminal
vesicle, and ejaculatory duct, also cloaca and spicule
– Female: ovary, oviduct, seminal receptacle, uterus, ovejector and vagina
Digestive system
female reproductive system
male reproductive system
PhysiologyPhysiology • The methods of obtaining food may be classified as
– Sucking with ingestion of blood (Ancylostoma)– Ingestion of lysed tissues and blood (Trichuris)– Feeding on the intestinal contents (Ascaris)– Ingestion of nourishment from the body fluids (filarial worms)
• Metabolism: mainly aerobic metabolism, and most species need free-living periods for larvae, which are capable of withstanding a wide range of environmental condition
• During larval development, nematodes pass through several molts or ecdysis, both inside and outside the host
Life cycleLife cycle • Geo-helminths
– Only one host: the larvae pass from host to host directly or after a free-living existence
– Transmission to a new host depends upon • the ingestion of the mature infectious
eggs with larvae (Ascaris, Pinworm)• the penetration of the skin or mucous
membranes by the larvae (Hookworm) • Bio-helminths
– Have an intermediate host – Transmission to a new definitive host is
intermediated by the arthropod--- (filarial worm)
Common medical nematodes Common medical nematodes speciesspecies
• Intestinal lumen residing nematodes: – Ascaris, Hookworm, Whip worm,
Pinworm----the adult parasite inhabit in human intestinal tract
• Blood and tissue residing nematodes: – Filaria, Thichinella----the location of the
adult parasite is blood or tissue
Ascaris lumbricoides( 似蚓蛔线虫 , 蛔虫 )
General IntroductionGeneral Introduction• Common saying “round worm of man”
• The largest of the intestinal nematodes
parasitizing humans
• The most common worm found in human
• It is worldwide in distribution and most
prevalent through out the tropics, sub-tropics
and more prevalent in the countryside than in
the city
• Adult: – Cylindrical in shape– Creamy-white or pinkish in color– The female averages 20-35cm in length, the largest
49cm– The male is smaller, averaging 15-31cm in length, has a
typical curled tail with a pair sickle like copulatory spines– On the tip of the head there are three lips, arranged as a
Chinese word “ 品 ”– Male has a single reproductive tubule– The female has two reproductive tubules and the vulva
is ventrally located at the posterior part of the anterior 1/3 of the body
MorphologyMorphology
Adult worm of A. lumbricoides
The lips of The lips of A. lumbricoidesA. lumbricoides
The three lips are seen at the anterior end. The margin of each lip is lined with minute teeth which are not visible at this magnification
Egg• There are three kinds of the eggs
– fertilized eggs– unfertilized eggs– decorticated eggs
• We usually describe an egg in 5 aspects– size, color, shape, shell and content
MorphologyMorphology
• Fertilized egg: – an average size 60×45µm– broad oval in shape– brown in color– The shell is thick– Albuminous coat is thick and stained brown by bile– The content is a fertilized ovum– There is a new-moon(crescent) shaped clear space at each end inside the
shell
MorphologyMorphology
• Unfertilized egg– Longer and slender than fertilized egg– The shell and albuminous coat are
thinner than those of the fertilized egg– The content is made of many refractable granules various in size
• Decorticated egg: – Both fertilized and unfertilized eggs
sometimes may lack their outer albuminous coats and are colorless
MorphologyMorphology
Life CycleLife Cycle
• Site of inhabitation: small intestine • Infective stage: embryonated eggs• Route of infection: by mouth• Blood-lung migration: intestine--- blood
stream --- right side of the heart --- lung --- respiratory tree --- coughed up and swallowed --- small intestine
Life CycleLife Cycle
• No intermediate and reservoir hosts• The time from the ingestion of
embryonated eggs to oviposition by the females is about 60-75 days
• Life span of the adult: about 1 year• Female may produce approximately
240,000 eggs per day, which are passed in feces
Life CycleLife Cycle
1. The blood-lung migration phase of the larvae: During the migration through the lungs, the larvae may cause a pneumonia (temporary).
– The symptoms of the pneumonia are low fever, cough, blood-tinged sputum, asthma
– The clinical manifestation is also called Loeffler’s syndrome
PathogenesisPathogenesis
2. The intestinal phase of the adults• No symptoms to vague abdominal pains or
intermittent colic, especially in children• A heavy worm burden can result in malnutrition• Wandering adults may block the appendical lumen
or the common bile duct and even perforate the intestinal wall which cause complications of ascariasis:
• intestinal obstruction• Appendicitis• biliary ascariasis (the most common one)• perforation of the intestine• cholecystitis, pancreatitis and peritonitis
PathogenesisPathogenesis
• The symptoms and signs are for reference only
• Intestinal ascariasis: feces are examined for the ascaris eggs– Direct fecal film: it is simple and effective
and is the first choice– brine-floatation method: – recovery of adult worms: when adults or
adolescents are found in feces or vomit and tissues
• Ascaris pneumonitis: examination of sputum for Ascaris larvae is sometimes
DiagnosisDiagnosis
• Worldwide distribution, very common in China, especially in the countryside.
Infection rate: rural >urban; children > adults
EpidemiologyEpidemiology
• Factors favoring the spread of the transmission:– Simple life cycle– Enormous egg production ( 240,000 eggs/ day/
female )– Eggs are highly resistant to ordinary disinfectants
( due to the ascroside) which may remain viable for several years
– Social customs and living habits.– Disposal of feces is unsuitable
• Treatment to ascariasis: Mebendazole( 甲苯咪唑 ) Albendazole( 阿苯达唑 )
• Sanitary disposal of feces.• Hygienic habits such as cleaning
of hands before meals.• Health education.
PreventionPrevention
HookwormsHookworms ( ( 钩虫钩虫 ))Two major species of hookworms can infect human Necator americanus
( 美洲板口线虫 ) Ancylostoma duodenale ( 十二指肠钩口线虫 )
General IntroductionGeneral Introduction• Human intestinal nematode of smaller size, inhabits the
small intestine• World-wide distribution, about 900 million infections in the
world• A. duodenale is prevalent in Southern Europe, North Africa,
Northern Asia (North China), and the more pathogenic one• N. americanus is the predominant species in the Western
hemisphere and equatorial Africa (South China)• Many areas are endemic for both species• Heavy infection may evoke anemia known as "Yellow
Laziness"
Morphology:Morphology: Adults Adults Ancylostoma duodenale • Female is 10-13 mm in
length by 0.6 mm in diameter
• Males are 8-11 mm by 0.4 mm
• Posterior end has an umbrella-shaped bursa with riblike rays
• Two pairs of curved teeth on the ventral wall of its buccal capsule
Morphology:Morphology: Adults Adults
Necator americanus • Females are 9-11 mm in
length by 0.4 mm in diameter
• Males are 7-9 mm by 0.3 mm
• Smaller than A. duodenale• A pair of semilunar cutting
plates on the ventral wall of the buccal capsule
Buccal capsule
Ancylostoma duodenale Necator americanus
Morphology:Morphology: Egg Egg
oval or can-shaped with a thin, hyaline shell, measured 60-75 by 36-40 µm.
Life cycleLife cycle
Life cycleLife cycle• No intermediate host is necessary• Larva takes a free living mode• The filariform larva is the infective stage• Infection routes: skin penetration(mainly); orally
swallow; maternal-child• Residing in human upper small intestine: duodenum,
jejunum• Blood-Lung migration: skin --- lymphatic system ---
right side of the heart --- lung --- respiratory tree --- coughed up and swallowed --- small intestine
• Persisting migrans( 迁 延 移 行 ): Ancylostoma duodenale
PathogenesisPathogenesis
1. Hookworm larvae dermatitis: Penetration of the skin by the filariform
larvae may be asymptomatic in previously uninfected individuals.
However, those experiencing repeated infections develop itching, known as "ground itch" or "dew itch".
Pathogenesis Pathogenesis 2. Migration of pre-adult cause
temporary pulmonary inflammation:In heavily infected individuals
(i.e., 500-1000 worms), there can be symptoms of pneumonia during the migratory phase in the developmental cycle of these worms
PathogenesisPathogenesis
3. Abdominal pains, diarrhea, loss of appetite…
4. Anemia– Especially in young children– Hypoproteinemic because of some loss of
serum proteins– Iron-deficiency
– Why the small worms can cause anemia?• The pump-like action when worms suck blood• The worms secrete an anticoagulant, which
facilitates bleeding• The worms usually change the sites when suck
blood
5. Allotriophagy (Geophagy): due to the iron-deficiency
6. Ancylostomiasis in infant
AllotriophagyAllotriophagy
Laboratory diagnosisLaboratory diagnosis
• Brine floatation is the method of first choice
• Hookworm larvae cultivation is used for species identification
• Hookworm larvae in sputum
EpidemiologyEpidemiology• Most prevalent in the tropical and
subtropical zones• In China, mostly mixed infected, while
A.duodenale is somewhat northward distributed and N. americanus in southward
EpidemiologyEpidemiology
• Moist, shady, sandy, or loamy soil favors persistence of these worms
• Larvae can survive for up to 6 weeks • Do not live long in clay, dry, hard
packed soils, or where temperatures are freezing, or are higher than 45C
Principles of ControlPrinciples of Control
1. Chemotherapy: Albendazole; Mebendazole
2. Sanitary disposal of human feces is the most effective control measure in preventing the spread of infection with the hookworms
3. Protection of the susceptible population