The Parasites of The Parasites of Medical ImportanceMedical Importance

Protozoa, Helminths, and Protozoa, Helminths, and Arthropod VectorsArthropod Vectors

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Chapter 23

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ParasitologyParasitology

• the study of eucaryotic parasites, the study of eucaryotic parasites, protozoa and helminthsprotozoa and helminths

• cause 20% of all infectious diseasescause 20% of all infectious diseases

• less prevalent in industrialized less prevalent in industrialized countriescountries

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Protozoans

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ProtozoaProtozoa

• single-celled, animal-like microbes, single-celled, animal-like microbes, usually having some form of motilityusually having some form of motility

• life cycles vary life cycles vary – most reproduce by simple asexual cell most reproduce by simple asexual cell

division of the active feeding cell division of the active feeding cell (trophozoite)(trophozoite)

– many undergo formation of a cystmany undergo formation of a cyst– others have a complex life cycle that others have a complex life cycle that

includes asexual & sexual phasesincludes asexual & sexual phases

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amoebas

ciliates

flagellates

Apicomplexans/sporozoans

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Entamoeba histolyticaEntamoeba histolytica

• alternates between a large alternates between a large trophozoite, motile by means of trophozoite, motile by means of pseudopods & a smaller nonmotile pseudopods & a smaller nonmotile cystcyst

• trophozoite has a large nucleus and trophozoite has a large nucleus and lacks most other organelleslacks most other organelles

• humans are the primary hostshumans are the primary hosts• Ingested (fecal-oral transmission)Ingested (fecal-oral transmission)• carried by 10% of world populationcarried by 10% of world population

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Entamoeba histolyticaEntamoeba histolytica

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Entamoeba histolyticaEntamoeba histolytica

• cysts are swallowed & arrive at the small cysts are swallowed & arrive at the small intestine; alkaline pH & digestive juices intestine; alkaline pH & digestive juices stimulate cyst to release 4 trophozoitesstimulate cyst to release 4 trophozoites

• trophozoites attach, multiply, actively trophozoites attach, multiply, actively move about & feedmove about & feed

• asymptomatic in 90% of patientsasymptomatic in 90% of patients• ameba may secrete enzymes that ameba may secrete enzymes that

dissolve tissues & penetrate deeper dissolve tissues & penetrate deeper layers of the mucosa layers of the mucosa

• causing dysentery, abdominal pain, causing dysentery, abdominal pain, fever, diarrhea & weight lossfever, diarrhea & weight loss

cyst

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Entamoeba histolyticaEntamoeba histolytica

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Entamoeba histolyticaEntamoeba histolytica

• life-threatening manifestations are life-threatening manifestations are hemorrhage, perforation, appendicitis, hemorrhage, perforation, appendicitis, & tumorlike growths (amebomas)& tumorlike growths (amebomas)

• may invade liver & lungmay invade liver & lung• severe forms of disease result in 10% severe forms of disease result in 10%

fatality ratefatality rate• effective drugs are iodoquinol, effective drugs are iodoquinol,

metronidazole, & chloroquinemetronidazole, & chloroquine

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Amebic brain infectionsAmebic brain infections

• caused by caused by Naegleria fowleri & Naegleria fowleri & AcanthamoebaAcanthamoeba

• ordinarily inhabit standing waterordinarily inhabit standing water

• primary acute meningoencephalitis is primary acute meningoencephalitis is acquired though nasal contact with acquired though nasal contact with water or traumatic eye damage.water or traumatic eye damage.

• infiltration of brain is usually fatalinfiltration of brain is usually fatal

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Naegleria fowleriNaegleria fowleri

Phase-contrast of Naegleria feeding

on bacteria. Organism is free-

living in fresh water

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Balantidium coliBalantidium coli

• an occupant of the intestines of domestic an occupant of the intestines of domestic animals such as pigs & cattleanimals such as pigs & cattle

• acquired by ingesting cyst-containing food acquired by ingesting cyst-containing food or wateror water

• trophozoite erodes intestine & elicits trophozoite erodes intestine & elicits intestinal symptomsintestinal symptoms

• healthy humans are resistanthealthy humans are resistant• rarely penetrates intestine or enters bloodrarely penetrates intestine or enters blood• treatment – tetracycline, iodoquinol, treatment – tetracycline, iodoquinol,

nitrimidazine or metronidazolenitrimidazine or metronidazole

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TrichomonasTrichomonas

• Small, pear-shapedSmall, pear-shaped• 4 anterior flagella & an undulating 4 anterior flagella & an undulating

membranemembrane• Exist only in trophozoite formExist only in trophozoite form• 3 species infect humans3 species infect humans

– T. vaginalisT. vaginalis– T. tenaxT. tenax– T. hominisT. hominis

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Trichomonas vaginalisTrichomonas vaginalis• causes an STD called trichomoniasiscauses an STD called trichomoniasis• reservoir is human urogenital tractreservoir is human urogenital tract• 50% of infected are asymptomatic50% of infected are asymptomatic• strict parasite, cannot survive long outside of strict parasite, cannot survive long outside of

hosthost• 3 Million new cases a year in U.S., a top STD3 Million new cases a year in U.S., a top STD• female symptoms – foul-smelling, green-to-female symptoms – foul-smelling, green-to-

yellow discharge; vulvitis; cervicitis; urinary yellow discharge; vulvitis; cervicitis; urinary frequency & painfrequency & pain

• male symptoms – urethritis, thin, milky male symptoms – urethritis, thin, milky discharge, occasionally prostate infectiondischarge, occasionally prostate infection

• metronidazolemetronidazole

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Trichomonas tenaxTrichomonas tenax

• smallsmall

• resides in oral cavity of 5-10%resides in oral cavity of 5-10%

• only flagellate in oral cavityonly flagellate in oral cavity

• not a true pathogen, but an not a true pathogen, but an opportunist in lesions of gingivitis & opportunist in lesions of gingivitis & peridontal pocketsperidontal pockets

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Trichomonas hominisTrichomonas hominis

• a resident of the cecum of a small a resident of the cecum of a small percentage of humans & great apespercentage of humans & great apes

• not associated with diseasenot associated with disease

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Giardia lambliaGiardia lamblia• pathogenic flagellatepathogenic flagellate• unique symmetrical heart shapeunique symmetrical heart shape• cysts can survive for 2 months in cysts can survive for 2 months in

environmentenvironment• cysts enter duodenum, germinate, & cysts enter duodenum, germinate, &

travel to jejunum to feed & multiplytravel to jejunum to feed & multiply• causes giardiasis – diarrhea, abdominal causes giardiasis – diarrhea, abdominal

painpain• diagnosis is difficult because organism diagnosis is difficult because organism

is shed in feces intermittentlyis shed in feces intermittently• Treatment: quinacrine or metronidazoleTreatment: quinacrine or metronidazole• agent is killed by boiling, ozone, & agent is killed by boiling, ozone, &

iodineiodine

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hemoflagellateshemoflagellates

• live in blood & tissues of human hostlive in blood & tissues of human host• obligate parasitesobligate parasites• cause life-threatening and debilitating zoonosescause life-threatening and debilitating zoonoses• spread by blood-sucking insects that serve as spread by blood-sucking insects that serve as

intermediate hostsintermediate hosts• acquired in specific tropical regionsacquired in specific tropical regions• have complicated life cycles & undergo have complicated life cycles & undergo

morphological changesmorphological changes• TrypanosomaTrypanosoma• LeishmaniaLeishmania

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Trypanosoma Trypanosoma

• distinguished by their infective stage, distinguished by their infective stage, trypomastigote is an elongate, trypomastigote is an elongate, spindle-shaped cell with tapered spindle-shaped cell with tapered ends, eel-like motilityends, eel-like motility

• 2 types of trypanosomiasis2 types of trypanosomiasis– T. bruceiT. brucei – African sleeping sickness – African sleeping sickness– T. cruziT. cruzi – Chagas disease – endemic – Chagas disease – endemic

to Central and South Americato Central and South America

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Trypanosoma bruceiTrypanosoma brucei

• causes African Sleeping Sicknesscauses African Sleeping Sickness• spread by tsetse fliesspread by tsetse flies• harbored by reservoir mammalsharbored by reservoir mammals• biting of fly inoculates skin with biting of fly inoculates skin with

trypanosome, which multiplies in blood & trypanosome, which multiplies in blood & damages spleen, lymph nodes & braindamages spleen, lymph nodes & brain

• chronic disease symptoms are sleep chronic disease symptoms are sleep disturbances, tremors, paralysis & comadisturbances, tremors, paralysis & coma

• treatment before neurological involvement treatment before neurological involvement melarsoprol, difluormethylornithinemelarsoprol, difluormethylornithine

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Trypanosoma Trypanosoma bruceibrucei

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Trypanosoma cruziTrypanosoma cruzi• causes Chagas diseasecauses Chagas disease• reduviid bug (kissing) bug is the reduviid bug (kissing) bug is the

vectorvector• infection occurs when bug feces are infection occurs when bug feces are

inoculated into a cutaneous portalinoculated into a cutaneous portal• local lesion, fever, & swelling of local lesion, fever, & swelling of

lymph nodes, spleen, & liverlymph nodes, spleen, & liver• heart muscle & large intestine heart muscle & large intestine

harbor masses of amastigotesharbor masses of amastigotes• chronic inflammation occurs in the chronic inflammation occurs in the

organs (especially heart & brain)organs (especially heart & brain)

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Trypanosoma cruziTrypanosoma cruziHeart pathology in Chagas

disease

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LeishmaniaLeishmania

• Leishmaniasis is a zoonosis Leishmaniasis is a zoonosis transmitted among mammalian transmitted among mammalian hosts by female sand flies that hosts by female sand flies that require a blood meal to produce eggsrequire a blood meal to produce eggs

• infected macrophages carry the infected macrophages carry the pathogen into the skin (cutaneous pathogen into the skin (cutaneous leishmaniasis) & bloodstream leishmaniasis) & bloodstream (systemic or visceral leishmaniasis), (systemic or visceral leishmaniasis), giving rise to fever, enlarged organs giving rise to fever, enlarged organs & anemia& anemia

(Kala azar is the most severe & fatal form)(Kala azar is the most severe & fatal form)

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Life cycle of Leishmania

Disseminated leishmaniasis

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Apicomplexan parasitesApicomplexan parasites

• sporozoanssporozoans• lack locomotor organelles in the mature statelack locomotor organelles in the mature state• alternate between sexual & asexual phases & alternate between sexual & asexual phases &

between different animal hostsbetween different animal hosts• most form specialized infective bodies that are most form specialized infective bodies that are

transmitted by arthropod vectors, food, water, transmitted by arthropod vectors, food, water, or other meansor other means– PlasmodiumPlasmodium– Toxoplasma Toxoplasma – CryptosporidiumCryptosporidium

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PlasmodiumPlasmodium

• causes malariacauses malaria

• female female AnophelesAnopheles mosquito is the mosquito is the vectorvector

• obligate intracellular sporozoanobligate intracellular sporozoan

• 4 species: 4 species: P. malariae, P. vivax, P. P. malariae, P. vivax, P. falciparum & P. ovalefalciparum & P. ovale

• 300-500 Million new cases each year300-500 Million new cases each year

• 2 Million deaths each year2 Million deaths each year

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PlasmodiumPlasmodium

• infective forms for humans (sporozoites) infective forms for humans (sporozoites) enter blood with mosquito saliva, enter blood with mosquito saliva, penetrate liver cells, multiply, and form penetrate liver cells, multiply, and form hundreds of merozoites, which multiply in hundreds of merozoites, which multiply in & lyse RBCs.& lyse RBCs.

• symptoms include episodes of chills-symptoms include episodes of chills-fever-sweating, anemia, and organ fever-sweating, anemia, and organ enlargement.enlargement.

• therapy is chloroquine, quinine, or therapy is chloroquine, quinine, or primaquineprimaquine

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Asexual phase in humans

as sporozoite enters

Liver phase (sporozoites invade & merozoites produced)

RBCs infected by merozoites from the liver

Gametocytes produced and ingested by mosquito

Sexual phase with

sporozoite formation in

the mosquito)

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Plasmodium falciparum infection of RBCs showing ring form

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Toxoplasma gondiiToxoplasma gondii

• obligate apicomplexan parasite with obligate apicomplexan parasite with extensive distributionextensive distribution

• lives naturally in cats that harbor oocysts lives naturally in cats that harbor oocysts in the GI tractin the GI tract

• acquired by ingesting raw meats or acquired by ingesting raw meats or substances contaminated by cat fecessubstances contaminated by cat feces

• most cases of toxoplasmosis go unnoticed most cases of toxoplasmosis go unnoticed except in fetus & AIDS patients which can except in fetus & AIDS patients which can suffer brain & heart damagesuffer brain & heart damage

• treatment: pyrimethamine & sulfadiazinetreatment: pyrimethamine & sulfadiazine

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Life cycle of Toxoplasma

gondii

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CAT scan of brain showing lesion

Biopsy showing clusters of intracelluar T. gondii

Toxoplasmosis in an AIDS patient

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CryptosporidiumCryptosporidium

• an intestinal pathogenan intestinal pathogen• infects a variety of animalsinfects a variety of animals• exists in tissue & oocyst exists in tissue & oocyst (passed in feces)(passed in feces) phases phases• 1990s – 370,000 cases in Milwaukee, WI due 1990s – 370,000 cases in Milwaukee, WI due

to contaminated waterto contaminated water• causes enteric symptomscauses enteric symptoms• AIDS patients may suffer chronic persistent AIDS patients may suffer chronic persistent

diarrheadiarrhea• no real effective drugsno real effective drugs

Oocysts shed in feces

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BabesiaBabesia

• causes babesiosiscauses babesiosis

• first protozoan found to cause a first protozoan found to cause a diseasedisease

• first protozoan found to be first protozoan found to be associated with a tickassociated with a tick

• infection resembles malariainfection resembles malaria

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HelminthsHelminths

• adults are large, multicellular animals with adults are large, multicellular animals with specialized tissues & organsspecialized tissues & organs

• adult worms mate & produce fertilized eggs that adult worms mate & produce fertilized eggs that hatch into larvae that mature in several stages hatch into larvae that mature in several stages to adults to adults (the sexes may separate or hermaphroditic)(the sexes may separate or hermaphroditic)

• HostsHosts– adults live in the adults live in the definitive hostdefinitive host– eggs & larvae may develop in the same host, external eggs & larvae may develop in the same host, external

environment, or environment, or intermediate hostintermediate host– a a transport hosttransport host experiences no parasitic experiences no parasitic

developmentdevelopment

• pathology arises from worms feeding on & pathology arises from worms feeding on & migrating through tissues and accumulation of migrating through tissues and accumulation of worms & worm productsworms & worm products

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Nematodes - roundwormsNematodes - roundworms

• Filamentous with protective cuticles, a Filamentous with protective cuticles, a complete digestive tract, & separate complete digestive tract, & separate sexessexes

• Ascaris lumbricoidesAscaris lumbricoides• Trichuris trichiuraTrichuris trichiura (whipworm) (whipworm)• Enterobius vermicularis Enterobius vermicularis (pinworm)(pinworm)• HookwormsHookworms• Strongyloides stercoralisStrongyloides stercoralis• Trichinella spiralisTrichinella spiralis• Filarial wormsFilarial worms

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Ascaris lumbricoidesAscaris lumbricoides• a large (up to a foot long) intestinal a large (up to a foot long) intestinal

roundwormroundworm

• 1 Billion cases worldwide1 Billion cases worldwide

• Most cases in the US occur in the Most cases in the US occur in the southeastern statessoutheastern states

• indigenous to humansindigenous to humans

• AscarisAscaris spends its larval & adult stages in spends its larval & adult stages in humans & releases embryonic eggs in humans & releases embryonic eggs in feces, which are spread to other humansfeces, which are spread to other humans

• ingested eggs hatch into larvae & burrow ingested eggs hatch into larvae & burrow through the intestine into circulation & through the intestine into circulation & travel to the lungs & pharynx & are travel to the lungs & pharynx & are swallowed. Adult worms complete cycle in swallowed. Adult worms complete cycle in intestines.intestines.

Ascaris lumbricoidesAscaris lumbricoides

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Ascaris lumbricoidesAscaris lumbricoides

• worms retain motility, do not worms retain motility, do not attachattach

• severe inflammatory severe inflammatory reactions mark the migratory reactions mark the migratory route,route,

• allergic reactions can occurallergic reactions can occur

• heavy worm loads can retard heavy worm loads can retard physical & mental physical & mental developmentdevelopment

Roundworm Zoonoses-1Roundworm Zoonoses-1• Don’t play with the animal feces !Don’t play with the animal feces !

• Don’t eat dirt !Don’t eat dirt !

• Dog and Cat Roundworms (toxocariasis)Dog and Cat Roundworms (toxocariasis)– estimated 10,000 new cases of roundworm estimated 10,000 new cases of roundworm

infection occur in children every year, most infection occur in children every year, most often as a result of eating dirt contaminated with often as a result of eating dirt contaminated with animal feces. animal feces.

– Most human infections are mild enough to go Most human infections are mild enough to go unnoticed and apparently produce no unnoticed and apparently produce no permanent damage……But….permanent damage……But….

– Visceral Larval Migrans (VLM) Visceral Larval Migrans (VLM) – Ocular Larval Migrans (OLM). Ocular Larval Migrans (OLM).

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Roundworm Roundworm Zoonoses-2Zoonoses-2• Raccoon roundworm (Raccoon roundworm (Baylisascaris Baylisascaris

procyonis)procyonis)– Raccoons are very common in the Raccoons are very common in the

urban/suburban environment, and urban/suburban environment, and perhaps 80%+ carry the roundworm.perhaps 80%+ carry the roundworm.

– Worm eggs are very hardy, surviving Worm eggs are very hardy, surviving years outdoors. years outdoors.

– When ingested by humans the larvae When ingested by humans the larvae migrate throughout the body. Some migrate throughout the body. Some enter the brain and death my ensue.enter the brain and death my ensue.

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Trichuris trichiuraTrichuris trichiura

• whipwormwhipworm

• humans sole hosthumans sole host

• trichuriasis has its highest incidence trichuriasis has its highest incidence in tropicsin tropics

• remains in intestineremains in intestine

Egg in fecal sample

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Enterobius Enterobius vermicularisvermicularis• pinwormpinworm• enterobiasis most common worm disease of enterobiasis most common worm disease of

children in temperate zoneschildren in temperate zones• eggs are picked up from surroundings & eggs are picked up from surroundings &

swallowed. swallowed. • after hatching in the small intestine, they after hatching in the small intestine, they

develop into adults develop into adults • anal itching occurs when mature females anal itching occurs when mature females

emerge from intestine to release eggsemerge from intestine to release eggs• self-inoculation is commonself-inoculation is common• tape testtape test

Tape test for pinwormsTape test for pinworms

Flashlight Test: At night, the female adult worms deposit their eggs

outside the rectum or anal area.

Enterobius Enterobius vermicularvermicular

isispinwormpinworm

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HookwormsHookworms• characteristic curved ends & hooked mouthscharacteristic curved ends & hooked mouths• Endemic to tropics and subtropicsEndemic to tropics and subtropics• Necator americanus & Ancylostoma duodenaleNecator americanus & Ancylostoma duodenale• humans shed eggs in feces, which hatch into humans shed eggs in feces, which hatch into

filariform filariform (threadlike)(threadlike) larvae & burrow into the larvae & burrow into the skin of lower legs skin of lower legs (may cause a local (may cause a local irritation…”ground itch”)irritation…”ground itch”)

• larvae travel from blood to lungs, proceed up larvae travel from blood to lungs, proceed up bronchi & throat & are swallowed.bronchi & throat & are swallowed.

• worms mature & reproduce in small intestine worms mature & reproduce in small intestine & complete cycle& complete cycle

• may cause pneumonia, nausea, vomiting, may cause pneumonia, nausea, vomiting, cramps & bloody diarrhea…blood loss can be cramps & bloody diarrhea…blood loss can be significant - anemiasignificant - anemia

HookwormsHookworms

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Strongyloides Strongyloides stercoralisstercoralis

• threadwormthreadworm• tiny roundworm tiny roundworm • completes life cycle in humans or moist soilcompletes life cycle in humans or moist soil• larvae penetrate skin & migrate to lungs, are larvae penetrate skin & migrate to lungs, are

swallowed & complete development in intestineswallowed & complete development in intestine• can reinfect the same host without leaving the can reinfect the same host without leaving the

bodybody• heavy worm loads can cause pneumonitis & heavy worm loads can cause pneumonitis &

eosinophilia, bloody diarrhea, liver eosinophilia, bloody diarrhea, liver enlargement, bowel obstruction & enlargement, bowel obstruction & malabsorptionmalabsorption

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Strongyloides stercoralisStrongyloides stercoralis

Worm migration

tracks under the skin

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Trichinella spiralisTrichinella spiralis

• causes trichinosiscauses trichinosis

• life cycle entirely within mammalian hostlife cycle entirely within mammalian host• acquired from eating undercooked pork acquired from eating undercooked pork (also bear) (also bear)

• larvae migrate from intestine to blood vessels, larvae migrate from intestine to blood vessels, muscle, heart, & brain, where it forms cystsmuscle, heart, & brain, where it forms cysts

• first symptoms –flulike, diarrheafirst symptoms –flulike, diarrhea

• second symptoms – muscle & joint pain, second symptoms – muscle & joint pain, shortness of breath, pronounced eosinophiliashortness of breath, pronounced eosinophilia

• no cure after larva have encystedno cure after larva have encysted

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Filarial Filarial wormsworms• long threadlike long threadlike

worms with tiny worms with tiny larvae that circulate larvae that circulate in blood & reside in in blood & reside in various organsvarious organs

• spread by biting spread by biting insectsinsects

• Wuchereia bancroftiWuchereia bancrofti – elephantitis– elephantitis

• Onchocerca Onchocerca volvulusvolvulus – river – river blindnessblindness

• Loa loaLoa loa – eye worm – eye wormEdema from blockage of lymphatics

Heartworm in dogsHeartworm in dogs

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Trematodes (flukes)Trematodes (flukes)

• flatworms with ovoid leaflike bodiesflatworms with ovoid leaflike bodies

• have digestive, excretory, have digestive, excretory, neuromuscular, & reproductive neuromuscular, & reproductive systemssystems

• lack circulatory & respiratory lack circulatory & respiratory systemssystems

• animals such as snails or fish are animals such as snails or fish are usually the intermediate hosts & usually the intermediate hosts & humans are the definitive hostshumans are the definitive hosts

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Blood flukes: SchistosomesBlood flukes: Schistosomes

• schistomiasis is the 2schistomiasis is the 2ndnd most prominent most prominent parasitic disease parasitic disease (after malaria)(after malaria)

• adult flukes live in humans & release eggs adult flukes live in humans & release eggs into water. The early larva develops in into water. The early larva develops in freshwater snail into a 2nd larva freshwater snail into a 2nd larva

• this larva penetrates human skin & moves this larva penetrates human skin & moves into the liver to mature; adults migrate to into the liver to mature; adults migrate to intestine or bladder & shed eggs, giving intestine or bladder & shed eggs, giving rise to chronic organ enlargementrise to chronic organ enlargement

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TapewormsTapeworms

• flatwormsflatworms

• long, very thin, ribbonlike bodies long, very thin, ribbonlike bodies composed of sacs (proglottids) & a scolex composed of sacs (proglottids) & a scolex that grips the intestinethat grips the intestine

• each proglottid is an independent unit each proglottid is an independent unit adapted to absorbing food & making & adapted to absorbing food & making & releasing eggsreleasing eggs

• Taenia saginataTaenia saginata

• Taenia soliumTaenia solium

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Taenia saginataTaenia saginata

• beef tapewormbeef tapeworm• very large, up to 2,000 proglottidsvery large, up to 2,000 proglottids• humans are the definitive hosthumans are the definitive host• animals are infected by grazing on land animals are infected by grazing on land

contaminated with human fecescontaminated with human feces• infection occurs from eating raw beef in infection occurs from eating raw beef in

which the larval form has encystedwhich the larval form has encysted• larva attaches to the small intestine & larva attaches to the small intestine &

becomes an adultbecomes an adult• causes few symptomscauses few symptoms

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Beef Tapeworm

Tanenia saginata

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Taenia soliumTaenia solium

• pork tapewormpork tapeworm• infects humans through ingesting infects humans through ingesting

cysts or eggscysts or eggs• eggs hatch in intestine, releasing eggs hatch in intestine, releasing

tapeworm larva that migrate to all tapeworm larva that migrate to all tissues & encysttissues & encyst

• most damaging if they lodge in heart most damaging if they lodge in heart muscle, eye, or brainmuscle, eye, or brain

• may cause seizures, psychiatric may cause seizures, psychiatric disturbancesdisturbances

Arthropod VectorsArthropod Vectors

• Vectors are animals that carry microbial Vectors are animals that carry microbial pathogenspathogens

• Arthropods are a common vectorArthropods are a common vector

• Some arthropods also serve as hosts for Some arthropods also serve as hosts for the pathogens they transmitthe pathogens they transmit

• Disease vectors belong to two classes of Disease vectors belong to two classes of arthropodsarthropods– ArachnidaArachnida– InsectaInsecta

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Tick Mite Flea Lice

Fly

Mosquito

Kissing Bug

ArachnidsArachnids• Adult arachnids have four pairs of legsAdult arachnids have four pairs of legs

• Ticks and mites resemble each other Ticks and mites resemble each other morphologicallymorphologically

• Ticks are the most important arachnid Ticks are the most important arachnid vectorsvectors– Serve as vectors for bacterial, viral, and protozoan diseasesServe as vectors for bacterial, viral, and protozoan diseases– Second only to mosquitoes in the number of diseases they Second only to mosquitoes in the number of diseases they

transmittransmit– Hard ticks are the most prominent disease vectorHard ticks are the most prominent disease vector– Transmit Lyme disease, Rocky Mountain spotted fever, Transmit Lyme disease, Rocky Mountain spotted fever,

tularemia, relapsing fever, and tick-borne encephalitistularemia, relapsing fever, and tick-borne encephalitis

ArachnidsArachnids

• Parasitic Parasitic mitesmites are are found wherever found wherever humans and humans and animals coexistanimals coexist– Transmit rickettsial Transmit rickettsial

diseases among diseases among animals and animals and humanshumans

InsectsInsects• Adults have three pairs of legs as well as a Adults have three pairs of legs as well as a

head, thorax, and abdomenhead, thorax, and abdomen

• FleasFleas– Most fleas are not associated with humans but a Most fleas are not associated with humans but a

few do feed on humansfew do feed on humans– Plague is the most significant disease transmitted Plague is the most significant disease transmitted

by fleasby fleas

• Body liceBody lice– Parasites that can also transmit diseaseParasites that can also transmit disease– Most common among poor or overcrowded Most common among poor or overcrowded

communitiescommunities

InsectsInsects• FliesFlies

– Among the most common insectsAmong the most common insects– Those that transmit disease are generally Those that transmit disease are generally

bloodsuckersbloodsuckers

• MosquitoesMosquitoes– Most important arthropod vector of diseaseMost important arthropod vector of disease– Carry some of the world’s most devastating diseasesCarry some of the world’s most devastating diseases

• Kissing bugsKissing bugs– Often take blood meals near the mouth of their Often take blood meals near the mouth of their

human hostshuman hosts– Feed on blood nocturnally while the host sleepsFeed on blood nocturnally while the host sleeps