Helminthic infectionsHelminthic infectionsHelminthic infectionsHelminthic infections

Infection vs. diseaseInfection vs. diseaseInfection vs. diseaseInfection vs. disease

• successful parasites live in, but do not successful parasites live in, but do not kill their hostskill their hosts

• protozoa multiply within hostsprotozoa multiply within hostsexpression of disease depends on host expression of disease depends on host

factorsfactors

• helminths do not multiply within hostshelminths do not multiply within hostsseverity of disease depends on parasite severity of disease depends on parasite

burden and immunologic response to burden and immunologic response to parasitesparasites

Parasite modes of entryParasite modes of entryParasite modes of entryParasite modes of entry

•IngestionIngestion

•Arthropod bitesArthropod bites

•Penetration of intact skin Penetration of intact skin or mucous membranesor mucous membranes

Spread and tropismsSpread and tropismsSpread and tropismsSpread and tropisms

•Some parasites must migrate to Some parasites must migrate to certain locations within the host certain locations within the host in order to complete their life in order to complete their life cyclecycle

•Non-human parasites, in Non-human parasites, in humans, often fail to migrate humans, often fail to migrate properly and properly and becomebecome “dead-end “dead-end infections”infections”

Mechanisms for evading the host response

Mechanisms for evading the host response

•antigenic variation - trypanosomes

• intracellular infection - plasmodia

•encystation* - amoebae, cestodes

•camouflage - schistosomes

* “cyst” has multiple meanings

Tissue damage and host Tissue damage and host responseresponse

Tissue damage and host Tissue damage and host responseresponse

•direct destruction of tissuedirect destruction of tissue

•hypersensitivity reactionshypersensitivity reactions

• eosinophiliaeosinophilia

–occurs with helminths, not protozoaoccurs with helminths, not protozoa

–results from tissue migrationresults from tissue migration

Classification of helminthsClassification of helminthsClassification of helminthsClassification of helminths

Nematodes (roundworms)Nematodes (roundworms)

Platyhelminthes (flatworms)Platyhelminthes (flatworms)

Trematodes (“flukes”)Trematodes (“flukes”)

Cestodes (“tapeworms”)Cestodes (“tapeworms”)

Helminthic diseasesHelminthic diseases

• Intestinal

–Others

–Strongyloides

• Invasive

–Trichinosis

–Filaria

–Schistosomiasis

–Cysticercosis

–Echinococcus

(autoinfection cycle)

(muscle pain, uncooked carnivores)

(worms in lymphatics or under skin)

(liver or urinary tract granulomas and fibrosis)

(cysts in brain, seizures)

(massive cysts in liver or lung)

roundworms

flukes

tapeworms

Intestinal nematodesIntestinal nematodesIntestinal nematodesIntestinal nematodes

Larvae passthrough lungs

Larvae penetratethrough intact skin

strongyloides hookworm

Eggs ingested

trichiurisenterobius

Larvae enterbloodstream

ascaris

Adult worms in the the intestine

Eggs

Larvae hatch from eggs

Strongyloides life cycleStrongyloides life cycle

Adult worms in the the intestine

Eggs

1st stage larvae hatch from eggs

Larvae penetratethrough intact skin

Larvae enterbloodstream

Larvae passthrough lungs

Larvae molt twice to formfilariform larvae (infectious)

Autoinfection

Strongyloides - clinical featuresStrongyloides - clinical features

• uncomplicated

–GI upset

• autoinfection

• hyperinfection

–rash

–bronchspasm, CXR infiltrates

–diarrhea

–profound eosinophilia

–recurrent Gram-negative bacteremia

Trichinella spiralisTrichinella spiralis - life cycle - life cycleTrichinella spiralisTrichinella spiralis - life cycle - life cycle

• ““cycle of carnivorism” among hogs and ratscycle of carnivorism” among hogs and rats

• humans ingest encysted larvae in infected, humans ingest encysted larvae in infected, undercooked porkundercooked pork

• larvae exist in stomach and burrow into small larvae exist in stomach and burrow into small intestinal mucosaintestinal mucosa

• adult males and female reemerge and produce adult males and female reemerge and produce larvae which penetrate intestine and circulate larvae which penetrate intestine and circulate in bloodstreamin bloodstream

• larvae enter skeletal muscle cells and encystlarvae enter skeletal muscle cells and encyst

Clinical features of trichinosisClinical features of trichinosisClinical features of trichinosisClinical features of trichinosis

•Most common sxs: Most common sxs:

–muscle pain and tenderness muscle pain and tenderness

–fever +/- chillsfever +/- chills

–edema (often periorbital)edema (often periorbital)

• >10% eosinophilia (often ~50%)>10% eosinophilia (often ~50%)

• elevated CPKelevated CPK

• +/- chronic neurologic/myocardial sxs+/- chronic neurologic/myocardial sxs

• self-limited (2% mortality)self-limited (2% mortality)

Treatment of trichinosisTreatment of trichinosisTreatment of trichinosisTreatment of trichinosis

• antihelminthic (albendazole) to antihelminthic (albendazole) to kill any intestinal adultskill any intestinal adults

• steroids to relieve inflammatory steroids to relieve inflammatory reactionsreactions

• antipyreticsantipyretics

Life cycles of two types of filariaLife cycles of two types of filariaLife cycles of two types of filariaLife cycles of two types of filaria

Arthropod vector

Adultworm pairs

Larvae(microfilariae)

Lymph- mosquitoes peripheral circulate dwelling lymphatics in bloodstream(e.g, Wuchereria bancroftii )

Skin- biting flies skin nodules migrate through dwelling or migratory dermis

O. volvulus microfilaria in skin snip

O. volvulus nodule

DirofilariaDirofilaria in a human lung in a human lung

Role of endosymbiont Role of endosymbiont WohlbachiaWohlbachia sp. in filiaria infectionsp. in filiaria infection

Role of endosymbiont Role of endosymbiont WohlbachiaWohlbachia sp. in filiaria infectionsp. in filiaria infection

• Rickettsia-like organisms required Rickettsia-like organisms required for fecundity and viability of filariafor fecundity and viability of filaria

•Wohlbachia-free worms produce Wohlbachia-free worms produce less inflammation in tissue (? LPS)less inflammation in tissue (? LPS)

• Implications for rx:Implications for rx:

–ivermectin kills microfilaria onlyivermectin kills microfilaria only

–tetracycline may destroy adult wormstetracycline may destroy adult worms

Geographic distribution of Geographic distribution of schistosomiasisschistosomiasis

Geographic distribution of Geographic distribution of schistosomiasisschistosomiasis

S. mansoniS. mansoni

S. hematobiumS. hematobium

S. japonicumS. japonicum

Schistosomiasis - life cycleSchistosomiasis - life cycleSchistosomiasis - life cycleSchistosomiasis - life cycle

S.m. S.h. S.j.

“pipestem” fibrosis

Schistosomiasis - pathogenesisSchistosomiasis - pathogenesisSchistosomiasis - pathogenesisSchistosomiasis - pathogenesis

• egg granuloma (type IV reaction)--> egg granuloma (type IV reaction)--> fibrosisfibrosis

•morbidity ~ worm (egg) burdenmorbidity ~ worm (egg) burden

• concomitant immunity to schistosomulaconcomitant immunity to schistosomula

• adult worms: invisible to the immune adult worms: invisible to the immune system (survive for years)system (survive for years)

Schistosomiasis- clinical featuresSchistosomiasis- clinical featuresSchistosomiasis- clinical featuresSchistosomiasis- clinical features

• Cercarial dermatitisCercarial dermatitis

• Intestinal schistosomiasis Intestinal schistosomiasis (granulomas --> (granulomas --> polyps, protein loss, malabsorption, strictures)polyps, protein loss, malabsorption, strictures)

•Hepatosplenic schistosomiasis Hepatosplenic schistosomiasis (portal (portal hypertension --> ascites, varices, splenomegaly, hypertension --> ascites, varices, splenomegaly, normal hepatic function)normal hepatic function)

• Urinary schistosomiasis Urinary schistosomiasis (hematuria, chronic (hematuria, chronic infection, obstruction)infection, obstruction)

• Other (cardiopulmonary, CNS, etc.)Other (cardiopulmonary, CNS, etc.)

Drug treatment of Drug treatment of schistosomiasisschistosomiasis

Drug treatment of Drug treatment of schistosomiasisschistosomiasis

• Praziquantel increases permeability Praziquantel increases permeability of adult parasite to Caof adult parasite to Ca++++..

• Tetanospasm --> deathTetanospasm --> death

Control of SchistosomiasisControl of Schistosomiasis

REDUCE CARRIERS mass rx program

ELIMINATE SNAILS molluscicides

destroy snail habitats

snail-eating fish

PREVENT WATER

CONTAMINATION latrines, toilets

public health education

PREVENT HUMAN

EXPOSURE water systems

TapewormsTapeworms

•Definitive hosts: harbor adult worms

• Intermediate hosts: harbor tissue cysts (containing worm heads)

•Humans acquire infection two ways:

–ingestion of eggs from feces (to acquire tissue cysts)

–ingestion of tissue cysts in undercooked meat (to acquire a tapeworm)

= Intermediate host

= Definitive host

TaeniasisTaeniasis

Tapeworm Cysticercosis

poorhygiene

poorsanitation

ingestion ofundercooked pork

CysticerciCysticerci Hydatid CystHydatid Cyst

Isolated cysticerci Hydatid cyst

EchinococcosisEchinococcosis

Cystic Hydatid Disease

contact with dogs

ingestion of entrails

ingestion ofeggs inpastures

Treatment of cysticercosis and Treatment of cysticercosis and echinococcosisechinococcosis

Treatment of cysticercosis and Treatment of cysticercosis and echinococcosisechinococcosis

• Antihelminthic therapy (e.g., Antihelminthic therapy (e.g., albendazole, praziquantel)albendazole, praziquantel)

• (Echinococcus only)(Echinococcus only)

–Surgical removalSurgical removal

–Irrigation-evacuation of cystsIrrigation-evacuation of cysts

Comparison of pork tapeworm and Echinococcus life cycles

Comparison of pork tapeworm and Echinococcus life cycles

Definitive hosts (adult tapeworms)

Intermediate hosts(tissue cysts)

Dead-end hosts

Dog

Sheep

Human

Pig

Human

Human