Parasitology I Flashcards
Endoparasites are divided into two major groups:
- protozoa (unicellular)
- helminths (multicellular worms)
Differentiate between the definitive host and the intermediate host
Definitive: host in which the sexual stage of the life cycle occurs
Intermediate: host in which asexual reproduction or development can occur
An ______ host is not an obligate part of a parasite’s life cycle
incidental/ accidental
What is a reservoir?
Animal host that maintains the natural cycle of infection in the wild, often not harmed by carriage
List the 5 CDC neglected parasitic infections in the US
- Chagas, caused by Trypanasoma cruzi
- Neurocysticercosis caused by Taenia sp
- Toxocariasis caused by Toxocara canis/ cati
- Toxoplasmosis: leading cause of foodborne deaths, congenital infection
- Trichomoniasis
Most protozoan infections elicit a _____ immune response.
Worms generally elicit a ________ immune response
protozoa: Th1
Worms: Th2/ eosinophils
Differentiate between: cyst, cysticeri, hyadatid cyst
Cyst: Dormant stage found encysted in host tissue (intermediate or definitive) so can be passed by eating undercooked meat
Cysticerci: Encysted cestode larval forms in tissues of infected intermediate hosts. Example: Humans/pork tapeworm
Cyst, Hydatid: Specialized cysticercal form of the cestode Echinococcus granulosus found in the intermediate host
Metacercaria, Miracidium, Microfilariae, Cercaria,
Filariform, Rhabditiform, Schistosomula, Sporocyst are alternate names for:
larvae
Class cestoda contains the
tapeworms
Class trematoda contains the
flukes
_____ have no internal digestive system and absorb nutrients across the cuticle.
_____ have a simple digestive system
Tapeworms- no digestive system
Flukes/ roundworms- have a simple digestive system
Describe the lifecycle of Taenia solium
Pork tapeworm
Pigs are the intermediate hosts and get cysticeri in their meat
Humans are the definitive host and shed eggs and proglottids in feces. Pigs do not shed eggs
Pigs become infected when they eat tapeworm eggs or proglottids
Humans become infected when they eat undercooked pork with cysticeri or tapeworm eggs form other humans
Only ___ shed eggs of Tania solium
humans
Distinguish between taeniasis and cysticercosis
When humans eat undercooked pork they get taeniasis- tapeworm in the intestine
When humans eat tapeworm eggs they get cysticercosis- larva in muscle, eyes, brain
beef tapeworm eggs are NOT infectious to people, only pork tapeworm eggs cause cystircercosis
Describe the location of Taenia solium infection
location: adult worms in intestin, cysticerci in any tissue but especially brain
What is the definitive host of Taenia solium
Humans
What is the intermediate host of Taenia solium
Humans or pigs
Describe the pathology of Taenia solium
- Taeniasis is often asymptomatic or causes abdominal discomfort, occasionally nausea, vomiting, diarrhea, weight loss & obstruction
- Cysticercosis cysticerci located in any tissue; in the brain can cause confusion, difficulty with balance, brain swelling, hydrocephalus, seizures, headaches and mortality
How is diagnosis of Taenia solium made?
Self or clinical- proglottids in stool
X ray, CT, MRI
Describe any immunity to Taenia solium
Humoral response to adults worms, reinfection is possible
Describe treatment for Taenia solium
Praziquantel, niclosamide or albendazole, single dose effective for adult worms but prolonged treatment for cysticerci
Dexamethasone added for infection of CNS
How can Taenia solium be avoided?
Fully cook pork
Public and personal hygiene
Describe the transmission of Diphyllobothrium latum
Fish tapeworm
Ingestion of undercooked fish containing plerocercoid
What is the definitive and intermediate host of Diphyllobothrium latum?
Definitive: Humans
Intermediate: copepod that infects fish
Where is Diphyllobothrium latum endemic?
Temperate zones, brought to new world by European immigrants
Describe the pathology of Diphyllobothrium latum
Like beef tapeworm; adults absorb 80-100% dietary B12 leading to deficiency, anemia, neurologic symptoms
Describe immunity to Diphyllobothrium latum
No clinically relevant immunity, reinfection is possible
How is Diphyllobothrium latum diagnosed?
Proglottids in stool, distinct from Taenia spp eggs
How is Diphyllobothrium latum treated?
praziquantel or niclosamide, single dose
How is Diphyllobothrium latum prevented?
Public hygiene, well cooked fish
_________ causes hydatid disease
Echinococcus granulosus
Ehinococcus granulosus localizes mainly to the:
lung, liver, spleen, kidney, heart, bone, CNS
How is Echinococcus graulosus transmitted
Ingestion of eggs from dogs
What is the definitive host of Echinococcus granulosus?
Wild and domestic canines
What is the intermediate host of Echinococcus granulosus
Wild and domestic ungulates, humans
Describe the life cycle of Echinococcus granulosus
- Basic cestode lifecycle; humans as intermediate/ dead end host only
- Requires intimate contact with dogs
How are dogs infected with Echinococcosis?
Ingest internal organs of sheep, goats, etc. Pastoral cycle
Describe the pathology of Echinococcosis
Hydatid cysts in liver (50-70%) and lungs (20-30%), but also spleen, kidney, bone and CNS
Latent periods up to 20 years
Disease onset when hydatid cysts cause pain or rupture
Cyst rupture can seed new sites by release of protoscolices
Anaphylaxis associated with rupture can be fatal but is rare
Describe immunity to Echinococcosis
Circulating antibodes to hyatid cyst antigens, more pathologic than protective
How is echinococcosis diagnosed?
Reside in endemic area or animal husbandry/ hunting
CT/ultrasound for cysts
Serology for confirmation
How is echinococcosis treated
percutaneous drainage wiht instillation of hypertonic saline, surgical removal, albendazole if not resectable (poor cure rate)
Describe measures to prevent echinococcosis
De-worm dogs, don’t feed intestines, good hygiene around dogs
Describe transmission of schistosomiasis
Invasive, aquatic free living cercaria penetrate skin
What are the definitive and intermediate hosts of schistosomiasis?
Definitie: humans, male-female pairings in blood
Intermediate: snails
Pathology of schistosomiasis is proportional to ________
worm burden
Schisosome _____ eggs are found in the stool and have a ____ spike
Schistosome ____ eggs are found in the urine and have a ____ spike
mansoni in stool, lateral spike
Haematobium in urine, terminal spike
Describe the stages of schistosomiasis pathology:
- Early: asymptomatic, rash that subsides and then fever, headache, nausea
- Middle: immune response to eggs, blood in urine/ stool, abdominal pain
- Chronic: eggs lodge in liver and intestine (mansoni, japonicum) or bladder (hematobium) and can lead to fibrosis and cancer
What is Katayama syndrome?
Intense reaction in patients infected with schistosomiasis for the first time, fever with onset of oviposition
Describe treatment of schistosomiasis
Praziquantel in single (S.m., S.h.) or multiple (S.j.) dose
Potentiates active immune system killing of adult worms
Describe the diagnosis of schistosomiasis
observation of eggs in feces, urine
Serology now available
Describe prevention measures for schistosomiasis
Treat infected individuals, proper waste disposal, control of intermediate hosts (snails), avoid contact with infected water
Describe the association between hepatitis C and schistosomiasis
earlier mass treatment (with tartar emetic) of Schistosomiasis in Egypt used contaminated needles leading to HCV infection.
Chronic inflammation from schistosomiasis exacerbates HCV
Be suspicious in middle aged Egyptian men
