Eukaryote agents of disease

Protists, Fungi and Helminthes

Apicomplexa

• Plasmodium falciparum• Babesia microti• Cryptosporidium• Toxoplasma gondii

Malaria

• Several species within the genus, Plasmodium– P. falciparum– P. ovale– P. vivax

• Severity and treatability varies by species• Anopheles spp. mosquitoes are vectors and definitive

hosts, where sexual reproduction occurs, transmit through injection of saliva

• Asexual stage occurs in humans when merozoites/trophozoites reproduce in RBC

Cryptosporidium spp.

• Cause cryptosporidiosis• Many mammalian reservoirs• Cysts are highly resistant to environmental stress and

water treatment (i.e. chlorination)• Cysts passed in feces of host, survive long periods in

water where they may be ingested by next host• May also be transmitted by direct fecal-oral route• Causes diarrhea, which may be severe in

immunocompromised patients• Massive outbreaks (Milwaukee) can occur when water

treatment malfunctions

Babesia microti

• Causes babesiosis• Often asymptomatic• flu-like symptoms usually not fatal• Difficult to treat• Parasite resemble P. falciparum in RBCs• rodents are main reservoir• Transmitted by black-legged ticks (Ixodes scapularis) to

humans

Toxoplasma gondii

• Causes toxoplasmosis• May be asymptomatic, or resemble low-grade infection

resembling mononucleosis• May lead to still births in congenital infections• Contracted through contact with cat feces, or

undercooked beef• Many mammals and birds may be infected but cats are

definitive hosts

Mastigophora

• Giardia intestinalis (lamblia)• Trypanosoma cruzi• Trypanosoma brucei gambiense, T.b. rodesiense.• Trichomonas vaginalis • Leishmania spp.

Trypanosomes

• Chaga’s disease- Trypanosoma cruzi

• African Sleeping Sickness– Trypanosoma brucei gambiense– T.b. rodesiense.

Leishmania spp.

• Visceral leishmaniasis (kala-azar)• Cutaneous leishmaniasis (Baghdad boil, oriental sore

other names)• Muco-cutaneous leishmaniasis (espundia)• Transmitted by sand fly

Trichomonas vaginalis

• Causes trichomoniasis, vaginitis• Symptoms include profuse vaginal discharge• Limited by normal vaginal acidity• Male prostate, seminal vesicles, urethra may be infefcted

Giardia intestinalis

• One of the most common protozoan parasites in U.S.

• Adheres to intestinal epithelium and disrupts absorption of water and nutrients

• Fecal-oral route of transmission, especially through water contaminated with feces of humans or reservoirs

• Many mammals can be reservoirs

Sarcodina

• Entamoeba histolytica• Naegleria fowleri• Acanthamoeba castellani

Entamoeba histolytica

• Amebic dysentery• Severity varies by strain and host• Invade intestinal mucosa and may result in long-term

infection and tumor-like masses (amebomas)• Extra intestinal infection may result in liver abcess• Severe cases may result in malnutrition• Many animals may harbor these parasites in their

intestines

Free-living amebas• Naegleria fowleri may enter through the nose of host from

fresh water– Enters NS through olfactory epithelium and into brain

where they cause severe tissue damage and hemorrhage

– Often fatal after only a few days – Treatment with Amphotericin B is possible if diagnosis is

made quickly

• Acanthamoeba castellani is Similar to N. fowleri, however, entry may be through ulcers or damaged tissues, such as corneal abrasions associated with contact lenses

Fungi

• Medical mycology is the study of disease-causing fungi• Can cause infection (Candida etc..) or intoxications (see

below)• Many fungi are saprophytes and live primarily off of dead

organic matter

Intoxicating fungi• Aflatoxins on moldy foods- Aspergillus flavus• Ergotism- Claviceps purpurea• Poor indoor air quality-black mold, Stachybotriys sp.

Candida albicans

• candidiasis (oral, intestinal, vaginal, cutaneous)• Often called thrush• Vaginitis (yeast infection)• Diaper rash in babies• Can invade many internal tissues and cause

toxic reactions (including sepsis)

Dermatophytes

• Superficial cutaneous mycoses caused by three genera: Trichophyton spp. Microsporum, and Epidermophyton spp.– Tinea pedis- atheletes foot (feet and hands)

– Tinea cruris-jock itch

– Tinea corporis (ringworm that actually forms the characteristic ring)- non-hairy surfaces of body

– Tinea capitus (ringworm of scalp)

– Tinea barbi (ringworm of facial hair)

Not scientific names of organisms but names of diseases

Other fungal skin diseases

• Sporotrichosis- Sporothrix shenckii• Blastomycosis- Blastomyces dermatitidis

Fungal respiratory diseases

• Coccidiomycosis- Coccidioides immitis• Histoplasmosis- Histoplasma capsulatum• Cryptococcosis- Filobasidiella (Cryptococcus)

neoformans• Pneumocystis pneumonia- Pneumocystis carinii• Aspergillosis- Aspergillus spp.

Helminthes

• Platyhelminthes-flatworms– Cestodes: tapeworms– Trematodes: flukes

• Nematoda-roundworms– Filarial worms– Others

Tapeworms (cestodes)

• Beef tapeworm- Taenia saginata- undercooked beef• Pork tapeworm- Taenia solium- undercooked pork

– Cysticercosis results from the ingestion of human feces. Cysticerci form in tissues all around the body including the brain can result in epilepsy and death

Other Tapeworms

• Broad fish tapeworm- Dibothrocephelus latus (Dyphyllobothrium latum) eating undercooked freshwater fish

• Hydatidosis or hydatid disease- Echinoccocus granulosus, dog feces cysts form in tissues including the brain

• Vampirolepis (Hymenolepis) nana- most common cestode infection of humans, animal feces

• Dipylidium caninum- children accidental hosts by ingesting fleas

Blood FlukesSchistosomiasis (bilharzia)

• Schistosoma mansoni, S. japonicum, S. haemotobium and others

• Distributed throughout Africa, South Asia and equatorial South America (S. mansoni)

• Female lives within body groove of male, female body adapted for laying eggs in blood vessel.

• Eggs pass in human feces and into natural water• Miracidium invades snail (intermediate host)• Cercaria invades human in water • Cercarial dermatitis (swimmers itch)-various genera of

schistosomes- an allergic reaction to a parasite that doesn’t normally infect humans

Other Flukes• Sheep fluke- Fasciola hepatica

– Snail intermediate host– Infective stage on aquatic vegitation

• Chinese liver fluke- Chlonorchis sinensis– Snail intermediate host– Second intermediate host commonly Grass Carp– Survive meat preparation other than cooking

• Lung fluke- Paragonemus westermani– Acquired through eating raw crabs– Metacercariae bore through GI tract and penetrate

the diaphragm and into the bronchioles, eggs transported out of lungs by cilia, swallowed and expelled with feces

Nematodes: Hookworm

• Main species :Ancelystoma caninum and Necator americanus

• Larvae penetrate skin and migrate to circulatory system, then travel to lungs, coughed up and swallowed, adults reside in intestines as blood feeders

• Cutaneous larva migrans (creeping eruption) caused by hookworms that can’t get into the blood stream

Nematodes: Filarial worms

• Onchocerciasis, River blindness – caused by Onchocerca vovulus a filarial worm that

migrates to various tissues including the eyes– Transmitted by black flies (Simuliidae: Simulium

damnosum)• Loaiasis

– Caused by Loa loa, filarial worm, that can end up in the eye but does not result in blindness

– Transmitted by deer flies (Tabanidae: some African spp. of Chrysops)

Lymphatic Filariasis

• Main species that cause LF are Wuchereria bancrofti and Brugia malayi

• Several species of mosquitos are vectors including Culex spp. Aedes spp.

• Periodic and subperiodic forms of transmission cycle, may also be diurnal or nocturnal

• Filarial worms cause inflammation and block the flow of lymph- this can result in elephantiasis

Common Nematode infections

Disease Nematode species Transmission

Ascariasis Ascaris lubricoides ingestion of contaminated soil

Whipworm Trichuris trichiura ingestion of contaminated soil

Pinworm Enterobius vermicularis

ingestion or inhalation of eggs

Other Nematode infections

Disease Nematode species Transmission

Trichinosis Trichinella spiralis Undercooked pork

Stongyloidiasis Strongyloides stercoralis

Penetration of skin

Can complete cycle in one host, easy transmission

Anasikiasis Anisakis spp. Undercooked fish

Raccoon roundworm infection

Baylissascaris procyonis

Ingestion of contaminated soil

Guinea worm Dracunculus medinensis

Ingestion of crustacean in water