Lecture 6: Parasites

(Parasites) Lecture 6 Parasites ① Protozoa ② Metazoa · Cyst form: a tough layer called the cyst or oocyst is formed ① Protozoa ↳ 1. nematodes a) eggs are infective stage b) larvae are infective stage ↳ 2. trematodes · protozoans: one celled eukaryotes outside of the plasma membrane ↳ this form is protective, not infective · Trophozoite form: the growing form where there is no cyst wall, just cytoplasmic membrane ↳ 3. Cestodes ↳ this is the infectious form ③ Ectoparasites Protozoans to know: 1. Entamoeba histolytica · agent of amoebic dysentry (severe diarrhea) · feeds on RBC · ulcer formation and bloody diarrhea · cyst and trophozoite forms · cyst has high resistance to chlorine 2. Giardia lamblia · agent of giardiasis "beaver fever" · intestinal upsets, flatulence, nausea, abdominal cramps, diarrhea 1. Entamoeba histolytica 2. Giardia lamblia 3. Trichomonas vaginalis 4. Acanthamoeba 5. Cryptosporidium parvum 6. Toxoplasma gondii 7. Trypanosoma 8. Leishmania 9. Plasmodium · cyst and trophozoite forms · cysts are hardy, high resistance to chlorine (Caused by drinking bad water) 4. Acanthamoeba sp 3. Trichomonas vaginalis "Trich" · grows in water, exists as a cyst form in dust · no cyst stage, transmitted sexually · can lead to eye loss · flagellate, motile · important for those who wear contact lenses · intense itching and inflammation of pubic area · cyst and trophozoite stage 5. Cryptosporidium parvum 9. Plasmodium species · chronic diarrhea, severe in immunocompromised, · transmitted by Anopheles mosquito · cows, rats, dogs, cats, to people · causes malaria, no vaccine serious even in immunocompetent · 4 main types · must use ZN stain ↳ P. falciparum (most dangerous) · oocysts have high resistance to chlorine ↳ P. ovale ↳ P. malariae · cyst stage 6. Toxoplasma gondii · life cycle in cats - cat feces contain oocysts · tissue cysts containing the protozoan can form in other animals · acquired from undercooked meat (tissue cysts) or cat feces (oocysts) ↳ P. Vivax · P. falciparum is most dangerous because it infects all ages of RBC (high level of parasitized RBC) · mosquito carries the sporozoite in saliva which reaches the liver within 30 min · symptoms of P. falciparum: -fever and chills caused by toxic breakdown · bad for pregnant women -sequestration (sticky collections)of parasites and RBC occlude capillaries and cause organ 7. Trypanosoma · blood parasites, transmission mostly in vectors death. Virulence factor P-EMP1 (a protein) · Severe consequences of P. falciparum malaria: · 2 types: ↳ cerebral malaria: clumping and occlusion of ↳ T. brucei gambiense/rhodesiense blood vessels, also Vasculitis ↳ T. cruzi ↳ kidney failure: caused by high levels of -causes african sleeping sickness (tsetse fly) ↳ anemia: caused by lysis of RBC -causes Chaga's disease (reduviid/kissing bug) hemoglobin breakdown products 8. Leishmania sp · ~20 different species transmitted by sand fly vector · visceral, cutaneous, and mucocutaneous syndromes · Live and develop in macrophages ② Metazoa (worms) 1. Nematodes · nematodes: roundworms with complete digestive system, including mouth, intestine, and anus a) eggs are the infective stage (2) 1) Enterobius Vermicularis (Pinworm) 2) Ascaris lumbricoides (Untreated manure) · spends whole life cycle in human · large round worms just outside of the anus · eggs in soil very hardy · usually not serious but easily infections · diagnoses by examination of feces · lives in large intestine, females migrate to anus, lay eggs · lives in small intestine of pigs, cows, horses · produces a glue (irritant) to stick the eggs to the skin · adult worms distinct sexes (dioecious) · eggs are the infections stage and transmitted by direct contact with eggs or ingestion of eggs stirred up in dust (Very infectious in daycare settings) Hyperactivity b) larvae as infectious stage (4) 1) Hookworms 2) Anisakis · -> lymph & circulatory system -> lungs -> coughed up larval form by hooks on the scolex (head) · Prevent by heating (60* for 10 min)or · eggs excreted days), OR Cleaning · infection by larvae, enter intact skin of bare feet · fish nematodes accidentally infect humans in and swallowed to small intestine, where they attach · rare infection · suck blood, causes anemia blast-freeze (-35* for 15 hours, -23* for 7 · only in warm climates -- 3) Trichinella spiralis · ingestion of undercooked pork, bear, boar, walrus · larvae encyst in striated muscle fibers (and heart) · muscle weakness is dominant symptom · difficult to treat 4) Blood hematodes (filaria) lymphatic filariasis (elephantiasis) ↳ adult worms live in lymph tissue onchocerciasis ↳ adult worms live in subcutaneous tissue · transmission by mosquitos · microfilariae (offspring of adult worms) circulate through bloodstream or migrate 2. Trematodes (Flukes) through subcutaneous tissue Schistosoma · Human infected by larvae that penetrate intact skin in fresh water ponds · adults hide from host immune system under a coat of protein acquired from host · worms reside in the venous plexus of bladder or intestine, depending on species · eggs cause inflammation · 3 types of schistoma: ↳ S. haematobium -inflammation of bladder wall -bladder cancer ↳ S. japonicum -intestinal parasite ↳ S. mansoni -intestinal parasite -Often in liver “Swimmers itch” Caused by duck schistosome Does not enter human circulation 3. Cestodes (tapeworms) · intestinal parasites, dependent on host for nutrients, no digestive system · head/scolex has suckers or hooks for attachment · body consists of segments called proglottics, each of which contains male and female productive organs · acquired by eating inadequately cooked contaminated beef, pork, or fish · Tapeworms cause 2 types of disease: ↳ Intestinal infection: mild clinical picture, produced by pork, beef, fish, or rodent tapeworms ↳ deep tissue infection: serious infections, pork tapeworm (cysticercosis) or echinococcosis (dog tapeworm) 1) Taenia saginata: beef tapeworm 2) Taenia solium: pork tapeworm · infectious tissue larvae (cysticerci) ingested by · more dangerous than beef tapeworm (cerebral · life cycle requires both humans and cattle humans in infested meat and mature into adult tapeworms in intestine · eggs passed in feces · usually mild symptoms · life cycle involves both pigs and humans cysts cause cysticercosis) · person to person transmission is possible · 2 modes of transmission: ↳ eggs: result in hatching of larva in intestine, which then escape and penetrate body tissues, including the brain 3) Echinococcus granulosus: dog tapeworm · small tapeworm, humans are dead end hosts · dogs, coyotes, dingos · larva develops into a hydatid cyst with hundreds of worm parts but cannot form a whole tapeworm in humans ↳ larvae: result in adult worm in intestine ③ Ectoparasites · live on skin, do not enter deep tissues · often result in secondary infections due to scratching 1. Sarcoptes scabei (Scabies) · fingerwebs, elbows, armpits, breasts, groin and buttocks · mites burrow into skin, feed, life span 30 days, mate, lay eggs in burrow · host defenses cause inflammation around the burrows, intense itching · secondary infections with skin bacteria · other sarcoptes mites to not thrive on humans 2. Phthirus pubis (public lice/crabs) and Pediculus humanus (headlice) · surface dwellers · penetrate skin with mouth, such blood · female glues eggs to hair shafts · eggs hatch in 5-10 days · secondary infections when lice feces are crushed into wounds