Microbiology and Immunology Lecture #7 PDF

Parasitism • Intimate and obligatory symbiotic relationship between two organisms of different species • Parasite is metabolically and physiologically dependent on host • Short term (mosquito) or permanent (tapeworm) • Very common way of life (50% of animal species) • “True parasit...

Parasitism • Intimate and obligatory symbiotic relationship between two organisms of different species • Parasite is metabolically and physiologically dependent on host • Short term (mosquito) or permanent (tapeworm) • Very common way of life (50% of animal species) • “True parasites” include protozoans (single -celled), helminths (worms), and arthropods (ectoparasites) “Success” of parasites defined in terms of:  prevalence in hosts  number of host species available  geographic range  number of offspring  available routes of transmission Giardia lamblia (syn. G. duodenalis , G. intestinalis ) HISTORY first described by Leeuwenhoek in 1681: “…I have sometimes also seen animalcules a -moving very prettily, their belly which was flatlike, furnisht with sundry little paws…” • Demonstrated to be a true pathogen in the early 1900’s • Most frequently identified intestinal parasite worldwide Symptoms – G. lamblia • Most infections are asymptomatic (carriers) • acute giardiasis: diarrhea, weight loss, abdominal discomfort, nausea, vomiting • de ficiencies in growth and development in young children (failure to thrive) Prevalence - G. lamblia • most common protozoan infection of intestinal tract worldwide • 2 -5% in industrialized world and 20 -30% in developing world; • prevalence rises through infancy and childhood and declines in adolescence (related to faecal -oral route of transmission) • Other high risk groups include travelers and immunocompromised Life cycle – G. lamblia -excystation -trophozoites in small intestine -longitudinal binary fission -encystation -cysts shed with faeces Waterborne Outbreaks of Giardiasis in Canada LOCATION YEAR CASES 100 Mile House, BC 1981 65 Banff, AB 1982 121 Edmonton, AB 1983 895 Penticton, BC 1986 362 Creston, BC 1986 83 Botwood, NL 1991 136 Creston, BC 1991 124 Corner Brook, NL 1992 50 Temagami, ON 1994 ? Deer Lake, NL 1994 9 Muskoka/Parry Sound, ON 1995 37 Camp Tawingo, ON 1995 35(?) Valemont, BC 1996 10 Swift Current, SK 1996 3(?) Les Escoumins, QC 1997 ? Ange Gardien, QC 1999 3 Foodborne Outbreaks in North America Location Year Cases Food Goodhue, Minn. 1979 29 canned salmon Peace River, Alberta 1982 22 ice Newtown, Conn. 1985 13 noodle salad Minnesota 1986 88 sandwiches New Jersey 1986 10 fruit salad Albuquerque, N.M. 1988 21 lettuce, tomatoes Washington State 1990 27 ice Hartford, Conn. 1990 27 raw vegetables Minnesota 1991 20 fresh fruit Illinois 1996 6 ice cream Washington State 1998 3 seafood Diagnosis – G. lamblia MICROSCOPY (stool exam) • cysts concentrated by flotation and identified using bright -field microscopy • immunofluorecence microscopy using fluorochrome -conjugated mAb’s that bind to cyst wall Diagnosis – G. lamblia cont’d Immunological Testing • detection of Giardia - specific antigens in faeces (eg. ELISA) Treatm e nt – G. lamblia Nitroimidazole derivatives - metronidazole and tinidazole are the drugs of choice; 2 g (single dose) daily for 3 days NB. drug resistance to metronidazole and furazolidone has been described Control - Water Treatment • resistance to chlorination • fewer outbreaks in municipalities using water filtration • ozone / UV light promising • EPA method 1623 Control – G. lamblia PUBLIC HEALTH EDUCATION • increase awareness of person -to -person transmission; improve hygienic practices (e.g., daycares) • food -borne infections (food handlers, wash produce) • backpackers drinking raw surface water are at risk (portable filters, boil water) • Advice to travelers (avoid tap water, peeled fruits) Trichomonas vaginalis • Possibly the most common sexually transmitted disease worldwide (200 million cases) • Transmitted through mucous membrane contact (no resistant cyst stage) Trichomonas vaginalis - Symptoms • 40 -50% asymptomatic carriage • Vaginitis (trichomoniasis) with itching, foul -smelling, sometimes frothy discharge • May increase susceptibility to cervical cancer and HIV infection • Infection during pregnancy may result in premature delivery and low birth weight • Males usually asymptomatic; occasionally urethritis, prostatitis Trichomonas vaginalis - Diagnosis • Microscopy (wet mounts) to identify trichomonads in vaginal or urethral discharge • Vary greatly in size (10 - 30µm) Trichomonas vaginalis - Treatment • metronidazole and tinidazole are drugs of choice • To avoid re - infection, testing and treatment of partners is important Toxoplasma gondii • Recognized as a human pathogen in early 1900’s • Very high seroprevalence in humans worldwide • Large number of mammals and birds act as intermediate hosts • cats are the only definitive hosts (shed oocysts) Life cycle of Toxoplasma gondii Toxoplasma gondii - Transmission 1. Ingestion of sporulated oocysts (10 -12 µm) - contaminated soil/sand - contaminated fruits and vegetables - waterborne outbreaks (Victoria, B.C., 1995) 2. Ingestion of tissue cysts - raw or poorly cooked meat 3. Congenital infection of fetus - infection acquired during pregnancy (most severe if acquired in first trimester) Toxoplasmosis - Foodborne Outbreaks Location Year Cases Implicated Food New York State 1968 5 rare hamburger New York, NY 1975 6 rare lamb California 1978 10 raw goat’s milk Quebec 1987 4 raw game meats Symptoms of toxoplasmosis 1. Immunocompetent host 90% asymptomatic, lymphadenopathy, headaches, muscle aches, fever, malaise 2. Immunocompromised host encephalitis, myocarditis, pneumonia (AIDS - defining disease) 3. Congenital infection hepatosplenomegaly, intellectual deficiency , retinochoroiditis, hydrocephalus Treatment of toxoplasmosis • Diagnosis based on serological assays • Immunocompetent patients normally don’t require treatment unless symptoms become severe or chronic • Immunocompromised patients require prompt treatment with a combination of pyrimethamine and sulfadiazine • Congenital infections: – Mother/fetus can be treated to reduce incidence and severity of fetal infection – Infected newborns can also be treated to minimize sequelae Malaria - Transmission • Anopheline mosquitoes (vectors) • Blood transfusion / shared needles • Congenital infection • “Airport malaria” Symptoms of Malaria • Spiking fever and chills • Flu - like symptoms (myalgias, headaches, abdominal pain, malaise) • Severe symptoms ( P. falciparum ) seizures, coma, renal failure, respiratory failure Malaria prophylaxis and treatment • Chloroquine and mefloquine are drugs of choice for prevention and treatment • drug resistance is a serious problem Control of Malaria • Largely a man -made disease (clearing of forests, building of irrigation canals) • Eradication or control of mosquitoes (resistance to insecticides) • Protection against mosquito bites – Avoid rural areas at night – Long -sleeved shirts/long pants – Insect repellent – Bed netting Cryptosporidium spp. • recognized as human pathogen (1976) • reported in humans worldwide • The most common symptom of cryptosporidiosis is watery diarrhea; other symptoms include dehydration, weight loss, abdominal pain, fever, nausea, vomiting • chronic, debilitating, and potentially life -threatening symptoms in immunocompromised • No drug treatment available! Life cycle – Cryptosporidium • complex life cycle including both sexual and asexual phases (oocysts 4 - 6 µ) • obligate intracellular protozoan which infects the intestinal epithelial cells of the host (typically in small intestine) Transmission - Cryptosporidium WATER • numerically the most important mode of transmission (contaminated drinking water) • recently numerous outbreaks associated with water parks/pools Waterborne Outbreaks of Cryptosporidiosis in Canada Location Year Cases Kitchener -Waterloo, ON 1993 1,4 0 0 Kelowna, BC 1996 15, 0 00 Collingwood, ON 1996 121 Cranbrook, BC 1996 136 Shoal Lake, MB 1997 64 North Battleford, SK 2001 1,9 0 7 NB. Milwaukee, Wisconsin, 1993 (400,000 cases, 100 deaths) Transmission - C. parvum PERSON - TO - PERSON • ingestion of oocysts due to poor hygiene (e.g., day cares, institutionalized patients) AUTOINFECTION • thin -walled oocysts are released into the lumen and cause autoinfection • responsible for chronic and life -threatening disease in immunocompromised Transmission - C. parvum ZOONOTIC • cattle serve as important reservoir hosts • calves with diarrhea can excrete up to 10 10 oocysts/day • environmental contamination; veterinary personnel and animal handlers at increased risk (petting zoo visitors) Foodborne Outbreaks – C. parvum Location Date Cas e s Food Maine 1993 160 apple cider Minnesota 1995 15 chicken salad New York 1996 31 apple cider Washington 1997 54 green onions Washington DC 1998 92 raw produce Diagnosis - C. parvum MICROSCOPY • oocyst shedding intermittent; multiple stools examined • concentration methods can be used when low oocyst shedding • wet -mounts or permanent stains are used (acid -fast) • Fluorescein -labelled IgG mAb is used in immunofluorescence microscopy Control - Water Treatment • Watershed management • Flocculation / Sand filtration • Resistance to chlorination • Ozone, UV light • Water testing (EPA method 1623) Control - C. parvum PUBLIC HEALTH EDUCATION • in endemic areas, avoid drinking tap water/ice cubes, raw fruits and vegetables unless you can peel them • immunocompromised patients should consider bottled water • exposure to temperatures above 60 ° C and below -20 ° C will kill oocysts Control - C. parvum PUBLIC HEALTH EDUCATION - cont’d • because crypto is spread person - to - person, handwashing helps prevent infection • precautions are required when caring for patients with crypto diarrhea; lack of effective disinfectants against oocysts (nosocomial infections) Cyclospora cayetanensis • Identified as a coccidian protozoan parasite and named in 1993 • Cases reported in North, Central, South America, Caribbean, S.E. Asia, Europe, UK, India, Africa • Endemic countries include Nepal, Haiti, Peru, and Guatemala Cyclosporiasis - Symptoms • Low infectious dose • Incubation period approximately 1 week • Profuse and prolonged diarrhea • Abdominal pain, nausea, vomiting, fatigue, fever, loss of appetite • Effectively treated with bactrim (trimethoprim - sulfamethoxazole) Cyclosporiasis - Diagnosis • microscopic examination of wet mount stool for oocysts (brightfield, differential interference contrast, autofluorescence) • staining methods (e.g. acid - fast) Cyclosporiasis - Transmission • Person - to - person transmission unlikely • Zoonotic transmission unlikely • Most earlier outbreaks were waterborne • 90 - 99% of cases in U.S. are foodborne • Numerous foodborne outbreaks in recent years U.S. / Ontario May -June 1996 1,465 raspberries/blackberries (Guatemala) U.S. / Ontario Apr. -May 1997 1,012 raspberries/blackberries (Guatemala) Washington DC June -July 1997 260 basil Virginia Sept. 1997 21 fruit plate Florida Dec. 1997 12 mesclun (Peru) Ontario May 1998 192 raspberries (Guatemala) Ontario May 1999 104 blackberries? Missouri July 1999 65 basil (Mexico or U.S.) Atlanta GA May 2000 21 raspberries (Guatemala) Vancouver BC May 2001 17 Thai basil Vermont Jan. 2002 22 raspberries (Chile?) Vancouver BC June -July 2003 10 cilantro? Texas / Illinois Feb. 2004 95 basil/mesclun? Vancouver BC May -June 2004 9 cilantro? Pennsylvania June -July 2004 <100 snow peas (Guatemala) Florida Mar. -Apr. 2005 >300 basil (Peru) Ontario Apr. 2005 40 basil (Peru) Ontario Apr. 2005 4 basil (Peru) Quebec June 2005 226 basil (Mexico) Foodborne outbreaks of cyclosporiasis in North America Contamination of Foods Direct contamination • infected pickers, sorters, inspectors, or other food handlers (poor hygiene, sporulation) Indirect contamination • contaminated water used for irrigation, mixing pesticides, washing equipment, washing hands Enterobius vermicularis (pinworm) • Prevalent world wide • Highest incidence in school - age children • Up to 50% of children in North America • More of a nuisance than a health problem • Eggs ingested (faecal - oral route) Pinworm - Symptoms • Mild infection of caecum/colon • May cause itching (pruritus ani) leading to disturbed sleep, irritability • Scratching may cause secondary infections Pinworm – Diagnosis/Treatment • Scotch - tape test of perianal area • Microscopic identification of eggs; adult female worms may also be present (8 - 13mm) • Drug of choice is pyrantel pamoate Pinworm - Control • Personal hygiene education for children (wash hands) • Discourage scratching, nail biting • Frequent bathing; regular change of underclothing, pajamas, and bedding • Small roundworm found worldwide in many carnivorous and omnivorous animals, including humans • Transmitted through ingestion of larvae in raw or poorly cooked meat • Survives as adult in small intestine; as larvae encysted in striated muscle Trichinella spp. Trichinella spiralis (domestic form) - humans, swine, rats (responsible for endemicity) - horses! (probably fed animal products as supplement) Trichinella nativa (sylvatic or wild form) - humans, bears, wild boar, wolf, fox, walrus, etc. T. spiralis adult female T. spiralis adult male Trichinellosis - Symptoms • Symptoms dependent upon phase of life cycle • When larvae excyst in small intestine - diarrhea, abdominal pain, vomiting • When next generation of larvae migrate into muscle tissues - facial edema, conjunctivitis, fever, myalgias • Occasional life -threatening manifestations include myocarditis, central nervous system involvement, and pneumonitis Trichinellosis - Treatment • Thiabendazole effective against intestinal phase • Mebendazole and albendazole have some effect on tissue phases • Steroids may be used to reduce inflammation Trichinellosis - Control • Rodent control • Avoid garbage feeding to livestock • Inspection programs (trichinoscopy, digestion, ELISA) • Cooking /freezing ( T. nativa very resistent to freezing) Diphyllobothrium spp. (Broad fish tapeworm) • large tapeworm (10 m long) • Adult tapeworm inhabits the small intestine of humans and other fish - eating mammals • Larval stages in freshwater fishes (e.g. pike, trout, perch, whitefish, salmon) which act as intermediate hosts Diphyllobothrium spp. (Broad fish tapeworm) • Transmitted through the consumption of raw or poorly cooked freshwater fish containing infective larvae Diphyllobothrium spp. - Symptoms • Most cases are asymptomatic • Abdominal pain, dizziness, fatigue, vomiting, diarrhea/constipation • Vitamin B12 deficiency with pernicious anemia Diphyllobothrium spp. – Diagnosis and Treatment • Stool examination for eggs (microscopy) or proglottids (segments) • Anthelmintic drugs effective (Praziquantel) Taenia spp. • Large tapeworms (up to 20 m in length) • Adult stage only found in humans • Transmitted through ingestion of larvae in raw or poorly cooked meat Taenia saginata – beef tapeworm scolex Gravid proglottid Taenia solium – pork tapeworm Taenia spp. Symptoms (adult tapeworm) -mild abdominal complaints Diagnosis -Eggs or proglottids in stool -Serological techniques Treatment -Anthelmintic drugs (Praziquantel) -surgery T. solium neurocysticercosis Infection with larval stage following ingestion of T. solium eggs (humans act as the intermediate host) Larvae migrate and develop in brain intracranial hypertension, hydrocephalus, convulsive seizures MRI of patient with neurocysticercosis Control – Taenia spp. • Both species are rare in Canada • Routine inspections in Canada by CFIA • Cooking meat readily kills larvae • In endemic countries - sanitation; prevent access of pigs to human faeces Schistosoma spp. (Blood flukes) • Worldwide, 200 - 300 million cases • Free - swimming larvae in fresh water penetrate skin and develop in blood vessels surrounding intestine or bladder • Three main species: S. haematobium, S. japonicum, and S. mansoni Symptoms of schistosomiasis • rare except in heavily infected individuals • Rash, itchyness from penetrating larvae • fever, lymphadenopathy, hepatosplenomegaly Diagnosis of schistosomiasis • Microscopic examination for eggs in faeces or urine • Treated with praziquantel S. mansoni egg Schistosomiasis - Control • Eliminate habitat for snails which act as intermediate hosts (e.g. drainage channels) • Spraying with molluscicides • Improved sanitation • Avoid contact with fresh water in endemic areas