Giardia 2015 - Foodborne Disease - PUBH 4104 PDF

PUBH 4104 Foodborne Disease Protozoan Infections Giardia 1 Giardia o Giardia is a flagellated enteric protozoan which has a global distribution o It is the most prevalent enteric parasite in the USA and Canada o Transmission is through: o Contaminated water...

PUBH 4104 Foodborne Disease Protozoan Infections Giardia 1 Giardia o Giardia is a flagellated enteric protozoan which has a global distribution o It is the most prevalent enteric parasite in the USA and Canada o Transmission is through: o Contaminated water or food o Person-to-person contact with an ill host o There are significant animal reservoirs: o Beavers were first implicated (“beaver fever”) o Also cats, dogs, muskrats and bears 2 Giardia o Giardia lamblia is the species known to infect humans o It is also known as G. intestinalis or G. duodenalis o The name comes from Vilem Lambl who first reported the organism in 1859 o The first description comes much earlier, in 1681, when Anton von Leeuwenhoek examined his own stool microscopically during a bout of diarrhea 3 Giardia o Populations at high risk of infection include: o Infants o Young children o Travelers o The immuno-compromised o Malnutrition and growth retardation are seen in resource poor regions where the prevalence of Giardia may be 20-30% o In the industrialized world the prevalence rate is 2-5% 4 Giardia o The G. lamblia life cycle has two stages, a trophozoite stage and a cyst stage o The trophozoite stage is: o 9-20 ㎛ long and 5-13 ㎛ wide o It is pear-shaped with: o A convex, dorsal surface o A flat ventral surface with a sucking disk o Four pairs of posterior flagella o A posterior placed median body o Two anterior nuclei 5 Drawing of Trophozoites and Cyst 6 A Giardia Trophozoite 7 Giardia o The trophozoite divides by binary fission with doubling occurring about every 9-12 hours. o Encystation occurs in the small bowel, probably due to bile salts and increased pH o The cyst is highly resistant and is passed out of the host in the feces, there may be hundreds of thousands of cysts per gram of stool. o The mature cyst is oval, 8-12 ㎛ long and 7- 10 ㎛ wide. 8 Giardia Life Cycle 9 Giardia o The cyst is the transmissible form of the parasite. Ingestion of one or more cysts may cause disease. o Once ingested, and exposed to gastric acids and pancreatic enzymes, undergoes excystation and releases 2 trophozoites to continue the cycle. 10 Giardia Life Cycle 11 Giardia o Released trophozoites attach to the brush border enterocytes by two proposed mechanisms: o Using the ventral disk o A receptor-ligand interaction o Attachment allows the parasite to avoid peristalsis 12 Giardia o Exact mechanism of injury is not known but several observations are known: o The brush border is damaged, causing a disaccharidase deficiency o Increased epithelial turnover leads to altered absorption (crypt hyperplasia) o Decreased bile salts concentration (reduced lipase activity and solubilization of fats) o Trypsin enzyme is inhibited o Thus the diarrhea of giardiasis is primarily malabsorptive 13 Giardia o Host immune response generates both antibodies and a cellular response. Secretory IgA seems to be most important in clearing and preventing infection o Protective immunity does not develop after a single infection (lot of antigenic diversity in G. lamblia isolates) o Patients with AIDS have no more severe illness than patients without AIDS 14 Giardia o After ingestion of G. lamblia cysts there are three situations that may occur: o Asymptomatic cyst passage o Self-limited diarrhea (acute giardiasis) o Chronic diarrhea with associated malabsorption and weight loss (chronic giardiasis) 15 Giardia o Acute Giardiasis o IP varying between 3-20 days o Patients seek medical care after about 7-10 days of symptoms o Diarrhea is seen in about 90% of patients, along with a generalized malaise o Start off with profuse, watery stools that progress to foul smelling and often greasy stools that float o Flatulence, bloating and abdominal cramps are common o Weight loss and vomiting are less frequent, fever is rare o Symptoms are self-limited to about 2-4 weeks 16 Giardia o Chronic Giardiasis o About 30-50% of those with acute giardiasis will progress to the chronic state o Profound malaise and lassitude are frequent o Diarrhea alternates with constipation, abdominal pain upon eating o Weight loss of 10-20% of body weight is common o May last for months to years and be difficult to treat. 17 Diagnosis o Diagnosis o Key to diagnosis is the identification of cysts or trophozoites in the stool o One stool has 50-70% diagnostic yield o Three stools collected over 2-3 days improves diagnostic yield to 85-90% (because of cyclic shedding) o Direct fluorescent antibody assays or enzyme immunoassays are popular as they: o Decrease exam time o Reduce the technician training required 18 Prevention and Control o Prevention and Control o Vast animal and human reservoirs mean total elimination is not expected o Focus is on primary sources of infection o Water contamination o Person to person contact o Chlorine is effective in certain concentrations, but not all chlorine products are effective. o Public water supplies should undergo chlorination, flocculation, sedimentation and filtration o Water filters should have pore sizes of 1-2 ㎛ 19 20