Waterborne Protozoan diseases

Single-celled organisms; commonly found in surface waters. Introduced into water by animal or human faecal contamination. Exist as dormant cysts or oocysts in water sources. Resistant to chlorination. Common waterborne protozoa are Giardia and Cryptosporidium

Amoebiasis/Amoebic dysentery

·         Entamoeba histolytica

·         Cysts and trophozoites;  cysts excreted in the stool

·         Following ingestion the cysts pass through the stomach, exposure to gastric acid stimulates release of the pathogenic trophozoite

·         Produce necrosis and ulceration in the large intestine- watery and bloody diarrhea; fever and chills

·         Invasion through the gut wall into blood stream, spread to other organs (primarily the liver) – abscesses in liver, lung, brain

·         Majority of infections restricted to the lumen of the intestine- (“luminal amoebiasis”) – may be asymptomatic

·         Amoebic colitis, or invasive intestinal amoebiasis, occurs when the mucosa is invaded- Symptoms include severe dysentery and associated complications

·         Severe chronic infections may lead to further complications such as peritonitis, perforations, and the formation of amoebic granulomas (amoeboma).

·          Amoebic liver abscesses are the most common manifestation of extra-intestinal amoebiasis

Giardiasis

·         First Water Borne Infectious Disease discovered: Giardia lamblia

·      Move very actively with its eight flagella, and attaches to epithelial surfaces by its cup-shaped anterior ventral disc

·         Inflammation of the epithelium and disrupts water uptake by microvilli

·         Incubation period of 7-10 days

·      Severe acute diarrhea to chronic mild diarrhea associated with flatulence, abdominal discomfort and/or intestinal malabsorption

·         Foul smelling stools- absorption of fats and vitamins inhibited

Cyst and Trophozoite

Cryptosporidiosis

·         Cryptosporidium parvum

·         Extensive watery diarrhea outbreaks

·         Seen in many animals, excreted in the stool as oocyst

·         Sporozoites released in intestine; infect enterocytes

·         Low fever, occasional vomiting, and a self-limited watery diarrhea.

·         Rarely lasts more than 2 weeks

·         In immunocompromised patients, the diarrhea is chronic, often severe, and may be fatal - a major problem in patients with AIDS

Meningoencephalitis

·         Naegleria fowleri (amoeba)

·         Propagates in warm, stagnant bodies of freshwater (typically during the summer months)

·      Enters the central nervous system from infected water by attaching itself to the olfactory nerve; multiplies itself greatly by feeding on nerve tissue. Approximately 3–7 days post-infection, the typical symptoms are parosmia, rapidly progressing  to anosmia with resultant ageusia- the nerve cells of the olfactory bulbs are consumed and replaced with necrotic lesions

·     Infection rapidly spreads  to the rest of the cerebrum – encephalitic  symptoms, headache, nausea, and rigidity of the neck muscles, progressing to vomiting, delirium, seizures , and eventually irreversible coma

·     Death usually occurs within 14 days of exposure as a result of respiratory failure  when the infection spreads to the brain stem.