Shapeshifting, parasitic, and hell-bent on destruction, E. histolytica amoebae are single-celled creatures with the uncanny ability to morph into different forms, primarily by extending and retracting their pseudopods aka "false feet" and posterior uropods in crawl-like locomotion. These bizarre, amoebozoan changelings wreak havoc upon dogs in a disease known as canine amebiasis, which is acute or chronic colitis. Fascinating, albeit only to scientists, these amoebae are downright dangerous microorganisms and catalysts of often severe amoebic infection in dogs and their people.
Amebiasis occurs in dogs who have ingested human feces infected with amoebic cysts, usually in contaminated water or food. Its ugly manifestation presents symptomatically as persistent bloody diarrhea or dysentery. Dramatically compromising a dog's health, especially if immunosuppressed, E_._ histolytica aggressively invades the large intestine and major organs such as the liver, kidneys, lungs, and brain with variable devastating effects — death is a frequent outcome.
What E. histolytica amoebae do inside your dog's body.
The invasive amoebic species, Entamoeba histolytica (E. histolytica_)_ responsible for amebiasis, was discovered in 1757 by Fedor Losch, a Russian physicist, and occurs in tropical and subtropical regions worldwide, as well as developing countries with inadequate sewage systems. Its prevalence in the United States has diminished over the last several decades, but amebiasis is still a significant disease in tropical areas and a concern in disaster zones where food and drinking water can become contaminated. It is common in people — affecting about 50 million worldwide — nonhuman primates, and sometimes dogs and cats. Humans are the natural reservoirs for the pathogen, thus the primary source of infection for dogs that ingest contaminated food or water.
Requiring no oxygen to thrive (anaerobic), E. histolyticam may die if exposed to oxygen. Once introduced into the body by mouth, the amoeba travel via the bloodstream (hematogenous spread) to the cecum, the cul-de-sac at the opening of the large intestine, then inside the large intestine itself where they may live with no clinical signs of illness in your dog.
On the other hand, if the amoebae invade the intestinal mucosa, it will result in mild to severe, ulcerative, hemorrhagic colitis. In severe cases, fulminating dysentery aka malignant dysentery may develop in which the intensely acute symptoms lead to prostration, collapse, and often, death. Conversely, this acute stage, in turn, can progress to a chronic stage or even resolve spontaneously.
Furthermore, in addition to the colon, the amoebae may also invade the perianal skin, genitalia, liver, brain, lungs, kidneys, and other organs. Signs of amebiasis may resemble those of other colonic diseases such as whipworm infection (trichuriasis) and large-intestinal infection with B. coli (balantidiasis).
Symptoms of chronic amebiasis.
Chronic amebiasis is a long-term amoebic infection which invades the intestines, tissues, liver, kidneys, and brain.
- Weight loss
- A lack or loss of appetite for food (anorexia)
- A continual or recurrent need to evacuate the bowels (tenesmus)
- Continual or intermittent, chronic diarrhea or dysentery
Symptoms of acute amebiasis.
- Severe abdominal upset and abdominal pain.
- Bloody diarrhea containing mucus.
- If major organs are affected, it is potentially fatal.
How is amebiasis diagnosed in dogs?
A definitive diagnosis of amebiasis requires several diagnostic tools, and the parasites are difficult to find since many dogs with extraintestinal amebiasis have no concurrent intestinal infection. Affected tissues from the colon will be biopsied and tested in the lab with saline smears and immunostaining revealing either E. histolytica trophozoites — a growth stage in the parasite's life cycle where it's absorbing nutrients from its host — or cysts in feces.
Fecal examinations must be done promptly because the anaerobic trophozoites die quickly once outside the body. Also, fecal leukocytes — white blood cells which counteract foreign objects and disease — may be mistaken for E. histolytica amoebae, so fecal smears using iodine, trichrome, iron hematoxylin, or periodic acid-Schiff reaction may be necessary to confirm identification. Ulcerations may be scraped or biopsied, and a colonoscopy may be required; all more effective than a fecal examination in diagnosing amebiasis or amoebic colitis.
Examinations may need to be repeated since the parasites may be passed in the feces. An ELISA-based antigen test which is used to diagnose amebiasis in people may also help confirm a diagnosis in dogs and other animals.
Treatment of amebiasis.
The antibiotic metronidazole is the generally accepted treatment protocol for canine amebiasis. The drug successfully controls the symptoms of colitis. But, unfortunately, blood-borne systemic infections are usually fatal, although symptomatic treatment will usually be attempted.