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Ameba Infection in Dogs

Canine Amebiasis

Amebiasis is a parasitic infection caused by a single-celled organism known as an amoeba. It can affect both humans and dogs, as well as cats. Although more commonly found in tropical regions, cases have been reported in North America as well.

Symptoms and Types

Two types of parasitic amoebas infect dogs: Entamoeba histolytica and Acanthamoeba.

Entamoeba histolytica:

  • Typically presents as an asymptomatic disease.
  • Severe infections can lead to colitis, characterized by bloody diarrhea.
  • Hematogenous spread (spread through the bloodstream) can cause damage and failure of major organ systems. Symptoms vary based on the affected organ system, but death is often the outcome.

Acanthamoeba:

  • Results in granulomatous amebic meningoencephalitis, causing inflammation of the brain. Symptoms include loss of appetite, fever, lethargy, eye and nasal discharges, difficulty breathing, and neurological signs such as incoordination and seizures.

Causes

Entamoeba histolytica is primarily transmitted through the ingestion of contaminated human feces. Two species of free-living Acanthamoeba, namely A. castellani and A. culbertsoni, inhabit various environments including freshwater, saltwater, soil, and sewage.

Dogs can contract the infection by ingesting or inhaling water, soil, or sewage contaminated with these amoebas. Acanthamoeba can also colonize the dog’s skin or cornea, leading to infection. Hematogenous spread through the bloodstream is another route of infection.

Infection originating from the nasal passages can extend into the brain. Young dogs and those with weakened immune systems are at higher risk of developing the illness.

Diagnosis

Typically, blood testing (complete blood cell count and blood chemistry profile) along with urine testing (urinalysis) are conducted, often yielding normal results. However, signs of dehydration, if present, may be evident in these tests.

Additional laboratory examinations recommended by your veterinarian may include:

  • Colon biopsies obtained through colonoscopy (an examination using a long cylindrical scope with a light). Biopsies may show damage to the intestinal lining and the presence of trophozoites, a stage in the life cycle of the infecting organism.
  • Fecal examination to detect trophozoites. Trophozoites can be challenging to find in fecal samples, so special stains are often used to enhance their visibility.
  • Central spinal fluid (CSF) taps. Infections related to the meningoencephalitis form of the disease may exhibit abnormalities such as elevated white blood cell counts, abnormal protein levels, and xanthochromia.
  • MRI of the brain may reveal granulomas in cases of meningoencephalitis.
  • Brain biopsies.

Treatment

Metronidazole is prescribed to manage the symptoms of colitis and generally proves effective. Nevertheless, systemic forms of the disease, such as those spread through the bloodstream, typically result in fatality despite treatment attempts, though symptomatic relief may be pursued.

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