Perhaps you’ve seen or read news stories about unfortunate children who were exposed to the ameba Naegleria fowleri while swimming. This deadly ameba causes encephalomeningitis, or severe inflammation of the brain and spinal cord, and is very difficult to treat. Sadly, most children die after becoming infected.
Thankfully, there have been no reported cases of this kind of amebic meningitis in dogs, but they are susceptible to getting another type of meningitis from an ameba called Acanthamoeba castellani.
Acanthamoebiasis, or infection with the aforementioned ameba, is rare in dogs, but can lead to a condition called granulomatous amebic encephalitis. Acanthamoeba can also lead to multisystemic disease in dogs, infecting the lungs, heart, lymph nodes, and kidneys.
Acanthamoeba is a microscopic ameba that is found all over the world in water and soil. Dogs are infected by ingesting or inhaling contaminated water or soil. Young dogs, whose immune systems are still developing, and immunocompromised dogs are most at risk from exposure to the ameba.
Clinical signs of infection with Acanthamoeba in dogs will likely be due to encephalitis. Neurologic abnormalities, such as seizures or circling, mood changes, decreased appetite, and abnormal gait can all be signs of encephalitis. Fever and lethargy will likely accompany these signs.
Diagnosis is difficult. While an MRI may show encephalitis, it will not show the causative organism. Because acanthamoebiasis is difficult, if not impossible, to treat, it is likely that definitive diagnosis will occur postmortem. While it may be possible to discover the presence of Acanthamoeba with a CSF tap, the chances of diagnosis in a sick animal are slim.
Thankfully, infection with the ameba Acanthamoeba is very, very rare in dogs. Humans who have been similarly infected by Naegleria fowleri are proving to be very difficult to treat, but new drugs are being developed to help combat the “brain eating” ameba. There is some hope that these drugs will also help our canine friends who fall victim to amebic disease.