The diagnosis is made via microscopic identification of the parasites infecting red blood cells or macrophages. Since macrophages
are the first cell line infected, tissue aspirates of affected organs such as the liver, spleen and lymph nodes may aid in
the early diagnosis when the RBC forms are not present. To accurately and rapidly identify C. felis in affected cats, a PCR test was developed. Historically, the disease has been considered uniformly fatal in affected cats,
but more recently there have been reports of cats surviving infection. Atovaquone and azithromycin combination therapy and
imidocarb dipropionate are used for the treatment of C. felis in naturally infected cats.
Feline babesiosis caused by Babesia felis has not been identified in the United States but is a common cause of anemia in cats in South Africa. The diagnosis of feline
babesiosis is dependent upon microscopy, but PCR can be performed on feline samples using broad-range primers designed to
amplify most Babesia species. The treatment of choice is primaquine, but the safety margin for the use of this drug in cats
is narrow. At least one other species of Babesia has been identified in cats and novel Babesia species have been found in
Recently cats with Ehrlichia infections have been associated with anemia. While IMHA has not been clearly defined in cats
with ehrlichiosis, veterinarians should consider testing cats with IMHA for ehrlichiosis since the full spectrum of disease
associated with ehrlichiosis in cats has not been defined.
Infectious causes for canines
Idiopathic IMHA is still the most-common diagnosis for dogs presenting with hemolytic anemia. However, there are a number
of infectious diseases that can be associated with IMHA in dogs.
Canine babesiosis is an important cause of canine IMHA worldwide. At least eight genetically distinct piroplasms have been
amplified by PCR from the blood of dogs.
Babesia gibsoni and the three subspecies of Babesia canis remain the most important of these pathogens. Canine babesiosis is characterized by hemolytic anemia, thrombocytopenia and
hyperglobulinemia. It is important to note that anemia is not present in every case.
Up to 85 percent of dogs with babesiosis will have a positive Coombs' test attesting to the immune-mediated nature of the
anemia. In most areas, babesiosis is transmitted by ticks, and dogs exposed to ectoparasites are at risk. Several studies
have implicated dog bites as risk factors for B. gibsoni infections. Other studies have shown that perinatal transmission of Babesia can occur as well. Additionally, there have been
several documented cases of babesiosis in dogs that have been recipients of blood transfusions from infected dogs.
There are breed associations with canine babesiosis [Greyhounds (B. canis) and American pit bull terriers (B. gibsoni)] that should prompt veterinarians to have an increased incidence of suspicion.
The three diagnostic tests available for babesiosis include microscopy, serology and PCR. None of these tests has 100 percent
sensitivity or specificity, and in many cases more than one modality is needed. Of the three tests available, PCR is the only
method to differentiate accurately which species is present in a given dog. Since there can be substantial genetic variation
between species, it is important to know which species will be detected by individual laboratory. Accurate differentiation
is important because the treatment will vary among species.
Clearing the parasite
Imidocarb dipropionate (6.6 mg/kg IM once and repeat in 2-3 weeks) is the treatment of choice for B. canis. This treatment appears to be effective in clearing the parasite. For B. gibsoni, a combination of atovaquone (13.5 mg/kg PO TID administered with a fatty meal) and azithromycin (10 mg/kg PO Q24) administered
simultaneously for 10 days appears to be effective. Treatment failures appear most common in dogs that have been splenectomized
or that have undergone prolonged (weeks to months) immune suppression prior to the diagnosis of babesiosis. Reserve immune
suppression therapy for the cases that are not rapidly responding (three to five days) to anti-protozoal therapy.
Canine rickettsial infections are important causes of morbidity and mortality worldwide. They can be caused by Rickettsia rickettsii, Ehrlichia species and Anaplasma species. Of these, E. canis appears to be the organism most frequently associated with IMHA.