Chapter 82: Canine and Feline Hemotropic Mycoplasmosis

Canine and Feline Hemotropic Mycoplasmosis

Séverine Tasker, Bristol, United Kingdom

Feline and canine hemotropic mycoplasmas (hemoplasmas) are small bacteria that reside on the surface of red blood cells and can mediate hemolytic anemia in their host. Initially the hemoplasmas, including members of the genus Haemobartonella, were classified as rickettsial organisms, but gene sequencing analysis and phylogenetic studies have resulted in their reclassification within the genus Mycoplasma. Haemobartonella felis is now named Mycoplasma haemofelis, whereas Haemobartonella canis is called Mycoplasma haemocanis, and these organisms are collectively known as the hemoplasmas. Molecular studies also have confirmed the existence of additional feline and canine hemoplasmas. These species differ in pathogenicity, and an understanding of their characteristics is important to enable the veterinary clinician to manage cases appropriately.

Existence of Multiple Species

M. haemofelis infection often is associated with the development of acute hemolytic anemia in cats. There are two additional feline hemoplasma species: “Candidatus Mycoplasma haemominutum” and “Candidatus Mycoplasma turicensis”. “Candidatus M. haemominutum” and “Candidatus M. turicensis” are less pathogenic than M. haemofelis but can induce anemia in some circumstances. Splenectomy is not necessarily required for these agents to induce disease in their feline hosts, although immunocompromise may play a role in allowing “Candidatus M. haemominutum” and “Candidatus M. turicensis” to cause disease.

M. haemocanis infection usually results in hemolytic anemia only in splenectomized or immunocompromised dogs. An additional canine hemoplasma species, “Candidatus Mycoplasma haematoparvum,” has been described in association with anemia in a dog that had undergone splenectomy and was immunosuppressed.

Phylogenetic studies have shown that, although M. haemofelis and M. haemocanis are distinct species, they are closely related. “Candidatus M. haemominutum” and “Candidatus M. haematoparvum” also are closely related. Some have referred to M. haemofelis and M. haemocanis as large forms of hemoplasma, whereas “Candidatus M. haemominutum,” “Candidatus M. turicensis,” and “Candidatus M. haematoparvum” sometimes are called small forms since the size of the former species, when seen cytologically on light or electron microscopy, may be larger than that of the latter, although variation does exist. In phylogenetic analysis “Candidatus M. turicensis” groups with rodent hemoplasma species.

Prevalence of Infection

Prevalence studies for feline hemoplasma species now have been performed worldwide. “Candidatus M. haemominutum” usually is most common and has been identified in 10% to 32.1% of cats sampled in different studies. M. haemofelis and “Candidatus M. turicensis” infections generally are less common, although occasionally high prevalences are reported: rates vary from 0.4% to 46.6% and from 0.4% to 26%, respectively. The characteristics of the cats sampled for these different studies have varied enormously, from healthy cats to cats suspected of having hemoplasmosis, and from client-owned cats to feral cats, which possibly explains some of the variation in the results obtained. In addition, geographic variation appears to exist, with cats in warmer countries having a higher prevalence of infection. Older male cats with outdoor access are more likely to be infected with hemoplasmas. An influence of retrovirus infection also is suggested in some studies. Of additional note is that infection with “Candidatus M. turicensis” often is associated with coinfection with one and occasionally both of the two other feline hemoplasma species, particularly “Candidatus M. haemominutum.” Reported prevalences for canine hemoplasma infection have ranged between 0% and 45% for M. haemocanis and 0% and 33% for “Candidatus M. haematoparvum.” Geographic variation is marked, possibly due to the presence of the proposed canine hemoplasma tick vector Rhipicephalus sanguineus, and kenneled dogs, young dogs, crossbreeds, and dogs with mange are more likely to be infected (Novacco et al, 2010).

Pathogenicity

Hemoplasma infections induce anemia by causing hemolysis, which is primarily extravascular, although intravascular hemolysis also has been reported. In addition, sequestration of infected red blood cells within the spleen may result in a reduction in packed cell volume (PCV). An increase in osmotic fragility has been reported in cats infected with M. haemofelis and “Candidatus M. turicensis.” Differences in pathogenicity exist among hemoplasma species.

“Candidatus Mycoplasma haemominutum”

Experimental “Candidatus M. haemominutum” infection of cats does not usually lead to significant clinical signs or anemia, although a fall in erythrocyte parameters can occur. A significant anemia has been seen following “Candidatus M. haemominutum” infection in some studies involving cats infected with retroviruses (feline leukemia virus [FeLV] and/or feline immunodeficiency virus [FIV]). Most studies in naturally infected cats have failed to find an association between “Candidatus M. haemominutum” infection and anemia. “Candidatus M. haemominutum”–associated anemia has been reported in immunosuppressed cats (e.g., those undergoing chemotherapy) and occasionally in cats without any evidence of immunocompromise.

Mycoplasma haemofelis

Experimental infection with M. haemofelis often results in a severe hemolytic anemia, although the severity of anemia varies considerably. Some studies of naturally infected cats have found an association between anemia and M. haemofelis infection, but others have not. It has been hypothesized that acute infection with M. haemofelis can result in severe hemolytic anemia but that chronically infected cats are not anemic.

“Candidatus Mycoplasma turicensis”

Experimental studies of “Candidatus M. turicensis” infection have shown variable results, ranging from only a slight reduction in red cell parameters without induction of anemia to induction of moderate to severe anemia, especially if immunosuppression is present. Difficulties are encountered in assigning clinical signs solely to “Candidatus M. turicensis” infection in naturally infected cats since many “Candidatus M. turicensis”–infected cats are coinfected with other feline hemoplasmas. Cats coinfected with either “Candidatus M. turicensis” and “Candidatus M. haemominutum” or “Candidatus M. turicensis” and M. haemofelis have significantly lower packed cell volumes than hemoplasma-free cats, whereas those infected with “Candidatus M. turicensis” alone do not (Willi et al, 2006). In addition, cats naturally infected with “Candidatus M. turicensis” often have concurrent diseases. Therefore it is possible that immunosuppression or stress influences the pathogenic potential of this species.

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Tags: Kirks Current Veterinary Therapy XV

Jul 18, 2016 | Posted by admin in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off

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