Hemotropic Mycoplasmas

Hemoplasmas may be transmitted by transfer of infected blood (blood transfusion or use of contaminated needles, surgical instruments, herd or flock management equipment) or via arthropod vectors such as lice, flies, ticks, and mosquitoes. Vertical transmission from mother to offspring has been reported in cats, swine, and camelids. Direct transmission associated with fighting is suspected in cats and supported by studies reporting presence of hemoplasma DNA in saliva, on gingiva, and on claw beds of infected cats.

Hemoplasmas are capable of causing a hemolytic anemia, but the severity varies greatly. In general, asymptomatic infections tend to occur in healthy adult animals, and more severe acute anemias are associated with splenectomy, immunocompromise, concurrent diseases (such as feline leukemia virus or feline immunodeficiency virus in cats), or coinfection with multiple hemoplasma species. The main exception is M haemofelis, which causes acute hemolytic anemia in healthy cats. The anemia may be severe and occasionally fatal. Typical clinical signs include lethargy, anorexia, and fever, with splenomegaly and icterus occurring less often.

M haemocanis causes acute hemolysis in dogs that are splenectomized, but infections are usually asymptomatic in healthy dogs. M suis causes hemolytic anemia accompanied by icterus in neonatal pigs, feeder pigs, and pregnant sows. Chronic infection is associated with poor growth rates, decreased conception rates, reproductive failure, and decreased milk production. M wenyonii infection in cattle is usually asymptomatic, but a syndrome of mammary gland and hindlimb edema, decreased milk production, fever, and lymphadenopathy has been described in young, nonanemic, primiparous heifers. Infection in young bulls has been reported to cause scrotal and hindlimb edema. M ovis infection in sheep and goats is often asymptomatic, but hemolytic anemia can occur in young animals, especially those with heavy intestinal worm burdens. Chronic infection may result in poor weight gain, exercise intolerance, decreased wool production, and mild anemia. Hemoplasma infection in camelids can cause a severe hemolytic anemia in young crias. The prevalence of chronic infection in sheep, pigs, and kennel-raised dogs is high, and outbreaks of acute disease have been reported in animals during research studies. Whether the infection is chronic or acute, it may affect experimental results and lead to misinterpretation of data.

The hemolysis caused by hemoplasma infections is typically extravascular and results in a regenerative anemia. Erythrocyte agglutination may be present, and Coombs’ test results are often positive in cats infected with M haemofelis. Splenectomized dogs with acute hemolysis due to M haemocanis may have agglutination, spherocytosis, and a positive Coombs’ test. Hypoglycemia secondary to glucose consumption by the bacteria has been reported in heavily parasitized pigs, sheep, llamas, and calves; however, rapid bacterial glycolysis in vitro may also cause artifactually decreased blood glucose concentrations.

Historically, diagnosis has been made based on detection of organisms on routine Wright-stained blood smears, on which they appear as small (0.5–3 μm), basophilic, round, rod, or ring-shaped structures present on erythrocytes individually or in chains, or sometimes seen free in the background. However, parasitemia in chronic infections can be cyclic, and organisms can disappear from circulation in as little as 2 hr. In addition, hemoplasmas dissociate from erythrocytes and die after a variable amount of time in EDTA, hampering detection of organisms in aged samples. Recent development of sensitive PCR assays capable of discriminating between various hemoplasmas has greatly enhanced diagnosis of these parasites and has led to identification of several new Mycoplasma species.

For acute infections, tetracyclines (doxycycline, oxytetracycline) have been the mainstay of treatment; enrofloxacin and marbofloxacin have also been effective against M haemofelis. Glucocorticoids may be useful to decrease erythrophagocytosis in cases of severe hemolysis; some animals may require blood transfusion. Treated animals remain carriers and may experience periodic clinical relapses. Blood donors should be screened using PCR-based DNA assays to prevent transmission to transfusion recipients. Iatrogenic transmission can be avoided by using properly sterilized needles and equipment. Control of arthropod vectors is recommended, as is minimizing stress in herd and flock situations.

Hemoplasma infections are usually species specific, except for M ovis, which infects both sheep and goats, and "Candidatus M haemolamae," which infects both llamas and alpacas. There are reports of human eperythrozoonosis from Inner Mongolia, China, but supporting evidence is not compelling. However, there have been rare reports of hemoplasma infections in immunocompromised people in which molecular methods were used for confirmation. One report documented an HIV-positive human patient coinfected with Bartonella henselae and a hemoplasma genetically similar to M haemofelis. This individual owned five cats and had multiple scratch and bite wounds. All five cats were PCR positive for Bartonella spp and two were positive for M haemofelis, suggesting the possibility of zoonotic transmission. The coinfection of a veterinarian in Texas with B henselae and M ovis also has been reported.