Hemotropic Mycoplasma Infections in Animals

Hemotropic Mycoplasma Infections (Hemoplasmas)

• What they are:

  • Bacteria in the genus Mycoplasma.

  • Lack cell walls.

  • Attach to erythrocytes of target hosts.

  • Epierythrocytic parasites.

  • Morphologic features include rod, coccoid, and ring-shaped structures on red cells.

  • Stain gram-negative due to lack of cell wall.

  • Cannot be cultured in vitro.

• Impact:

  • Potentially cause host immune-based anemia.

  • Severity of hemolytic anemia varies greatly.

  • Many infections are asymptomatic.

• Important Species of Veterinary Importance:

  • Dogs: Mycoplasma haemocanis (formerly Haemobartonella canis), "Candidatus Mycoplasma haematoparvum".

  • Cats: Mycoplasma haemofelis (formerly Haemobartonella felis) (Most pathogenic), "Candidatus Mycoplasma haemominutum" (formerly Haemobartonella felis) (Most common), "Candidatus Mycoplasma turicensis".

  • Pigs: Mycoplasma suis (formerly Eperythrozoon suis), Mycoplasma parvum (formerly Eperythrozoon parvum).

  • Cattle: Mycoplasma wenyonii (formerly Eperythrozoon wenyonii).

  • Sheep and goats: Mycoplasma ovis (formerly Eperythrozoon ovis).

  • Llamas and alpacas: "Candidatus Mycoplasma haemolamae".

• Transmission:

  • Transfer of infected blood (blood transfusion, contaminated needles, surgical instruments, herd/flock management equipment).

  • Via arthropod vectors (lice, flies, ticks, mosquitoes).

  • Vertical transmission from mother to offspring (reported in cats, swine, camelids).

  • Direct transmission (possibly associated with fighting, suspected in cats - DNA in saliva, gingiva, claw beds).

• Clinical Findings:

  • Severity varies widely, most animals develop asymptomatic infections.

  • More severe, acute anemias associated with certain strains, splenectomy, immunocompromise, concurrent infection (e.g., FeLV/FIV), or coinfection.

  • Typical signs (when symptomatic): lethargy, anorexia, and fever.

  • Less often: splenomegaly and icterus.

  • Specific Host Findings:

    • Dogs (M. haemocanis): Usually asymptomatic in healthy dogs. Causes acute hemolysis in splenectomized dogs.

    • Cats (Feline Infectious Anemia - FIA, M. haemofelis): Acute, potentially severe or fatal hemolytic anemia in healthy cats. Clinical signs include weakness, pallor of mucous membranes, tachypnea, tachycardia, and occasionally collapse. May be febrile (acute) or hypothermic (moribund). Other signs: cardiac murmurs, splenomegaly, icterus.

    • Pigs (M. suis): Hemolytic anemia accompanied by icterus (neonates, feeder pigs, pregnant sows). Chronic infection associated with poor growth rates, decreased conception rates, reproductive failure, decreased milk production.

    • Cattle (M. wenyonii): Usually asymptomatic. Can cause mammary gland and hindlimb edema, decreased milk production, fever, and lymphadenopathy (young primiparous heifers).

    • Sheep and goats (M. ovis): Often asymptomatic. Hemolytic anemia can occur in young animals. Chronic infection may result in poor weight gain, exercise intolerance, decreased wool production.

    • Camelids (M. haemolamae): Severe hemolytic anemia in young crias.

  • Anemia Type: Immune-mediated, typically extravascular, resulting in a regenerative anemia.

  • Laboratory Findings: Moderate to marked regenerative anemia. Erythrocyte agglutination may be present. Coombs’ test results are often positive (e.g., M. haemofelis, splenectomized M. haemocanis). Hypoglycemia can occur secondary to glucose consumption by bacteria in heavily parasitized animals. In cats, increased nucleated RBCs, polychromasia, anisocytosis, Howell-Jolly bodies, and increased reticulocyte count are expected.

• Diagnosis:

  • Based on clinical signs, patient history [implied].

  • Laboratory testing: Microscopy or PCR.

  • Microscopy: Detection of organisms on Wright-stained blood smears. Organisms appear as small, basophilic, structures on erythrocytes or free. Sensitivity can be poor because parasitemia is cyclic and organisms disappear quickly. Organisms dissociate from erythrocytes in EDTA. Specificity is also poor if characteristic morphology is absent.

  • PCR: Greatly enhanced diagnosis. Capable of discriminating among hemoplasmas. Can be run on whole blood and aspirates of the spleen. Considerably more sensitive and specific than blood-smear evaluation. Used to screen blood donors.

  • Serologic assays are not commercially available [implied by lack of mention].

• Treatment and Control:

  • Antimicrobial and supportive treatment.

  • Antimicrobials: Tetracyclines (doxycycline, oxytetracycline) are mainstay for acute infections. Doxycycline for M. haemofelis (minimum 2 weeks). Pradofloxacin and marbofloxacin are effective against M. haemofelis and suitable alternatives to doxycycline.

  • Supportive Care: May include oxygen and blood transfusions. Blood transfusion recipients must be monitored as parasites can rapidly infect transfused cells.

  • Adjunct Therapy: Glucocorticoids may be useful to decrease erythrophagocytosis in cases of severe hemolysis, or when primary immune-mediated hemolytic anemia is a possible cause.

  • Outcome: Treated animals may remain carriers and experience periodic clinical relapses with stress or immunocompromise. No therapeutic regimen completely clears the organisms [implied by carrier state].

  • Immunity: Protective immunity develops against repeat M. haemofelis infection after control, but duration and applicability to other species is unknown.

  • Control Measures: Screen blood donors using PCR. Avoid iatrogenic transmission with properly sterilized needles/equipment. Control arthropod vectors. Minimize stress in managing herds/flocks.

  • Treating PCR-positive, healthy cats is not currently recommended as no curative regimen is known.

• Zoonotic Risk:

  • Typically species specific.

  • Exceptions: M. ovis (sheep/goats), "Candidatus M. haemolamae" (llamas/alpacas).

  • Reports of human eperythrozoonosis exist but supporting evidence is not compelling.

  • Rare reports in immunocompromised people, confirmed by molecular methods.

  • Possible zoonotic transmission suggested in cases of coinfection with Bartonella henselae in humans.

• Prognosis: Varies depending on the species and host health. Without treatment, one third of acutely ill cats may die. Infections can be severe or fatal. Often asymptomatic or manageable.