PATHOGENS

Haemoptrophic (hemotropic) mycoplasmas, formerly known as Haemobartonella and Eperythrozoon, are small (<1 mm), pleomorphic bacteria that attach to red blood cells of various mammalian species (Willi et al., 2007). Until recently, they were classified as rickettsial organisms, based on their small size, Gram-negative staining properties, red blood cell parasitism and proposed transmission by blood-sucking arthropods (Kreier and Ristic, 1984). Meanwhile, based on molecular characterization, a closer relationship to members of the class Mollicutes has been described (Neimark et al., 2001; Rikihisa et al., 1997). This molecular relationship and some further phenotypic characteristics led to a reclassification of the genera Haemobartonella and Eperythrozoon within the genus Mycoplasma (family Mycoplasmataceae) as haemoptrophic/hemotropic mycoplasmas (Neimark et al., 2001), also denominated haemoplasmas (hemoplasmas) as trivial name (Neimark et al., 2001).

These haemoplasmas are characterized as small (0.3–0.8 mm), unculturable, epierythrocytic bacteria that are capable of causing severe haemolytic anaemia (Sykes, 2010).

Relevant species described in cats are Mycoplasma haemofelis (Mhf) (formerly designated the “large form” or Ohio strain/isolate), Candidatus Mycoplasma haemominutum (CMhm) (formerly designated the “small form” or California strain/isolate) (Foley and Pedersen, 2001; Neimark et al., 2001; Tasker and Lappin, 2002) and Candidatus Mycoplasma turicensis (CMt), identified in a Swiss pet cat for the first time (Willi et al., 2005, 2006).

In dogs, two species have been described. Mycoplasma haemocanis (Mhc), formerly known as Haemobartonella canis, has been described in 1959/1960 (Benjamin and Lumb, 1959; Donovan and Loeb, 1960), but early reports of sporadic cases of haemobartonellosis in dogs in the United States even date back to 1935 (Knutti and Hawkins, 1935; McNaught et al., 1935). As with the feline species, the pathogen has been reclassified to Mycoplasma haemocanis (Messick et al., 2002). In 2004, a second haemotrophic mycoplasma was identified in a splenectomized immunocompromised dognamed Candidatus Mycoplasma haematoparvum (CMhp) (Sykes et al., 2004, 2005).

Recently, the two feline species CMhm and CMt were also detected in dogs (Obara et al., 2011; Soto et al., 2017), and Candidatus Mycoplasma haematoparvum-like was found in cats (Sykes et al., 2007; Martínez-Díaz et al., 2013; Vergara et al., 2016).