Mycoplasma haemofelis

Feline infectious anaemia was described for the first time in 1942. For a long time, the causal agent went by the name of Haemobartonella felis, although based on molecular studies using PCR it has now been reclassified by the name Mycoplasma haemofelis. In fact, it cannot be considered as a single agent but rather as a group of infectious agents known as haemotropic mycoplasmas (haemoplasmas), a group of gram-negative bacteria that infect the erythrocytes in the epicellular form and that can lead to haemolytic anaemia.

There are apparently three strains of haemotropic Mycoplasma called M. Haemofelis, Candidatus M. Haemominutum and Candidatus M. Turicensis, which present different types of pathogenicity; of the three, M. haemofelis is the most pathogenic. Feline haemoplasmosis has spread around the world, as the main means of transmission are fleas, ticks and blood transfusions. The tick Rhipicehalus sanguineus seems to be responsible for the transmission of the disease, but fleas are also frequently mentioned by many authors as a major source of disease transmission. Ctenocephalides felis is incriminated in the transmission of haemoplasmosis among cats, although to date only a transient transmission of M. haemofelis through the haematophagic activity of Ct. felis has been demonstrated. Experimentally, a transmission has been described by the inoculation of infected blood orally, intraperitoneally and intravenously. Other unproven routes of infection are lactation or by other unknown carriers.

The incubation period of the disease ranges from 7 to 15 days, although in some cases it can last as long as 3 or 4 weeks. The disease is characterized by an acute, a recovery and a carrier phase.

During the acute phase there is the greatest number of parasites in circulation and anaemia is the most important clinical sign. Most cats show severe signs which, if not treated properly, may lead to the death of the animal. However, there are patients that during this phase show no clinical signs or very mild signs. The first period is followed by the recovery phase, during which the haematocrit (Hct) returns to normal values ​​though the parasites continue to be present, albeit in lesser quantities. Subsequently, some animals remain infected and continue to be carriers; during this stage the parasite can still be found, although in most cases the Hct suffers only mild variations. In situations of stress (pregnancy, cancer or other infections), relapses have been reported, also possible because of the use of immunosuppressive agents or corticosteroids.

Other risk factors for the development of haemoplasmosis are a concomitant chronic anaemia, FeLV  (Feline Leukaemia Virus) or  FIV (Feline Immunodeficiency Virus) infections, abscesses due to bites, being under 3 years old or being a stray cat. It is unclear whether the cats suffering from this disease develop any type of immunity.

Table 1. Feline mycoplasmas. The identified species of feline haemoplasmas vary in pathogenicity; some isolates clearly induce anaemia, while others cause moderate or extremely mild clinical signs.

CLINICAL PICTURE

The clinical signs are highly variable, non-specific and closely related to the haemoplasma species involved. The most frequent are apathy, anorexia, weight loss, weakness, pale mucous membranes, or jaundice (Figs. 1 and 2). During the acute phase it is common to note fever (in over 50% of cases), which is not characteristic of the other phases. Less frequent is the presence of splenomegaly or hepatomegaly and generalised lymphadenopathy. Cats suffering from haemoplasmosis in association with other clinical disorders have a much more severe clinical picture, as the clinical signs add up with  those of the concomitant disease causing a more or less severe anaemia.

The main characteristic of the disease caused by Mycoplasma  haemofelis is still a typical strongly regenerative anaemia.

Infections caused by C. M. haemominutum and C. M. turicensis are, on the contrary, almost never connected to an equally significant anaemia (Table 2). The clinical picture of moderate/severe anaemia may be evident when the infection is caused by 'Candidatus mycoplasma haemominutum'' in cats infected with retroviruses, particularly in those infected with FeLV. However, many studies on naturally infected animals have usually failed to demonstrate a direct association between anaemia and ‘Candidatus Mycoplasma haemominutum’.

M. haemofeliscan induce anaemia through different mechanisms, but mainly by extravascular haemolysis that occurs in the spleen and liver, but also in the lung and bone marrow. The haematological picture can be worsened by phenomena of intravascular haemolysis, in particular because of the increased osmotic fragility of erythrocytes parasitised by haemoplasma. The frequent positivity to the Coombs’ test and to autoagglutination is indicative of the presence of erythrocyte-binding antibodies, and the presence of these antibodies can be responsible for the immune-mediated destruction of the erythrocytes.

Table 2. Pathological conditions induced by M. haemofelis.

LABORATORY ANALYSIS

Anaemia is the most evident alteration. During the acute phase, the cat may present a very low haematocrit, between 10% and 20%. In most cases, anaemia is progressive (between 7 and 15 days after infection) and is the consequence of extravasal  haemolysis. Anaemia is usually macrocytic, hypochromic, associated with the presence of many polychromatic cells, reticulocytosis and spherocytosis (Figs. 3 and 3b), and is typically of the regenerative type, with a very high percentage of reticulocytes. Sometimes, if the diagnosis is very early or if there are concomitant myelosuppressive diseases such as FeLV, it is possible that a massive regeneration is not yet present, but usually within 24-48 hours there is a marked increase in the percentage of circulating reticulocytes.

The condition of anaemia and of destruction may have periods of apparent recovery. This process of destruction and recovery is due to the regenerative response of the bone marrow, with the release of the red blood cells sequestered in small vessels and of the ones that have become devoid of parasites from the spleen, liver and lung. These "clean" red blood cells, free of parasites, have a greater fragility and, consequently, a reduced half-life. During the phases of haemolysis and increase in the haematocrit, a common finding is the presence of fever, often waxing and waning, and variable leukocytosis. Although anaemia is extravascular, the values ​​of jaundice and bilirubinuria are seldom particularly high. Due to the phenomena described above, anaemia associated with haemoplasmosis is classified as clearly regenerative; in most cases, during the acute phase it has a positive Coombs’ test result. Cats that overcome the haemolytic crisis start to gradually recover normal haematocrit values, then enter the recovery phase and finally they become asymptomatic carriers.

DIAGNOSIS

The most sensitive and commonly used diagnostic tool is the search for the parasite in a blood smear with a Giemsa, Wright's or Diff Quick stain. However, using this technique, the organisms are visible in no more than 50% of the blood samples of anaemic cats. In the blood smear, parasites appear as ring-shaped structures, orange cocci or bacilli adherent to the erythrocyte membrane (Fig. 4)

Mycoplasma haemofelis can be located within the erythrocyte membrane in isolated form, in groups or in the form of chains. The isolated and elongated shape is the simplest to diagnose, given that the other forms can easily be confused with artifacts that are formed both inside and outside the erythrocyte. When the presence of parasites is very high, it is extremely difficult to distinguish them from Howell-Jolly bodies, stain deposits or, in areas where they can be found, from other types of pathogens such as Babesia felis or Cytauxzoon felis.

The development of molecular techniques has opened interesting scenarios, especially for cats in the recovery phase or for asymptomatic carriers. Currently, PCR is the technique of choice in the diagnosis of Mycoplasma haemofelis. This method makes it possible to detect the parasite when the clinical signs are highly compatible but it is not yet possible to see the parasite with a microscope or when very few microorganisms are present. PCR, however, can fail to find parasites in cats that have undergone treatment. In addition, various strains of Mycoplasma haemofelis exist, and therefore it is necessary to properly evaluate the use of all the various PCRs available. In recent years, various studies have demonstrated the effectiveness of real-time PCR in the diagnosis of Mycoplasma haemofelis.

TREATMENT

Mycoplasma haemofelisis normally treated with oxytetracycline or doxycycline; the latter is the most frequently used oral drug. It seems, however, that oxytetracycline and other types of tetracyclines are unable to determine the complete elimination of the parasite, even after months of treatment. Other antibiotics that have proven effective against Mycoplasma haemofelis are quinolones, even though they have not demonstrated the same degree of effectiveness of doxycycline.

In the cat, doxycycline should be administered in capsules or in paste form orally; with these formulations, the risk of oesophagitis secondary to treatment is decreased.

Recent studies have shown that enrofloxacin (5 mg/kg every 24 hours for 15 days) and marbofloxacin (2 mg/kg every 24 hours orally) seem to have the same efficacy as doxycycline. On the contrary, azithromycin or imidocarb propionate are not effective for the treatment of Mycoplasma haemofelis. In cats with severe anaemia the combined use of doxycycline (5 mg/kg every 12 hours orally for 3 weeks) and corticosteroids (2 mg/kg every 12 or 24 hours, parenterally) is recommended, to reduce the degree of  haemolysis and immune-mediated reactions. The effectiveness of pradofloxacin has been documented recently: a treatment at the recommended doses of 5mg/kg every 24 hours orally for 14 days has been able to eliminate the clinical signs, restore the haematological values ​​and significantly reduce the number of copies of M. haemofelis in the blood.

Use of corticosteroids. It has been demonstrated that haemoplasma-induced anaemia is partly immune-mediated, so the use corticosteroids as  an adjunctive therapy is recommended. Initially, immunosuppressive doses of corticosteroids should be used, followed by a gradual dose reduction as the haematocrit starts to normalise.

The usefulness of corticosteroids has however not yet been demonstrated in randomised trials. These drugs should therefore be used only in cases in which critical alterations are maintained, despite the proper use of antibiotics, or in cases where the presence of a severe immune-mediated anaemia (IMHA) can be demonstrated.

Supportive treatment. It is often observed that many cats with haemoplasmosis are extremely debilitated and dehydrated. In these cases it is important to adequately correct the dehydration and the resulting electrolyte imbalances with an intravenous fluid therapy. In the more serious cases, subjects may also suffer from severe anorexia, and such condition must also be corrected. Finally, if the anaemia is critical, a transfusion is required to allow the organism to survive while awaiting the necessary regeneration of circulating red blood cells.

PREVENTION

The control of carriers is the most effective method of protecting cats from Mycoplasma haemofelis. It is therefore important to use pesticide baths, sprays, collars or spot-on products that are effective against ticks and fleas. Since Mycoplasma haemofelis is transmissible through blood transfusions, potential donors must be carefully controlled, as many cats can be asymptomatic carriers of the disease. In this context PCR, or better yet real-time PCR, plays an important role in prevention.

Suggested readings

1. Severine Tasker. Haemotropic mycoplasmas in cats; what’s their real significance in cats. JFMS, (2010), 12:369
2. Sykes JE, Drazenovich NL, Ball LM, Leutenegger CM. Use of conventional and real-time  polymerase chain reaction to determine the epidemiology of hemoplasma infections in anemic and
3. nonanemic cats. J Vet Intern Med 2007; 21: 685–93.
4. Sykes JE, Terry JC, Lindsay LL, Owens SD. Prevalences of various hemoplasma species among cats in the United States with possible hemoplasmosis. J Am Vet Med Assoc 2008; 232: 372–79.
5. Tasker S, Peters IR, Papasouliotis K, et al. Description of outcomes of experimental infection with feline haemoplasmas: copy numbers, haematology, Coombs’ testing and blood glucose
6. concentrations. Vet Microbiol 2009; 139: 323–32.
7. Willi B, Boretti FS, Baumgartner C, et al. Prevalence, risk factor analysis, and follow-up of infections caused by three feline hemoplasma species in cats in Switzerland. J Clin Microbiol 2006; 44: 961–69.
8. Tasker S, Caney SMA, Day MJ, et al. Effect of chronic FIV infection, and efficacy of marbofloxacin treatment, on ‘Candidatus Mycoplasma haemominutum’ infection. Microbes Infect 2006; 8:653–61.