Canine hemoplasmosis

Hemoplasmosis, formerly called haemobartonellosis, is a tick (and sometimes flea) transmitted disease that affects both dogs and cats. Hemoplasmosis targets the red blood cells. In cats, it is called feline infectious anemia or feline hemotropic mycoplasmosis. There have been no reported cases of hemoplasmosis in man, although organisms resembling hemotropic mycoplasms have been found in people with suppressed immune systems.

Pathogen

Previously, dogs were thought to be infected by Haemobartonella canis, an organism transmitted by the Brown Dog tick, Rhiphicephalus sanguineus. Based on genetic analysis, dogs are now known to be infected by two distinct bacterial species, Mycoplasma haemocanis and Candidatus Mycoplasma haematoparvum, both belonging into the genus Mycoplasma of the family Mycplasmataceae.

Distribution

The distribution of both mycoplasms is largely unknown, but both species have been isolated from dogs in Europe and the USA. The Brown Dog tick, a common tick species in Europe, USA and Australia, is known to transmit these pathogens. In France, 71 out of 460 dogs were positive for DNA of one or both of the organisms. It is possible that Mycoplasma haemocanis is more common in kennel raised dogs.

Disease transmission

Fleas and ticks become infected with hemotropic mycoplasms by feeding on an infected animal and may subsequently transmit the pathogen to another animal. As intraerythrocytic organisms, the mycoplasms can be transmitted to mammals via blood transfusion. In the cat, hemotropic mycoplasms may also be spread from the mother to her kittens. There are indications that bitches can also pass mycoplasms to their puppies, but this has not been proven so far.

Diagnosis

Sometimes the organism can be detected in a blood smear in its typical location inside the cell. But the number of pathogens in the peripheral blood can fluctuate massively, so that blood smear examination can be false negative up to 50% of the time. Due to the high sensitivity of PCR assays, these tests are the method of choice for Mycoplasma diagnostic in dogs. Real time PCR to quantify hemoplasma DNA has been developed and can be used to monitor response to treatment. The PCR blood test to detect hemotropic mycoplasms is commercially available.

Clinical signs

Clinical signs of the disease depend on the degree of anemia, the stage of infection, and the immune status of the patient. However, neither organisms appear to be primary pathogenic in dogs. Generally the disease is clinically inapparent, unless the dog is splenectomized or immunosuppressed. Such an activation of a latent infection will result in hemolytic anemia. Acute clinical signs may then include depression, loss of appetite, weight loss, and fever. In severe cases, death can occur. A chronic form of the disease has been reported rarely and may cause slight weakness, an increase in appetite, and pica.

Since ticks are vectors for diverse types of pathogens, more than one agent might be transmitted during the bite of a tick (e.g., causing hemoplasmosis, ehrlichiosis, babesiosis). These co-infections with more than one tick-borne pathogen at a time are quite frequent. Co-infection with Ehrlichia sp. and a subsequent suppression of the dog's immune system can cause clinical acute hemoplasmosis.

Treatment

Treatment with antibiotics such as tetracycline, oxytetracycline or doxycycline given for three weeks with or without glucocorticoids can control the hemolytic anemia. In some animals, it is necessary to give one or multiple blood transfusions. However, similar to feline hemoplasmosis, antibiotic therapy is unlikely to eliminate the infection.

As with other diseases transmitted by fleas or ticks, ectoparasite control is the basis of prevention. Products which repel and kill ticks and fleas such as those containing permethrins are the appropriate means of choice for dogs.

Further information

• Lappin, M.R.: Bartonella and Haemobartonella in cats and dogs: Current knowledge. In: The Bayer 7th Int. Parasite Symposium, Proceedings of the BSAVA Pre-Congress Symposium, Birmingham, 2006 (Download)