This is a epicellular parasite of feline erythrocytes.
Distribution
It has been reported from many places of UK and USA including Asia, Australia and other countries.
Aetiology
It is caused by a rickettsial parasite known as Haemobartonella felis. It is a gram negative epicellular parasite of cats erythrocytes. In Europe and Australia, the parasite was known as Epyerythrozoon felis. H. felis is noted as cocci in thick smear and as rod or ring in thin areas of the blood film. The size varies from 0.2 to 1 micrometer from coccoid form and upto 3 micrometer in rod forms.
The organisms are mostly noted on the surface of RBC. Occasionally in the plasma. Organisms appear as dark-red violet bodies while stain with wright giemsa stain.
Now a days, the organism is grouped under Mycoplasma. Thus, the present name of the organism is Mycoplasma haemofelis. This is for large form. While it is proposed for small form as Myplasma haemominutum.
Susceptible Hosts
All domestic and wild cats. Fleas can also be infected naturally.
Mode of Transmission
Cats get the infection through fleas. Naturally, cats and fleas can be infected by M. haemofelis and M. haemomonium. Infected cat may also transfer the organism to fleas mechanically.
It can be transmitted experimentally through oral or paentaral route through transfer of small amount of infected blood. Intra-uterine infection is postulated. Laterally infection may spread to the susceptible population through blood transfusion. Transmission through bite is suspected.
Pathogenesis
In experimental cases, incubation period ranges from 1 to 5 weeks. Prevalamce of naturally occuring disease is more in younger age group. Many cats may carry the organism in a latent form.
Red blood cell destruction is due to immune-mediated mechanism. It is thought that co-infection with feline leukemia virus pre-dispose the condition and helps in precipitation of the disease.
RBC is damaged as a consequence to immune mediated mechanism. Parasitized RBC may be injured by antibody-complement interaction against the organism, antigen initially coombs test remain positive but it becomes negative during carrier stage.
Clinical Findings
Anaemia is the cardinal signs. There is pale mucous membrane, inappetance; depression and occasionally signs of jaundice and enlargement of spleen. Intermittent fever even upto 106° F is observed in chronically infected cats. A large prpportion of cats with fever may be infected with M. haemofelis. It indicates that cat may suffer due to fever of unknown origin.
In experimental cats there may be two or more parasitic episodes before development of anaemia.
Lesions
Necropsy findings will show splenomegaly but mesenteric lymph nodes may be enlarged. Bone marrow may have hyperplastic changes.
Diagnosis
It may be made on clinical signs and laboratory findings.
Blood picture:
(i) Anaemia – Macrocytic normochromic
(ii) May also be Macrocytic hypochromic.
- Regenerated anaemia characterized by diffuse basophilic granule in large RBC, nucleated RBC, poly chromasia, anisocytosis, Howel-Jolly bodies and increased count of reticulocytes. Non-regenerative anaemia may develop i the onset of anaemia is rapid.
- Neutrophilia and monocytosis may be observed in some cases.
- Red blood cell count may be as low and haemoglobin values.
- Erythrophagocytosis and auto agglutination may be observed in peripheral blood.
- Biochemical changes comprised of increased ALT, AST, bilirubin and total protein and blood sugar may be decreased.
Test
PCR is the test of choice due to sensitivity. Primers are available that will amplify a segment of 165 rRNA gene common to all Mycoplasma spp.
Differential Diagnosis
This is to be differentiated from cytozoonosis – this is a theilaria like parasite. Cytoxzoon to looks as intra cellular ring, rod or coccoid measuring 0.5-2 micrometer within RBC. On the other hand M. felis used to form chains on the surface of RBC.
Treatment
Treatment is of two types (a) supportive and (b) specific
(a) Supportive treatment
- Severe dyspnoeic cats may require oxygen therapy.
- Severe anaemic cats may need whole blood or packed RBC therapy.
- Potential arthropod vectors to be treated.
- Other symptomatic treatments should be resorted.
(b) Specific treatment
Tetracycline at the dose rate of 20 mg/kg thrice daily orally.
Doxycycline has less side effects therefore it can be given @ 10 mg/kg orally for every 24 hours atleast for 14 days.
While cat is intolerant to Doxycycline in that case Enrofloxacin may be given @ 5 mg/kg orally at 24 hours interval or @ 10 mg/kg orally for 14 days.
Glucocorticoid is recommended where there is evidence of immune mediated RBC injury. Prednisolone @ 2-4 mg/kg orally daily may be used along with antibiotic.
Response should be judged based on disappearance of clinical signs and PCR negative findings.
Control
- Potential vectors to be eradicated with acaricides.
- House and the premises should be made free from vectors.
- Before donation of blood, cat should be brought under PCR test. 9.8% cats as donor may have infection.
- Infected one should be segregated from cat house.
