Canine Hepatozoonosis appears in two forms, one is asymptomatic and the other being severe and often life threatening. It is a tick borne protozoan disease.
Distribution
Canine Hepatozoonosis is prevalent in most parts of the world, where tick vector is abundant. In India, the presence of such disease is reported.
Aetiology
The disease is caused by two agents, one is H. canis prevalent in old world and the other is H. americanum prevalent in southern United States of America. The disease exists as asymptomatic parasitaemia to severe anaemia. The main vector of H. canis is brown tick Rhipicephalus sanguines. This tick is present in warm and temperate regions all over the world. But, the vector of H. americanum gulf coast tick is Amblyoma macaculatum. This is restricted to some part of America. Both the agents are transmitted transstadially from nymph to the adult stage in tick vectors.
Susceptible Hosts
It is primarily a disease of dogs. But, other wild canidae may also suffer. Coyote may get the infection.
Mode of Transmission
Contrary to other tick borne parasite where the transmission takes place through the salivary glands of infected tick, but here the transmission takes place by ingestion of infected ticks or fragments of it.
Pathogenesis
Following ingestion of ticks by the host, sporozoites are released from the oocyst in the intestine of dogs and they penetrate the gut wall. The sporozoites than invade mononuclear cells and disseminate through blood or via the lymphatic to the target organs. Merogony occurs in the parenchymal tissues of dogs followed by gametogony in leucocytes. The tick which acts as an agent gets infected while feeding on infected dog H. gamonts release from the dog leucocyes within the tick gut and the gametogenesis takes place there upon fertilization and sporogony and finally oocyst in the tick’s haemocoel takes place.
H. canis primarily affects blood, vascular and lymphatic tissues as well as blood generating organs (bone marrow, spleen, lymph node). H. americanum mainly infects skeletal and cardiac muscle and cause myositis and severe lameness.
Clinical FIndings
It appears in two forms:
(a) Asymptomatic form shows a mild form where clinical signs may not be observed. But on examination of blood, parasites may be observed. Here the parasitaemia may range from 1.5%.
(b) Severe form: The signs are high rise of temperature, lethargy, weight loss, anaemia. Here the parasitaemia rates may be as high as 100% in the peripheral blood neutrophils. One survey in Israel showed that it was 33% through sero epidemiological studies.
Co-infection with parvovirus E. canis, T. gondii and L. infantum may show severe infection leading to death. Most cases will show fever, abnormality in gait, muscular pain, muscular atrophy, muco-purulent ocular discharge. Giat abnormalities may be in the form of lumbar involvement, cervical spine involvemet, joint involvement, stiffness of joints, paresis, ataxia and finally unable to rise.
Lesions
The lesions are marked in liver causing hepatitis, kidneys causing nephritis, lungs causing pneumonia. Muscular changes in the form of myositis. Skeletal muscles may show pyogranulomatous myositis and large round to oval cyst containing a central nucleus surrounded by concentric rings of membranes. These cyst are ascribed as “onion peel” for such appearance.
Diagnosis
It is based on history of tick infestation, clinical findings, parasitaemia lesions, radiology and serological tests.
(a) Microscopic detection of H. canis gamonts in the blood smear especially within the neutrophils.
(b) Neutrophilia: Neutrophil level may go as high as 1,50,000/leucocytes/microlitre of blood.
(c) Histopathology of biosied muscles. Myositis onion peel appearance.
(d) Radiography: Long bones may show peiosteal proliferation.
(e) Serology:
- ELISA – for the detection of HAI antibody
- IFAT – for the detection of HAI antibody
Treatment
- Treatment may be rendered with Imidocarb dipropionate @ 5-6 mg/kg every 14 days till gamonts disappear.
- Orally Doxycycline @ 10 mg/kg/day for 21 days may be used. It can be combined with imidocarb. Generally 8 weeks time is required for eliminatio of gamonts.
- Combination therapy with sulpha-trimethoprim 15 mg/kg at 12 hours interval, pyremethamin (0.25 mg/kg every 24 hours) and clindamycin (10 mg/kg every 8 hours) may be used.
- Following remission anticoccidial like decoquinate @ 10-20 mg/kg mised in food at 12 hours interval may prevent relapse.
- Supportive therapy for fever and pain may be resorted.
Control
It can be had by reducing the risk of exposure of dogs to the infected ticks. For this, acaricides are to be used as a routine measures in those Kennel and Zones where canine hepatozoonosis exist in wilder proportion.
