Hepatozoon felis Patton, 1908
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ETYMOLOGY:Hepato (liver) + zoon (animal) and felis for cat.
SYNONYMS:Haemogregarin felis-domesticae Patton, 1908; Hepatozoon felisdomesticae (Patton, 1908) Wenyon, 1926; Leucocytozoon felis-domestici (Patton, 1908) Patton, 1908. Some consider this a synonym of Hepatozoon canis (James, 1905) Wenyon, 1926.
HISTORY: This parasite was first described in the blood of domestic cats in India in 1908 by Patton. Since that time, there have been few other reports of Hepatozoon in cats. Schizonts were first reported in capillaries of cats in 1973 (Klopfer et al., 1973).
GEOGRAPHIC DISTRIBUTION: Patton (1908) observed Hepatozoon felis in cats in India. In Nigeria, Hepatozoon was reported from the blood of a cat that was part of a survey between 1966-1976 (Leeflang and Ilemobade, 1977). In Israel, stages of Hepatozoon have been observed at necropsy in the hearts of 30% of 50 cats that had been submitted for rabies examination (Klopfer et al., 1973) and in 42% of stray cats that were used for laboratory demonstrations (Nobel et al, 1974). Hepatozoon was seen in the liver of a cat that had originated from Hawaii (Ewing, 1977). The only other report has been from South Africa (van Amstel, 1979).
LOCATION IN HOST: The circulating gamonts have been found in polymorphonuclear lymphocytes. In the cat, the only site in which schizont stages have been observed are in capillaries of the myocardium; however, it would be expected that other tissues would also be involved.
PARASITE IDENTIFICATION: In the circulating neutrophils, the gamonts are elongate bodies with rounded ends, about 5 µm by 10 m in size. There is a central compact nucleus that stains a dark red with Giemsa stain. The cytoplasm stains a light blue.
Within histological sections of the myocardium, the schizonts that have been described are of two types (Klopfer et al., 1973). In one type, the schizont appeared to be filled with individual merozoites. In the other type, the schizonts appeared to contain developing merozoites located around the periphery.
LIFE CYCLE: The life cycle of Hepatozoon felis has been considered to be the same as that of Hepatozoon canis which some actually consider the same parasite. Dogs can be infected by being fed a Brown Dog Tick, Rhipicephalus sanguineous, that has previously been given a blood meal on a dog with circulating gametocytes (Nordgren and Craig, 1984). In the dog, two types of schizonts are formed that have been termed microschizonts and macroschizonts. There has been no work on the vectors that may be involved in the transmission of this parasite between cats, and there has been very little examination of the development of different stages found within the cat.
CLINICAL PRESENTATION AND PATHOGENESIS: Clinical disease is rare with schizonts being found in tissues of domestic cats at necropsy more frequently that clinical disease occurs. Progressive weight loss, ulcerative glossitis with hypersalivation, intermittent anorexia and pyrexia, progressive non-responsive anemia, and serous nasalocular discharge have been reported in one cat. Lymphadenopathy and icterus have also been reported. A progressive monocyte count with an increasing number of circulating monoblasts in peripheral blood resulting in a misdiagnosis of monocytic leukemia was made in one cat. The necrospy revealed the presence of Hepatozoon felis in the liver. A careful search of blood smears, bone marrow, and sections of other tissues failed to reveal any other organisms.
TREATMENT: there is a lack of effective treatment. Treatments tried in dogs have included oxtetracycline, chloramphenicol, sulfadimethoxine, diminazene aceturate, an dimidocarb diprpionate. The cat in South Africa treated by Van Amstel (1979) responded to treatment with oxytetracycline (50 mg/kg, BID, for 7 days) along with a single treatment of primaquine (2 mg per os two days after the initiation of oxytetracylcine treatment.
EPIZOOTIOLOGY: It is possible that the species in the cat actually represents infections with other species of Hepatozoon, such as Hepatozoon canis of the dog, Hepatozoon procyonis which is common in raccoons (Procyon lotor) in the southern United States and in Central America, and Hepatozoon spp. of the bocat (Lynx rufus) which is also comon in the sourthern United States.
HAZARD TO OTHER ANIMALS: Probably none, unless the cat also introduces the tick vector into the establishment. It might then be possible for the pathogen to be transmitted between animals in a boarding facility.
HAZARD TO HUMANS: None known.
CONTROL/PREVENTION: Infection requires that the cat ingest and infected tick; therefore, it is important that the infestation of the cat with the tick be prevented. Unfortunately, the Brown Dog Tick, Rhipicephalaus sanguineus, will quite readily establish itself within a household. Thus, it may be necesaary to hire exterminators to remove the tick if it has been introduced.
REFERENCES:
BanethG, Lavy E, Presentey B-Z, Shkap V. 1995. Hepatozoon sp. Parasitemia in a domestic cat. Feline Practice 23:10-12.
Ewing GO. 1977. Granulomatours cholangiohepatitis in a cat due to a protozoan parasite resembling Hepatozoon canis. Fel Pract 7:37-40.
Klopfer U, Nobel TA, Neumann F. 1973. Hepatozoon-like parasite (Schizonts) in the myocardium of the domestic cat. Vet Pathol 10:185-190.
Leeflang P, Ilemobade AA. 1977. TIck-borne disease of domestic animals in northern Nigeria. Trop An Prod 9:211-218.
Nobel TA, Neumann F, Klopfer U. 1974. Histopathology of the myocardium in 50 apparently healthy cats. Lab An 8:119-125.
Nordgren RM, Craig TM. 1984. Experimental transmission of the Texas strain of Hepatozoon canis. Vet Parasitol 16:207-214.
Patton, WS. 1908. The haemogregarines of mammals and reptiles. Parasitology 1:318-321.
Van Amstel S. 1979. Hepatozoönosis in 'n kat. J S Afr Vet Assoc 10:215-216.
Wenyon CM. 1926. Protozoology. Baillere, Tindall, and Cox, London, England.