Dogs are definitive hosts of Neospora caninum.

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

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Epidemiology and Control of Neosporosis and Neospora caninum

A review of Neospora caninum and neosporosis

Toxoplasma gondii infection in humans and animals in the United States.

Neospora caninum is a coccidian parasite of animals. It is a major pathogen for cattle and dogs and it occasionally causes clinical infections in horses, goats, sheep, and deer. Domestic dogs are the only known definitive hosts for N. caninum. It is one of the most efficiently transmitted parasite of cattle and up to 90% of cattle in some herds are infected. Transplacental transmission is considered the major route of transmission of N. caninum in cattle. Neospora caninum is a major cause of abortion in cattle in many countries. To elicit protective immunity against abortion in cows that already harbor a latent infection is a major problem. This paper reviews information on biology, diagnosis, epidemiology and control of neosporosis in animals.

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Review of Neospora caninum and neosporosis in animals.

Histologic sections and case histories from 23 dogs with proven fatal toxoplasmosis-like illness at the Angell Memorial Animal Hospital were reviewed. Toxoplasma gondii was identified in 13 dogs. A newly identified parasite, Neospora caninum, structurally distinct from T gondii, was found in 10 dogs. The newly discovered organism, belonging to a new genus and new species, formed meronts in many tissues of the dogs, especially the brain and spinal cord. Neospora caninum was located directly in the host cell cytoplasm without a parasitophorous vacuole; it divided by endodyogeny, contained more than 11 rhoptries, and did not react with the anti-T gondii serum in the immunoperoxidase test. Meningoencephalomyelitis and myositis were the main lesions associated with N caninum. Ulcerative and fistulous dermatitis was the major lesion in 1 dog.

Newly recognized fatal protozoan disease of dogs

Neospora caninum tissue cysts were found in the brain and spinal cord of a 1-wk-old lamb that was unable to stand after birth. The lamb was originally diagnosed as having toxoplasmosis, but ultrastructural and immunohistochemical techniques used in the present study permitted a definitive diagnosis of Neospora caninum tissue cysts in the brain and spinal cord of this lamb. This is the first report of N. caninum in sheep.

Fatal congenital Neospora caninum infection in a lamb.

Neospora canium tachyzoites and tissue cysts were found in tissues of a goat fetus aborted after 3.5 months of gestation. The fetus had hydrocephalus and a hypoplastic cerebellum. The predominant lesion in the fetus was severe encephalitis associated with numerous N canium tissue cysts. Parasites in fetal tissues reacted positively with N caninum antibodies in immunohistochemical tests. The doe was clinically normal and had a 1:800 antibody titer to N caninum as determined by use of an indirect fluorescent antibody test 9 months after abortion. Five of 77 other does from this herd also had indirect fluorescent antbody titers to N caninum that were > or = 1:100.

Neosporosis-associated abortion in a dairy goat

Numerous developmental stages of Caryospora sp. were seen in skin and lymph node of a 2-mo-old-dog with severe pyogranulomatous dermatitis. Schizonts were up to 20 microns long and contained up to 25 merozoites. Gamonts, unsporulated oocytes, sporulated oocysts, and caryocysts were seen in macrophages, connective tissue cells, and in unidentifiable host cells. Caryocysts were up to 18 microns long, and had thin walls, and contained a host cell nucleus and 1-3 sporozoites. All developmental stages of the coccidium reacted positively with anti-Caryospora bigenetica serum when examined in an immunoperoxidase test.

Caryospora-associated dermatitis in dogs.

Two of 8 littermate Rottweiler dogs developed persistent diarrhea at 6.5 weeks of age. Dog 1 was euthanatized at 14 weeks of age and had hepatitis characterized by necrosis and mixed leukocyte infiltrations in association with a previously unrecognized Sarcocystis-like protozoon. The organism was free in the hepatocyte cytoplasm without a parasitophorous vacuole, had divided by schizogony, and stained with anti-Sarcocystis serum, but did not stain with anti-Toxoplasma gondii or anti-Neospora caninum serum in an immunohistochemical test. Dog 2 was euthanatized at 10 weeks of age. This dog had large necrotic, hemorrhagic mesenteric lymph nodes. Numerous T gondii tachyzoites were observed in association with these lesions. The organism divided by endodyogeny and stained specifically with anti-T gondii serum.

M. J. Topper

Papers

Newly recognized fatal protozoan disease of dogs

Fatal congenital Neospora caninum infection in a lamb.

Neosporosis-associated abortion in a dairy goat

Caryospora-associated dermatitis in dogs.

Acute sarcocystosis-like disease in a dog