Medico Veterinario

Neospora sp.
Neospora caninum has been identifi ed as a cause of abortion
in cattle. Similarities to other carnivore-borne protozoans
suggest that carnivores, specifi cally the domestic
dog, are the primary host and shed oocysts in their feces
that are infectious to cattle. N. caninum has been confi
rmed as a major cause of abortion in cattle in the
United States and other countries.Abortions may occur
between 3 and 9 months, with the majority occurring at
4 to 6 months gestation. Following transplacental infection,
the central nervous system of the fetus is the major
target area, and protozoan encephalomyelitis ensues. In
addition to abortions, calves may be born weak or with
obvious neurologic defi cits. Some cattle that have aborted
once because of Neospora sp. infectionmay subsequently
deliver calves with neurologic lesions and concurrent
paresis as a result of congenital Neospora infection. Onfarm
studies of precolostral antibody levels in calves on
endemic premises suggest that the risk of endogenous
vertical transmission by a chronically infected dam may
be as high as 95%, but the vast majority of congenitally
infected calves will be normal.
Verticaltransmission is the primary mode of transmission
once the infection has been introduced into a
herd. Experimental confi rmation of vertical transmission
in cattle is well documented. Nonsuppurative myocarditis
has also been reported in fetuses or calves with
congenital focal necrotizing encephalomyelitis.
Neospora parasites have been isolated from aborted
fetuses. In addition, otherworkers have found protozoan
abortion in one herd of cattle that was concurrently
infected with Hammondia pardalis thought to be
related to a large feral cat population.
In most affected herds, protozoan abortion has
seemed to be associated with close confi nement of cattle.
Abortions may be sporadic, endemic, or epidemic,
and the prevalence varies greatly.
Clinical signs are limited to abortionand the birth of
calves with neurologic signs secondary to congenital infections
of the central nervous system. Infected cows are
asymptomatic. Diagnosis is based on immunohistochemical
staining of fetal or calf tissues and an enzymelinked
immunosorbent assay (ELISA) test on serum. The
current immunohistochemical procedure performed on
tissue samples is an immunoperoxidase test usingantisera
against N. caninum or the bovine Neospora (BPA1)
isolate on paraffi n-embedded sections. All tissues should
be examined, but the brain and heart are most likely to
show lesions. The ELISA test currently is recommended
for screening of cattle and precolostral calves showing
signs or considered at risk of congenital infections. Serology
may be a helpful screening procedure to detect thepresence of the Neospora-like organism in a herd or suspect
calf. If all tested animals are negative, the disease is
not likely to exist on that farm, and immunohistochemical
staining may not be indicated. Milk ELISA test may be
useful to assess herd status. Diagnostic laboratories studying
aborted fetuses will need to use immunohistochemical
stains to detect the organism in fetal tissues,however.
Practitioners should inquire regarding the availability of
these tests before sending samples to specifi c laboratories.
A vaccine has recently become available in many
parts of the world. Although effi cacious in reducing incidence
of abortion, it does not eliminate it.
Epizootic Bovine Abortion
Etiology
Epizootic bovine abortion is a disease of uncertain etiology
that occurs inthe foothill regions of the Sierra Nevada
Mountains, including parts of Nevada, Oregon, California, and northern New Mexico. Although the specifi
c etiologic agent is unknown, the disease occurs only
in areas harboring Ornithodoros coriaceus, so the disease is
thought to be tick-borne. Cattle and deer are the primary
hosts of this tick. Chlamydia was long considered to be
the cause, but...