NEW PARASITIC DISEASE CAN CAUSE REPRODUCTIVE FAILURE
by: Mel Pence
DVM, University of Georgia College of Veterinary Medicine
Neospora is a parasitic disease of cattle that causes reproductive failure, primarily abortion. The infection is caused by a small singlecelled protozoan parasite - Neospora
caninum. The parasite gets into the brain and nervous tissue of a developing fetal calf and causes it to abort. Those calves that survive the infection are often born abnormal.
This is a relatively new infection of cattle that was first recognized in 1988. It has been more of a problem in the western states, but has recently (1999 2005) been diagnosed here in Georgia. At one time, 42 percent of all cattle abortions in California were diagnosed as having been caused by Neospora. This has the potential to become a significant problem in the Georgia cattle industry.
Signs in Your Herd
The primary sign of a herd infection is abortion. This is especially true when a herd is infected for the first time. Clinical signs associated with neosporosis, other than abortion, have only been described in cattle younger than two months of age.
Abortion is the only clinical sign seen in infected cows above this age. Cows of any age may abort between three months and nine months of gestation, but the typical time is five to six months of pregnancy when they abort. A number of different things, however, may happen to infected fetuses: they may abort, be reabsorbed, turn into mummies, be stillborn, or they may be born alive but diseased. Occasionally, calves are born diseased but look normal and will be chronically infected so that they may abort as first calf heifers.
Affected calves may be underweight, unable to rise or may have no outward signs. Infected calves may have their eyes affected. They may have small or misshapen eyes. Calves that are born alive may show signs of infection that are related to the nervous system, including having seizures or their hind limbs may be held in rigid flexion or extension.
Transmission of the Disease
The transmission of this disease follows one of two routes. In the first route, a dog or potentially a coyote or fox is involved in transmission. An aborted fetus will have a large number of infective Neospora in its brain, nervous tissue and other tissues. If a dog consumes the fetus, it becomes infected and a carrier of the disease.
Dogs may have signs of infection, but most importantly to the cattle industry, they will pass the Neospora in their feces. If the dog passes feces in feed, forage or water, cattle can ingest this, and when pregnant this can lead to infection of the fetus and subsequent abortion. The cow herself is likely to resist infection.
The second route of infection is more direct. Neosporosis may be transmitted from an infected cow or heifer to the calf during pregnancy through the placenta. If the calf survives, it will be infected for life, which is known as congenital infection, and is likely to abort subsequent calves.
Diagnosis of Neospora is made by examining aborted fetuses or affected newborn calves. The nervous tissue of infected fetuses is the best specimen to examine. Somewhere in the nervous system, usually the brain, you will find microscopic evidence of this disease.
To diagnose this disease you need to have your veterinarian submit the aborted fetus and/or serum from the cow to a diagnostic lab. A positive serum titer of the disease from a blood or serum sample is only a presumptive diagnosis as the cause of abortion, but certainly indicates the cow has been exposed. A negative blood test, however, does not completely rule out neosporosis as the cause of abortion, as even some infected cattle can harbor the organism without exhibiting an immune response.
Previous vaccination will produce a positive serum titer to the disease, and this could possibly be confused for signs of infection. In an unvaccinated cow, a positive titer is indicative of exposure in that cow, but not necessarily infection. Definitive diagnosis is made by direct visualization of the organism in affected tissue using a microscope and ruling out other potential causes of abortion such as noninfectious causes or infectious diseases like IBR, BVD, trichomonas, vibrio or leptosporosis.
Prevention centers around biosecurity and vaccination. Killed vaccinations are available and may decrease the incidence of disease, but may not completely protect an individual cow given a high exposure to Neospora. Two vaccinations two to four weeks apart are necessary along with annual boostering.
Checking serum titers of new additions and heifers pre breeding for antibodies to Neospora and eradication of positive cattle may be a good idea. This practice, however, may not eliminate congenitally infected cows that are not actively producing antibodies from the herd. In a herd where Neospora status is unknown, testing serum titers of at least 10 percent of the herd may help identify whether or not Neospora is a problem. In a negative herd, vaccination can be limited to only incoming additions and replacement heifers.
Keeping feed sources free of contamination is the key to controlling Neospora. Keeping feeders off the ground, using tarps to cover feeds, good fencing around feed storage areas and other measures can help prevent contamination by dogs, coyotes and foxes.
Overall, neosporosis has the potential to become a devastating disease for the cattle industry. Already, Neospora caninum has been found in several herds in Georgia and could potentially spread throughout the state. Fortunately, this disease can be managed in your herd through good biosecurity techniques and/or the use of strategic vaccination.
by Elizabeth Cuttin, Derrich Phillips and Dodd Sledge, University of Georgia
College of Veterinary Medicine Class of 2006.