Until October 1999, Brucella melitensis had not been reported in Texas for a quarter of a century. Epidemiologists are attempting to pinpoint how a herd of mixed-breed, meat goats became infected and whether the disease may have spread. The herd was located in Starr County, South Texas.
Veterinarians and animal health inspectors from the Texas Animal Health Commission depopulated and buried the herd of nearly 120 goats and sheep, with assistance from USDA-APHIS Veterinary Services.
What brought the infected goat herd to light was the sale to slaughter of a cow late last summer by a neighboring rancher. Two brucellosis field tests on the cow were positive. The USDA National Veterinary Services Laboratories confirmed the presence of B melitensis.
Worldwide, brucellosis remains a major zoonosis, with B melitensis the principal cause of human brucellosis.
Dr. Valerie Ragan, national brucellosis epidemiologist with USDA-APHIS Veterinary Services, told JAVMA, "This is the first case of Brucella melitensis infection that has ever been confirmed in a cow in the United States. The last time the organism was isolated in the United States was in the early 1970s, and that was also in sheep and goats in South Texas."
According to Dr. Terry Conger, epidemiologist with the Texas Animal Health Commission, "We tested the remaining animals in the rancher's cattle herd and found four other animals that carried a low titer. These cattle were depopulated and buried, to protect workers who might be exposed to airborne bacteria when handling infected carcasses at the slaughter plant."
Investigators tested nearby goats, sheep, and other susceptible species but found no more infected animals until they broadened their search and located an infected goat herd a quarter mile from the herd that had included the infected cow. Epidemiologic investigation revealed that the rancher had purchased cattle from the goat herd owner. Although the infected cattle wore no tags or brands that would have enabled traceback, the goats were the only other infected animals found within one mile of the cattle herds.
Dr. Ragan commented that, although B melitensis exists in Mexico, the source of the South Texas infection has not been determined.
The state health department has notified physicians, veterinarians, and public health clinics in South Texas to be alert for patients who may have contracted this form of brucellosis. As of Feb 1, no human cases were reported.
"We're particularly concerned about Brucella melitensis, as it can cause serious illness in humans if they consume unpasteurized milk or cheese, or process the meat from an infected goat without taking precautions," Dr. Conger said.
"We're urging South Texas ranchers to have their goats tested for the disease, particularly if they are planning to use milk from the nannies, or slaughter the animals."
Texas, one of six states that have not yet eliminated bovine brucellosis caused by B abortus, has two known infected cattle herds currently under quarantine.