Historical overview of anthrax in Texas’ livestock population (1974-2022)
Narayan Paul, DVM, MS, PhD, ACVM
Anthrax is caused by a gram positive, rod-shaped bacteria called Bacillus anthracis. This is a spore forming bacteria that can persist in dry, alkaline soil of endemic areas such as southwest Texas. Cattle, sheep, goats, deer, and horses are more susceptible to infection than pigs, birds and carnivores, like dogs and cats. In herbivores, anthrax is often characterized by sudden death of animals with leakage of unclotted blood from natural orifices and no prior clinical signs. Anthrax cases in horses are usually acute and clinical signs include loss of appetite, colic, enteritis, subcutaneous edema, and bloody diarrhea.
TVMDL Bacteriology sections in College Station and Canyon receive samples for anthrax testing from all over Texas, but primarily from the endemic regions. Anthrax tests are performed seven days a week and results are typically available within 24-48 hours. At TVMDL, anthrax tests are performed using bacterial culture, which is considered the gold standard method for diagnosing anthrax. The recommended specimen is unclotted blood or bloody fluid collected from an orifice of the dead animal. Samples are streaked onto different bacterial culture media. Anthrax colonies are visually distinctive, generally present within 18-24 hours of incubation, and are further tested for bacteriophage lysis and penicillin susceptibility as confirmatory tests. Anthrax bacteria are positive for bacteriophage lysis (Fig. 1) and susceptible to penicillin antibiotics (Fig. 2).
Every year TVMDL confirms culture-positive anthrax cases. Historical data from the last 50 years shows there were many positive anthrax cases back in 1974, 1975 and 1976 confirmed by TVMDL (Fig. 3). In 2019, a spike of anthrax positive cases was observed in Texas in different animal species including cattle, white-tailed deer, goats, horses, and exotic antelope. The majority of the cases were from the “anthrax triangle”, an endemic area between Eagle Pass, Uvalde, and Ozona.
TVMDL data from 1999 to present show that June, July, and August are the most anthrax- prevalent months followed by September and October. However, anthrax positive cases were also observed in nearly every month of the year (Fig.4).
TVMDL strongly encourages animal owners who suspect anthrax to first contact their local veterinarian. From there, TVMDL is glad to assist veterinary clients with questions regarding sample collection, submission, and testing.