Anthrax From a Lamb in Winter: A Texas Rancher's Case, 2023–2024

Anthrax is a rare but serious infection passed from animals to people, caused by the spore-forming bacterium Bacillus anthracis. In North America, animal outbreaks usually come in hot, dry summer weather, and the rare human cases usually follow direct contact with, or processing of, infected animals or their hides, hair or wool. In early 2024, an unusual winter case of cutaneous (skin) anthrax was investigated in Texas.

The case

The patient, a man in his 50s, was one of five people exposed to the lamb: he and one other seasoned and cooked it, and three more ate it. Only he fell ill, and nobody had signs of gastrointestinal anthrax.

The Anthrax Triangle is the part of Texas bounded by Eagle Pass, Ozona and Uvalde, covering Crockett, Edwards, Kinney, Maverick, Sutton, Uvalde, Val Verde and Zavala counties, where lab-confirmed animal anthrax is most frequent.

Confirming it without culture

Nothing grew in culture — not from the patient's swabs, nor from the ewes' swabs — so the diagnosis rested on other tests at Laboratory Response Network sites:

• PCR: two of the patient's wound swabs were positive for B. anthracis DNA at the Texas Department of State Health Services laboratory.
• Antibodies: anti-protective antigen IgG rose more than fourfold between blood samples taken 11 days apart — evidence of exposure.
• Toxin: lethal factor, a toxin B. anthracis makes, measured 11.9 ng/mL in the first sample — one of the highest levels ever recorded in a cutaneous anthrax patient, at CDC or anywhere.
• The meat: cooked lamb, kept frozen for 2 weeks, tested PCR-positive in all three tissue sections, though nothing grew.

What the investigators concluded

• Cephalexin may explain the failed cultures: older evidence suggests first-generation cephalosporins may act on B. anthracis — yet they are not to be used for naturally occurring anthrax, because of intrinsic resistance, and the patient recovered only on effective anthrax drugs.
• The ewes' negative cultures may reflect late sampling (at least 12 hours after death) or how swabs were handled, stored or shipped. No other animals died that winter.
• Cooking at high temperature may have killed the bacteria in the meat — but there is no safe way to prepare meat from an animal that died of anthrax.
• The ranch is near the site of a 2019 human cutaneous case tied to an animal outbreak with 25 culture-positive animals. Both patients had handled carcasses with bare skin.

Recommendations:

• Don't process animals that die suddenly of unknown causes in this region — in any season. If a carcass must be moved, wear protective equipment.
• Vaccinate animals routinely against anthrax. This herd had no clear vaccination history, and it is unknown whether the rest were vaccinated after the three deaths; concerns about vaccine side effects in goats and horses have been reported in the area.

Sources

Based on Thompson JM, Spencer K, Maass M, et al., "Notes from the Field: Anthrax on a Sheep Farm in Winter — Texas, December 2023–January 2024," MMWR Morbidity and Mortality Weekly Report, volume 73, Centers for Disease Control and Prevention; a work of the United States government in the public domain.