A rancher in Texas contracted anthrax earlier this year after butchering a lamb that died suddenly on his ranch, CDC researchers said.
Two wound swabs from the rancher, a male in his 50s, were positive for Bacillus anthracis DNA, representing an “unusual case of confirmed cutaneous anthrax acquired during the winter in a geographic region with enzootic anthrax,” Cari Beesley, MS, of the CDC, and colleagues reported in Morbidity and Mortality Weekly Report (MMWR).
“This outbreak occurred on a farm adjacent to the Anthrax Triangle in Texas and near the location of a 2019 human cutaneous anthrax case that was associated with an outbreak in animals, which included 25 culture-positive animal cases,” Beesley’s group wrote. “In both the 2019 case and the current case, the patients reported direct skin exposure to animal carcasses, emphasizing the importance of avoiding processing carcasses of animals that unexpectedly die of unknown causes in this region regardless of the season. If animals must be moved, personal protective equipment should be worn.”
“There was no clear history of routine vaccination against anthrax for this herd, or whether the remaining herd was vaccinated,” they added. “Concerns about vaccine-associated adverse events among goats and horses were previously reported in this area, and routine animal vaccination remains essential in preventing anthrax in animals and subsequent spillover into humans.”
In the case of the rancher, he was evaluated at a hospital on January 4 after not responding to a course of cephalexin prescribed by a general practitioner for soft tissue infection, Beesley and colleagues reported. He presented at the hospital with a fever, leukocytosis, a black eschar on his right wrist, and extensive edema and blistered lesions on his right arm.
Eleven days earlier, he had butchered the lamb, which had shown no signs of disease prior to its death. After butchering the animal, the rancher and another individual had seasoned and well-cooked its meat, which was then consumed by them and three other people. Only the rancher developed symptoms consistent with cutaneous anthrax. None of the other individuals experienced symptoms consistent with gastrointestinal anthrax.
At the hospital, dual therapy for anthrax (ciprofloxacin and clindamycin [Cleocin]) was initiated for the rancher, who showed signs of systemic involvement, Beesley and colleagues reported.
After being transferred to a larger hospital, the Texas Department of State Health Services Laboratory performed PCR testing and culture from the patient’s wound swabs. Though two wound swabs were positive for B. anthracis DNA by real-time PCR, culture did not yield an organism consistent with B. anthracis.
During the patient’s hospitalization, two ewes also died on his ranch, Beesley and colleagues reported. Test results from nasal swabs from the ewes were sent to the Texas A&M Veterinary Medical Diagnostic Laboratory and cultured for B. anthracis. Although the results were negative, a “high level of clinical and epidemiologic suspicion for anthrax remained.”
Ultimately, the rancher recovered and was discharged from the hospital after 1 week.
Paired sera from the patient were sent to the CDC to measure anti-protective antigen (PA) antibodies and lethal factor (LF), a toxin produced by B. anthracis, using enzyme-linked immunosorbent assay (ELISA) and mass spectrometry, Beesley and colleagues noted.
“A more than fourfold increase in the concentration of anti-PA immunoglobulin G was noted between serum specimens collected 11 days apart, indicating exposure to B. anthracis,” they wrote. “LF concentration was 11.9 ng/mL in the acute serum sample, one of the highest LF levels ever measured in a patient with cutaneous anthrax at CDC or any other location.”
The CDC also performed DNA extraction on three sections of tissues from cooked meat from the butchered lamb, they noted. All were positive for B. anthracis by real-time PCR despite no culture growth.
“Nonculture testing through real-time PCR, ELISA, and mass spectrometry at CDC Laboratory Response Network sites was critical to confirming the diagnosis of anthrax considering of the unusual seasonality and inability to culture B. anthracis,” Beesley and colleagues wrote.
With regard to the rancher, they noted that older evidence suggests first-generation cephalosporins might have prevented culture growth. And in the case of the ewes, the lack of culture growth could have been attributed to factors like delayed sampling as well as handling and shipping of swabs.
As for the lamb, the “infecting bacteria possibly were inactivated when the meat was cooked at high temperatures; however, there is no safe way to prepare meat for human consumption from an animal that has died of anthrax,” they added.
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Jennifer Henderson joined MedPage Today as an enterprise and investigative writer in Jan. 2021. She has covered the healthcare industry in NYC, life sciences and the business of law, among other areas.
Disclosures
A co-author reported travel support from the Association of Public Health Laboratories and the Texas Department of State Health Services.
Primary Source
Morbidity and Mortality Weekly Report
Source Reference: Beesley CA, et al “Anthrax on a sheep farm in winter — Texas, December 2023–January 2024” MMWR 2024; 73(Suppl-22); 517-520.
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