Toxigenic Corynebacterium diphtheriae Infection in Cat, Texas, USA

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D iphtheria, caused by toxigenic strains of the bac- terium Corynebacterium diphtheriae, can result in life-threatening respiratory disease or cutaneous infections.Toxigenicity is contingent on successful bacterial expression of diphtheria toxin, encoded by a toxin gene (tox).Toxigenic C. diphtheriae is considered nearly exclusively a human pathogen, and humans are believed to be the reservoir.Because of high population coverage with diphtheria toxoid-containing vaccines, few diphtheria cases are reported in the United States.The most recently reported toxigenic infections were cutaneous and associated with international travel (1-4).A 2016 article reviewing available literature on C. diphtheriae isolated from animals identified 12 cases globally, 4 in dogs, 4 in cats, 2 in horses, 1 in a cow, and 1 in a fox.These infections were toxigenic only in 2 dogs and the 2 horses; 1 of the horses was identified in the United States (5,6).In contrast, toxigenic Corynebacterium ulcerans is a zoonotic organism that causes diphtheria-like illness in humans clinically indistinguishable from illness caused by toxigenic C. diphtheriae; it is more common than the diphtheria pathogen among household pets and their owners (7).To date, toxigenic diphtheria has not been detected in cats; however, nontoxigenic strains have been identified, including 2 from the ears of cats in the United States and 1 from the nose of a cat in Belgium (8,9).Although these 3 strains contained the tox gene, they were not toxin producing.Of note, the strains identified in the United States have recently been reclassified as a novel species, C. rouxii, because of biochemical and genetic differences with C. diphtheriae (10).Recommended public health response to toxigenic diphtheria infections in humans in the United States involves isolating and treating the index casepatient, identifying contacts, and vaccinating the patient and contacts with diphtheria toxoid-containing vaccine if it has been >5 years since the last dose (11).After treatment is completed, the index case-patient should be tested to confirm eradication of toxigenic C. diphtheriae and contacts monitored for development of diphtheria illness for 7-10 days after their most recent exposure; nasal and throat swab specimens should be collected to test for carriage, and prophylactic antibiotics should be administered.No formal recommendations exist for toxigenic diphtheria in animals because of its rarity, but health departments may pursue interventions similar to those to prevent transmission in humans.In October 2020, a veterinary clinic in southern Texas, USA, evaluated a male domestic shorthair cat 10 years of age for an oozing wound with multiple abscess pockets in its left flank.The clinic reported culturing Mycobacterial farcinogenes from a similar lesion on the cat in May 2018.A swab of the new wound was submitted for culturing to the Texas A&M Veterinary Toxigenic Corynebacterium diphtheriae Infection in Cat, Texas, USA

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