OAHN Poultry Project: Weak turkey cases (2024/2025) most likely botulism

Project Lead: Dr. Emily Martin

Project Report

In the summer and fall of 2024 there were multiple meat turkey flocks (approx. 10) in the 10-15 week age range that presented with weakness and inability to stand. Extensive testing did not identify an etiologic agent for these cases. OMAFA was approached in early September of 2024 to request funding for additional testing. At that time there were 9 cases (July 30- August 15, 2024) and one new case (September 6,2024) of weak and neuro issues in turkey hens (morbidity between 10-80%, 2-3 weeks of duration) having a wide geographic location distribution. A meeting with AHL and practice veterinarians held on September 5^th did not reveal a definitive diagnosis. Several tests and histology had been performed on each affected flock with a wide variety of lesions identified with no specific pattern between cases.

Lesions detected: Encephalitis (mild), focal cerebral cortical necrosis, peripheral neuritis (mild); myodegeneration (mild), necrotizing myositis, lymphoplasmacytic tenosynovitis (very mild) and epicarditis; conjunctivitis (heterophilic), stomatitis (heterophilic); sinusitis, lung mineralization; thymic and bursal lymphoid depletion (mild to marked), parathyroid hyperplasia (mild); necrotizing enteritis, ventriculitis, proventricular mineralization; septicemia, bronchitis (mild to moderate), hepatic necrosis, coccidiosis.

The additional funding request to OMAFA was an attempt to expand the list of differential diagnosis by including testing on: Avian metapneumovirus, Avian encephalomyelitis and Avian paramyxovirus subtype 3 to rule out the immediately notifiable diseases. At the time of application, 2 new suspicious cases were submitted allowing a wider variety of tests to be pursued. Unfortunately, all additional tests including those listed above were negative and a definitive diagnosis was not reached.

At the beginning of 2025 there were 2 turkey barns that presented with either high mortality (Avian Influenza negative) or clinical signs similar to the 2024 weak leg cases described above. Both flocks tested positive on PCR for C. botulinum toxin type C. Considering turkeys are extremely sensitive to botulism toxin, the AHL requested funding from OAHN to forward samples from select weak turkey cases to NVSL in the USA for mouse inoculation testing (MIT)/mouse bioassay (MBA) to determine if the samples test positive with this gold standard test.  In addition, samples from the recently affected farm (3 samples from each of 3 barns – feed, water, feces and a manure pile sample) were collected and tested using the C. botulinum PCR at AHL in an attempt to identify the source of botulism. The feed samples from the affected barns were also forwarded to NVSL for the mouse bioassay testing. Table 1 shows a comparison of the AHL botulism PCR test and the NVSL bioassay. It should be noted that NVSL did have issues with their mouse bioassay being unable to type the toxin. The initial injection provided a presumptive positive but during the addition injection for toxin typing, all mice died.

Table 1. Comparison of test results for Botulism PCR and Mouse Bioassay (MBA) – Meat Turkeys

* Insufficent sample for further toxin typing.

# Direct screening showed clinical signs consistent with positive botulinum intoxication. Toxin typing against types A and C were inconclusive.

Overall, it is still unclear if the weak turkey cases from 2024 have a primary etiology of botulism. Also, when the AHL botulism PCR is positive, the NVSL MBA is also positive, increasing that confidence in a positive AHL botulism PCR.