Have you ever seen a duck, goose, coot or any other waterbird laying long out on the ground or surface of the water? Do these birds look tired to you? If so, they might be suffering from botulism.
Avian botulism, also known as Limberneck, is the most significant disease for migratory birds around the globe. Outbreaks of the disease have been reported in wild birds from every continent (except Antarctica). Furthermore, outbreaks are now more frequent in urban areas. This is due to the infection being spread by animals that have succumbed to the disease. Their remains continue to be a host for the pathogen (C. botulinum) and infect those who feed on it. This infection is spread through the food chain and returns to the species that are most susceptible to it.
Botulism infections in urban areas are on the rise [1,2,3] and its peak season, from June to the beginning of September, is right upon us. Our primary way to counter an epidemic is to remove the animals that have died and are now a disease vector for everything nearby. To do this we must locate the diseased remains, which can be difficult depending on how densely populated the area is. In Hawai’i, researchers have attempted to train dogs to detect these remains and found that canine searches improved the detection rate of carcasses [2].
Alternatively, we could find the diseased animals before they die to reduce infections. In this case, they will not become a disease vector for anything else in their vicinity as other animals will not feed on their remains. Furthermore, with our help recovered individuals may actually have a high chance of survival [3]. It is thus important to increase awareness of the signs of botulism in the general public so residents may be more likely to recognize and report cases.
To this end, I would like to go through some signs that could indicate that your local waterfowl (mainly ducks/geese) could be experiencing botulism. If you notice these signs, you should call your local wildlife rehabilitation center to confirm and pick up the sick individual(s).
The characteristic signs of botulism are a progressive flaccid paralysis usually indicated by the inability to hold their head upright (having a weak neck) and having difficulty flying or diving underwater. The bird’s legs will usually be weakened first then the wings will start ‘drooping’ and fall down a bit vertically. All while their neck progressively loses the ability to hold their head up. Usually they will be found sitting and reluctant to move. The progression of the disease differs between infections, but botulism signs will usually develop within 1 to 17 days after infection.
What causes botulism?
Until now I have been saying that those infected by botulism will infect others but where do the original infections come from? Botulism is caused by BoNT’s (Botulism neurotoxins) produced by a heterogeneous group of bacteria known as Clostridium botulinum.
The life cycle of C. botulinum begins in environments that contain C. botulinum spores. These spores can persist in the sediments and algae of the environment and can start to germinate under favorable conditions by growing in the cells of decomposing organic material where it releases BoNT’s. In an urban environment these favorable conditions include large amounts of stagnant water, where C. botulinum spores can hibernate, and a temperature of 25-40 degrees celsius, which will allow the pellets to switch to their active form. Spores or carcasses infected with C. botulinum are then ingested by neurotoxic insensitive invertebrates (e.g. maggots or worms). These small invertebrates become prey to birds, fish and other aquatic vertebrate species. These vertebrate species are sensitive to BoNT’s and can become infected with botulism, resulting in paralysis, decreased fitness or death. These infected dead now become a disease vector, feeding into the botulism cycle.
With this blog I hope to make it more clear for readers how to spot botulism in waterfowl and the importance of reporting these cases to the local authorities, dead or alive! Reporting the living might save them but reporting the deceased could help save other resident birds!
References
[1] Rocke, T. E., & Bollinger, T. K. (2007). Avian botulism. Infectious diseases of wild birds, 377-416.[2] Reynolds, M. H., Johnson, K. N., Schvaneveldt, E. R., Dewey, D. L., Uyehara, K. J., & Hess, S. C. (2021). Efficacy of detection canines for avian botulism surveillance and mitigation. Conservation Science and Practice, 3(6), e397.
[3] Rossetto, O., Pirazzini, M., & Montecucco, C. (2014). Botulinum neurotoxins: genetic, structural and mechanistic insights. Nature Reviews Microbiology, 12(8), 535-549.
[4] Botulism (no date) PoultryDVM. Available at: https://duckdvm.com/condition/botulism.
Further reading about avian botulism: https://www.usgs.gov/diseases-of-terrestrial-wildlife/avian-botulism
Featured photo: © Mike Prince, some rights reserved
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