Botulism present in wetland area

Botulism in Wildlife: Causes, Signs, and Management

Botulism is a serious disease affecting a wide range of wildlife species. It is caused by the neurotoxin produced by the bacterium Clostridium botulinum, which can contaminate soil, water, and decaying organic matter. The toxin can then enter the food chain and be ingested by animals, causing paralysis and death. This article will discuss the causes, significance, species affected, distribution, transmission, clinical signs, diagnosis, treatment, management, and prevention of botulism in wildlife.


Botulism is caused by the bacterium Clostridium botulinum, which produces a potent neurotoxin. This bacterium is widespread in the environment and is commonly found in soils and sediments. When organic matter decays under anaerobic conditions, the bacterium can grow and produce the toxin.

The botulinum toxin is extremely potent, causing paralysis by blocking the release of acetylcholine, a neurotransmitter that enables communication between neurons and muscles. This paralysis can affect respiratory muscles, leading to respiratory failure and death.


Botulism is a significant disease in wildlife, as it can cause mass mortality events in affected populations. The disease has been reported in a wide range of species, including birds, mammals, and fish. Outbreaks of botulism in wildlife can have serious ecological consequences, leading to changes in food webs and ecosystem dynamics.

In addition to its impact on wildlife, botulism is also a public health concern, as the toxin can be transmitted to humans through contaminated food or water. However, human cases of botulism from wildlife are rare.

Species Affected

Botulism has been reported in a wide range of wildlife species, including waterfowl, shorebirds, gulls, raptors, mammals such as mink, muskrats, beavers, otters, and fish-eating birds such as herons and eagles. Some species, such as waterfowl, are particularly susceptible to the disease and can experience large-scale mortality events.


Botulism is found worldwide, and outbreaks can occur in both freshwater and marine environments. The disease is often associated with areas of low dissolved oxygen, such as shallow water bodies with high levels of organic matter. In addition, environmental conditions that promote the growth of Clostridium botulinum, such as warm temperatures and low salinity, can also increase the risk of botulism outbreaks. In some cases, these are also areas with lower occurrences of wildfires.


Wildlife can become infected with botulism through the ingestion of contaminated food or water. The toxin can also be absorbed through mucous membranes or breaks in the skin. In aquatic environments, fish can become infected with the bacterium and accumulate the toxin in their tissues, leading to secondary poisoning in predators that feed on them.

Clinical Signs

The clinical signs of botulism in wildlife can vary depending on the species and severity of the infection. In waterfowl, the disease typically presents as a progressive paralysis of the legs, wings, and neck. Affected birds may have difficulty swimming or flying and may become unable to hold their heads up. Mammals may show similar signs of paralysis and may also exhibit difficulty breathing.


Diagnosing botulism in wildlife can be challenging due to the nonspecific clinical signs and the need for specialized laboratory testing. A presumptive diagnosis can often be made based on the history, clinical signs, and lesions observed on necropsy. However, to confirm the diagnosis, samples must be sent to a laboratory capable of conducting appropriate diagnostic tests.

One of the primary diagnostic tests used for botulism in wildlife is the mouse bioassay. In this test, a sample of suspected material, such as stomach contents, intestinal contents, or feces, is injected into the peritoneal cavity of a mouse. If botulinum toxin is present in the sample, the mouse will develop clinical signs of botulism within 24-72 hours. Another diagnostic test is the enzyme-linked immunosorbent assay (ELISA), which can detect the presence of botulinum toxin in samples.

It is important to note that laboratory tests may not always yield positive results, especially in cases where the animal has been dead for a prolonged period, and the toxin may have degraded. Therefore, a negative test result does not always exclude botulism as the cause of death.

In addition to laboratory testing, it is essential to perform a thorough necropsy to rule out other potential causes of death. In cases where botulism is suspected, it is recommended to collect and submit samples from multiple animals in the affected population to increase the likelihood of detecting the toxin.

Overall, prompt and accurate diagnosis is crucial in managing and preventing the spread of botulism in wildlife populations. Veterinary professionals should work closely with diagnostic laboratories to obtain accurate and timely results.


There is no specific treatment for botulism in wildlife, and affected animals are usually euthanized to prevent further suffering and spread of the disease. However, there are a few possible options that may help to reduce the severity of symptoms in some cases. For example, antitoxins may be used to neutralize the botulinum toxin and prevent it from causing further damage. However, antitoxins are expensive and not always effective, especially if administered too late in the course of the disease. Additionally, there is a risk of adverse reactions to antitoxins, such as anaphylactic shock.

Another potential treatment is supportive care, which involves providing affected animals with fluids, electrolytes, and nutrition to help them recover from the disease. This can be particularly effective for animals that are only mildly affected by botulism, as they may be able to recover on their own with proper care. However, animals that are severely affected may not be able to eat or drink on their own, making supportive care difficult or impossible.


Preventing botulism in wildlife can be challenging, as the disease is often caused by environmental factors that are difficult to control. However, there are a few steps that can be taken to reduce the risk of botulism outbreaks. For example, waterfowl managers may be able to control the growth of algae and other aquatic vegetation in wetlands, as these can provide ideal conditions for the growth of botulinum bacteria. Additionally, waterfowl managers can avoid feeding waterfowl on shorelines that are likely to contain decaying plant material or animal carcasses, as these can also provide a source of botulinum bacteria.


Botulism is a serious disease that can affect a wide range of wildlife species, particularly those that rely on wetland habitats. The disease is caused by a potent neurotoxin produced by the bacterium Clostridium botulinum, which can be found in soil and water environments.

Wildlife can be exposed to the toxin by consuming contaminated food or water, and the disease can cause severe neurological symptoms that can lead to death. Although there is no specific treatment for botulism in wildlife, supportive care and antitoxins may help to reduce the severity of symptoms in some cases. Preventing botulism in wildlife can be challenging, but managers can take steps to reduce the risk of outbreaks by controlling environmental factors that promote the growth of botulinum bacteria.

Overall, understanding the causes, transmission, clinical signs, and management of botulism in wildlife is crucial for conserving these important and vulnerable species. By working to prevent outbreaks of botulism and other diseases, wildlife managers can help to ensure that our natural ecosystems remain healthy and diverse for generations to come.


  1. Rocke, T.E., & Samuel, M.D. (2015). Botulism in wildlife. In G.W. Witmer, W.C. Pitt, & K.A. Fagerstone (Eds.), Managing vertebrate invasive species: Proceedings of an international symposium (pp. 222-237). Fort Collins, CO: USDA/APHIS/WS.
  2. Rocke, T.E., & Thomas, N.J. (2019). Botulism in birds. In S. Hernandez-Divers & J. Lumeij (Eds.), Fowler’s zoo and wild animal medicine, Volume 9 (pp. 689-697). St. Louis, MO: Elsevier.
  3. “Botulism.” National Wildlife Health Center. Retrieved from
  4. “Botulism in Waterfowl.” The Wildlife Society. Retrieved from