Science

Disease Monitoring on the SBSSNWR  512

Wildlife disease is nothing new for the Salton Sea. The first recorded disease die-off occurred in 1917, a decade after the filling of the Sea.  Disease outbreaks have occurred on and off at the Sea up until the current day, and will probably continue in the future. Fortunately, the occurrence of disease and numbers of sick and dead birds has been declining over the past few years.


 

Wildlife Disease


 Why does the Salton Sea have a disease problem?     

There is no clear-cut answer to this question. Rather, it contains a series of possible answers. The Salton Sea is a unique and complex ecosystem. It is nutrient-rich with millions of birds that visit every year, with extreme temperature changes ranging from 120° in the summer to 50° in the winter. It has many different habitats, including salt water, freshwater, brackish water, marsh areas, and upland areas. All of these characteristics contribute to the potential of disease occurring at the Salton Sea.  

Wildlife Disease: Avian Botulism    

The main culprit in the Salton Sea’s bird die offs is avian botulism. The bacteria Clostridium botulinum, responsible for botulism outbreaks, is a common bacteria in wetland ecosystems. Once birds are infected, a maggot cycle can begin and spread the bacteria to large numbers and species of birds. 

There are two types of botulism that have been found at the Salton Sea. Type C botulism is typical for waterfowl, is the most common botulism strain found in wildlife and poses virtually no human health risks. The second type of botulism is Type E, which has been found largely in fish eating birds. It is much rarer than Type C, but poses greater risks to humans.  

Mode of transmission    

Toxin production takes place in decaying animal carcasses. Flies deposit eggs on carcasses, which are fed upon by resulting maggots. These maggots then concentrate the toxin, and the toxic maggots are ingested by birds. These birds then die, leading to the proliferation of more maggots. As the cycle accelerates, major die-offs occur. These dying fish become easy prey for the birds that then ingest fatal doses of the toxin. Due to the rapid spread of botulism through the maggot cycle, carcass removal (as seen above) is critical to prevent and minimize the spread of the disease. 

Symptoms    

Birds initially lose ability to control muscles and appear weak and limp. They have an inability to fly, followed by the inability to walk. Eventually, control of neck muscles is lost and the bird can no longer hold up its head, resulting in drowning.  

 

For more information, please call 760-348-5278.