Let’s finish the series on birds this week with one of the most ubiquitous diseases that affect our distinguished guests on Thanksgiving: fowl cholera. First, we will look at what cholera is including a general overview of its structure and transmission. We will then explore the clinical symptoms and if there are any treatments to protect birds. We will then conclude with a farewell to our series on turkeys and introduce our next topic: plant diseases.
Pasteurella multocia was first characterized in the 1880’s by Louis Pasture as the causative agent of fowl cholera. It was soon recognized that P. multocia had three distinct subspecies multocida, spetica, and gallicida with gallicida being the most common. All birds are susceptible to cholera to varying degrees with waterfowl and turkeys being more susceptible than chickens or other land birds. P. multocia is a gram negative coccobacillus that stains with Wright stain on its variable carbohydrate surface. It resists phagocytosis by macrophages and neutrophils with a lipopolysaccraccharide capsule covering a highly hydrated polysaccharides cell wall (Chung et al. 2001). No single virulence toxin has been shown to cause virulence, however several proteins are suspected: capsule endotoxin, outer membrane proteins, iron binding systems, heat shock proteins, neuraminidase, antibody cleaving enzymes, and P. multocida exotoxin (Chung et al. 2001). The bacterium is highly motile in water and can transfer hosts without direct contact when in close proximity.
The disease is spread primarily by feces or nasal fluids, however it can also be spread by contaminated water, food, bedding, humans (shoes and clothes), and other animals, primarily pigs. P. multocia causes explosive greenish diarrhea and nasal and oral discharges that can directly infect new hosts (Overview, 2014). Infected birds can also pass the bacterium by touching feed with open lesions, distended wattles and combs, and contaminated feathers. Introducing new or wild birds that have not been properly quarantined can introduce the infection to otherwise healthy flocks. Reservoirs such as pigs and dogs are known to harbor the pathogen as asymptomatic carriers and can spread it to flocks if allowed to mingle with the birds. Transmission is also a problem with humans when moving between flocks because contaminated feces can stick to boots or other clothing and then be picked up by birds through open cuts or mucus membranes. Finally, transmission is very common with asymptomatic carriers in large flocks such as factory farms and is less of a problem in free range birds because the bacterium is susceptible to heat and drying out (PM-Onveax,).
Cholera is known for its high morbidity and sudden mortality in large numbers of birds. Symptoms of infection anorexia, ruffled feathers, oral and nasal discharge, and depression, so careful observation of animals should be carried out routinely. Other signs might include fibrous contents in distended waddles and excessive red blood cells in livers in post mortem autopsies. Treatments with penicillin and proactive bacteria can be effective against P. multocia, however caution should be used because antibiotic resistance has been shown to occur rapidly (Fowl cholera, 2014). A new cholera vaccine is being developed using a highly pathogenic attenuated isolate while an established vaccine uses a mild variant administered under the wing (Hertman et al. 1979).
In conclusion, turkeys are susceptible to bacterial infections primarily by fecal-oral transfer and open lesions. The most common treatment is oral penicillin or live attenuated vaccination injected under the wing. With Thanksgiving tomorrow, remember to take extra care of our feathered friends—they can get sick just like us, but with the proper treatment we can take care of them.
This concludes our session on diseases that affect birds; birds are all around us and their diseases deserve to be studied more in-depth because they can teach us a lot about diseases that affect mammals.
Our next series will cover fungal plant diseases in preparation for the winter festivities.
Image Credit: Plainville Farms
Chung, J. (2001, January 1). Role of Capsule in the Pathogenesis of Fowl Cholera Caused by Pasteurella multocida Serogroup A. Retrieved November 22, 2014.
FOWL CHOLERA – Diseases of Poultry. (n.d.). Retrieved November 22, 2014, from http://www.thepoultrysite.com/publications/6/diseases-of-poultry/181/fowl-cholera
Hertman, I., Markenson, J., Michael, A., & Geier, E. (1979). Attenuated Live Fowl Cholera Vaccine I. Development of Vaccine Strain M3G of Pasteurella multocida. Avian Diseases, 24(4), 863-863. Retrieved November 22, 2014.
PM-ONEVAX-C®. (n.d.). Retrieved November 22, 2014, from http://www.merck-animal-health-usa.com/products/130_163369/productdetails_130_163757.aspx
Overview of Fowl Cholera. (n.d.). Retrieved November 22, 2014, from http://www.merckmanuals.com/vet/poultry/fowl_cholera/overview_of_fowl_cholera.html