Avian cholera, also known as Avian Pasteurellosis and Avian Hemorrhagic Septicemia, is caused by the gram-negative aerobe bacterium, Pasteurella multocida. This bacterium has multiple serotypes or strains that vary considerably in their ability to cause disease. At least 16 serotypes of Pasteurella are identified and differentiated by DNA fragmentation. There is evidence that some serotypes may differ from free ranging birds along the eastern United States vs the rest of the nation.

Infections with P. multocida are considered a contagious disease and death can be acute occurring within 6-12 hours post exposure. Most commonly death may occur 24-48 hours post exposure. The acute nature of this disease may be affected by the sex, age, genetic variation, previous exposure, concurrent infection, immune status, nutritional status, strain virulence and route of exposure of the affected bird.

Spread of disease

Waterfowl and several other types of water birds are most often involved with disease outbreak. Environmental contamination from these birds is a primary source of infection. High concentrations of P. multocida will be found in the waters for several weeks following disease outbreak.  This can lead to aerosol transmission. As birds’ bath, take flight or land in contaminated bodies of water, they aerosolize this bacterium and enhance the ability of disease to spread. Avian and mammalian scavengers feeding on contaminated carcasses can also spread the disease.  Direct contact from bird to bird is also a means of spreading infection.

There are four major focal points for Avian Cholera in waterfowl:

1. California Central Valley
2. Tule Lake and Klamath Basins of northern California and southern Oregon
3. Texas Panhandle
4. Nebraska’s Rain Water Basin

The bacterium may spread any time of year, however in poultry the disease is most prevalent in the late summer, fall and winter. In California, this disease seems to follow seasonal waterfowl migration from late fall to early spring.

Carriers of P. multocida

Carrier states do exist resulting in the bird being chronically infected. This can be seen in poultry and documented in snow geese breeding colonies.  This bacterium is most likely harbored in the mouth and transmitted from contaminating the environment and bird-to-bird contact. There is no evidence that this bacterium is passed through the egg.

Signs of disease

Signs vary with the stage of infection.  The bird may show weakness, weight loss, discharge from the mouth, eyes or nostrils with or without infraorbital swelling. Difficulty in producing sounds and neurologic signs leading to seizures can be present. Acute death or chronically infected birds can die of septicemia resulting in serositis, micro-abscess throughout the body (especially the liver) and hydropericardium (fluid within the pericardium). Septicemia often leads to Disseminated Intravascular Coagulation (DIC) a rapidly terminal event.

In some raptors infected with pasteurella, small white plaques may be seen in the oral cavity. Mortality in poultry flocks can reach 50%. Peak mortality in wild waterfowl has exceeded greater than 1000 birds/day.

How do raptors become infected?

Birds of prey can become infected with P. multocida by eating infected prey (waterfowl and rodents).  Most mammals, with the exception of the cat and raccoon, do not transmit P. multocidato the raptor.  Bites from the cat or raccoon can cause a fatal septicemia in the raptor. It is not uncommon that a cat bite or scratch can result in septicemia and death within three days.

It has been documented that mice when eating infected waterfowl can then become a source of infection to Short Eared Owls and Northern Harriers as they eat the infected mice.

Diagnosis of disease

Diagnosis of the disease can be made through cultures, serologic testing and molecular diagnostics. Cultures of the heart blood, liver and bone marrow (pasteurella can persists for several weeks to months in the bone marrow) can led to a positive diagnosis. Certainly gross necropsy and histopathology of infected birds can be diagnostic.

Treatment

For all birds infected with this bacteria and clinically ill,  supportive care will include fluid therapy, nutritional support and antibiotics. Several antibiotics (penicillins, doxycycline, enrofloxacin, chloroamphenicol, trimethoprim sulfadiazine, cefotaxime, pipercillin/tazobactam) or combination antibiotic therapy may be use to combat clinical disease. Therapy must be aggressive to prevent the possibility of septicemia.

 

Suggested Reading

Field Manual of Wildlife Diseases: Birds  (chapter 7)

Pasteurella multocida in raptors: prevalence and characterization

Teresa Morshita, Linda Lowenstine, Dwight Hirsh

Lesions associated with pasteurella multocida infection in raptors

 Teresa Morshita, Linda Lowenstine, Dwight Hirsh