13.2.5. Avian Cholera: a Major New Cause of Waterfowl Mortality

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Waterfowl Management Handbook US Fish & Wildlife Service January 1989 13.2.5. Avian Cholera: A Major New Cause of Waterfowl Mortality Milton Friend U.S. Fish and Wildlife Service Follow this and additional works at: https://digitalcommons.unl.edu/icwdmwfm Part of the Environmental Sciences Commons Friend, Milton, "13.2.5. Avian Cholera: A Major New Cause of Waterfowl Mortality" (1989). Waterfowl Management Handbook. 4. https://digitalcommons.unl.edu/icwdmwfm/4 This Article is brought to you for free and open access by the US Fish & Wildlife Service at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Waterfowl Management Handbook by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. WATERFOWL MANAGEMENT HANDBOOK 13.2.5. Avian Cholera: A Major New Cause of Waterfowl Mortality from cattle have not been shown to readily cause Milton Friend clinical disease in birds. U.S. Fish and Wildlife Service Scavenger species such as crows and gulls are National Wildlife Health Research Center commonly diagnosed as having died from this dis- 6006 Schroeder Road ease, but deaths of raptors such as hawks and Madison, WI 53711 eagles from avian cholera are far less frequent (Fig- ure 1). Species losses for most major outbreaks are closely related to species composition and abun- Synonyms dance during the period of the die-off. Fowl cholera, avian pasteurellosis Distribution Cause Avian cholera was unreported in free-living mi- Avian cholera is a highly infectious disease gratory birds in the United States before 1944. caused by the bacterium, Pasteurella multocida. Losses have now been reported coast-to-coast and Acute infections are common and can result in border-to-border. The occurrence of this disease death 6 to 12 hours after exposure. Under these cir- within the United States has increased dramati- cumstances “explosive” die-offs involving more than cally since 1970, and avian cholera now ranks with 1,000 birds per day have occurred in wild water- avian botulism and lead poisoning as major causes fowl. More chronic infections with longer incubation of waterfowl mortality. The frequency and severity times and less dramatic losses also occur. Transmis- of avian cholera outbreaks vary greatly among ar- sion can occur by bird-to-bird contact, ingestion of eas (Figure 2). This disease has also been diagnosed contaminated food or water, and perhaps in aerosol in waterfowl in many countries, including Canada, form. but not Mexico. This is probably due to the lack of surveillance and reporting rather than to absence of this disease in Mexico. Species Affected In the United States there are four major focal points for avian cholera in waterfowl: the Central It is likely that most species of birds and mam- Valley of California; the Tulare Lake and Klamath mals can become infected with P. multocida. Most Basins of northern California and southern Oregon; (if not all) bird species are susceptible to clinical dis- the Texas Panhandle; and Nebraska’s Rainwater ease following exposure to virulent strains of P. Basin. The movement of avian cholera from these multocida commonly found in waterfowl. Specific re- areas follows the well-defined pathways of water- lations between bird and mammal strains of this fowl movement. Spread of this disease along bacterium are not well understood. Strains isolated the Missouri and Mississippi river drainages is also Adapted from: Friend, M., editor. 1987. Field guide to wildlife diseases. U.S. Fish Wildl. Serv., Resour. Publ. 167. 225 pp. Fish and Wildlife Leaflet 13.2.5. • 1989 1 approached quite closely before attempting escape. When captured, these birds often die quickly, sometimes within a few seconds or minutes after being handled. Other birds have convulsions, swim in cir- cles, or throw their heads back between their wings and die. These signs are similar to those seen in duck plague and in some types of pesticide poisoning. Other signs include erratic flight, such as flying upside down before plunging into the water or onto the ground and attempting to land a foot or more above the surface of the water. Always suspect avian cholera when large num- bers of dead waterfowl are found in a short time, few sick birds are seen, and the dead birds appear to be in good flesh. When sick birds are captured and die within a few minutes, avian cholera should also be suspected. None of the signs described above are unique to this disease; their occurrence should be recorded as part of any history being submitted with specimens and must be considered along with lesions seen at necropsy. Gross Lesions Figure 1. Relative occurrence of avian cholera in wild birds. Under most conditions, birds that have died of avian cholera have substantial amounts of subcuta- neous and visceral fat (except for seasonal losses of consistent with waterfowl movement. No consistent fat). The most prominent lesions seen at necropsy patterns of avian cholera outbreaks exist within the involve the heart and liver and sometimes the giz- Atlantic Flyway except for periodic occurrences in zard. Hemorrhages of various sizes are frequently eiders nesting off the coast of Maine (Figure 3). found on the surface of the heart muscle or the coro- nary band. Hemorrhages are also sometimes visible on the surface of the gizzard. Areas of tissue death Seasonality that appear as small white to yellow spots are com- Losses can occur at any time of the year. A ma- monly seen within the liver. Where the area of jor loss of snow geese occurred in spring on tissue death is greater, the spots are larger and in Canadian breeding grounds, in addition to losses of some instances the area of tissue death is quite ex- breeding eiders in Maine and Quebec. Outbreaks in tensive. California normally start during fall and continue The lower portions of the digestive tract (below into spring. Late winter is the peak time for avian the gizzard) commonly contain thickened yellowish cholera in the Texas Panhandle, and spring migra- fluid that is heavily laden with P. multocida. tion has resulted in annual losses from this disease in Nebraska’s Rainwater Basin since 1975 and in western Saskatchewan, Canada, since 1977. Diagnosis As with all diseases, isolation of the causative Field Signs agent is required for a definitive diagnosis. Submit- ting a whole carcass provides the diagnostician with Few sick birds are seen during avian cholera the opportunity to evaluate gross lesions seen at ne- outbreaks because of the acute nature of this dis- cropsy and also provides all appropriate tissues for ease. However, the number of sick birds increases isolation of P. multocida. when a die-off is prolonged over several weeks. Sick When it is not possible to send whole carcasses, birds often appear lethargic or drowsy and can be tissues should be sent that can be collected in as 2 Fish and Wildlife Leaflet 13.2.5. • 198 9 Figure 2. Reported distribution of avian cholera in wild birds. Figure 3. The occurrence of avian cholera in waterfowl seems to be closely related to bird movements west of the Mississippi River. There is no apparent pattern for outbreaks along the Atlantic seaboard. Fish and Wildlife Leaflet 13.2.5. • 1989 3 sterile a manner as possible in the field. The most attract (decoy) other birds, thereby increasing the suitable tissues for culturing are heart blood, liver, probability for infection. Scavenging of carcasses and bone marrow. Remove the entire heart and also results in disease transmission through the di- place in a Whirl-Pak bag for shipment as identified rect consumption of diseased tissue (oral exposure). in the “Field Guide to Wildlife Diseases”; do not at- Care must be exercised during carcass collec- tempt to remove the blood from the heart. The liver tion to minimize the amount of fluid discharged into should also be removed and placed in a separate the environment from the mouths of birds. Pick bag; if it cannot be removed intact, submit a major birds up head first, preferably by the bill, and imme- portion of this organ (at least half). Refrigerate diately place in plastic bags. Double-bagging is these samples as soon as possible after collection recommended to prevent fluids leaking from punc- and insure that they are kept cool during shipment. tures that may occur in the inner bag. Bags of When shipment is to be delayed for more than a day carcasses should always be securely closed before or transit time is expected to exceed 24 hours, being removed from the area. freeze these specimens. Prompt carcass removal also prevents scaveng- Pasteurella multocida persists for several ing by birds that can mechanically transport weeks to several months in bone marrow. The infected material to other sites or by feeding or wings of badly scavenged or decomposed carcasses drinking at other locations following consumption of should be submitted whenever avian cholera is sus- infected tissue. This situation is aggravated by ap- pected as the cause of death and more suitable parent longer disease incubation times in gulls, tissue samples are not available. crows, and some other avian scavengers. Instead of dying within hours or 1 to 2 days after exposure to virulent strains of P. multocida, death more typi- Control cally occurs after several days to 1 to 2 weeks. Death may occur at locations far from the site Spread of avian cholera through waterfowl and where the bird was exposed. When these birds die, other migratory bird populations is enhanced by the they serve as new potential focal points for contami- gregarious nature of most waterfowl species and by nation.

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