zoonoses and communicable diseases common to ... - PAHO/WHO

204 BACTERIOSESby means of aerosols. Dogs and cats rarely suffer from pasteurellosis (with theexception of wounds infected with pasteurellae in fights) and are healthy carriers.Other mammals acquire the disease from members of their own species eitherthrough the respiratory or digestive tract, or by falling victim to the pasteurellae intheir own respiratory tracts when stress lowers their defenses. There is much evidencethat stress factors play an important enabling role in unleashing the respiratorysyndrome of shipping fever, and that these factors permit multiplication ofserotype 2 of P. haemolytica (Frank and Smith, 1983). Serotypes 6:B and 6:E,which cause hemorrhagic septicemia in cattle and water buffalo, are perpetuated bymeans of carriers and chronically ill animals that serve as a source of infection fortheir kind.Role of Animals in the Epidemiology of the Disease: Pasteurellae survive onlya very short time in the environment. It is certain that animals constitute the mostimportant reservoir of the pasteurellae that are pathogenic for man.Diagnosis: In the case of human infection, diagnosis is made by isolating andidentifying the etiologic agent from wounds or other sites.In hemorrhagic septicemia or fowl cholera, the etiologic agent can be cultivatedfrom the animal’s blood or viscera. In pneumonia of domestic animals, a pure cultureof pasteurellae may indicate their role in the pathology, but does not revealwhether these bacteria are primary or secondary agents of the disease.Control: Measures to reduce the likelihood of bites, such as elimination of straydogs, can prevent some cases of human infection.Control in animals lies mainly in adequate management of herds or poultry farms.Bacterins as well as live attenuated vaccines are in use, or are being tested, againstP. multocida and P. haemolytica. Protection against homologous serotypes is satisfactory,but protection is only partial or irregular against heterologous serotypes. Ingeneral, attenuated live vaccines give better immunity than bacterins. In Asia, extensiveexperimentation proved that a bacterin with an oil adjuvant can offer solidimmunity against hemorrhagic septicemia. A single dose of live vaccine with astreptomycin-dependent mutant strain conferred immunity against hemorrhagic septicemiain 66.6% to 83.3% of calves and in 100% of young buffalo (De Alwis andCarter, 1980).The use of PI3 vaccine has been recommended for the control of shipping fever.It is better to vaccinate against the principal viral agents before weaning or transportinganimals. The bacterins of P. haemolytica and P. multocida have been questioned.Attenuated live vaccines or vaccines from subunits, such as the cytotoxin(leukotoxin) of P. haemolytica (Confer et al., 1988), are more reliable. Attenuatedlive vaccines of P. haemolytica are being tested. A bacterin containing multiple antigensof the prevalent serotypes, incorporated into a polyvalent anticlostridial biologicalwith aluminum hydroxide adjuvant, has been tested against P. haemolyticapneumonia in lambs and has given satisfactory results (Wells et al., 1984). Severallive vaccines are available against avian cholera, some of which can be administeredin the drinking water. Selection of Pasteurella strains within the serotypes that causethe disease is important in immunization.Bovine hemorrhagic septicemia should be considered an exotic disease andappropriate measures should be taken to prevent its spread to disease-free areas.