**2. Epidemiology**

*Pests, Weeds and Diseases in Agricultural Crop and Animal Husbandry Production*

capsular type B and E isolates [6].

pleurisy. Affected pigs may have fever of up to 1060

organism is also a primary or secondary pathogen and responsible for a wide range of economically important diseases in domesticated animals throughout the world. Pasteurellosis is an infection of cattle, buffalo, swine and other species of animals caused by Gram-negative coccobacillary bipolar organism, *Pasteurella multocida*. It is OIE list B disease of ruminants in the tropical countries. *Pasteurella multocida* strains express a polysaccharide capsule on their cell surfaces and the antigenic specificity of the capsule determines the serogroups: A, B, D, E or F [4]. It has long been recognized that there is relationship exist between the capsular type and disease predilection [5], which suggests that the capsular polysaccharide type plays a role in host and disease specificity. For example, the majority of cases of fowl cholera are caused by capsular type A strains. Progressive atrophic rhinitis (PAR) of pigs is associated predominantly with capsular type D isolates, bovine and porcine pneumonia are associated mainly with capsular type A strains and haemorrhagic septicaemia of cattle and water buffaloes is caused exclusively by

Capsular types A and D cause economic losses in swine because of their association with progressive atrophic rhinitis and enzootic pneumonia [7]. Its association with acute septicemic pasteurellosis in pigs has been recognized. *Pasteurella multocida,* a part of the commensal flora in the upper respiratory tract of pigs is shown to appear intermittently in the nasopharynx and subsequently shed in nasal secretions [8]. During this period, the carrier animal act to become a source of infection for in-contact susceptible animals. The role of pig as a reservoir of *Pasteurella multocida* for the transmission of the disease between pigs and cattle has been suggested. *Pasteurella multocida* is an important pathogen of pigs. It causes pneumonic pasteurellosis and is characterized by pneumonia, purulent bronchopneumonia and

to move. They show significant respiratory distress, often breathing through the mouth. Death is common after a clinical course of 4–7 days. There is a marked tendency of the disease to become chronic, resulting in reduced weight gains and frequent relapses. On post mortem examination there is a chronic bronchopneumonia with abscessation. Pleuritis is common and there may also be pericarditis. Peracute cases show an acute necrotizing fibrinous bronchopneumonia. Septicaemic disease with death asymptomatic acute deaths may occur within 12 hours in piglets. In India, it is associated with infection by capsular serotype B. The disease occurs in all ages of pigs including adults and is manifested by fever, dyspnoea and congestion

Yet, Pasteurellae have been shown to be a common microflora of the upper respiratory tract in normal animals [9]. The organisms more often than not act as secondary invaders in animals with concurrent diseases or suffering from debilitating stressful conditions. HS is a peracute disease and is considered to be one of the most economically important diseases in Asia particularly in South and South East Asia leading to huge economic loss in livestock industry. *Pasteurella multocida* type B:2 assumed to be transmitted between the animals by aerosol infection and ingestion of contaminated river water or material with *P. multocida* especially during the HS outbreak. The clinical indication of this disease is often characterized by rapid course of high fever, respiratory distress, dullness, depression followed by death [10]. Pathogenesis of *P. multocida* is a complex interaction between host specific factors and specific bacterial virulence factors; therefore, understanding the disease pathogenesis is complex and depends on the bacterial strain, the animal model and their interactions. The key virulence factors identified in *Pasteurella multocida* include capsule, lipopolysaccharides, surface adhesions, iron regulated and iron

F, are anorectic and disinclined

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on serosal surfaces.

acquisition proteins [11].

The scope of epidemiology in modern animal husbandry practice is continuously widening. Epidemiological data provide information on various diseases which are pre-requisite for planning, execution and monitoring of disease control programmes. It is an important requirement for assessing economic impact of a disease and also for developing disease forecasting system. The disease is usually associated with wet, humid weather and increased incidence is recorded during wet, humid weather and during wet seasons. In countries where systemic epidemiological studies have been carried out, it has become evident that outbreaks do occur throughout the year but those occurring during wet seasons tend to spread presumably due to the longer survival of the organism under moist conditions [8]. Zhao *et al*. [12] examined one hundred and sixty-four clinical isolates of *Pasteurella multocida* recovered from two swine herds in Minnesota. The isolates were characterized by restriction endonuclease analysis (REA) and rRNA gene restriction fragment length patterns. They concluded that these genomic fingerprinting techniques were highly discriminatory and that capsular serotyping in combination with REA or ribotyping was an appropriate technique for epidemiological studies of *Pasteurella multocida* of swine origin.
