Swine influenza
DEFINITION
- It is a specific highly contagious disease of pigs characterized clinically by fever and signs of respiratory involvement.
ETIOLOGY
- Type A influenza virus
- The virus acts in combination with a gram negative bacterium Haemophilus influenza suis
- The virus closely related to the virus of human influenza type A
- First appeared in United States immediately following the 1918 pandemic of human influenza
- It was caused by adaptation of human influenza virus to pigs.
- H1 N1 strain of virus can be found in the pig tissues at slaughter
SUSCEPTIBILITY
TRANSMISSION
- The influenza virus may be transmissible between humans and pigs
- Swine lung worms can act as intermediate host Droplet inhalation
- Direct contact
- Infection is provoked by the presence of Haemophilus influenza suis
PATHOGENESIS
- It is primarily a disease of the upper respiratory tract, the trachea and bronchi particularly involved.
- Secondary lesions may develop in the lung due to drainage of copious exudates from the bronchi
- Enzootic pneumonia in pigs
- Secondary pneumonia due to Pasteurella multocida infection
CLINICAL SIGNS
- Incubation period -24-48 hours
- Fever, rhinitis, cough and inappetence
- Above symptoms subside after 3-5 days but in some cases, transitory fever may recur within 3 weeks
- Dyspnoea
- Pneumonia
- Mortality rate is about 1 per cent
- Morbidity rate may approach 100 per cent
GROSS LESIONS
- Mucopurulent exudate lies over the tracheal and bronchial mucosa
- Plugging of these bronchi and bronchioles results in sharply demarcated areas of atelectasis
- Consolidation of the lung parenchyma occurs around the bronchi
MICROSCOPIC LESIONS
- Virus produces necrosis of lining cells of alveoli, bronchi and lower parts of trachea
- The pneumonia is characterized by necrosis of alveolar walls with formation of hyaline membrane lining the alveolar sacs
- Congestion, focal haemorrhages , severe perivascular and intralobular oedema, and infiltration of mononuclear cells
- Peribronchiloar alveoli often consolidated as a result of infiltration of mononuclear cells or the ingrowth of respiratory epithelium
DIAGNOSIS
- Symptoms
- Gross and microscopic lesions
- Definitive diagnosis depends on the demonstration of a significant elevation of virus neutralizing or anti-haemagglutinin antibodies in the sera of pigs
- Isolation and identification of the swine influenza virus type A
- Demonstration of viral antigens with immunological staining techniques
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Last modified: Monday, 19 March 2012, 5:22 AM