Swine influenza

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

  • Young pigs

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
Last modified: Monday, 19 March 2012, 5:22 AM