Swine flu or Hog Flu:

• It is highly contagious viral disease of pigs characterized by respiratory disease with clinical signs of sneezing, nasal discharge, high temperature, painful cough.
• It is also known as atelectasis of lungs.
• Pigs of all ages are susceptible to infection but young ones are most susceptible.
• Outbreaks mostly occur in cold months of years- late autumn or early winter.

Etiology:

• Type A influenza (H₁N₁, H₁N₂, H₂N₃, H₃N₂)
• Enveloped, negative-stranded RNA virus with a segmented genome and belongs to the Orthomyxoviridae family.
• AV has two main antigenic proteins, named hemagglutinin and neuraminidase. These proteins are responsible for viral attachment to cells, release of virions from infected cells, and determination of the virus subtype.
• Three main subtypes responsible for influenza infections in pigs (H1N1, H1N2, and H3N2). Other subtypes have been reported sporadically.

Epidemiology:

• In North America, outbreaks of IAV in swine occur during all seasons but are most common in fall or winter, often at the onset of particularly cold weather.
• In warmer areas of the world, infection may occur at any time.
• Influenza is endemic and widespread in pigs worldwide, and evidence of IAV infection, antibodies, or circulating virus has been well documented in Europe, North America, South and Central America, and Asia.
• Swine influenza was first proposed to be a disease related to human flu during the 1918 flu pandemic, when pigs became ill at the same time as humans.
• First identification of an influenza virus as a cause of disease in pigs occurred about ten years later, in 1930.
• For the following 60 years, swine influenza strains were almost exclusively H1N1.
• Between 1997 and 2002, new strains of three different subtypes and five different genotypes emerged as causes of influenza among pigs in North America.
• In 1997–1998, H3N2 strains emerged
• Reassortment between H1N1 and H3N2 produced H1N2.
• Swine flu outbreaks were reported in Nepal in the spring of 2015.

Transmission:

• Infection spreads rapidly within herd; mainly by aerosolization
• Direct contact with infected pig
• It can be transmitted from pig to human or vice-versa

Pathogenesis:

1. After entry of virus, it first multiplies in bronchial epithelium
2. Focal necrosis of bronchial epithelium ‘focal atelectasis’ and gross hyperemia of lungs
3. After 24 hrs, bronchial exudate and widespread atelectasis lesion continue to develop within 72 hours.

Clinical Signs:

• Incubation period is of 2-7 days
• Initially high fever around 107°F
• Anorexia and severe prostration
• Animal disincline to move because of stiffness and pain
• Coughing, dyspnea, weakness, sneezing and painful cough
• Congestion of conjunctiva with watery ocular and nasal discharge
• Clonic convulsion in terminal stage of disease

PM Findings:

• Swelling and edema of cervical and mediastinal lymph node
• Congestion of pharynx, trachea and bronchi
• Copious exudate in bronchi
• Dark red-purple in color and leathery consistency of lungs
• Atelectatic areas of lungs is emphysematous and shows petechial lungs.

Diagnosis:

• Based on clinical findings
• Based on PM findings
• Isolation and identification of virus
• RIDTs, Direct immunofluorescence, RT-PCR, Virus culture

Treatment and Control Measures:

• No specific treatment is available. Supportive treatment including antipyretics and antimicrobials to prevent secondary bacterial infection.
• Expectorants also may help relieve signs in severely affected herds.
• Sow vaccination either prefarrowing or the entire herd at once (mass vaccination) are the most common vaccination protocols.
• Good management practices, such as strict all-in/all-out procedures; limiting movement of pigs and sows within farrowing rooms and between pens, rooms and barns; and freedom from stress, particularly due to crowding and dust, help reduce transmission and losses.
• Use of protective clothing such as apron, gloves, mask should be used while handling pigs in herds.