Swine influenza is a respiratory disease induced by influenza A virus infection. (IAV). It is extremely infectious and primarily affects swine. The disease is characterized by fever, wheezing, sneezing, lethargy, and nasal discharge. Due to the fever brought on by the disease, pregnant sows may also undergo abortions. The diagnosis of swine influenza can be made using PCR or virus isolation. The disease is predominantly controlled by vaccination, but secondary bacterial infections can be treated with antibiotics.
It is essential to note that swine IAV strains do not typically spread readily among humans. As they can replicate influenza viruses of both avian and human origin, pigs can contribute to the emergence of zoonotic strains with pandemic potential. In 2009, a swine-origin H1N1 IAV strain spread worldwide, infecting humans, swine, and other animals. Human seasonal influenza viruses can also become established in swine, contributing to the genetic diversity of IAVs identified in swine. Globally, swine influenza is prevalent in regions that produce pigs.
Swine Influenza Management in Pigs/Swine
Causes of Swine Influenza Disease in Swine
The influenza A virus (IAV), a segmented, negative-stranded RNA virus with a sheath, causes swine influenza. Hemagglutinin and neuraminidase, the two primary antigenic proteins of IAV, define the virus subtype and are in charge of viral attachment to cells and viron release from infected cells.
H1N1, H1N2, and H3N2 are the three major subtypes of the swine IAV virus, and there are various strains of each subtype. Pigs frequently contract other viruses and germs, which puts them at risk of contracting swine influenza. These include Mycoplasma hyopneumoniae, Glaesserella parasuis, Actinobacillus pleuropneumoniae, and pig reproductive and respiratory syndrome virus. Disinfectants make it simple to inactivate the infection.
Disease Cycle of Swine Influenza Disease
Outbreaks of swine influenza occur year-round in warmer regions of the globe. Still, they are most prevalent in autumn and winter in North America. Aerosolization, direct pig-to-pig contact, and fomite transfer accelerate the spread of the disease within a herd. Swine influenza is endemic globally and pervasive in the global swine population.
Before weaning, piglets are a reservoir of influenza infection capable of transmitting the virus to other farms. Often, pigs act as vectors to spread IAV to herds and countries that have never had it before. The spread of new flu infections is helped by the fact that pigs move between crates and enclosures and that there are no all-in/all-out rules. As immunity in antibody-positive livestock declines, recurrent outbreaks may occur.
What are the Symptoms of Swine Influenza Disease?
- Symptoms include wheezing, sneezing, nasal discharge, elevated rectal temperatures, lethargy, difficulty breathing, and decreased appetite. Reproductive disorders such as abortion are rarely associated with these symptoms.
- The initial clinical symptoms include fever, puffy eyes, anorexia resulting in weight loss, depression, prostration, and huddling resulting in weakness.
- The sudden onset of acute respiratory symptoms, including paroxysmal coughing, wheezing, abdominal breathing irregularity, and ocular and nasal discharges, follows.
- Abortions, infertility, the production of small, feeble litters, and an increase in stillbirths may occur in breeding stock.
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Diagnosis of Swine Influenza Disease
Swine influenza can be diagnosed based on clinical symptoms. Still, confirmation necessitates the detection of the influenza virus through RT-PCR, virus isolation, or antibody detection. The virus can be isolated from nasal and oral discharge, infected lung tissue, and udder swabs. In acute and convalescent serum samples, the hemagglutination inhibition test can be used to demonstrate an increase in virus-specific antibody titers.
Before diagnosing uncomplicated influenza infection, it is crucial to rule out other conditions. Using this test, a retrospective diagnosis can also be made. The sequencing and characterization of viral isolates may be required to evaluate virus-specific antibodies or produce customized vaccines.
Treatment and Control of Swine Influenza Disease
There is currently no effective treatment for swine influenza. Still, antipyretics and antimicrobials can be used to treat secondary bacterial infections. Additionally, expectorants can alleviate symptoms in severely afflicted herds. Vaccination, strict import controls, and sound management practices, such as limiting pig movement and reducing stress, can help reduce transmission and losses.
There are available sow vaccination, piglet vaccination, and custom-made vaccines. In 2017, a live-attenuated flu vaccine became commercially available. A seasonal vaccination of personnel interacting with swine is also recommended to prevent the virus’ bidirectional transmission from pigs to humans.
Preventive and Management Measures to Control Swine Influenza Disease
- Preventing and managing Swine Influenza Disease requires good husbandry practices and strict biosecurity measures.
- All-in/All-out procedures, which reduce the number of pig movements, should be followed to limit the spread of the disease. Providing fresh, clean drinking water is also essential.
- Contamination with ducks and turkeys, which can act as reservoirs for the virus, should be avoided. Staff should take precautions to avoid contact with these birds.
- Infected buildings should be thoroughly cleaned and disinfected. Strict disinfection protocols should be implemented to prevent transmission of the virus. Proper waste management and air filtration systems can also help reduce the spread of the disease.
Vaccination Schedule for Swine Influenza Disease in Swine
- Vaccination is important for preventing and controlling Swine Influenza Disease (SIV) in pigs.
- The vaccination schedule for SIV may vary based on the farm’s epidemiological situation, the type of vaccine used, and the level of herd immunity.
- Sow vaccination is the most common method used to control SIV. Vaccination is administered either pre-farrowing or to the entire herd at once.
- Piglet vaccination is also possible, but reduced efficacy due to maternal antibodies is a concern.
- Commercially available killed vaccines that contain both H1N2 and H3N2 subtypes are commonly used, and autogenous vaccines prepared with farm isolates are also available.
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Impact of Swine Influenza Disease
Influenza A virus infection in swine ranges from subclinical to acute. In the acute form, the virus multiplies in the bronchial epithelium, causing necrosis, atelectasis, and hyperemia of the lungs. The virus rarely causes systemic infection, and losses in reproduction associated with outbreaks are secondary to the high fever response.
Conclusion
Swine influenza is an extremely contagious respiratory disease that can result in substantial economic losses. Good husbandry practices, such as all-in/all-out procedures, vaccination, and stringent import controls, can control the disease. For secondary bacterial infections, supportive care and antimicrobials are prescribed. Early detection and swift action can aid in preventing the disease’s spread.
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