Swine Influenza is an acute, febrile respiratory disease of swine with high morbidity and low mortality. It is commonly known in the industry as Swine Flu, Hog Flu, and Pig Flu. The etiology of Hog Flu is a Type A Influenza virus which belongs to the Orthomyxoviridae family. It is an enveloped, RNA virus with a lipid envelope and a helical nucleocapsid.There are two structural proteins present on the virus. A Hemagglutinin and Neuraminidase protein. There are 13 different types of Hemagglutinin proteins. This hemagglutin protein is responsible for the attachment of the virus to the host-cell and for fusion of the viral envelope to the host-cell membrane. This results in agglutination of red blood cells. There are 9 different types of the neuraminidase protein. It is responsible for elution of virus from erythrocytes. It may play a role in the release of virus from infected cells.
These proteins play important roles in antibody formation and function. Antibodies to the hemagglutinin are responsible for preventing infection with an influenza virus containing the same hemagglutinin protein. Where as antibodies against the neuraminidase restrict the spread of virus from infected cells.
The antigenic characteristics of the 2 surface glycoproteins are the bases for dividing the virus into subtypes. The four main subtypes which have been isolated in swine are H1N1, H1N2, H3N2, and H1N7. Studies have shown that 30% of the entire swine population in the U.S. have been exposed to H1N1. More specifically, 51% of swine in the north central U.S. have been exposed.
Transmission
Influenza is transmitted primarily pig-to-pig by the nasopharyngeal route. Nasal secretions are laden with virus during the acute febrile stage. The virus is easily carried and spread by avian species, particularly waterfowl, and humans. Care should be taken to prevent spread from and between birds and humans to swine. The virus can be shed for 30 days post-inoculation and has been recovered from clinically normal animals.
Influenza is transmitted primarily pig-to-pig by the nasopharyngeal route. Nasal secretions are laden with virus during the acute febrile stage. The virus is easily carried and spread by avian species, particularly waterfowl, and humans. Care should be taken to prevent spread from and between birds and humans to swine. The virus can be shed for 30 days post-inoculation and has been recovered from clinically normal animals.
Clinical Signs
The clinical signs of Swine Influenza are typical flu-like symptoms. The pigs will develop a fever, (40.5oC - 41.7oC), nasal and ocular discharge, and severe spasms of coughing. They will appear lethargic and become anorectic. These signs will appear very suddenly, spread rapidly throughout the entire barn, and persist for about 7 days. Then the pigs will almost recover about as quickly as they develop clinical signs. These outbreaks typically occur in the fall and early winter, and are more frequently seen in nursery through finishing age pigs.
The clinical signs of Swine Influenza are typical flu-like symptoms. The pigs will develop a fever, (40.5oC - 41.7oC), nasal and ocular discharge, and severe spasms of coughing. They will appear lethargic and become anorectic. These signs will appear very suddenly, spread rapidly throughout the entire barn, and persist for about 7 days. Then the pigs will almost recover about as quickly as they develop clinical signs. These outbreaks typically occur in the fall and early winter, and are more frequently seen in nursery through finishing age pigs.
Pathogenesis and Pathology
It is speculated that pigs maintain the virus by passing the virus to young susceptible animals. The virus is probably in constant circulation but there is not any evidence to confirm the existence of a long term true carrier state. The incubation period for swine influenza virus ranges from 1 to 3 days. The virus is inhaled and deposited on the surface of the lower respiratory tract. Research has shown that a widespread interstitial pneumonia will exist up to 21 days after infection and hemorrhagic lymph nodes will be seen. A major concern with Swine Influenza is the economic loss seen with uneven growth and prolonged finishing time. It has been documented that these pigs will lose from 5 to 12 pounds of body weight over a 3 to 4 week period.
It is speculated that pigs maintain the virus by passing the virus to young susceptible animals. The virus is probably in constant circulation but there is not any evidence to confirm the existence of a long term true carrier state. The incubation period for swine influenza virus ranges from 1 to 3 days. The virus is inhaled and deposited on the surface of the lower respiratory tract. Research has shown that a widespread interstitial pneumonia will exist up to 21 days after infection and hemorrhagic lymph nodes will be seen. A major concern with Swine Influenza is the economic loss seen with uneven growth and prolonged finishing time. It has been documented that these pigs will lose from 5 to 12 pounds of body weight over a 3 to 4 week period.
Typically, uncomplicated infections have changes seen in the cranial ventral lung lobes. There is generally a sharp line of demarcation between normal and affected lung tissue. The involved areas are often purple and firm. Some interlobular edema may also be evident. The airways are likely to be filled with blood-tinged fibrinous exudate. Often the bronchial and mediastinal lymph nodes are enlarged. Severe cases may result in a fibrinous pleuritis. Microscopic lesions usually consist of airways filled with exudate, widespread alveolar atelectasis, interstitial pneumonia and emphysema. Peribronchial and perivascular cellular infiltration is also seen.
Diagnosis
Diagnosis of Swine Influenza can be based on clinical signs, virus isolation, histopathological confirmation of lesions, paired serology, and antigen detection.
Diagnosis of Swine Influenza can be based on clinical signs, virus isolation, histopathological confirmation of lesions, paired serology, and antigen detection.
Treatment
The treatment for Swine Influenza is pretty basic. The primary treatment is supportive therapy. These infected pigs require a dry, clean, dust free environment. We need to decrease any drafts which may be in the barns so that the pigs will be as comfortable as possible. Be sure to avoid any stress to the animals. Do not move any animals or mix animals from different pens. Antibiotics are also essential to treat and control any secondary bacterial infections that usually develop. Water medication does not seem to work as efficiently as parenteral injections to clinically infected animals. Expectorants are commonly used as a herd treatment and are administered in the drinking water.
The treatment for Swine Influenza is pretty basic. The primary treatment is supportive therapy. These infected pigs require a dry, clean, dust free environment. We need to decrease any drafts which may be in the barns so that the pigs will be as comfortable as possible. Be sure to avoid any stress to the animals. Do not move any animals or mix animals from different pens. Antibiotics are also essential to treat and control any secondary bacterial infections that usually develop. Water medication does not seem to work as efficiently as parenteral injections to clinically infected animals. Expectorants are commonly used as a herd treatment and are administered in the drinking water.
Prevention and Control
The best way to deal with Swine Influenza is to prevent the occurrence and spread of the disease. There are certain parameters that one can follow that will prevent and control the disease in a herd.
The best way to deal with Swine Influenza is to prevent the occurrence and spread of the disease. There are certain parameters that one can follow that will prevent and control the disease in a herd.
Limited movement ia a herd is essential. Try to avoid purchasing new stock and avoid taking animals to exhibits where they will be in contact with other animals. One should also avoid moving any animals within the barn itself to eliminate any excess stress. If any new herd additions are to be entered into a herd, be sure to isolate these animals, preferably in a separate building. Screen these animals by serology to determine if these animals have been exposed to Swine Influenza, and if so virus isolation should be considered.
Standard sanitary measures can also help prevent and control the spread of virus. Influenza A viruses are inactivated by soap, heat, and formalin. Be sure to clean and disinfect trucks, trailers, and any equipment which may be contaminated. If a group of finishing pigs had Swine Influenza, be sure to clean and disinfect the house completely before the next group enters.
Vaccination is another means of controlling Swine Influenza. There have been commercial vaccines available in Europe for a while which have had considerable variation in antibody response and protection from infection following vaccination. Only within the last year has there been a vaccine licensed for use in swine in the U.S. It was developed by Syntro Vet Incorporated and is an oil-in-water vaccine containing Influenza A, H1N1 subtype. Results from various studies show that vaccinated animal exposed to Swine Influenza Virus have markedly reduced nasal shedding, virus infection in lung tissue, and lung pathology than nonvaccinated animals.
Studies have also shown than maternally derived antibody in vaccinated sows protected 5 week old pigs from clinical disease, virus infection in the lung, and lung pathology. Maternal antibody did not prevent nasal viral shedding. There is more research underway to determine when pigs from vaccinated sows can be actively immunized and to determine the duration of immunity.
2009 H1N1 flu outbreak
Main article: 2009 H1N1 flu outbreak
In March and April 2009, more than 1,000 cases of swine flu in humans were detected in Mexico, the southwestern United States, New York City metropolitan area, and two in Kansas, causing more than 80 deaths in Mexico. Following a series of reports of isolated cases of swine flu, the first announcement of the outbreak in Mexico was documented on April 23. Some of the cases have been confirmed by the World Health Organization to be due to a new genetic strain of H1N1. The new strain has been confirmed in 16 of the deaths and 44 others are being tested as of 24 April 2009. The Mexican fatalities are mainly young adults, a hallmark of pandemic flu.
In March and April 2009, more than 1,000 cases of swine flu in humans were detected in Mexico, the southwestern United States, New York City metropolitan area, and two in Kansas, causing more than 80 deaths in Mexico. Following a series of reports of isolated cases of swine flu, the first announcement of the outbreak in Mexico was documented on April 23. Some of the cases have been confirmed by the World Health Organization to be due to a new genetic strain of H1N1. The new strain has been confirmed in 16 of the deaths and 44 others are being tested as of 24 April 2009. The Mexican fatalities are mainly young adults, a hallmark of pandemic flu.
The current vaccine against the seasonal influenza strain H1N1 is thought unlikely to provide protection. Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, said that the United States cases were found to be made up of genetic elements from four different flu viruses—North American swine influenza, North American avian influenza, human influenza A virus subtype H1N1, and swine influenza virus typically found in Asia and Europe. For two cases a complete genome sequence had been obtained. She said that the virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).
The new strain appears to be a recombinant between two older strains. Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S
Hiram Diaz, 8, left, gives his 6-year-old sister Adely Diaz a ride on the pegs of his bicycle while wearing protective masks near the market where their parents own a store in Mexico City, Saturday, April 25, 2009. Mexico is struggling with a new strain of swine flu that has killed 68 and sickened more than 1,000. The World Health Organization declared the outbreak a 'public health emergency of international concern.' (AP Photo/Houston Chronicle, Julio Cortez)
A quarantine official checks the temperatures of arriving passengers on a thermographic imaging device placed in front of the quarantine station of Narita international airport, east of Tokyo April 25, 2009. The device has already been place at the airport, but an airport quarantine official said that they have strengthened its monitoring activities in the wake of a swine flu outbreak in Mexico.REUTERS/Yuriko Nakao (JAPAN HEALTH IMAGES OF THE DAY)
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