Infected piglets birthed from infected but sub clinical sows help to maintain the disease within a population. The incubation period of CSFV ranges from 2 to 14 days but symptoms may not be apparent until after two to four weeks.
Since the virus causes acute secondary respiratory infections, it may spread eventually in a polluted atmosphere. Hence, it is known as ’Swine Flu’. Usually swine flu rarely affects humans. But the current outbreak is apparently not solely due to swine influenza virus. It is due to a new Influenza A virus subtype H1N1, which is a derivative of swine influenza virus. According to the World Health Organisation (WHO) reports, strain has not been isolated form swine. It passes with apparent ease from human to human, an ability to an unidentified mutation.
History of Influenza A virus in the human population:
The various types of influenza virus are clearly illustrated in the above figure. Solid squares show the appearance of a new strain causing recurring influenza pandemics. The dotted line indicates the unidentified strains.
The H1N1 form of swine flu is one of the descendants of the Spanish flu that caused a devastating pandemic in humans during 1918 -1919. It would have been persisting in pigs and was then circulated into humans during the 20th century, contributing to the normal seasonal epidemics of influenza.
This virus constantly changes its form, thereby eluding the protective antibodies that people may have developed in response to previous exposures to influenza vaccines. Every two or three years, the virus undergoes minor changes.
But at intervals, a bulk of world’s population has developed some level of resistance to these minor changes and it easily infect populations around the world, often infecting hundreds of millions of people whose antibody defenses are unable to resist it.
In 1957, an Asian flu pandemic infected 45 million Americans and killed 70,000. It caused about two million deaths globally. Once again, the cycle turns back in 2009. So far, 300 peoples in Mexico have been infected by the influenza A swine strain. Thus making evident, the outbreak of swine flu and making contingency plans for a possible global pandemic.
Symptoms of Swine flu
According to Centre for Disease Control and Prevention (CDC), the symptoms of swine flu were similar to those of influenza and of influenza like illness. It includes fever, sore throat, body aches, headaches, chills and fatigue.
The 2009 outbreak has shown an increased percentage of patients reporting diarrhea and vomiting. In United States, CDC advised physicians to consider swine influenza infection in the differential diagnosis of patients with acute febrile respiratory illness.
The presumed pathophysiology indicates that influenza viruses bind through hemagglutin on to sialic acid sugars on the surfaces of epithelial cells, which typically affect the nose, throat and lungs of humans. The viruses are 80-120 nm in diameter.
Transmission of Swine flu in humans:
People who work either in poultry and swine with intense exposures are increased risk of zoonotic infection with influenza virus and constitute of human hosts in which zoonosis and reassortment can occur.
Prevention of swine influenza has three components:
Prevention in swine:
The spread of swine influenza can be controlled by executing facility management, herd management and vaccination. Standard commercial swine flu vaccines are effective in controlling the infection, when the virus strains match enough to have significant cross protection and custom vaccines should be given to the animals.
Prevention of transmission to humans:
The transmission from swine to human is believed to occur mainly in swine farms where farmers are in close contact with live pigs. Since the outbreak of transmission had occurred, the farmers were requested to use face mask while treating with infected animals.
Prevention of spread in humans:
Influenza spreads between humans through coughing or sneezing but it is restricted to pork products, since the virus is not transmitted through food. Swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children can remain contagious for up to 10 days. The standard infection control, which includes frequent washing of hands with soap and water or with alcohol based hand sanitizers. A new H1N1 starin vaccines are being developed and could be ready as early as June 2009.
If a person becomes sick with swine flu, antiviral drugs can make the illness milder and make the patient feel better. As soon as the symptoms are detected, antiviral drugs should be started soon. The US CDC recommends ostelamivir and zanamivir for the treatment and prevention of infection with swine flu influenza viruses. The virus outbreak in 2009 were found be resistant to amanatadine and rimantadine.
Epidemiology in India
The 18 outbreaks of Swine fever investigated by various DI Labs in State shows that 892 pigs were at risk, 472 severely affected and 253 died during the last decade. Though a proper system of recording outbreaks is lacking in the State. An outbreak of swine fever in Pigs occurred during the year 2004-05, 05-06 and 06-07 and pigs were vaccinated against swine fever.
All above epidemiological studies are only indicative of the diseases in the State. The proper recording system of epidemiological outbreaks of various contagious diseases in the State is being developed. The truth is that a far more number of outbreaks than investigated by DI-Labs during the last decade (1990-2000) are in existence. Till now, there are no records of mortality in humans in India. But protective measures have to be considered for the control of the outbreak of the prevailing swine flu.