A History of Swine Flu
Swine influenza is a respiratory illness in pigs caused by swine influenza A (and, less commonly, swine influenza C) viruses. In rare cases, infected pigs may transmit the illness to humans who come into contact with them. The virus may then spread among other humans in the same way other influenza viruses are transmitted, such as through coughing and sneezing. The disease does not spread through eating cooked pork or pork products, as the virus cannot withstand high temperatures used in cooking.
The beginning of finding the link between swine flu and human illness first came about during the 1918 influenza pandemic, which infected approximately one-third of the world’s population at that time and killed an estimated 50 million people. During that period, it was observed that both pigs and humans were affected with similar illnesses at the same time. However, evidence backing up the connection was not discovered until the 1930s, when scientists found closely related influenza viruses in both pigs and humans. Today, we know these viruses as H1N1 viruses. Further research showed that H1N1 viruses were involved in the 1918 influenza pandemic.
Since then, there have been few reported cases of swine flu being transmitted to humans. In the United States, there were cases of swine flu in 1976 in Fort Dix, New Jersey, with more than 200 people infected and one person dying. When it was discovered that the virus involved was a related strain to the virus causing the 1918 influenza pandemic, vaccination efforts were mounted. The outbreak never rose to the level of a pandemic; however, there were deaths that were attributed to side-effects from the vaccine rather than the swine influenza itself. It was later found that, in some people, the vaccine caused a reaction resulting in Guillain-Barré syndrome, which could cause paralysis and even death.
Another incidence of swine flu viruses infecting humans was reported in Wisconsin in 1988, wherein one woman died from the illness. Health care workers who were in contact with the woman, as well as the woman’s husband, were also found to be infected, although no community outbreak resulted. From 2005 to January 2009, there have only been 12 reported cases of swine flu infecting humans in the US. Another swine flu outbreak was reported in the Philippines in 2007, but the disease was limited to pigs and was not reported to have been transmitted to humans.
Other flu pandemics in history were not caused by strains of swine flu itself, but by other related viruses. One pandemic of note was the Asian flu, which lasted from 1956 to 1958. It was caused by influenza type A(H2N2). Another related virus, influenza A(H3N2), caused a global pandemic from 1968 to 1969.
The current swine influenza outbreak, also referred to as influenza A(H1N1), has involved enough cases and deaths to also be designated as a pandemic. This particular virus is thought to be a new strain hailing from the reassortment of five other influenza viruses: a strain that normally infects humans, a North American avian influenza strain, and three swine influenza strains from Asia, Europe, and North America. Since March of 2009, the laboratory-confirmed cases of influenza A(H1N1) increased in number to more than three hundred thousand. Almost four thousand deaths have been reported, and the disease has spread to 191 countries around the world, across all continents except Antarctica.
Influenza A(H1N1) is believed to have originated in Mexico. In February of 2009, residents of La Gloria, a village in the state of Veracruz in Mexico, reported some residents suffering from respiratory illness. Flu-like symptoms, such as muscle pains, vomiting and diarrhea, headaches, and fever, were also observed. By March, an estimated 60% of the village’s residents were believed to be infected with influenza-like illness (ILI). Other cases of ILI were being reported in the United States. Several of these would be later confirmed to be cases of swine flu.
In April 2009, the unusual number of ILI in La Gloria caused local health authorities to investigate the illness. The outbreak was subsequently reported to the Pan American Health Organization (PAHO), the regional office of the World Health Organization (WHO). Further investigation of the disease ensued. The first known casualty of the outbreak was a woman in Oaxaca state, Mexico, who died on April 13.
Meanwhile, in the United States, the Centers for Disease Control and Prevention (CDC) received samples from cases of ILI in California, and confirmed them to be infected with the Influenza A (H1N1) virus. On April 24, the WHO issued its first statement about the outbreak, reporting it as "Influenza-like illness in the United States and Mexico" caused by swine influenza A(H1N1) viruses that “have not been previously detected in pigs or humans.” At this time, there were enough cases for the WHO to subsequently declare the outbreaks as "a public health emergency of international concern." Steps were taken to contain the outbreak, such as the shutting down of a school district in Texas. However, the disease continued to spread, causing the WHO to declare a pandemic alert level Phase 4, indicating a "significant increase in risk of a pandemic." By the end of April, cases of influenza A(H1N1) were confirmed in Canada, Spain, Scotland, Israel, New Zealand, Germany, Austria, the Netherlands, Switzerland, and Ireland. Several deaths due to disease were also reported in Mexico and one in the United States. At this time, the WHO further raised the pandemic alert level to Phase 5, warning health authorities around the world that a pandemic was imminent.
Alongside efforts to minimize the impact of the disease, research was being conducted into the true nature of the virus. The CDC was able to publish the first complete genome sequence of the influenza A(H1N1) strain causing the outbreak by April 27. The Public Health Agency of Canada also completed sequencing of viruses from Mexico and Canada by May 6. Research efforts by other institutions around the world were also under way, such as the World Influenza Centre in London’s National Institute for Medical Research. It was found that certain anti-viral drugs, namely oseltamivir and zanamivir, were effective against the virus. These anti-virals limited both the severity of symptoms and the duration of the disease. However, the virus was discovered to be resistant to other anti-virals such as amantadine and rimantadine.
The beginning of May 2009 saw further spread of the disease across the world. More European countries found confirmed cases of influenza A(H1N1). In Asia, the first documented case was discovered in Hong Kong. South Korea, Japan, China, Taiwan, and India soon followed. South American countries reported cases of influenza A(H1N1) as well. Talks between the WHO and various pharmaceutical companies about the manufacture of a swine flu vaccine had begun; however, difficulties arose as whether demand would far outstrip supply. There were also concerns about whether manufacturing a swine flu vaccine would take away the capacity to manufacture vaccines for other strains of influenza. Available vaccines against other known strains of influenza viruses were found to be ineffective against the virus causing the current outbreak. Further research regarding immunity against influenza A(H1N1) showed that a small percentage of the adult population had antibodies against the virus even without vaccination, but children and young adults had little to no antibodies against it.
Meanwhile, in the absence of a vaccine, the WHO and other health authorities advised simpler preventive measures, such as being more vigilant with personal hygiene. Travel restrictions were not yet recommended nor imposed by the WHO; however, some countries, such as China, began to limit flights to and from Mexico and the United States.
Other patterns regarding the behaviour of influenza A(H1N1) began to emerge. Unlike other respiratory illnesses and strains of seasonal influenza, it was observed that influenza A(H1N1) more frequently affected infants, children, and young adults, and rarely affected the more elderly segments of the population. It was also noted that this particular strain was more contagious than seasonal influenza, although the symptoms it caused in otherwise healthy people were very mild. Concerns were raised about the possibility of the virus mixing with other strains and subsequently producing a more virulent mutation causing more severe disease. However, by June the WHO allayed these fears by stating that, so far, the virus was stable, although close monitoring was still called for.
At the beginning of June, over seventeen thousand cases had been reported to the WHO since the first case in Mexico. More than a hundred people had died as a result of influenza A(H1N1). In less than two weeks, the number of cases further increased to almost thirty thousand. On June 11, the WHO raised the pandemic alert level to Phase 6, the highest there is, indicating that a "global pandemic is currently under way." The last global flu pandemic had been the previously mentioned 1968-1969 influenza A(H3N2) outbreak. The first death in Asia due to influenza A H1N1 was confirmed in the Philippines on June 22, making three out of six WHO affected by mortality due to the virus.
With regard to treatment, the virus began showing resistance to the previously effective oseltamivir. The first case was reported in Denmark. Subsequent cases were then reported in Chile, Japan, Hong Kong, Canada, and Argentina.
As the disease continued to spread, researchers also found more clues as to the origin of the virus. Researchers from Edinburgh, Oxford, and Hong Kong showed that the virus had probably been circulating in pigs for years before it was transmitted to humans. This raised concerns that insufficient monitoring of disease by the pork industry may have contributed to the development of the current influenza A(H1N1) strain. Further research also raised the possibility of the virus having had infected humans before the first reported outbreak of illness in Mexico, perhaps as early as January 2009. More concrete steps toward the production of vaccines were also taken. In July, the WHO gave pharmaceutical companies full approval to manufacture vaccines against this particular strain of influenza A(H1N1). The first human trials for vaccines were begun in Australia, and recruitment for human test subjects in the United States was also initiated.
By the end of July, the total number of influenza A(H1N1) cases had risen to an estimated 134,000, with over eight hundred deaths. There was a growing number of community outbreaks in the southern hemisphere. Even with the increasing number of cases and fatalities, however, there was no indication that the virus had mutated, nor did it seem to cause more severe disease than it had previously. Those most at risk for complications were people at extremes of age (i.e., infants and the elderly), pregnant women, and those with chronic illnesses or weakened immune systems.
This changed in August when the disease took on a more severe form. Aside from the above-mentioned groups, otherwise healthy young adults were observed to be infected with influenza A(H1N1) that directly attacked the lungs. Rather than showing mild symptoms of cough, colds, and fever, these cases were observed to go into acute respiratory distress syndrome (ARDS). The patients with ARDS subsequently required intensive care. Currently, there is no way to predict whether or not a person infected with influenza A(H1N1) will have a mild or severe form of disease, although present research indicates the answer may lie in human leukocyte antigen (HLA), a component of the immune system.
Treatment also proved to be more difficult as more and more cases of resistance to oseltamivir were reported. Resistance was seen in Thailand, Brazil, China, Singapore, the United States, and Peru. The WHO and the CDC cautioned against the overuse of oseltamivir and other anti-viral medications, asking that these drugs be reserved for confirmed cases of swine flu who were at high risk for complications.
By the end of August, influenza activity in the southern hemisphere appeared to have declined. However, it was observed that there was still widespread or even increasing influenza activity in South Asia and Southeast Asia, and the equatorial and tropical regions of South America. At this time, the WHO predicted a shift in activity toward the northern hemisphere. This was proven correct by the end of September, where there was an increase of reports of new cases in the United States, Europe, and Central and Western Asia.
Currently, the pandemic alert level is still at Phase 6, meaning that the influenza A(H1N1) pandemic has by no means abated. Vaccines against the virus are expected to be ready by October. As there is still the possibility that this virus may further evolve, research still continues.
