As alarm bells ring across the world at the prospect of a pandemic caused by the H1N1 virus, the so-called "swine flu", Giovanna Montalbetti looks into what is known about this new threat to human health and the best ways to control it As the alarm about a swine flu pandemic and its consequences continues, many people have found themselves, perhaps for the first time, stopping to think about swine flu and other sorts of influenza A-type viruses. With the media giving exhaustive coverage to the issue, the public might feel overwhelmed by the apparent sea of terms and the endless news-flashes. However, now that Mexico has said that the numbers of those infected with the swine flu virus in the country are decreasing, and that the worse may soon be over, it may be a good time to take a deep breath and look at the global situation, while also clarifying some of the key concepts concerned. A COLD OR THE FLU? Like the common cold, influenza or the flu is caused by a viral infection that affects the respiratory system. Although they are caused by different viruses, both illnesses have similar symptoms, which can make them difficult to differentiate except through the special tests that can be done within the first few days of the illness. As a general rule, colds are usually milder than the flu and generally do not result in serious health problems such as pneumonia, bacterial infections or hospitalisations. Fever, body aches, extreme tiredness and a dry cough are some of the symptoms present in both the flu and a cold, although they are much more intense in the flu. Although antibiotics will work for the bacterial infections that may come as a side effect of these diseases, they will not help against a cold or the flu themselves, as these are both viral infections. Antibiotics work exclusively on bacteria, not on viruses. Self- medication using antibiotics in cases of colds or the flu can therefore be a common mistake and one that may even lead to the development of resistance to antibiotics. Bearing this in mind, it becomes all the more important to consult a doctor during the present threat of swine flu before using medications, especially when children, adults aged 65 or older, or people with certain medical conditions such as metabolic diseases (like diabetes), chronic lung, heart, kidney, liver or blood diseases, or with weakened immune systems, are concerned. WHAT IS A VIRUS? Viruses are microscopic biological entities, much smaller than bacteria and having a relatively simple basic structure. They consist of a piece of single or double- stranded nucleic acid (DNA or RNA) surrounded by a protein shell known as a capsid. Some may present outer protein and lipid envelopes. Viruses are inactive when outside a living cell, but when inside they act very much like parasites. They can attach themselves to a host cell's walls, injecting their genetic content into the host cell and taking over the cell's metabolic machinery to produce new viruses ( virions ). It could be said that a virus takes control of a cell in order to reproduce. At a certain point the resulting virions emerge through the host cell's wall, killing it and spreading out through the body. Viruses are classified according to whether they contain DNA or RNA, as well as by their size, the shape of their capsid and the presence of an outer envelope. Virus infection cycles may vary: sometimes viruses are highly aggressive, and sometimes they remain dormant inside host cells. Flu viruses can be classified into different types, of which the Influenza A virus is one. This causes flu in birds and in some mammals, and it can be found abundantly in wild birds, although actual disease is uncommon. Depending on the composition of their outer envelope, A- type flu viruses can be classified into different subtypes, each of which can mutate into different strains with specific pathogenic profiles that include annual flu (affecting mostly humans), swine flu, avian flu, horse flu and dog flu. According to the Merck Veterinary Manual, swine flu is common in certain areas of the US, Mexico, Canada, South America, certain regions of Europe, Kenya, Japan, mainland China, Taiwan and other parts of East Asia. Transmission to humans is uncommon, and when it occurs it does not always cause external symptoms. Why then has swine flu recently become pandemic in such a short period of time? According to one authority, it is because the virus has very little to do with pigs at all. The reason the disease was given this name is because parts of its DNA resemble those found in flu viruses that commonly affect pigs, and this is one of the reasons many organisations, including the World Health Organisation (WHO), have debated whether "swine flu" is a misnomer when referring to the strain causing the present situation. Several alternative names have been put forward, the WHO opting for reference to the virus type and subtype, in other words to Influenza A, H1N1. This subtype is apparently the result of a combination of human, avian and swine influenza H1N1 virus strains. Its origins are unknown, but it has not remained confined to pigs. Outbursts of different strains of the H1N1 virus have occurred periodically since 1918, with various outcomes. The problem with the present virus is that it is a new strain, so populations have less immunity to it. TIMELINE OF A PANDEMIC: The disease was first detected on 18 March, when Mexican authorities reported unusually high levels of a flu-like illness. Almost a month later, on 13 April, a woman from Oxaca (Mexico) became the first suspected casualty of the disease. At this point, the disease had not yet been confirmed as "swine flu", but soon afterwards, on 17 April, some 1,455 cases of suspected swine flu were starting to be investigated, this first phase ending on 25 April. It was on 21 April that alarm bells really started to ring, with US authorities reporting the first two confirmed cases of the illness in California. Canadian laboratories testing Mexican samples then confirmed that both countries were dealing with the same disease. On 24 April, seven new cases were confirmed in the US, and one day later the WHO declared a public health emergency of international concern. Events then began to move more rapidly, with France, Spain, the UK, Israel, Australia and New Zealand starting to investigate suspected cases from 26 April onwards. On the 27th, fear started to spread as Spain and the UK confirmed the first cases of what was now commonly being referred to as "swine flu". Meanwhile, in Mexico over 100 deaths were being investigated, 20 of which were reported as having been caused by swine flu. On 28 April, Israel and New Zealand joined the list of countries with confirmed cases of Influenza A virus H1N1, while Australia, Brazil, Peru and South Korea reported suspected cases. Mexico announced that it had a suspected 1,600 cases, though health officials claimed the number of new hospital admissions was decreasing. On 29 April, a Mexican child being treated in Texas became the first person to die as a result of swine flu outside Mexico. However, at the same time the Mexican authorities revised their confirmed death toll down from 20 to seven cases. Austria and Germany also confirmed their first cases of H1N1 flu. On 30 April, as Costa Rica, Switzerland and the Netherlands reported their first confirmed cases of the disease, the WHO warned that the risk of a pandemic was imminent and called for a Level 5 pandemic alert. On 1 May, Denmark and Hong Kong reported two new cases, with the US, Canada, Spain, Germany and the UK confirming cases of secondary transmission. One day later, on 2 May, six countries (Mexico, the US, Canada, Spain Germany and the UK) confirmed that the virus was being transmitted from human to human. France, Italy and Hong Kong also added a further four new cases to those recorded worldwide. On 3 May, the WHO confirmed that there had been 898 confirmed cases of swine flu in 18 different countries, Colombia and Ireland being the latest additions to the group. Last Monday evening WHO's secretary-general, Margaret Chan, announced that according to the organisation's latest data there had been 1,003 confirmed cases of swine flu in 20 countries. However, the world was not facing a situation similar to that of the 1918 flu pandemic, when a virus of the same type (then named "Spanish flu") caused the death of millions of people. A few hours later, Colombia confirmed its first case and Canada for the first time hospitalised a flu victim. The New York school that had been the main focus of the disease in the US also re-opened its doors. PREVENTIVE MEASURES WORLDWIDE: Various countries have taken measures aimed to halt the spread of swine flu. On 26 April, Russia decided to prohibit all meat imports from Mexico, Texas, California and Kansas and also prohibited pork imports from several Central American countries and other regions of the US if the meat had not been thermally treated. This measure was seen as drastic by other countries, given that the virus has not yet been isolated in swine. However, it is not the only measure that has been taken to try to stall the advance of the pandemic, with the US, for example, declaring a sanitary state of emergency to allow it to control all visitors to infected zones. Many countries, such as Canada, Spain, Brazil, Chile and Peru, are also increasing border surveillance and are giving recommendations to those travelling to risk areas. Guatemala has gone a step further by declaring a yellow national alert and establishing a sanitary cordon with Central America. In Japan, thermal imaging systems have been installed at airports to detect travellers arriving with a fever, and in China quarantine and inspection measures are being considered. New Zealand and other countries have also opted for quarantine and isolation of confirmed cases, although perhaps it has been Hong Kong that thus far has acted most controversially by deciding to isolate 350 guests inside a hotel as a preventive measure. A few days after Egypt made public its intention of slaughtering all the country's pigs, France announced that it would ask the European Union to suspend all flights to Mexico. Although some airline companies have supported this proposal, most EU countries and the European Commission have opposed it. ARE SWINE A DANGER? According to the WHO, thus far there have been no confirmed cases of pig- to-human transmission of swine flu. On the other hand, a few days ago officials said that about 220 pigs from a herd of 2,200 on a Canadian farm had been infected by a worker who had recently been to Mexico. Moreover, at last Sunday's press conference at the WHO's headquarters in Geneva, Peter Ben Embarek, the WHO senior scientist on food safety, assured the audience that any fear of pork products was unjustified and that consuming ham, sausages, pork and so on was completely safe. Embarek said that the processing used for pork products, the maturing of cured hams and the cooking of meat all destroy the virus. In this light, Egypt's decision to slaughter its estimated 300,000 pigs in order to prevent the animals from passing the disease to humans has been greeted with scepticism. As Egypt has thus far had no confirmed case of swine flu, this preventive measure has seemed both drastic and unnecessary to international specialists such as Barbara Straw, professor of large animal clinical science at Michigan State University's College of Veterinary Medicine, and Joseph Domènech, responsible for the Food and Agriculture Organisation's animal health service. In addition, as there is currently no evidence from any of the countries suffering from the pandemic that the flu strain causing the illness is present in pigs, it seems logical to assume that slaughtering healthy animals will neither prevent nor solve the problem. International opinion therefore has echoed the complaints of Egyptian pig farmers who fear that this is a move directed against them, despite the authorities' declarations that it is a matter of public health unrelated to H1N1. MORE PREVENTIVE MEASURES: Swine flu spreads largely in the way that the common cold does, with transmission occurring when someone is exposed to the virus either by touching infected surfaces or breathing air contaminated by an infected person. In order to prevent the spread of the disease, the WHO recommends covering the mouth and nose with a disposable tissue when coughing or sneezing and washing hands thoroughly with soap on a regular basis. The WHO also recommends avoiding close contact with people who might appear unwell and who have a fever and cough. If such contact is unavoidable, then the WHO's recommendations include the above as well as wearing masks, improving air ventilation in a sick person's room, isolating a sick person at least one metre from other family members, keeping a clean environment with household cleaning agents, informing family and friends about the illness to reduce contact with other people, and contacting a doctor or healthcare provider to report symptoms before travelling to a health facility. Should a patient not be able to contact a healthcare provider in advance, then he or she should notify providers of symptoms on arrival at a healthcare centre. Although there is still no specific vaccine against this new strain of the Influenza A virus H1N1, research is underway, with some encouraging results.
