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Dororthy H. Crawford is Professor of Medical Microbiology and Assistant Principal for Public Understanding of Medicine at the University of Edinburgh. She is the author of several books and papers, most recently for OUP, Deadly Companions: How Microbes Shaped our History. In the post below she compares the current swine flu outbreak with previous flu pandemics, and asks why this one is apparently more serious in Mexico than elsewhere and how it might develop.

She has previously written for OUPblog on the UK Foot and Mouth Disease outbreak in 2007.

Ironically, while all those trying to predict the next flu pandemic are monitoring the antics of bird flu in Asia and North Africa, swine flu escapes from a pig farm in Mexico and goes global. This unpredictability is typical of flu virus which is constantly mutating and recombining its genes, eventually producing a ‘new’ strain that can infect and spread in humans unrecognised by our immune system.

This unruly behaviour gives an average of three pandemics (defined as a spreading infection in more than one continent at once) per century. In the 20th century we had Hong Kong flu in 1968, Asian flu in 1957, and the post WW1 Spanish flu in 1918 that killed around 40M people.

Within days of Mexico reporting a flu epidemic, now with some 985 infections and 25 deaths, cases appeared in around 20 countries, including the UK, all directly seeded from Mexico thanks to our efficient trans-global airliners. Scientists at the Centre for Disease Control, Atlanta, US, quickly identified the virus as H1N1; a common subtype in humans. But the ‘Mexican’ pig virus, which has been traced to one that has been circulating in pigs since the 1930s, is very different from the human H1N1 strain. It has occasionally jumped to humans before but until now it has never succeeded in spreading between humans.

Flu viruses have RNA genomes with eight separate gene segments that mutate and recombine rapidly. The ‘Mexican’ virus has six genes derived from North American swine flu and two from Eurasian swine flu; a combination that has never been found infecting humans before. It is not clear how or why it jumped species, but given that it is now spreading between humans, and most of us are likely to be non-immune, this is a recipe for a pandemic.

At present events are moving so fast that whatever I write will not only be out of date, but may even be proved wrong, by tomorrow, so I will restrict myself to speculating on the following: why is ‘Mexican’ flu apparently more serious in Mexico than elsewhere’? and: ‘how might the pandemic develop’?

Traditionally, respiratory infections like flu are a threat to the very young, the very old and those with chronic diseases, causing thousands of deaths in these groups in the UK every year. Generally the death rate from flu is less than 1%, so the rate of around 2.5% reported from Mexico (985 cases of flu and 25 deaths) is high. But outside Mexico cases seem to be mild, with the only death reported being a child in the US where over 160 cases have been diagnosed. So what is the explanation?

In all flu outbreaks those who seek help represent the tip of the iceberg, with many more infections being too mild to require medical attention. It is likely that the Mexican figures represent only those sufferers who consulted a doctor and are therefore distorted towards the severe end of the spectrum. More research is needed to uncover the actual prevalence of the disease in the community before a reliable death rate can be calculated.

Reports of deaths among young adults in Mexico are worrying as this is reminiscent of the 1918 H1N1 virus with its high death rate in the young. The explanation may be that the older generation are partially protected by having met a similar strain of H1N1 in the past, but again we need more details from Mexico before specific risks can be assessed.

In the Northern hemisphere flu epidemics usually strike in the winter when the virus transmits more easily between people who are huddled inside trying to keep warm. But in the UK the 1918 pandemic began with a small outbreak in the Spring which receded in the Summer only to take off again in the Autumn, causing thousands of infections and deaths. Given the present pattern, we may now be witnessing the equivalent of the 1918 Spring outbreak, heralding a full pandemic in the Autumn. If so this could be good news as it gives us a 6 month breathing space – time enough to prepare a vaccine to protect our vulnerable groups.

Dorothy H. Crawford is a Professor of Medical Microbiology and Assistant Principle for the Public Understanding of Medicine at the University of Edinburgh. Her most recent book, Deadly Companions: How Microbes Shaped Our History, takes us back in time to follow the interlinked history of microbes and man, impressing upon us how a world free of dangerous microbes is an illusion.  In an excerpt this morning we looked at SARS.  The excerpt below looks at the effect of poverty on disease.

It is glaringly obvious from a glance at the figures that poverty is the major cause of microbe-related deaths. On a worldwide scale microbes are still major killers, accounting for one in three of all deaths. But the huge discrepancy in the death rates between rich and poor nations reveals the stark reality. Whereas only 1–2 per cent of all deaths in the West are caused by microbes, this figure rises to over 50 per cent in the poorest nations of the world, and it is in these highly microbe-infected areas where over 95 per cent of the global deaths from infections occur. Most of the 17 million killed by microbes each year are children in developing countries where the link with poverty is clear. It is the poor who are malnourished, live in filthy, overcrowded urban slums and go without clean drinking water or sewage disposal, and therefore they are the ones who fall prey to the killer microbes: HIV, malaria, TB, respiratory infections and diarrhea diseases like cholera, typhoid and rotavirus; all eminently preventable and treatable given the resources.

The spread of HIV is an excellent example of how microbes exploit the poor, striking at the most disadvantaged in the community. The virus emerged in Central Africa and spread silently throughout the continent in the 1970s, given a head start by its long silent incubation period, and aided by despotic leaders, corrupt governments, civil wars, tribal conflicts, droughts and famines. Carried by undisciplined armies and terrorists, the virus infiltrated city slums, infected commercial sex workers, was picked up by migrant workers and passed on to their wives and families. While malnutrition accelerated the onset of AIDs, breakdown of health-care services in the political turmoil of Africa excluded any possibility of medical support for the millions in need.

Now we are living through the worst pandemic the world has ever known, with 40 million living with HIV, 25 million already dead and around 10,000 dying daily—the equivalent of over three 9/11disasters every twenty-four hours. A third of people living in sub-Saharan African cities are HIV-infected, and while highly active antiretroviral therapy (HAART) has converted this lethal disease into a manageable chronic infection in the West, presently only a tiny proportion of Africans living with HIV receive this treatment; for most there is no hope of obtaining the drugs vital for keeping them alive.

The dynamics of HIV in Africa reflects its mode of spread. As the virus is sexually transmitted gender inequalities mean that women are particularly vulnerable. In general they are poorer and less well educated than their male counterparts, and are often powerless to choose or restrict their sexual partners, or to insist on condom use. Indeed many are forced to exchange sex for essentials like food, shelter and schooling. Now one in four African women are HIV-infected by the age of twenty-two years (compared to one in fourteen men of the same age), and women account for 60 per cent of all those living with HIV.

Over 90 per cent of HIV-positive women in Africa are mothers, and the virus has created 15 million orphans worldwide, 12 million of them in sub-Saharan Africa. These children are bearing the burden of the HIV pandemic; they miss school to care for their sick mothers or to earn the family income; the virus has not only deprived them of their parents but their childhood and their education as well.

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Although real pink flamingos aren’t indigenous to Florida, I’m pretty sure the plastic ones are. When I first moved to the Sunshine State, plastic pink flamingos graced many yards, always in multiples of two (being sold only in pairs). I thought they were kind of funny. I liked their pink color. I bought a pair.

Union Products, the company that manufactured these popular birds, ceased the PPF production on this day in 2006. But don’t reach for your tissues—HMC International has purchased the copyright and original plastic molds, and the Plastic Pink Flamingo shall rise once again (or at least be stuck in ground on its metal wicket legs).