Aids day this year fell in the middle of the outbreak of bacterial meningitis in Cardiff and other university campuses, and coincided with the outbreak of the E. coli infection in Lanarkshire. What is going on? Why are we being assaulted by apparently novel infections against which familiar remedies are ineffectual? It is a shock that ten people have already died in Scotland from a variant of a bug that leads an otherwise benign existence in everybody's intestines. It happened in Japan in July, when the same strain of E. coli killed ten children and hospitalised more than 100 of them. Super-hygienic Japan reacted with shame and shock.
The past quarter of a century has been replete with previously unknown infections. Remember Legionnaires' disease, which surfaced in the US in July 1976 and was eventually linked to a bacterium adapted to life in water-cooled air-conditioning systems? Aids followed soon after.
Since then, infectious disease has hardly been far from the news. Edwina Currie's career in British politics was cut short by it, and BSE is an infection, after all. Malaria is resurgent in India and the World Health Organisation is alarmed at the appearance of virulent, drug-resistant strains of the tuberculosis bacillus. There are also repeated alarms about the epidemic infections of Africa, caused by viruses named after the places where they were identified-Lassa, Marburg and Ebola. (Marburg is in Germany, not Africa; its connection goes back to 1967, when a shipment of green monkeys from Uganda infected 30 German laboratory workers and killed 7 of them.) Fears that the Ebola virus may spread to the urban centres of South Africa keeps many people awake at nights.
What is going on? From the point of view of the micro-organisms, the bacteria and the viruses, the name of the game is simply to produce as many of their kind as possible. Often (as in the human gut) they compete for scarce resources-undigested food, in that case-with other micro-organisms. Over many decades, the micro-organisms' world has become more dangerous, but there are more opportunities for it to flourish than there used to be, too.
What are the dangers for the bugs? Hygiene is one. The disappearance of disease carriers-mosquitoes which carry malarial parasites, tsetse flies which carry sleeping sickness and rats which carry plague-infested fleas-is another. Vaccines, which induce the invaded body of an animal to kill off bacteria and viruses, are a further problem.
But as the annual influenza wave shows, vaccines can sometimes be circumvented: the virus simply has to change the structure of one of the proteins in its coat into a form that the immune systems of previous victims will not recognise.
And new carriers can sometimes be found. The tick that carries the bacillus responsible for Lyme disease (now infecting 20,000 people a year in the US) will feed on dogs, cattle and squirrels if it cannot find its preferred host-a forest deer.
For bacteria, the big threat of the past half century has been the flood of antibiotics. The standard bacterial defence has been to make an enzyme that destroys them, molecule by molecule. From the bacterial point of view, this is eas-ily arranged. Bacteria, like people, are infected by virus particles (called bacteriophage) that often carry pieces of genetic DNA from other bacteria: that is how the spread of antibiotic resistance can be quite rapid.
The emergence of the new strain of E. coli (called 0157:H2) seems to have been provoked along with resistance to antibiotics by ordinary bacteria living in the intestines of cattle. (Cattle grow faster if fed with antibiotics.) The strain has acquired the capacity to make a toxin related to that produced by Shigella, like Salmonella one of the classic causes of food poisoning. Presumably the benefit (to the micro-organism) is that the cattle (which are also affected) leave more food undigested. That the same strains can be fatal to people is an accident.
The use of antibiotics in animal husbandry has always been controversial. What the spread of 0157:H2 shows is that only restrictions that are internationally agreed and enforced could have prevented the emergence of the new strain.
If, as is likely, outbreaks such as that in Scotland have their roots in animal contamination, better hygiene is the most immediate defence. Stopping the use of antibiotics in animal feed might make sense, but finding the source of the Lanarkshire bacteria is a necessary first step.
For the long haul, there are two things to remember. First, we are not being overwhelmed by infection. In the past few years there has been encouraging progress against several tropical diseases. In advanced societies, the benefits of using antibiotics in human medicine far outweigh the disadvantages of resistance. And there is a good chance of much more specific remedies and vaccines flowing from the rapid exploration of these infections.
Second, vigilance is still necessary. The British government's parsimony towards the few research laboratories in the field is imprudent. More worrying is that local authorities have mostly swapped the expertise of their medical officers for environmental officers. Medical officers used to be the first line of defence against the ageing lukewarm pork pie.
