Malaria is one of the biggest health problems facing developing nations at present. It can cause severe fevers and is often fatal if untreated. But what is perhaps less well known is that malaria was once a problem native to Western Europe, including Britain and Ireland. Could it ever return to these countries? Given the suitability of a large percentage of land cover for mosquito breeding, and the possibility of global temperatures rising by at 2.5°C this century, it seems likely that malaria will once again become indigenous in Britain and Ireland within our children’s lifetime.
Let’s look at the reasons why malaria might become a problem in these countries. First of all, Britain and Ireland are particularly wet places, with a lot of standing water, such as lakes, wetlands, and fields impeded by slow-draining soils. This water cover provides ample habitat for indigenous Anopheles mosquitoes, the species that carry malaria. Anopheles mosquitoes behave as generalist aquatic breeders and will reproduce in almost any wet environment if undisturbed.
So the habitat,and the mosquito species that carry malaria are already present. But what about malaria itself? Malaria does occur in Britain and Ireland, but it is not yet indigenous. It is brought in by people returning from countries where malaria is a daily fact of life. But the infection is usually treated, and in those cases where it is not, malaria hits a brick wall. Why? The only reason that the species of Plasmodium responsible for this blood-borne disease do not multiply in these countries at present is because ambient temperatures are currently too low. The bottom line: it is too cold here for malaria to get a foot-hold. But that could change if temperatures rise. And that is precisely what climatologists are predicting.
What if that happens, and temperatures hit the required level for Plasmodium to reproduce? Well, another three prerequisites must be satisfied for malaria to become native: (1) people return from abroad carrying the disease and it goes untreated, (2) the specific mosquito hosts then bite the infected person/s, and (3) the parasite develops within the mosquito. Once all of these prerequisites have occurred, the infection may spread and malaria will soon have become indigenous.
But there may be some hope, even if that does happen. Because of the localised nature of the human-mosquito-Plasmodium relationship, the first outbreak of indigenous malaria is likely to be small and limited to a particular area, which will probably be marshy or coastal. If infections go unchecked, however, it is likely that the outbreak will spread; a worst-case scenario would involve an outbreak in an area with a high population density, such as London, Dublin, or Cork.
The mosquito species that carry malaria are already present in Britain and Ireland, as are the parasites responsible. It is only a matter of time before the climate in these countries changes sufficiently to allow malarial Plasmodium species to multiply and become indigenous. Whether it will then become epidemic is largely a matter for public health infrastructures to decide.