Malaria mosquitoes have now been tagged as the newest indicator of pervasive climate change. This conclusion is supported by a new 20 year study indicating that the prevalence of the disease increases at higher elevations in warmer weather, but decreases when colder weather patterns return.
The study was published in the current edition of the journal Science by Menno Bourna, who lectures at the London School of Hygiene and Tropical Medicine. Bourna focused on the prevalence of the Plasmodium parasite that causes malaria and the Anopheles mosquito that carries the parasite by using medical records going back 20 years .
The study’s results appear to indicate that worldwide mosquito control efforts aimed at the eradication of malaria may be doomed by climate change, as warmer, wetter climates move into previously cooler, drier areas.
The bad news behind this study is that, while people who live in mosquito infested areas can, and often do, build up an immunity or at least a tolerance to the disease, people in upland areas have no such immunity and therefore the rate of infection and malaria-related deaths is bound to increase when malaria moves into those regions.
Every year, 220 million people are stricken with malaria, which is a mosquito-borne disease associated with warm, wet environments where mosquitoes breed in still water. Mortality statistics from different sources vary, but estimates indicate 600,000 to 1 million people die each year from the malady. Data collection for malaria is difficult because the areas where malaria is prevalent are often hostile to Western researchers.
Malaria is easily preventable, say epidemiologists. Just kill all the mosquitoes, or avoid getting bitten by a disease-carrying mosquito. The first solution is basically impossible because mosquitoes are building up immunities against the prevalent insecticides used against them.
Stronger insecticides may kill as many people as the disease, which is why strongest and most effective antimalarial insecticides were banned, just as they were getting the upper hand on the disease. Draining swamps to eliminate mosquito breeding grounds is equally impossible because that water has to go somewhere and, wherever it goes, it creates a new mosquito breeding ground.
Avoiding the mosquito bite is almost 100% effective, less than a perfect solution because the disease can also be transmitted from human fecal matter, fluid transfers and blood transfusions. Avoiding mosquitoes is, however, virtually impossible. Mosquito nets work. They are cheap enough to be distributed freely, but they come with a built-in drawback: people can not stay under their mosquito nets all the time. Repellent sprays work, to an extent, but they are expensive and the strong ones carry their own health risks. More sophisticated bug-killers such as electric grids work only where there is a low concentration of the bugs. In higher concentrations, the mosquitoes overwhelm electronic measures, and they are much more expensive per square foot of coverage.
Treatment is equally problematic. The traditional treatment for the disease, quinine, has its own drawbacks, including the fact that the side effects of the treatment are often very similar to the disease itself. Headache, diarrhea, vomiting, all associated with Malaria, are also associated with quinine. and there are other, more serious side effects. These range from temporary blindness and hearing loss to death from pulmonary edema. The tonic in gin and tonic contains quinine, which is why generations of British expatriates were so found of the drink. More modern drug treatments for malaria are becoming ineffective as the parasite responsible for the malaria infection builds up an immunity to each of them in turn as they are promoted as the malaria panacea.
Over time, people who survive the disease build up a tolerance for the effects of the parasite in their systems, but that tolerance disappears if they move away from an infected area and then move back again, suggesting that a constant influx of fresh parasites is somehow connected with the temporary immunity or tolerance to the disease.
The pattern of malaria infections is not seasonal according to the study, because the malarial mosquitoes are killed off during normal winter weather. It is only when the year-round temperature range increases the malarial infections are found where they were previously absent.
Research into methods for interrupting the mosquitoes’ life cycle are continuing. Genetic manipulation to sterilize large batches of female mosquitoes hold some promise of destroying the mosquitoes. Scientists in India have come up with what may be a very practical methodology consisting of producing carbon nano particles infused with nitric acid that, when sprayed on mosquito breeding grounds, prevents the mosquito eggs from developing into larvae. Mosquitoes are also responsible for spreading several other diseases, in addition to malaria, including encephalitis and the West Nile virus, making mosquito eradication a high priority goal for the World Health Organization.
Malaria mosquitoes, now tagged convincingly as another indicator – or side effect – of climate change, carry another warning for the world. Humanity might need to brace itself for a global onslaught of a debilitating disease as climate change creates new malarial breeding grounds.
by Alan M. Milner