By Gift Briton
Three decades ago, all malaria transmissions happened in rural settings with female Anopheles mosquito primarily responsible for human transmission of the disease.
However, according to scientists, the changing transmission landscape and the emergence of invasive vectors such as Anopheles stephensi, a mosquito species that has adapted and is capable of transmitting malaria in urban settings, may lead to an increase in urban malaria and outbreaks in Africa.
Furthermore, other factors including rapid urbanization, climate change-induced flooding, and human displacement as a result of war and conflict could also potentially lead to an increase in transmissions, thereby worsening the problem.
Speaking during the 4th Kenya national malaria forum, happening concurrently with the 13th KEMRI annual scientific and health(KASH) conference in Nairobi, Dr. Eric Ochomo, Senior Research Officer, Kenya Medical Research Institute(KEMRI) Centre for Global Health Research, revealed that the progress towards elimination of malaria diseases has stagnated with the changing transmission landscape where the malaria parasites are increasingly becoming resistant to insecticides and behavior change.
According to him, through cuticles modification, the parasites’ cuticles become either thicker or non-porous to the insecticides, adding that unlike the past, malaria parasites have developed a tendency to start biting at hours when people are away from their bed nets and therefore getting exposed to infectious bites.
Thus, Dr. Ochomo notes that, if additional gains are to be realized in the fight against malaria, new tools are urgently needed to complement the current control methods of long-lasting insecticidal nets (LLINs) and indoor residual spraying(IRS).
“Malaria was mostly found in western Kenya and parts of the coastal region. It was rare in the urban setting. However, as many people move to urban areas the parasites also move with them and the poor drainage and careless dumping in those areas create favorable breeding sites for mosquitoes. Therefore, over time, we might start having transmission of malaria in the urban settings,” he said.
“At the moment, the burden of malaria is in western Kenya and some of the coastal counties. If the vector spreads and establishes in urban settings like Nairobi and other parts, this could lead to a malaria outbreak in the country.”
During a plenary session at the malaria forum, Dr. Ochomo highlighted some of the novel vector control methods which could potentially contribute to malaria elimination if their use is guided by proper surveillance.
Among the new tools, most of which are still under piloting and evaluation by the World Health Organization(WHO), explore multiple aspects of the mosquito life cycle including spatial repellents and endectocides (anti-parasitic drugs), attracting targeted sugar baits(ATSBs), genetically modified mosquitoes and larval source reduction and more.
The spatial repellants-chemical-based devices that when placed in a room, make that room non-conducive for mosquitoes- prevent mosquitoes from entering a household and therefore reduce the probability that mosquitoes will bite a person who may be inside and interfere with their ability to detect humans. The repellants can also kill and interfere with the mating behavior of mosquitoes making them unable to reproduce.
According to Dr. Ochomo, an evaluation of the pilot study done in Busia county indicates that the mosquitoes die over a long period of exposure to these repellants. However, their efficacy in reducing mosquito biting and therefore malaria transmission is still under evaluation by the WHO.
Another novel vector control method he highlighted is the use of attractive targeted sugar baits (ATSB), which use the mosquitoes’ own drive for sugar meals against them. Mosquitoes are attracted to the baits using sugar sources and there they are exposed to small doses of insecticides that kill them.
According to the scientist, laboratory and field studies have also highlighted the potential of anti-parasitic drugs in malaria control. Dr. Ochomo said that Ivermectin and other anti-parasitic drugs could soon serve as novel malaria transmission control tools by reducing the longevity of Anopheles mosquitoes that feed on treated hosts. Thus, potentially decreasing malaria transmission when used as mass drug administration (MDA).
“For the period of time you are on ivermectin, your blood becomes toxic to the mosquito so that if the mosquito bites you, it actually dies and the drug remains effective in your body for up to 30 days,” he noted.
Moreover, genetically modified mosquitos can also be used in controlling malaria transmission. They are mass-produced in a laboratory with a self-limiting gene that prevents female mosquito offspring from surviving to adulthood.