The war on malaria rages on in Tanzania

Does the mosquito infect man with malaria or is it vice versa? When it comes to this question, scientists seem not to agree.

“It’s a chicken and egg situation,” begins Halfan Ngowo, a research scientist at the Ifakara Health Institute (IHI) in Tanzania.

Arnold Mmbando, also a research scientist at the same institute however unequivocally states “it is the man who infects the mosquito which only acts as a vector that carries and transfers Plasmodium falciparum, the parasite that transmits malaria.”

But Fredros Okumu, a parasitologist and entomologist, who currently works as director of science at IHI, “malaria is one of the few parasites in the world that has evolved in such a way that part of its life cycle survives in human beings and the other part in mosquitoes.”

Malaria is transmitted to humans by the female Anopheles mosquito. Female mosquitoes take blood meals for egg production, and these blood meals are the link between the human and the mosquito hosts in the parasite life cycle. When a mosquito bites a person infected with the parasite, it infects the mosquito which can then transmit the disease to someone else.

The size and genetic complexity of the parasite means that each infection presents thousands of antigens (proteins) to the human immune system, adds Dr Okumu.

Over time the parasite has developed a series of strategies that allow it to “confuse”, hide, and misdirect the human immune system.

“We observed a shift in mosquito biting to earlier hours of the evening, before individuals are indoors and protected by bed nets, followed by a return to pre-intervention biting rates,” notes Mmbando, adding that although mosquitoes are nocturnal in nature, the time of biting no longer matters.

At the Ifakara Health Institute (IHI) mosquitoes being reared for research do not have any parasite.

“We test the people who are going to feed the mosquitoes in the insectary, and if they are found to have the malaria parasite they are not allowed to feed the insects. The objective is to have malaria-free insecticide which we can use to test different strategies to know their efficacy,” added Mr Mmbando.

What is malaria?

Malaria caused by Plasmodium parasites (P. falciparum, the most common form of malarial parasite in sub-Saharan Africa), is responsible for most deaths globally. Plasmodium parasites are transmitted to humans through the female Anopheles mosquitoes. The parasites travel through the infected person’s blood to the liver, where they grow, multiply, and then spread throughout the body’s red blood cells, destroying them in the process. Individuals with weaker immune systems, particularly children under five, are the most vulnerable. Pregnant women are also at high risk for becoming sick and passing the disease to the foetus.

In 2019, the Lancet commission released a report on the world’s prospects of eradicating malaria concluding that ending the deadly disease was no longer a dream, but is now possible in our lifetime.

“For too long, malaria eradication has been a distant dream, but now we have evidence that malaria can and should be eradicated by 2050,” said Richard Feachem, co-chair of the Lancet Commission on malaria eradication.

Indeed, the world has made significant progress: More than half the countries in the world are now malaria-free. About 188 million insecticide-treated mosquito nets were distributed in 2020 and the number of children under five years who died of the disease plummeted.

Following the end of the global malaria eradication programme in 1969, reduced political commitment and funding for malaria control led to resurgences of the disease in many parts of the world – particularly in Africa.

Within the last decade, increasing numbers of partners and resources have rapidly increased malaria control efforts. This scale-up of interventions has saved millions of lives globally and cut malaria mortality by 36 per cent from 2010 to 2020, leading to hopes and plans for elimination and ultimately eradication.

In most malaria-endemic countries, four interventions—case management (diagnosis and treatment), insecticide-treated bed nets (ITNs), intermittent preventive treatment of malaria during pregnancy (IPTp), and indoor residual spraying (IRS)—make up the essential package of malaria interventions. Between 2001 and 2015, a substantial expansion of these interventions contributed to a 30 percent reduction of the global incidence of malaria and a 47 percent decline in malaria mortality rates.

“The creation of new financing mechanisms coupled with a steep increase in malaria funding enabled the wide-scale deployment of these malaria-control strategies that led to reductions in disease and death on a scale that had never been seen before,” the World Health Organisation’s (WHO) director-general Tedros Adhanom Ghebreyesus said in 2020.

Through treatments, insecticide-treated bed nets, and efforts to develop vaccines, much of the developed countries have now eradicated malaria. Based on the progress, the world set goals to eliminate malaria by 2030. The Global technical strategy for malaria 2016–2030 adopted by the World Health Assembly in May 2015 sets the target of reducing global malaria incidence and mortality rates by at least 90 percent by 2030.