Super-mosquito ‘invasion’ could trigger malaria surge, WHO warns

The invasion of a mosquito that adapts easily to urban environments poses a real risk, say experts . Photo / James Gathany / CDC via AP

An “invasion” of super-mosquitoes that thrive in cities could trigger a surge in malaria cases across Africa, according to the World Health Organisation.

In the annual World Malaria Report, the UN agency warns the arrival of the Anopheles stephensi in at least five African countries is a “threat to malaria control and elimination” – especially if the insect gains a foothold in the continent’s rapidly urbanising megacities.

The mosquito – which is native to parts of Asia and the Arabian peninsula – was first detected in Djibouti in 2012 and drove a 2800 per cent surge in infections over the following eight years. It has since been found in Ethiopia, Sudan, Somalia and most recently Nigeria.

Unlike the Anopheles gambiae, the most widespread carrier of malaria, the highly adaptable stephensi mosquito thrives in urban areas and breeds almost anywhere – in a dirty puddle between slum shacks, a rubbish dump, or even water in an abandoned car tyre.

It also survives in high temperatures in dry seasons, when malaria transmission usually lulls, and is resistant to many of the insecticides used to curb the parasitic disease.

“It is a very efficient vector that … has already been implicated in an upsurge of cases in some parts of the Horn of Africa,” said Dr Abdisalan Noor, a member of the WHO’s Global Malaria Programme. “Of great concern now is that it’s also been reported in Nigeria.”

The WHO said the mosquito’s arrival is of particular concern because Africa is rapidly urbanising; 40 per cent of the population already live in cities, and 13 of the world’s 20 biggest urban centres will be in the continent by 2100.

“The invasion of a mosquito that adapts easily to urban environments, Anopheles stephensi, poses a real risk,” said Dr Tedros Adhanom Ghebreyesus, head of the WHO. The UN agency added it has launched a new programme to specifically target the mosquito in Africa.

Despite huge progress since the millennium, malaria remains one of the world’s deadliest diseases. According to the latest report, it killed roughly 619,000 people in 2021 – a slight drop from 625,000 in 2020, but up from 568,000 before the Covid pandemic struck.

The report estimated that in total, 63,000 malaria deaths between 2019 and 2021 were caused by “disruptions to essential malaria services during the Covid-19 pandemic”.

Global cases also increased by 13 million between 2019 and 2020, rising from 232 million to 245 million because of Covid-related disruption. But the WHO said this surge had been largely halted, with 247 million cases in 2021.

“Following a marked increase in malaria cases and deaths in the first year of the Covid-19 pandemic, malaria-affected countries redoubled their efforts and were able to mitigate the worst impacts of Covid-related disruptions to malaria services,” Tedros said.

There were also reasons for optimism, he added. The rollout of the first malaria vaccine, RTS,S, is set to be expanded to disease hotspots in early 2023, while there are several other shots in the pipeline – including Oxford University’s R21 jab, and BioNTech’s mRNA candidate.

Last month scientists also published results from a trial in Mali, which suggests a high dose of an antibody drug developed by the US National Institute of Allergy and Infectious Diseases is 88 per cent effective at shielding adults from malaria over a six-month season.

While researchers stressed these are early results and need to be confirmed in larger trials, they could be a game-changer. Other studies suggest current drugs are roughly 72 per cent effective at treating the diseases, and there are concerns this will drop as resistance increases internationally.

“Rising resistance to insecticide-treated nets and to antimalarial drug regimens remain a major concern – particularly in Africa,” Tedros said, adding that malaria parasites have developed mutations allowing them to escape detection from the most widely used diagnostic tests in some areas.

Noor added: “As a result of these and other challenges, including inadequate funding, the effectiveness of some of our primary malaria control interventions is declining. This is especially true of pyrethroid-only insecticide-treated nets, which have been the bedrock of the malaria response for 20 years.

“All of these risks raise serious concerns for national malaria programmes and global partners seeking to control and eliminate malaria,” he said.

Gareth Jenkins, interim chief executive at Malaria No More UK, said: “The findings of the 2022 World Malaria Report are a sharp reminder that, despite some stabilisation of deaths and cases, they remain at an unacceptably high level post-pandemic.

“This news is disheartening given the progress made over the last decade and we are now facing a narrowing window of opportunity to get back on track,” he said.