Africa's most lethal creature

Half past noon.

In the pin-drop silence, we stroll down the corridor to a special room in the farthest end of the building.

Milcah Gitau opens a door that leads to another tightly-shut, heavy door.  “I cannot open this one until you close the other one. Mosquitoes do not like bright, white light,” she warns.

Ironically, this tiny but dangerous creature is afraid of a little light. “When you turn on an outdoor light at night, mosquitoes can become confused during their hunt though may try to navigate closer to the light. This is why we use red bulbs that are dimly lit in here,” says Ms Gitau.

This attraction to light sources is called phototaxis.  However, it does not apply to all spectrums of light as mosquitoes prefer ultraviolet light.

For this reason, it is commonly thought that yellow and red lights will repel mosquitoes. Although these lights do not necessarily act as a repellent, yellow or red outdoor lights will also not attract them.

The mosquito is a creature of contradictions.

The female mosquito simply wants to reproduce, but that is what makes her dangerous.

Her delicate wings are a marvel, but her buzzing torments us. Her eyes are stunning, but they help her find our flesh.

Her mouth is a perfect model for painless hypodermic needles but what it deposits in our veins could kill us and most of all her astounding survival skills means there are billions more of her. 

Ms Gitau is in charge of the mosquito mass rearing laboratory in the human health division at the International Centre of Insect Physiology and Ecology (Icipe) Duduville campus. She works in the animal rearing and containment unit (Arcu).

Arcu was set up in 1970 at the inception of Icipe. “Growing up, I loved all sort of insects. Therefore, I trained in entomological programmes as well as vector control management,” she says.

She adds: “For over 30 years, I have been working here, rearing several species of haematophagous and phytophagous arthropods for research. I am very happy they gave me the job I love the most.”

She has seen mosquitoes beat them at their own game over the years by fighting every strategy they develop.

At the unit, the insects buzz in sharp stentorian screams.

Sparked his interest

The HealthyNation team finds Dr Dan Masiga taking staff members through a presentation of activities.

“I am an infectious disease biologist and currently the head of human and animal health at Icipe.  My undergraduate training was at the University of Nairobi in Biochemistry and Zoology, and postgraduate studies in Molecular Genetics and Parasitology,” Dr Masiga introduces himself.

His personal experiences growing up sparked his interest in infectious diseases.

Dr Masiga was raised in rural Western Kenya and experienced firsthand as infectious diseases such as malaria held the region hostage. 

“I know the annoyance of buzzing mosquitoes and the ‘itchiness’ that accompanied chloroquine treatment before the era of rapid diagnostic tests and the artemisinin-based treatment. One dreaded the after-effects of the treatment,” he recalls.

Inside the adult insectary, mosquitoes are equipped with chemical, visual and heat sensors to determine where their prey is. This neatly-arranged room is pitch dark.

Ms Gitau tells HealthyNation they also have a larva insectary, where they hatch the enemy. “When the demand is high, I supply 6,000 to 8,000 of all stages of mosquitoes from larvae to adults and produce 14,000 to 16,000 pupae per day for supply and continuation of the colonies,” she explains.

A major challenge she encounters is the fact that she has to work in high temperatures of between 32 and 34 degrees Celsius, combined with a high humidity of 70 to 80 per cent. This is the most conducive environment for mosquitoes.

“I understand mosquitoes and what they require to be happy. This helps us bring the enemy closer and strike an effective blow,” she says.

Interestingly, despite the fact that there are about 500 chemicals in our body oduor, mosquitoes do not like all of them.

To find their prey, they look for warm, moving bodies that are emitting carbon dioxide. They can follow a plume of the gas to its source until they find a nice landing spot with exposed skin to dig into.

Mosquitoes have a chemo-receptive organ known as labium that looks for chemicals in the skin such as lactic acid and sugars in order to find the best place to bite.

“The female mosquito is usually after the prey giving off the most enticing chemicals,” says Ms Gitau.

Mosquitoes endeavour to be as close to the blood vessel as possible.  

Surprisingly, mosquitoes mate once and use the sperm they store for a life-time. They sing to each other as a form of flirting.

“The anopheles mosquito is not much of a mother. She lays eggs and leaves them. But, because adult mosquitoes flap their wings up to 1,000 times per second, their whiskers create currents that drive food to the larvae,” she explains.

Shockingly, they are poor flyers and travel at most 200m from where they hatch.

This blood sucker kills more animals than all other animals combined and has been in existence for more than 210 million years yet experts have still not been able to stop them.

According to Dr Masiga, there are over 3,500 known species of mosquitoes but only about 150 to 200 transmit diseases. “They are technically part of the fly family - the culicidae - and the reason they are so effective in transmitting pathogens is because of their blood-sucking mechanism, their proboscis (the mosquito’s mouth),” he reveals.

Easy to suck blood

It is a sophisticated system of six thin needle-like mouthparts called stylets each of which pierce the skin, find the blood vessels, making it easy to suck blood.

The maxillae is comprised of two serrated needles that pierce the skin while the other two that hold it open are called mandibles.  It then inserts the two remaining needles into her prey.

The hypopharynx injects an analgesic (like a pain reliever) and an anticoagulant to prevent the victim from noticing the bite and keep blood from clotting while the labrum sucks the blood.

As blood races into the insect filling the abdomen, the system filters out the water from the blood so that it can pack and accommodate more nutritious red blood cells. Once full, it leaves with a loaded barrel, having almost tripled its weight.

Mosquitoes only get one blood meal in their life. Those that bite multiple people are the ones that spread disease.

The Anopheles Gambiae infects her prey with malaria while the Culex Pipiens, a bird biter that also bites humans, transmits the West Nile Virus.

Other mosquitoes like Aedes Aegypti transmit Dengue Fever, Chikungunya, Zika Virus, Mayaro virus and Yellow Fever.

Mainly aquatic

Icipe makes blood meals available for the enemy. In fact, Ms Gitau takes out a sealed box with an opening in which she inserts her hand, allowing the mosquitoes to feed away.

“I am used to it. They may feed on animal blood if they have no option but they do not like it,” she says. Some of the animals they also go for include fish, snakes and birds.

The itching and swelling on its prey comes later after Ms Gitau’s immune system kicks in disseminating antibodies to destroy what is left of the mosquito’s saliva.

Female mosquitoes need protein from blood for the development of their eggs.

They inject plasmodium, the malaria parasite, into the skin along with their saliva. If a mosquito bites a person suffering from malaria, it dies, according to the biologist.

The female mosquito lays eggs in clutches of up to 300 and may do so in swamps, stagnant water or ponds.

One or two days later, the eggs hatch into larvae which can immediately swim and hunt small animals in the water.

According to Ms Gitau, they are entirely aquatic but swim up to the surface to breathe via the respiratory siphon, a small tube at the end of their tail.

Two weeks later they pupate. “They can still swim but stop eating up to four days while breathing through two tubes called trumpets. After this a mature adult mosquito emerges,” she adds.

Male mosquitoes, on the other hand, feed only on plant juices, such as nectar, to get the sugar they need for energy and survival. Because they do not bite, they cannot transmit diseases.

Last year, Icipe made a groundbreaking discovery of a microbe in anopheles mosquitoes that blocks malaria transmission from the insects to people.

The microbe, named Microsporidia MB, was found through studies conducted on mosquitoes in their natural environments, mainly on the shores of Lake Victoria in Kenya.

Mosquitoes carrying the microbe were found not to harbour malaria parasites either in nature or after experimental infection in the laboratory.

In addition, it is passed from female mosquitoes to their offspring at high rates and experts assure that the microbe does not kill or cause obvious harm to the mosquito host.

Later the same year, Icipe commenced further research to investigate the natural ability of these microbes to spread in the laboratory and in the field, and determine how they can be used most effectively.

According to the World Health Organization (WHO), globally 400,000 people still die every year from malaria, a majority in Africa.
Between 2000 and 2014, significant progress was made in tackling the disease, and the number of malaria-related deaths fell by an estimated 40 per cent.

However, in recent times, progress has stagnated and the search for new initiatives for control is imperative if progress is to be made to achieve malaria eradication by 2040, says Dr Masiga.

Sugar baits

Prof Charles Mbogo, the Pan-African Mosquito Control Association (PAMCA) president, insists that to fully combat the enemy, Sub-Saharan Africa needs to work as a team. “As PAMCA we focus on all mosquito-borne diseases, not just malaria,” he says.

He says lymphatic filariasis, a disease that affects the lymph nodes and vessels, is   spread by the same mosquitoes that transmit malaria.

Their bites deposit a parasite that travels to the lymph system.

Most cases are symptomless and might cause long-term damage to the lymphatic system, swelling in the legs, arms and private parts.

The disease also increases the risk of frequent bacterial infections that harden and thicken the skin (elephantiasis). “As a team, we compare notes because we think about cross-border transmissions if we are to reduce malaria in Kenya, Uganda and Tanzania. The problems mosquitoes present in these countries can only be solved by the scientists there,” he explains.

The professor discloses that the enemy has done more harm in Tanzania than in Kenya.

According to Tanzania’s National Bureau of Statistics Malaria Indicator Survey, the infection rate in Tanzania as of 2017 was at 7.3 per cent. 

President Samia Suluhu’s government is currently pressing on with the second phase of a mosquito control project. The initial phase cut infection rate in southern Tanzania region by 4.9 per cent from 25 per cent between April 2015 and June 2018. The second phase began in July 2019 and ends in June 2021. 

A study carried out in Bagamoyo in 2018 and published by the National Library of Medicine, recommends the use of attractive toxic sugar baits (ATSBs) as a new method of controlling mosquitoes in the region.

ATSBs kill both female and male mosquitoes attracted to sugar because the insects feed on a sugary solution containing a mosquitocidal agent. It may be used indoors or outdoors.

The previous year, a group of researchers had found that a sugar-baited resting place containing a toxic dose of ivermectin (an antiparasitic drug used to treat several neglected tropical diseases) was effective against the Anopheles Arabiensis, a common species in the region.

By the end of their trials, over 95 per cent of the mosquitoes were knocked down 48 hours post-sugar feeding.

In Uganda’s Tororo district, a historically high transmission area, interventions by scientists have resulted in a decline in the human biting rate from 19.6 to 2.3 per cent from female anopheles mosquitoes per house per night. Previously, the predominant species in the region was the Anopheles Gambiae sensu stricto, but currently it is the Anopheles Arabiensis.

Tororo has almost completely eliminated the Anopheles Gambiae sensu stricto, with only 0.5 per cent remaining.

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the malaria control interventions primarily responsible for reductions in transmission across Sub-Saharan Africa.

House screening

At Icipe, integrated vector management initiatives that are serving the African region have been successfully executed, thanks to extensive science knowledge, tools and strategy on mosquitoes.

According to the organisation, the aim is to demonstrate the potential benefits of integrating readily available, but not-widely used vector control tools like winter larviciding and house screening in Botswana, Namibia, Mozambique, Eswatini, Zambia and Zimbabwe, to sustain malaria control and elimination.

Larviciding is the regular application of insecticides to water bodies to kill mosquito larvae.

Icipe’s study reports that in Nyabondo, Western Kenya, where there is intense all-year round malaria transmission, combined use of LLINs and screening of house eaves with mosquito-proof wire mesh reduced malaria cases by between 63 and 100 per cent, compared to when LLINs  were used on their own.

Their second study shows that in Tolay, Ethiopia, where malaria prevalence is generally low, the disease was reduced by a further 50 per cent when usage of LLINs was supplemented with the application of a biolarvicide.

Yellow fever and dengue fever are among key emerging arthropod-borne virus threats in Africa.

New studies have revealed variations between two regions in regard to the bionomics (composition, abundance, human blood index, survival rates) and breeding ecology among key Yellow Fever and dengue fever mosquito vectors in the region.

They include Aedes Aegypti, Aedes Simpsoni and Aedes Africanus.

A protocol for molecular differentiation of mosquito species complexes has been adopted for population characterisation and vectorial capacity estimates.

Samples from people and primates have been collected and biobanked for analysis.

Using Rift Valley Fever, a zoonotic disease that affects livestock and people, as a model the fight against mosquitoes has established that large herbivore loss resulted in a marked decrease in abundance and reduced survival of Aedes Mcintoshi, a key mosquito vector of the disease.

For over four years the researchers say they have been testing a novel community-based one health intervention package.

As of 2020, several strains of an entomopathogenic fungus, Metarhizium Anisopliae, were tested under laboratory and semi-field conditions, to create a strain and dosage for several biting arthropods.

The M. Anisopliae strain ICIPE 7, which is currently commercially being developed for tick control under the trade name Tickoff®, has been found to be effective against malaria mosquitoes, ticks and tsetse flies.

Clifford Mutero, a Kenyan medical entomologist, praises the progress but insists that the war is far from over.

“During the past two years Kenya has secured political good will, with President Uhuru Kenyatta becoming the chairperson of the African Leaders Malaria Alliance (Alma),” says Mr Mutero, who is also a visiting professor with the School of Health Systems and Public Health, University of Pretoria.

Also, in February, Health Cabinet Secretary Mutahi Kagwe launched the End Malaria Council.

Five-year grant

Upon taking over the chairmanship of Alma, President Kenyatta called for the establishment of country-led malaria councils and funds.

Last year Mr Kenyatta announced the launch of Kenya’s Zero Malaria Starts with Me campaign.

Kenya’s malaria prevalence stands at 5.6 per cent.

The country has made significant progress against the disease in recent years with increased access to malaria prevention tools such as insecticide treated nets and indoor residual spraying.

“County governments are fighting for budgetary allocations daily but none is directed towards malaria. A lot more can be gained by funding research,” says the expert who authored Mosquito Hunter – chronicles of an African insect scientist.

The Nation recently reported that African scientists had protested over a global health funding imbalance. This followed the announcement of a $30 million (about Sh3.2 billion) five-year grant allocated to foreign research firms to conduct malaria research in Africa by the US President’s Malaria Initiative.

The grant is meant for operational research and programme evaluation geared towards helping partner countries ensure they are making the most effective and efficient use of resources to fight malaria and save lives.

Mr Mutero says researchers are working round the clock to ensure that they stay ahead of the mosquito. “When you subject insects and parasites to a lot of pressure, they adapt and start to undo the gains you have made,” he says.

Dr Masiga agrees and also talks of new developments. “We have been evaluating new products that are biologically friendly and made from artemisia, neem among other plants. They are put in water to deal with mosquito larvae. We are also engaging with affected communities to understand the politics of the bed-net in those communities,” he says.

Battery-powered light lamps

The experts collectively agree that to date the journey has yielded new knowledge and better use of existing tools. “We are following up genetically on how these populations of mosquitoes are changing but the biggest worry is from the Anopheles Stephensi mosquito, which has migrated from India and Iran. It has now reached Djibouti and might soon be entering the East African region,” Dr Masiga cautions.

The mosquito seems to be adapted to breed in suburbs within water tanks and as a result the scientists are now keener on surveillance.

But scientists have noticed it does not survive in homes that have spiders and more specifically the evarcha culicivora and paracyrba wanlessi species that easily spot the blood they store in their abdomen.

These spiders are commonly found in our homes and will even ignore other insects in order to chow down on a mosquito.
“We are currently developing tools that will be needed and as we speak we have a bacillus thuringiensis israelensis (Bti) factory in Tanzania. It has no known effect on humans but when swallowed by mosquito larvae it is harmful,” says the expert.

BTI dissolves in water killing the larvae by eating up the walls of their stomachs thus preventing them from hatching.

Another product is currently being developed in Kakamega Forest in the   western part of Kenya at a small production facility.
“It is derived from a plant known as ocimum gratissimum, an indigenous traditional shrub in most parts which is grown by the community. Its oil is used to make the product as the plant is traditionally a repellant,” the expert reveals.

Dr Masiga insists on an integrated approach to eliminate malaria. He observes that because the country keeps getting outbreaks in places like Baringo, a suitable plan for the region is a priority. 

Rift Valley Fever transmission surveillance is still ongoing with a key focus on how mosquito-borne diseases circulate between human beings and livestock.

Dengue Fever, according to the experts, is prevalent Mombasa, Malindi and Mandera while elephantiasis has been noted to affect the scrotums of many men along the Kenyan coastline.

“We would love to do research on what is causing all this and why these regions but we lack the funds,” says Dr Masiga.

In Tanzania, CRISPR gene editing, a genetic engineering technique in molecular biology by which the genomes of living organisms may be modified, is being used.

According to The American Journal of Tropical Medicine and Hygiene, the mechanism was envisioned to use synthetic genes with the capability of spreading in populations to reduce mosquito populations or alternatively render them less competent to transmit pathogens.

However, as brilliant as it sounds, there is still endless debate on the possible adverse effects the method may have on humans, animal health or the environment.

For years, Prof Mbogo has been training and working with the Mosquito Scouts of Malindi, a volunteer group helping in the malaria war.

“Residents report pools of stagnant water and blocked drainages to them and so they comb shanty towns for potential breeding grounds," he explains.

Breeding grounds are marked with global positioning system coordinates. The municipal authorities are first informed to drain the water and if they fail to, the scouts take it upon themselves to save the day.

The scouts also hand free mosquito nets to women and children.

They also hand out battery-powered light lamps that will attract, trap and poison mosquitoes.

Without a doubt, the female mosquito holds immense power over us. She was here before us, she might outlive us and so our battle continues. Until we win, she is on the loose, we are on the chase.