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Sightsavers from the field

Catching the urban mosquito: how our research fights NTDs

To tackle disease, we need to know who is affected. In Liberia, we’ve studied mosquitoes and tested children to see how migration affects the spread of lymphatic filariasis.

June 2022
Two women stand in a flooded area outside a house, where they are checking a mosquito trap.

As the urban population swells in Liberia due to ongoing migration from rural areas, the Sightsavers team in Monrovia have been conducting vital research to help stop the spread of lymphatic filariasis.

Lymphatic filariasis (LF) is a neglected tropical disease (NTD) transmitted by the bite of an infected mosquito. If left untreated, it can affect the lymphatic system, causing enlarged body parts and painful disability. Together with the Liberian Ministry of Health, Sightsavers set its focus on discovering the prevalence of the disease in Monrovia, where LF had not been treated before.

In the past, LF has been largely associated with rural areas, in part due to the practical and financial challenges of tackling the disease in urban settings, including the size of the treatment area, population spread and different lifestyle patterns. But as migration to towns and cities increases, so too does the risk of LF occurring in these densely populated areas. Where there is increased migration, understanding transmission and prevalence becomes more difficult.

Participants at a blood collection training session.

About our research

Sightsavers holds independent research organisation status, and we use the evidence we generate to shape our programmes.

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Two women stand outside a house to check a mosquito trap.
Researchers Rose and Fatmata collected mosquitoes during the rainy season in northwestern Liberia. The mosquitoes were then taken to the lab to be tested for LF.

Abakar Gankpala, Sightsavers’ research coordinator during the project, shares the challenges migration can cause in the fight to eliminate NTDs. “If you live in a rural area and you’ve been consistently bitten by mosquitoes that spread LF, then you move to the city and are bitten by other mosquitoes, they will pick up the LF parasite from your blood and spread the disease to others.”

Add the fact that parasitic worms that cause LF can live in humans for a number of years, if people in urban areas test positive it is not necessarily an indication that LF is being transmitted there.

Always ready to overcome a challenge, Sightsavers’ Liberian research team came up with two methodologies to determine if LF was prevalent in Monrovia: school-based screenings of students who were born in the city, and collecting and testing mosquitos to find out if they carry the parasites that cause LF.

“If you move to the city and are bitten by other mosquitoes, they will pick up the LF parasite from your blood and spread the disease to others.”

A man sits at a table with research forms in front of him, while a woman standing next to him shows him some documents. A group of primary school children wait by the table watching.
Lab technician Anthony took blood samples from students at a school in Johnsonville, near Monrovia, to check for LF.

Step 1: training community health workers and screening school children

Before the screenings for students began, a blood collection training session was organised for community health workers. Its purpose: to teach them how to collect informed consent from students and their parents, safely and accurately conduct the tests (taking a pinprick of blood and applying it to a filarial test strip), read the results, and label and manage the samples.

Over the course of six months, more than 1,800 children aged nine to 14, who were born in Monrovia, gave a blood spot sample to find out if they were infected with the parasites, also known as filaria, that causes LF. By focusing on children who had spent their lives in the city, researchers could identify whether transmission was happening locally.

Community health worker Rob Dennis, who helped to carry out the screening at a school in Johnsonville, near Monrovia, said: “We’ve tested 14 children. They’ve come with their parents to be tested, and so far, no one has tested positive.”

“We’ve tested 14 children, and so far no one has tested positive.”

A health worker wearing surgical gloves takes a blood sample from a school student.
To conduct the test, health workers took a pinprick of blood and applied it to a filarial test strip.

In total, 106 school-based screenings were carried out across the four health districts in the city, and results showed that 96 students tested positive. All the children who had positive results were referred for treatment. If caught early, LF can be treated with a combined dose of two medicines given to people every year to people in high-risk areas.

Abraham Nyenswah, the national lymphatic filariasis coordinator for the Ministry of Health in Liberia, says: “The research is highly significant to the elimination process of lymphatic filariasis. It will inform us if there is ongoing transmission of the disease or no transmission at all, and it tells us whether we’re making significant progress through mass drug administration or if we need to change our implementation strategies.”

The results of the school-based screenings did identify a prevalence of lymphatic filariasis in Monrovia, and this has helped the Ministry of Health to determine that mass drug administration to treat the disease is needed in the area.

“The research tells us whether we’re making progress or if we need to change our strategies.”

A large group of smiling children gather for a group photo outside their school.
By testing school children who have spent their lives in the city, researchers were able to see if LF was being spread locally.

Step 2: Collecting mosquitoes in the community

The second element of the team’s research was to find out whether mosquitos in the community carry the parasite that spreads LF. Mosquitos have short lifespans (less than three months), breed locally and tend to remain in the area where they hatch. This means that if urban mosquitoes have the parasites, people are potentially at risk from local transmission.

Over a six-month period, the research team set up 267 mosquito traps at community members’ homes across two health districts in Monrovia. The research was conducted during the rainy season, as it provides the perfect climate for mosquitos to breed.

Entomologists and community researchers in designated communities were charged with putting traps in and on houses and then collecting the mosquitos.

“It’s been very challenging because it’s the rainy season and there’s lots of flooding.”

Rose Washington, an entomologist from the Liberian Ministry of Health and researcher on the project, shared her experiences. “It’s been very challenging because it’s the rainy season and there’s lots of flooding. I have to wear rain boots and stand in deep water to collect the mosquitoes. But the community has been so friendly and welcoming, and they are happy to be part of the project.”

In the Kpelleh district of Monrovia, Joe is one of many community members who agreed to have a mosquito trap attached to his house. “Before this project I saw people with LF, but I didn’t know how they got it,” he explained. “It will be beneficial [for us to take part] because the mosquitoes can bring diseases to our communities.”

Joe smiles as he looks off-camera.
Joe is one of many community members who had mosquito traps added to their house.
Four researchers work at a large table with samples and papers in front of them.
Entomologists from the Liberian Ministry of Health analysed mosquitoes on the same day they were collected.

Step 3: Testing mosquitoes in the lab

Once mosquitoes were collected from their traps, they were brought to the lab for identification and testing. “The mosquitoes are brought in alive, but the first thing we do is put them to sleep: we don’t want them to escape,” explains Abakar. “Then the researchers categorise them.”

First, the researchers separate the mosquitoes by gender, as only females spread LF by taking blood. The females are then further separated by abdominal state: gravid, semi-gravid, fed and unfed. Next, they are inspected and tested to find out if they are carrying the parasite that causes the disease.

“This research is special: it’s going to build capacity for Liberian entomologists and lab technicians because everything can be done here,” says Abakar. “We’ve trained people who can now confidently identify a mosquito, its species, whether it’s fed or unfed, and then how to process the mosquitoes and test them for the disease.”

The good news is…

Parasites were not found in captured mosquitos during this project, indicating that the risk of LF spreading locally in Monrovia is low. However, the fact that there is a prevalence of LF among a number of city-born students means that continued screening and mass drug administration needs to happen here.

More follow-up work is being planned by the Sightsavers team. The research already undertaken is being used to inform the development of a standardised and recommended protocol for taking similar action within other urban areas of the West African region where there are growing urban populations and ongoing migration from rural areas.


Images © John Healey

A close-up of a man's hands inspecting mosquitoes under a microscope.
In the lab, mosquitoes are separated by gender, type and abdominal state before being tested.
A group of male and female researchers gather around a table where there are papers and microscopes.
The research team at the lab following mosquito collection.

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