Catching the urban mosquito: how our research fights NTDs

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.

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.

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.”

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.

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.”