Microscopic Worms in Mosquitoes: Lymphatic Filariasis

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This post in the Neglected Tropical Disease series will be exploring a disease called Lymphatic Filariasis. Check out my previous blog post here to find out what a Neglected Tropical Disease is and to learn more about this series.


Lymphatic filariasis is a parasitic disease caused by a roundworm that is spread from person to person by mosquitoes. A worm being carried by something already as small as a mosquito seems inconceivable and almost alien, but these worms are microscopic. If you were to take the worm out of the mosquito, you would not be able to see it with the naked eye, only under a microscope with sufficient magnification can it be seen. There are three types of worm that cause lymphatic filariasis, these are called Wuchereria bancrofti, Brugia malayi and Brugia timori. Wuchereria bancrofti are mainly found in Sub-Saharan Africa, whilst Brugia malayi are restricted to South and South East Asia.

The worm has different stages throughout its development, this is a similar concept to humans developing from baby to adult. The stage of the worm which the mosquito carries is called the larvae, this form enters the human body when the mosquitoes bite. The different types of worms are carried by different species of mosquito inhabiting both urban and rural areas, highlighting the potential geographical distribution of the disease as high. Once this larvae form is inside the human body, they develop into adult worms which will live in the lymphatic system, hence the name of the disease. The lymphatic system comprises tissues and organs that help rid the body of toxins and waste. Adult worms can live up to 10 years inside a human, often without humans presenting any external clinical symptoms so infections go undetected. Adult worms release microfilariae, which are ultimately the offspring of the adult worm. It is at this stage where mosquitoes can also pick up infections from humans when they bite. The mosquito will pick up the microfilariae offspring in the blood when they bite infected humans. A mosquito can give humans the infection when they bite, but it can also acquire the disease when they bite infected humans, this cycle of mosquito-human-mosquito transmission shows how the disease can spread easily with the help of the versatility of a mosquito.

The photographs I have taken below show the view under a microscope (x100 magnification) of human blood samples containing the Wuchereria bancrofti worms in the microfilariae stage. It is at this stage of the worm’s development that an infected person can be diagnosed. Blood samples of suspected infected people should be taken at night, as this is when the microfilariae are most active in the bloodstream, thus are most likely to be detected. The worms are not actually purple, this is just the result of them being stained in order to view them under the microscope. 

The dark purple dots inside the worm are called the nuclei, this is the scientific term for the genetic material. Genetic material controls everything about the worm, from its appearance to its behaviour.

You may have to squint to spot this, but the very pale string you can see coming off the tails of the worms, indicated within the blue circles, are the sheaths. The sheath covers the entire worm, but in Wuchereria bancrofti worms, the sheath extends beyond the tail, which is what is observed here. The sheath is very important for differentiating the types of worm, which is useful for diagnosis. The role of the sheath from the worm’s point of view is not yet known for certain, it could be for protection or to elicit a response against the human immune system to aid their survival

Only Wuchereria bancrofti are shown here, but the different worms have very subtle differences observed under the microscope. Brugia malayi tend to be slightly longer, and often have two distinctive nuclei at the very end of their tail. It is difficult to spot these subtle differences, but it is extremely important for identifying what type of infection a person has.


A common name for lymphatic filariasis, but discouraged due to the stigmatisation it holds, is elephantiasis. The main symptoms of this disease explain the reasoning behind this name, these include swelling of arms, legs, breasts and genitals. The swelling seen in this disease can be so severe that individuals can be permanently disfigured or disabled. Many other symptoms are associated with this disease, including extreme thickening of the skin, bacterial skin infections due to the swelling, and hernias. This disease results in physical and psychological problems, these will be explored in this paragraph, in addition to how poverty increases the severity of these associated problems.

A health worker demonstrating proper leg hygiene technique on a Lymphatic Filariasis patient. Management of the disease through hygiene practices will be explored further down in this post.

Photo credit: Caitlin M. Worrell, M.P.H
Content provider: CDC/ CDC Connects
Website: https://phil.cdc.gov/

The swelling can be extremely disfiguring, carrying social stigmatisation in many communities, with some viewing these disfigurements to be the work of witchcraft. Without education regarding these areas, it is understandable how many can come to these explanations. Women with disfigurements are less likely to marry, which in the culture of some communities can restrict many opportunities they are presented with later on in life. This stigmatisation could force someone out of their community, along with their sense of self-worth and stable mental health. The swelling can also be extremely disabling, often preventing people from going to work or carrying out the essential daily tasks of life. Without work, there is no income. Without income, there is no food. A lack of food can easily lead to malnutrition which can increase susceptibility to other infections due to a general lack of good health. A family may be entirely dependent on one person in their household to provide the necessities to survive, and if that person is now unable to work, the downward spiral into poverty can be quick and undiscriminating. This cycle of poverty is a recurring theme for these diseases, such as snakebite, which is explored in a previous blog post here. It seems that one change can rapidly change a whole family’s security, survival and lifestyle. If you have not been burdened with this disease directly, you can still feel the heavy weight of its impact, for example, if the head of the household can no longer provide, this responsibility must be passed on, as does the responsibility to care for those affected. Often, children will have no choice but to sacrifice their education in order to take over as head of their household. The effects of lymphatic filariasis has stripped many individuals of their already limited choice of lifestyle, and with this, freedom has also been taken from them.

You may be asking, how are these extreme symptoms managed, and could this reverse the devastating physical and psychological effects of stigmatisation that many are subjected to? Unfortunately, the cases of extreme swelling cannot be reversed by drugs, it can only be handled by amputating the affected limbs. Medical procedures on this scale require surgery and hospitalisation, possibly for an extended length of time. The risks involved are not softened by the guarantee of quality medical supplies or trained staff, a lack of funding often means a lack of essential medical supplies. The finances for travelling to the hospital are often not available for many, let alone the finances for the surgery itself and aftercare. As seen in the snakebite blog post here, life changing decisions must be made here. The decision to access the hospital at a financial cost to the individual and likely to their family, or, avoid this financial strain but endure the burdening effects of lifelong physical disfigurement and stigmatisation. The effects of surgery will still come with drastic lifestyle changes, including changes in work, responsibility roles and continual stigmatisation. Lymphatic filariasis causes ongoing psychological problems for those affected and those caring for those affected. These psychological effects can impact other aspects of life, causing more financial strain, which seems all too common in these diseases of poverty.


The risk of lymphatic filariasis revolves around the risk of being bitten by an infected mosquito. Preventing mosquito bites requires access to bed nets that are coated in a substance that kill insects, commonly called an insecticide. These types of nets are called insecticide-treated nets. This type of net is more effective than a normal net, as once the mosquito lands on an insecticide treated net, it will die. A normal net just prevents mosquitoes accessing people inside the nets, but the mosquito can easily fly off to bite someone else who is not under the net at that time. This explains how insecticide-treated nets offer community protection as well as individual protection. These nets are often expensive and distributing them to many people is challenging. Appropriate use of nets is imperative for their success, which means that education on how to use them must be given. There are many cases of incorrect use, such as utilising them for fishing, or for clothing construction. Mosquito repellents could be used in an attempt to ward off the mosquitoes, but these are also expensive, and to ask someone to coat themselves in a strong-smelling spray at all times is unreasonable and impractical.

Many mosquitoes dwell around standing water sources, these sources are also many communities’ sources of water. This congregation into a risk area for mosquito exposure is especially prominent in rural areas, often the poorer areas. However, this does not mean mosquitoes are absent in urban areas. Storing water in big containers is common in urban areas, and containers are very attractive to some species of mosquito. Any form of stagnant water is a welcoming site for a mosquito, and unfortunately, the means of accessing a continual and clean water supply that is not a breeding site for mosquitoes is not often possible. Coverings these sources, and the use of polystyrene beads that lay on top of the water thus creating a barrier, are simple but often inaccessible measures. If more developed water resource management were implemented in these areas, would this affect the level of lymphatic filariasis?

As seen in the photographs above, diagnosis of lymphatic filariasis is via microscopic examination. This can be a laborious process, requiring quality equipment, trained staff and plenty of time. This process must be undertaken at night, which is when the worms are active. As you can imagine, being waken up at night by a stranger who wants to take a sample of your blood will likely be met with suspicion and non-compliance. All these considerations will result in less people getting tested and treated, thus allowing more infected people going unnoticed, allowing mosquitoes to continue to pick up infections and pass it on.


The World Health Organization launched the Global Programme to Eliminate Lymphatic Filariasis (GPELF) in 2000. During 2000-2017, over 7.1 billion treatments were delivered to a targeted population of 900 million people. The Global Alliance for the Elimination of Lymphatic Filariasis (GAELF) was created in 2000 to support GPELF in fundraising, advocacy, communications and technical assistance. Both programmes rely on donations of drugs from pharmaceutical companies. In 1997, GlaxoSmithKline (GSK) agreed to donate one of the drugs for lymphatic filariasis, called albendazole, for as long as it is needed to eliminate the disease. In 1998, Merck & Co. Inc agreed to provide a different drug, called ivermectin, in Africa for as long as necessary. Different drugs and combinations of them are used for this disease, this is because if an individual infected with lymphatic filariasis has an underlying infection of one of the two diseases, onchocerciasis or Loiasis, the drug can cause serious side effects. Diagnosis of these co-infections, and an understanding of geographical distributions of infection, are necessary to stop dangerous drug reactions.

GPELF has two strategies of control:

1. Mass drug administration

This is the annual large-scale administration of the suitable drug combinations, often for prevention of infection in the first place rather than treatment of an active infection. This often must be sustained for years in order to fully disrupt transmission of this disease. Distribution and monitoring of this drug taking can be challenging, which can affect the success of these mass drug programmes. The role of distribution is often given to community drug distributors, these are individuals, often volunteers, in a community that are well-trusted. However, successful distribution relies on a lot of factors, such as timing of distribution to ensure the most amount of people will be available, and also how community drug distributors will be perceived by certain members of the community. Not accepting drugs from female drug distributors due to the gender inequalities in some communities can be problematic and forfeit the success of the entire drug programme. This reinforces the importance of integration of social culture and perceptions with health and disease understanding. They are constantly influencing each others’ success, highlighting how integrated communication is crucial.

2. Morbidity management and disability prevention

The disfigurements seen as a result of this disease cannot be reversed by taking drugs, which is why it is important that people affected have access to care and are provided with the knowledge on how to handle their swellings. This involves training health-care workers on how to educate the people affected about the importance of keeping the skin clean, exercising and elevating affected limbs. This offers a more holistic approach to the disease, recognising that life must go on, but it must go on in a way that allows the affected individual to be comfortable and confident in this completely new way of life.


Lymphatic filariasis is a disease that causes immense suffering, lifelong disabilities and impairs childhood growth. The disease’s promotion of poverty and stigmatisation can impair education and economic development. Lymphatic filariasis is on a path to elimination, but without the drug donations, the state of this path could have been completely different, and it still has this potential to regress. It is crucial that donations are continually given, and that the decrease in infections does not give us a false sense of security. A tiny mosquito has the power to completely flip someone’s life upside, without the opportunity for them to fight back. Something as simple as a net has the capacity to stop these lifelong devastations, with the burden falling on many others than just the individual with the infection. Next time you get an annoying, itchy mosquito bite, recognise that is the extent of it, often just a nuisance. Give a thought to those who are suffering from this debilitating disease at the hands of a mosquito.

Links to Organisations Currently Tackling Lymphatic Filariasis

Global Programme to Eliminate Lymphatic Filariasis

Global Alliance to Eliminate Lymphatic Filariasis

The A.WOL Approach

2 Replies to “Microscopic Worms in Mosquitoes: Lymphatic Filariasis”

  1. Thank you, Lucy. I appreciate your thorough research on this health issue. But above all, I can see your caring heart. The world is a better place with scientists like you.

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