By Fr. Tom Streit, Director–University of Notre Dame Haiti Program, on behalf of those working on LF in Haiti
The program to eliminate lymphatic filariasis (LF) is the largest public health program you never heard about. In fact, most people who work in global health are shocked when they hear that more than 500 million people in over 40 countries were treated last year. That is an impressive number, but it still represents less than one half of the total number that will need to receive annual treatment (for five or more years) if LF is to be eliminated.
These parasites are transmitted by mosquitoes and are best recognized as a cause of elephantiasis. Adult worms live in the lymphatic vessels in humans and the female worms release motile stages called microfilaria into the blood. It is this stage that is picked up by mosquitoes when the mosquito takes a blood meal. After maturation in the mosquito, a process that takes one to two weeks, the larval stage is ready to infect another person during a blood meal. For most people, the infection has no apparent symptoms, but some are incapacitated. People with elephantiasis or men with scrotal swelling (also called hydrocele) can be so disabled by LF that they are unable to work or support their families. They are often ostracized in their communities because of the fear and misunderstanding about the cause of the disease.
As scientists, we continue to be fascinated by these parasites at the same time we have committed to getting rid of them. I recognize the paradox here, but if we can reduce the suffering associated with LF and other NTDs, we should, even if it leaves the scientific community with a number of unanswered questions, including a few I’d like to share with you.
In many parts of the world, the microfilaria stage of the parasite is only found in the blood at night – when the mosquitoes are most likely to take a blood meal. How does this work? What signals is the parasite using to do this?
Why do only a relatively small percentage of people get elephantiasis? We know that elephantiasis tends to occur in families, but why? Is this related to genetic effects, environmental conditions or a combination? Why does the parasite disappear from most of these people as the swelling develops?
On the opposite side of that question, why are some people more likely to acquire infection and maintain microfilaria in their blood for years or decades? How does the worm avoid the host immune response? For LF and many infections, we believe that children are more likely to acquire infection if their mothers were infected during pregnancy. How does this affect other immune responses?
In truth, we don’t need to know the answers to these questions to eliminate LF. China and Korea have succeeded; we also know that LF disappears on its own following economic development as it did in the United States. We are now faced with an historic opportunity – as with small pox and now polio and guinea worm – to make a conscious effort to remove the threat of LF permanently. I, for one, can live with unanswered questions.
