Lymphovenous Canada: Dr. Maclean talks about lymphatic filariasis in Canada

I've been at Montreal Hospital for 40 years. I started the McGill Centre of Tropical Diseases about 20 years ago. My motto is: if you hang around long enough things will eventually happen.

I've always been a traveler. I got a fellowship to work in Zambia as a medical student and that's what started my interest in tropical diseases. I got a degree in tropical medicine in London, England. After London I was in Japan for a year and in Malaysia and Indonesia for a couple of years after that. I was in Kenya. I worked on a number of projects with the World Health Organization in Burma.

While I was abroad I was affiliated with Care Medical in Malaysia and Indonesia, the University of Hawaii in Japan and affiliated with McGill in Kenya. Since coming back to Canada I have worked at McGill. Now I leave the traveling to the younger members of my team and do most of my traveling within Canada. An individual who works in our Centre here is part of a center of excellence with the World Health Organization.

There are three major presentations for filariasis: lymphedema, scrotal swelling (hydrocoele) and Chyluria (intermittent leakage of intestinal lymph (chyle) into the renal pelvis and consequently into the urine) You tend not to see these symptoms in the same person. In China you tend to see more Chyluria than lymphedema; in Africa you tend to get lymphedema.

The percentage of individuals infected with lymphatic filaria who develop lymphedema is difficult to determine because edema usually occurs after the parasites can no longer be measured. It may be as high as 100% in males who will have scrotal findings and 10% in individuals who have been generally infected with filariasis. In both cases lymphedema develops long after microfilaria can no longer be found. The epidemiology is very complicated for lack of good markers of adult filaria presence. (These conclusions are based on Srividya A et al The dynamics of infection and disease in Bancroftian filariasis. Trans Roy Soc trop Med Hyg 85:255-259, 1991)

60-70% of our practice tends to be people who spend less than 2 years abroad. In those individuals - Canadians - I don't think we have ever seen lymphedema that has been permanent. We see other filariasis more frequently - the ones which involve skin and other subcutaneous parts of the body.

Lymphedema tends to occur in individuals who have lived in the tropics for years who have been reinfected many times. No one really understands frequency and infection and why the more infection you get the more likely you get scarring and therefore obstruction. The first thing is to get bitten by a mosquito with a filarial parasite which then develops into an adult and then the adult produces the microfilariae (offspring).

In the beginning we see people with inflammation around the groin. We used to see this in GI's from the Philippines in the second and first world war. Most of the people we see now have the microfilariae but they won't have overt signs of lymphedema. Does that mean they won't have scarring of the lymphatics? There is some suggestion that as time passes there is some scarring but not enough to produce lymphedema.

There seems to be a connection between the amount of time you spend in the tropics or whether you spent your youth in the tropics and whether you get lymphedema. Tourists - and those who spend less than a year in the tropics - tend not to get it. They sometimes get lymphangitis (an infection of the lymph nodes and lymph channels) which is the first inflammation caused by filarial. That rarely goes on to be a problem because it doesn't last longer than about five years and when they treat it with antibiotics it tends to go away.

Most persons wouldn't know they have it - but we would have a suspicion they have got it because they would have a changes of a marker in their blood cells which indicates they have a worm.

It could have any number of causes - it could be filariasis or it could be caused by walking on bare feet in silica (a mineral) in the sand or soil which gets taken up into the lymph nodes - then you can get lymphedema. Often we can't tell what was the cause - they are 30 years old - they had a history of walking barefoot in the tropics in an area where there is filariasis. Is there more filariasis there or is there more silica? Because the filarial are often dead and gone, leaving the scarring, we just don't know.

The tools are poor; the treatment is inadequate. The attempt has moved from treating people to preventing people from giving it to other people - cutting down the contagion of infection. If you get rid of the microfilariae people can't be infected by the mosquito. The mosquito can't then bite their child or somebody else in the house and give them filariasis.

There are three drugs available to us: Diethylcarbamazine - which is extremely hard to get in North America; Ivermectin, Albendazole, and maybe in the future we will use Tetracycline as well.

If you have a filarial living in your groin and your lymphatics - and you irritate it with a drug, you kill all of the microfilariae but you are not getting rid of the disease - it is the adult that is causing it. Are we just getting rid of microfilariae until this fellow dies of old age? Maybe. It may be good hygiene to ensure that the host doesn't get bacterial lymphangitis on top of it.

If you give someone a drug every six months to a year that kills all of the microfilariae and you do that for 5 to 10 years - that's what the WHO means by eliminating filariasis in the world. It is a preventive approach to filariasis rather than a therapeutic approach to filariasis.

There is some suggestion that if you keep giving Diethylcarbamazine or another drug every six months to a year you may decrease adults. There are no great studies on this.

The size of the adult worm could block the lymphatics. The fact that we see eosinophilia in the blood is a sign that the host does have an inflammatory response. We know that the host does have antibodies in the blood. Does bacteria live in the adult filarial - yes - is it the cause of the inflammation? It is part of it - it is a foreign antigen just like the parasite it. It looks like if you get rid of that bacteria the parasite stops producing babies. But it doesn't look like it kills the adult and nobody has shown that it is the inflammatory source in blocking the lymphatics. This is all to be resolved.

We are a lot better off though than we were five to ten years ago. The fact that the WHO is saying that they are going to try to eradicate lymphatic filariasis by 2020 means that they are going to concentrate their minds and resources to do this or concentrate their capacity to get other people to do it.

There is no good screening method for filariasis. Our tests might show that the adult worms are all dead and gone - but you might still have lymphedema as result of repeated infections. You might have to visit a plastic surgeon to reduce the volume. The same limited remedies are available to these people as it is for people who were born with primary lymphedema.

Because the adult worms have done their damage - maybe in their dying they have done as much damage as when they were living. A dead worm may create more of an inflammatory response than a live worm because a live worm wants to avoid inflammatory response because it might kill the worm. It has some kind of response to protect itself from the inflammatory response whereas the dead worm doesn't have one.

If the individual had it for 30 years and the tests for the worm show nothing - then the three drugs will not be helpful for them- although Diethylcarbamazine does have an anti-inflammatory aspect to it. You are screening for something that might not even turn into lymphedema.

We are not seeing an increase in lymphatic filariasis. People who are traveling the world aren't getting lymphatic filariasis. We are seeing malaria - but we aren't seeing an increase in lymphatic filariasis. Maybe we are missing it. And we are not seeing anyone getting sick later. All sorts of people get parasites - but they don't get the disease. Are people coming back to Canada, getting infections and getting antibiotics for it and not developing the condition? Maybe. Is that so bad? That's a good question.

We tend to concentrate on those parasites which tends to produce significant pathology and not spend it on people who might have a potential on pathology. There would have to be a significant climate change for lymphatic filariasis to become common in Canada and we would probably see other tropical conditions become serious first.

Note to reader: since this interview in 2003, new research undertaken by the Liverpool School of Tropical Medicine in the Lancet, June 18 suggests the effective use of an inexpensive antibiotic, doxcycline, which kills parasites through indirect means. "New Treatment found for advanced cases of lymphatic filariasis (elephatiasis)".