Monday, 22 August 2011

Naegleria fowleri, Terror of Swimmers

It’s two thirds of the way through a long hot summer (in some places) and numerous swimming holes have had lots of time to warm up to temperatures well above average. Tragically, this sometimes results in deaths due to infection with Naegleria fowleri, especially in warmer regions such as the southern United States. Naegleria, sometimes referred to as the “brain-eating parasite,” is an environmental amoeba that can, given the opportunity, gain access to the human brain through the back of the nose.

Naegleria Thrives Where Water is Warm

Naegleria does not habitually parasitize humans, but it does multiply in warm waters, and if swimmers draw water up the nose, infection can follow. (This year, one victim reportedly infected himself using a neti pot – a device used to rinse the sinuses.) Once infected, very few people survive the dreadful illness that Naegleria causes. Victims, of course, are typically those who enjoy water sports and games – the young, fit, and healthy.

Deaths due to N. fowleri are often widely reported, especially now that we have the internet. After such a death, people call for disclosure of the bodies of water involved, more public education, and surveillance. This is entirely understandable, but these demands really do miss the point. Naegleria is an environmental organism, widely distributed in nature, and well known for multiplying in warm bodies of water. It could be in any warm water, even the stuff in your hot water tank (as in the neti pot story). We can’t eradicate it, or even pinpoint where it will turn up next except in the most general terms.

If you really want to avoid this risk (and it is a small small risk) don’t swim in water warmer than 80F (26.7C). Never draw warm water up your nose unless it has been sterilized. If there is a risk of drawing water up the nose, use nose plugs or a nose clip.

Naegleria Deaths in Perspective

The reality is that any activity carries a certain risk, even sitting at home. For comparison, the number of fatalities from N. fowleri in the United States in the decade from 2001 to 2010 is thought to be about 30, an average of three per year:

  • In that same time period, National Geographic reports that more than 400 people were killed by lightening.

  • In 2004, an average of nine people accidentally drowned per day in the United States (Poseidon).

  • In 2004, almost 4000 people died in fires, mostly residential.

  • Each year, more than 33,000 people are killed in automobile accidents in the United States (NHTSA).

Deaths due to N. fowleri are quick, horrifying, and tragic, but this disease shouldn’t be blown out of proportion. It’s rare. Exercise reasonable caution while swimming (submerged hazards, drowning, pathogens, dangerous aquatic animals etc.) and enjoy the summer.

Tuesday, 16 August 2011

Is Babesia Spreading or Not?

Babesia microti was first recognized as a potential cause of human infection in New England in 1969. Before this, human cases of babesiosis involving other Babesia species were recognized in other places, chiefly Europe. The appearance and persistence of Babesia microti have been associated with high deer populations, increased human contact with the deer tick, Ixodes scapularis, and the presence of Lyme disease.

[caption id="attachment_316" align="alignleft" width="300" caption="Ixodes scapularis, image by Stuart Meek"][/caption]

In 2003, a paper published in the American Journal of Tropical Medicine and Hygiene noted “Human babesiosis generally is detected in sites where Ixodes ticks are endemic only after Lyme disease has become well established” (Krause et al, “Increasing Health Burden of Human Babesiosis in Endemic Sites," 68(4)). Why?

It’s tempting to explain away the late appearance of babesiosis by saying, well, physicians aren’t familiar with it, no one is looking for it, and most cases are mild anyway, so it’s simply being missed. As well, no one’s collecting data on diagnosed cases, so the incidence is unknown.

A current article published on discusses the work of Stephen Rich at the University of Massachusetts Amherst's Laboratory of Medical Zoology (Clark, “Much to Learn About Babesia’s Spread”). Rich’s research on Ixodes scapularis suggests that Babesia microti is spreading inland at a much slower rate than Borrelia burgdorferi, the organism that causes Lyme disease.

Rich’s work tells us that the organism truly is not well established in new locales – there’s not as much of it there. This likely explains why cases of babesiosis lag behind cases of Lyme disease, but it still raises a big question mark. If ticks and Lyme are spreading, why is Babesia not spreading just as quickly? The answer isn’t clear, but it appears that something is slowing down transmission of Babesia from host to host.

Rich doesn’t say that Babesia is absent in places where ticks and Lyme have appeared, he says there is a “much lower incidence” (qtd. in Clark). I suspect that incidence will rise over time – it may take years – and eventually make babesiosis a significant health concern over a much larger geographical area. I hope surveillance and medical knowledge stay ahead of it. If nothing else, the risk of contamination of the blood supply should fuel increased interest in this organism.