L & R: Trophozoites of N. fowleri in brain tissue, stained with H&E. Center: Ameboflagellate trophozoite of N. fowleri. Credit: DPDx
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The famous adage, retold to almost every beginning medical student, is that if you are in Central Park, and you hear hoof beats coming up behind you . . . think horses . . not zebras.
Simply put, doctors should always seek to rule out the most likely diagnoses first, not some obscure and exotic disease.
Of course, every once in awhile you run into a zebra.
Among the rarest of the rare diseases that a doctor might encounter in the United States is a form of meningitis caused by infection with the Naegleria fowleri parasite.
Dubbed the `Killer Amoeba’ or `Brain Eating Amoeba’ by the press - only 32 cases have been reported in the United States over the past decade.
As rare as it is, this week we’ve seen media reports of two suspected cases (one in Florida, one in Virginia) of PAM (Primary Amoebic Meningoencephalitis) likely due to this parasite.
First described in 1965 by Fowler & Cutler of Australia, more than 140 cases have since been diagnosed worldwide.
Most occur in young children or teens exposed while swimming along the bottom of warm, often stagnant fresh water lakes or streams, although several years ago N. fowleri contaminated tap water in Karachi, Pakistan may have caused 13 cases over 18 months.
With no effective treatment, tragically survival is exceedingly rare.
For media reports on the two infections this week, you can visit:
Test results expected Monday on whether Courtney Nash was killed by an amoeba
Millions of people swim in waters that may carry this amoeba every year, and only 2 or 3 people become infected. So the odds of acquiring this infection are extremely low.
But the Florida Department of Health has some safety advice on how to avoid this parasite.
Photo Credit – Florida DOH
For more information on the Naegleria parasite, you can visit the CDC’s Naegleria webpage.
A few excerpts from the Naegleria FAQ follow:
What are the symptoms of Naegleria fowleri infection?
Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.
Initial symptoms of PAM start 1 to 7 days after infection. The initial symptoms include headache, fever, nausea, vomiting, and stiff neck. Later symptoms include confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within 1 to 12 days.
What should I do if I have been swimming or playing in freshwater and now think I have symptoms associated with Naegleria fowleri?
Infection with Naegleria fowleri is very rare. The early symptoms of Naegleria fowleri infection are more likely to be caused by other more common illnesses, such as meningitis. People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting, particularly if they have been in warm freshwater recently.
To put the risks in perspective, over the past 10 years only 32 infections were reported in the United States, while between 1996 and 2005 there were roughly 36,000 fatal drownings.
Still, if you are swimming in warm, fresh water this summer, it is worth being aware of the risks and heeding the advice offered by the Florida Department of Health.
