Naegleria fowleri: Summer’s silent scourge

This is the second of two posts from participants in Baylor College of Medicine's National School of Tropical Medicine Summer Institute program with Baylor University. View the first post.

Summer is in full-swing, and down in the southern United States, that means blistering heat and unrelenting sunshine. Before escaping the heat in a favorite lake or river, it is important to be aware of the risks of Naegleria fowleri. N. fowleri is a free-living amoeba, or single-celled organism, that lives in soil and warm freshwater bodies around the world, including lakes, rivers, ponds and hot springs. Unfortunately, infection with N. fowleri can cause a life-threatening condition known as primary amebic meningoencephalitis (PAM). PAM causes swelling of the brain and destruction of brain tissue. As a result, N. fowleri is often referred to as the "brain-eating amoeba." However, swearing off favorite freshwater activities is not necessary. PAM is rare with fewer than 10 confirmed cases a year in the U.S. Given the severity of the condition, conduct a risk assessment before engaging in summer water activities.

How does infection with N. fowleri occur?

Infection from N. fowleri involves the passage of the ameba through the nose cribriform plate. PAM occurs when water contaminated with N. fowleri is forced through the nasal cribriform plate (i.e., following diving into warm freshwater bodies), attaching to the olfactory nerve and traveling into the brain. But that's not all. Infections have been known to occur after using a sinus rinse, a device commonly used to reduce nasal congestion, with non-sterile water. Importantly, oral ingestion of water containing N. fowleri does not cause infection, and N. fowleri cannot be transmitted from person-to-person, according to the Centers for Disease Control and Prevention.

How can you avoid N. fowleri?

It is important to acknowledge again that infection with N. fowleri is exceedingly rare, and steps to reduce the risk of infection are straightforward. Staying away from freshwater when water temperatures are warm is an option. When in warm freshwater, avoid submerging your head in shallow water areas. Specifically, avoid forceful submersion (i.e., diving or jumping into water) to prevent translocation of the ameba through the nasal passage. Additionally, inspect the freshwater source for cloudy, silty water which may indicate microbial contamination. At home, when rinsing sinuses with a device, use tools that have been sterilized and distilled and sterile water to avoid pushing contaminated water into the nose.

How do I know if I've got PAM?

PAM is a rapidly-progressive neurological condition with symptoms starting within five days of infection. Initial symptoms of PAM include headache, fever, nausea and vomiting. Later symptoms progress to stiff neck, confusion, loss of balance, seizures, coma and ultimately death, according to the CDC. Unfortunately, clinical outcomes are poor. PAM has a fatality rate of more than 98%, and globally, there have only been seven survivors out of 318 confirmed cases. Death typically occurs between one to 18 days after first symptoms occur.

What do I do if I have been exposed to freshwater and now have PAM symptoms?

The first step is scheduling a medical appointment or going to the emergency room. Given the severity and rapid progression of N. fowleri infection, an early diagnosis is crucial. Diagnosis is difficult, and only a few labs globally can identify N. fowleri. However, it can be done. The CDC's Free-Living and Intestinal Amebas (FLIA) lab performs a combination of diagnostic assays, including molecular tests (polymerase chain reaction or PCR), immunohistochemistry and immunofluorescent staining and direct visualization of the organism in cerebrospinal fluid for N. fowleri.

I've got the infection - what now?

The preferred treatment for N. fowleri infection is liposomal amphotericin B, an antibiotic effective against a wide range of fungal infections. However, most treatment regimens emphasize the importance of using a combination of drugs, including liposomal amphotericin B, rifampin, fluconazole and miltefosine for approximately four weeks, the CDC reported. More robust clinical trials to evaluate the efficacy of combination therapy are needed; however, since the infection is so rare, these large-scale clinical trials have not been conducted.

The future of PAM and N. fowleri

Despite its low prevalence, infection with N. fowleri due to exposure to warm freshwater can have serious consequences. Climate change, including the warming of freshwater bodies, may increase the risk of N. fowleri infection and PAM in the future. N. fowleri infection and PAM have been reported as far north as Minnesota. Given the importance of early diagnosis, diagnostic ability and access to diagnostic assays should be improved. While the U.S. has reported the highest number of cases of N. fowleri, this statistic may be misleading as it shows a lack of available diagnostic assays in resource-limited areas around the world. This contributes to underreporting of global cases. In low-resource areas, N. fowleri infection is commonly missed, leading to a lack of targeted therapy and resulting in poorer outcomes for patients. Even with treatment, the survival odds remain low. Gaining a greater understanding of effective treatments and encouraging community education on human risk factors of N. fowleri infection serve as key steps in reducing PAM globally.

If you have concerns about a case of primary amebic meningoencephalitis (PAM), contact the CDC Emergency Operations Center at 770-488-7100.

By Jack Tebbutt

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