Maybe it’s the Halloween spirit and all the zombies I’ve been seeing everywhere, but this week I can’t help but write about two very different kinds of microbes that infect the brain.  I’ve already covered a virus that causes encephalitis and meningitis, and many bacteria can cause septic meningitis. However, the two organisms in the news this week that are causing fatal brain infections are neither a virus or bacteria, and much less common. The first is Naegleria fowleri, a warm-water dwelling amoeba; the second is Exserohilum rostratum, a nearly ubiquitous fungus found in the soil and on plants. These organisms normally live in very different environments but both have the unusual ability to infect the brain under very specific circumstances with fatal outcomes.

Click through to read more about these miniature brain-invaders and how they got into human brains in the first place.

Thankfully, neither of these are contagious conditions. They must be contracted in very specific and preventable ways, making these extremely rare cases.

The literal brain-eater of the two is Naegleria fowleri, a single-celled eukaryotic organism. This is an amoeba that lives in warm fresh -water bodies such as lakes, ponds, and hot springs and normally feeds on bacteria.

The chances of contracting this disease are slim, but certain cultural practices coupled with exposure to contaminated water can result in infection. The ongoing outbreak in Pakistan can be traced to the practice of ablution and the contact between the nostrils and contaminated water prior to prayer. If the amoeba was present in the water used for ablutions it could easily end up inside the nostrils and result in a brain infection.

Neuroinvasive N. fowleri occurs after water containing the amoeba gets into the sinuses, usually when swimming or during the use of sinus irrigators such as neti pots with non-sterile tap water. Once inside the sinus cavity N. fowleri is capable of breaching the olfactory mucosa and traveling along the neural tissues and into the brain. At this point the amoeba literally begins to eat your brain one cell at a time, bite by bite. It really is like a single-celled zombie. This action results in the development of primary amoebic meningoencephalitis (PAM) within 3 to 14 days post exposure. Sadly, those who develop this condition have only a 1-2% chance of survival. Even fully immune-competent persons are not protected and there is no definitive best practice for treating this disease; making the disruption of the transmission cycle critical for effective prevention of PAM.

Currently, 10 people have died as a direct result of PAM in the last 4 months in Karachi. However, this disease can easily be prevented by boiling water prior to allowing it to contact the sinuses. This is a critical step to take in areas where water is not chlorinated and may harbor a wide variety of different pathogens. Thanks to the identification of  N. fowleri  as the causative agent, people in this region have been advised to boil water before performing ablutions and hopefully no new cases will be reported.

The second exotic brain infection in the news is a nationwide outbreak of fungal meningitis in the United States. Current CDC data places the death toll at 12 persons with a total case count of 137. This outbreak has been traced to contaminated lots of preservative-free methylprednisolone acetate produced by the New England Compounding Center in Framingham, Massachusetts. A compounding center is a facility where pharmaceuticals are remixed and repackaged for sale to consumers who may need different formulations of drugs. However, these facilities are not under FDA jurisdictional review and therefore not subject to the same oversight in regards to laboratory conditions and safety as primary pharmaceutical manufacturing facilities.

What most likely happened is that during the repackaging process a fungus called Exserohilum rostratum got into the lot and contaminated these batches due to a breakdown in the sterile barrier between fungal spores and the steroid lots. This is not uncommon, as anyone who has ever tried to maintain aseptic conditions can attest.

Exserohilum is an extremely common mold and its spores are found in soil and grass. Normally we can contact hundreds of these spores a day and nothing bad happens. However, the steroids contaminated with spores were injected into the spinal column of patients, allowing the fungus direct access to the brain in an environment with a low immune response. Once in the brain it can cause meningitis, which is an inflammation of the lining of the brain that can be fatal if not caught early and treated. Fungal infections of the brain can also result in stroke as the fungal filaments invade small vessels in the brain and cause them to hemorrhage. There are approved anti-fungal agents such as Voriconazole or liposomal amphotericin B that can help treat this disease and a full recall of all infected batches was initiated last week, meaning that no more contaminated drugs are being administered to patients. However, those exposed must wait 1-4 weeks to see if they develop symptoms of fungal meningitis, meaning that the current case count will go up before this over.

These are both unusual brain infections but much more manageable than the brain-eating zombies we see in movies. The causative agent for both of these outbreaks has been identified and the proper steps needed to curtail new cases are underway, be it treatment or prevention. Despite this, the ubiquity of these organisms in our environment means that we must always be aware of the potential for new cases in at-risk populations.

Related articles

• What is the “brain-eating” amoeba found in Pakistan? (cbsnews.com)
• WHO: ‘Brain-eating amoeba’ kills 10 in Pakistan (sfgate.com)
• 13,000 may be at risk for fungal meningitis (vitals.nbcnews.com)