Saturday, April 14, 2012

Naegleria fowleri

So for my first post, I thought it would be appropriate to start with something small. One of my friends studied this organism for her thesis work and her defense is next it seemed like a great place to begin!

      This protozoan is a member of phylum Percolozoa because they are able to transform between amoeboid, flagellate, and encysted stages. These organisms also belong to class heterolobosea, which is closely related to the euglenozoans.  They belong to order schizopyrenida and family vahlkampfidae. The genus Naegleria was named after Mathiew Naegler, a zoologist from France.

Life Cycle
      The cysts of N. fowleri form from the trophozoite stage under harsh conditions, such as overpopulation, limited availability of food, cold temperatures (below 10°C), desiccation, etc.When temperatures rise (especially after they reach 42°C), the free-living, reproductive life stage (the trophozoite) undergoes binary fission. The trophozoite moves via pseduopodia and feeds on bacteria within freshwater lakes, rivers, or hot springs. When these trophozoites become exposed to changes in ionic concentrations of their environment, they transform into the biflagellate body form within minutes of said exposure.

     This organism may opportunistically infect humans by entering the nose of unwary swimmers while existing in the flagellate stage.  Most often, significant increases in temperature and/or a reduced amount of rainfall can induce pre-existing trophozoites to enter into the flagellate form. After entering a human host, this amoeba travels to the brain and proceeds to inflame the meninges.

Primary Amoebic Meningoencephalitis

      PAM was first documented in 1965 from Austrailia.  The causative agent was not identified until 1968. Between 1963 and 1965, 16 cases were reported from Usti nad Labem in the Czech Republic. The amoeba finally was given the name Naegleria fowleri in 1970. Recent cases include a 7-year-old girl from Stillwater, Minnesota in 2010 and a 16-year-old-girl from Mims, Florida in August 2011. Two individuals from Louisiana contracted the parasite in December 2011 after inhaling infected tap water.  These individuals were using a neti pot.      
      This disease affects the central nervous system. It begins with N. fowleri entering the nasal cavity of a human host and attaching itself to the olfactory nerve. It then makes its way into the olfactory bulbs within the forebrain and begins to feed on nerve tissue and to multiply. 3-7 days post infection, patients begin having trouble properly identifying smells (a symptom called "parosmia") and eventually lose the ability to detect odors at all ("anosmia"). This will often lead to an inability to detect the basic taste sensations (known as having "ageusia"). As the olfactory bulb nerve cells are eaten, necrotic lesions begin to develop. 
      The infection quickly progresses to the rest of the cerebrum, which causes an inflammation of the meninges. During this time, patients experience headaches (a.k.a. "cephalgia"), stiff neck muscles, nausea, vomiting, seizures, delirium, and eventually coma. Once the infection spreads to the brain stem and begins feasting on the cells of the medulla oblongata (about 14 days post-infection), death usually results from respiratory failure.
      Infection by this protist is extremely rare and this disease has a mortality rate of approximately 97%. Due to the rapid progression of the disease and the symptoms that are easily mistaken for symptoms of other problems, positive diagnosis is difficult. To diagnose, microbial culturing from CSF is needed, but if PAM is suspect, treatment will often begin prior to confirmed diagnosis. The battery of antiamoebic drugs that are typically administered are somewhat dangerous taken together and this is often not a pleasant experience for the patient.

Moral of the Story
       Don't swim in stagnant water, especially during droughts or particularly hot summers! And always heed are NOT immune to Naegleria infection!

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