Parasite profile: The "brain-eating" Naegleria fowleri

Naegleria fowleri is a parasitic amoebo-flagellate that infects humans, causing severe illness and in many cases, death. This single-celled protist can be found in warm freshwater bodies, soil, and various contaminated water sources.

 Photo credit: www.soakersforum.com

Life Cycle


Naegleria fowleri can exist in three different forms during its life cycle: a cyst, a trophozoite, and a flagellate. The cyst is environmentally resistant and can protect the parasite during periods of poor environmental conditions. Once favorable conditions return, the parasite excysts as a trophozoite where it feeds and reproduces via binary fission. The trophozoite can then go on to the encysted or free-swimming flagellated form.

Life cycle stages for  N. fowleri from left to right: Cyst, trophozoite, flagellate. Photo credit: Wikipedia

How do people become infected?

Humans can become infected with N. fowleri when swimming in lakes, ponds, or untreated swimming pools, playing water sports, or even when irrigating sinuses with contaminated water. In addition, it is purported that inhaling viable cysts in dust can also lead to infection. Once the parasite contacts the nasal epithelium, it travels up the nasal mucosa and to the brain through the olfactory nerves.

Photo credit: Centers for Disease Control and Prevention

Symptoms, diagnostics, and treatment

    

Once the parasite enters the brain, it causes primary amebic meningoencephalitis (PAM), which is fatal in almost all cases. 

The onset of PAM is characterized by the following symptoms:

-fever

-headache

-changes in sense of smell or taste (due to destruction of the olfactory bulbs)

-stiff neck

-sensitivity to light

-changes in mental status

-seizures

-coma

-death  

Cerebrospinal fluid or tissue samples may be collected and analyzed for the presence of trophozoites. Treatment usually consists of administering high doses of amphotericin B and miconazole, although it is suggested that the rapid progression of infection makes successful treatment very difficult. As such, patients exhibit a high mortality rate.

Find out more about Naegleria fowleri:

Centers for Disease Control:
http://www.cdc.gov/parasites/naegleria/

National Society for Biotechnology Information:
http://www.ncbi.nlm.nih.gov/books/NBK7960/

Medscape:
http://emedicine.medscape.com/article/223910-overview

Zombifying flies and their honeybee hosts

Honey bees around the world have been dying at alarming rates, creating widespread concern and bafflement among both public and scientific communities. In the United States, symptoms of these impending declines are collectively referred to as Colony Collapse Disorder, or "CCD". CCD is primarily characterized by hive abandonment, where no or few honeybees are present in a hive even though a live queen remains.  While many factors contribute to bee declines such as mites, viruses, bacteria, fungi, and pesticides, Dr. John Hafernik, a biology professor at San Francisco State University, discovered another contender by accident: the parasitoid fly Apocephalus borealis. With the help of colleagues and his graduate student Andrew Core (the lead author), the team worked to figure out this mysterious host-parasite relationship. Recently, their fascinating findings were published in pLoS one.


It turns out that female A. borealis flies will locate honeybee hosts and land on them, depositing their eggs or "ovipositing" them into the bee's abdomen. The fly larvae develop inside of the bee and approximately seven days later they emerge, killing the bee in the process. This is very reminiscent of the movie "Aliens" isn't it?

The parasitoid fly and it's honeybee host. A) An adult female Apocephalus borealis fly. B) A female A. borealis fly deposits eggs into the abdomen of a honeybee (note how small the fly is). C) Two A. borealis fly larvae exiting the host. Photo credit: Core et al. 2012.

The even more curious thing is that the parasitized bees exhibit very unusual behavior before fully succumbing to the parasites. They abandon their hives at night; healthy bees usually leave their hives during the day to forage. They wander about aimlessly in circles, appearing disoriented and unable to properly balance. Moreover, the bees become attracted to light at nighttime. Core and colleagues suggest that the parasites may manipulate the light sensitivity or circadian rhythm of their hosts in some way, but more work is needed to fully investigate these possibilities.


The troubling realization from all of this is that honeybees usually occur in high densities, and colonies are often found in close proximity to each other. These conditions could make it very easy for fly populations to boom and further decimate honeybee populations that are already in decline. Honeybees are crucial for the pollination of many plants and agriculturally important crops, and for the production of their highly prized honey.  Research conducted by groups such as Core and colleagues is vital to the preservation of these important insects.

Find out more about colony collapse disorder:

USDA Agricultural Research Service

http://www.ars.usda.gov/News/docs.htm?docid=15572

Environmental Protection Agency:
http://www.epa.gov/pesticides/about/intheworks/honeybee.htm


Bromenshank et al. 2010:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013181