Saturday, April 21, 2012

Leishmania mexicana

     Today, I helped a friend attempt to catch woodrats (Neotoma micropus) and sandflies. She is working on her thesis....she's on the hunt for a particular parasite.  This parasite isn't a big problem in this area, but it is a problem in other areas. She's looking to see if it is here...and for good reason. In 2007, dermatologists in Dallas, Texas diagnosed NINE cases of cutaneous leishmaniasis...but we will get to that later. First things first, taxonomy!

L. mexicana Promastigote
     This parasite is a protist withing the excavate clade. Leishmania in the phylum Euglenozoa....which contains the commonly known free-living Euglena; an elegant example of a flagellate often found in pond scum.  Leishmania belongs in class Kinetoplastida and order Trypanosomatida alongside other trypanosomes such as Trypanosoma cruzi (which causes Chagas' disease) and Trypanosoma gambiense (which causes sleeping sickness).  The genus, Leishmania, has many pathogenic species. The Leishmania donovani species complex causes the most terrible form of this disease, which is known as visceral leishmaniasis (a.k.a. "Kala-Azar"). Leishmania braziliensis causes mucocutaneous leishmaniasis. Many other species cause cutaneous leishmaniasis, but only one is found in the new world....this is Leishmania mexicana.

L. mexicana Amastigote (in green)

Life Cycle
     The life cycle of this organism involves two body forms. An infected female sandfly takes a blood meal from an uninfected human. During this feeding, Leishmania mexicana promastigotes make their way into their new host's blood stream. As the body's immune system goes to work, macrophages ingest the promastigotes. While inside of the macrophages, the promastigotes transform into an amastigote form (the green ovoid organism in the picture on the right). The amastigotes reproduce within the macrophages and other cells. Then, along comes an innocent, uninfected female sandfly hungry for a delicious blood meal. As the sandfly sucks the blood of the infected human, she ingests the infected macrophages. Once inside of the sandfly, the amastigotes burst from the macrophages and transform into the promastigote stage within the midgut of the sandfly. Then the promastigotes migrate to the proboscis of the fly, where they await for the fly to have its next blood meal...completing the life cycle.

Cutaneous and Diffused Cutaneous Leishmaniasis
     These forms of leishmaniasis are less dangerous than visceral forms. The cutaneous form manifests as ulcers at the site where the sandfly bites its host. In this form, the amastigotes don't spread to other areas. The ulcers show up anywhere from a few days to a few months post-infection. This form usually heals on its own given time. 

     The diffused form of cutaneous leishmaniasis only manifests after the amastigotes cutaneously spread due to defective immune cells (such as T-cells). This can cause sores and ulcers all over the body that do not respond well to drugs. Penstostam is a drug that is often used in the US to treat this form of leishmaniasis. Penstostam works by inhibiting ATP synthesis.  There is ongoing research into vaccine development that works against the promastigote life stage.
     These diseases are typically only found in Central and South America. However, there have been cases reported right here in Texas. Cases began appearing in South Texas years ago, but it wasn't until the last few years that it was reported further north. In 2007, nine different cases were reported from around the Dallas area. Researchers believe that sandflies infect woodrats as they search for blood meals. These woodrats then become what we call a "reservoir". This means that they are able to serve as a sort of storage space for the propagation of the Leishmania mexicana protozoans without a human host. This keeps the protists circulating in the sandflies, making them potential disease vectors.

Moral of the Story
     There is strong evidence to suggest that if sandflies and woodrats are present, so could be present this parasite. People in rural areas are more at risk despite the sandflies' recent movements into more urban areas. Using insect repellants will reduce the risk of being bitten, so keep that in mind the next time you head out to the boonies! :p

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!