Monday, April 19, 2010

Secret Benefits of Thalassemia

I didn’t think it would happen, but I actually had a request for my next blog entry!

I can’t exactly tie this one into any overly religious, candy-laden holiday, but it happens to be one of my more favored parasites that are often mistaken for a virus… any guesses?



Malaria!

I’m not sure why, but I’ve heard many people refer to malaria as a viral infection, when it is actually a hemolytic parasite. Maybe it’s the fact that early malaria was associated with the air content of the prevalent environments (often murky or musty), which gave rise to the naming of malaria-- meaning “bad air”. This can be drawn to some viruses and their airborne, or aerosolized, transmission technique. Yet, we (as in…scientists, duh.) quickly discovered that malarial transmission was not through aerosolization of a virus, or from any direct contact. The only other similarity that the parasite genus Plasmodium has to common viral infections is the series of flu-like symptoms, such as fever and chills. In initial diagnosis trials, malaria was often misdiagnosed as an ongoing influenza with rhythmic symptom cycles. Seasonal influenza causes anywhere between 250,000 and 500,000 deaths annually, whereas Malaria causes approximately 1 million deaths annually. Needless to say, there are major differences.

So, now that we know Malaria is, in fact, a parasite, the details of its lifecycle can help answer many further questions (also, one specifically that has been requested).

Malaria is actually, roughly, an umbrella term that can be used to describe the disease in humans that is caused by four parasites: Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae and Plasmodium ovale.

Plasmodium ovale is regionally specific to West/sub-Saharan Africa, with a much lower prevalence (~5%) in places like the Philippines, Papua New Guinea and Cambodia. P. ovale is very specific in region and may seem to have a stippled appearance. P. ovale is also the only form of malaria that is fibronated.

Plasmodium ovale: trophozoite after "ring stage"

Plasmodium vivax is the most common form of malaria that causes reoccurring symptoms, or is tertiant in its cycle. P. vivax is found widely spread over Asia, Latin America and some parts of African, and causes debilitating, reoccurring symptoms that are mostly non-fatal. It can also cause splenomegaly, or enlargement of the spleen, which is highly fatal.

Plasmodium vivax: immature schizonts in human blood smear

Plasmodium malariae is very similar to P. ovale, in that it causes “milder”, or less fatal symptoms in very specific areas. P. malariae is thought to be the oldest form of Malaria causing parasites, and is relatively non-commensal. P. malariae undergoes a quartant cycle, replicating every 72 hours. Sometimes, the meroxoites form in a rosette fashion. My parasitology professor always used to say “if you have to choose which type of malaria to be infected with, choose Plasmodium malariae.”

…right. It’s so convenient how those Anopheles are giving you a choice, these days.

 Plasmodium malariae: trophozoite illustrating the "ring stage" in human blood smear

Now, my favorite, Plasmodium falciparum is the most deadly of the four. To illustrate its fatal nature, it is shaped like a banana. Yea, a deadly banana. Aren’t you scared?

P. falciparum is often termed as the “newest” of the four because it is so dangerous and deadly. In recent years, it has accounted for more than 95% of all malarial infections, and over 90% of all the deaths caused by malarial infections. P. falciparum has the unique ability to infect one cell with multiple merozoites. Essentially, P. falciparum is like a sniper version of malaria: it gets the job done. Like I said, deadly banana.


Plasmodium falciparum: banana shaped gametocytes in human blood smear

The lifecycle of malaria occurs in two parts: the sexual cycle that occurs within the vector’s gut, and the asexual cycle that occurs within the human host’s tissues and circulatory system.

Within the human, the Plasmodium sporozoites infect the liver cells and release merozoites. These merozoites infect red blood cells, replicate, and cause the red blood cells to literally rupture and explode in order to infect other red blood cells nearby. Eventually, this causes chaos in your liver tissues and circulatory system. 

Credit: NIAID

Yet, interestingly enough, if you already have Thalassemia, you have the added bonus of an evolutionary “immunity” to malaria diseases. Thalassemia is a disease associated with globin gene mutations (both α- and β-globin genes can be mutated, yet α-globin mutations are most common). Since your α- or β-globin gene is recessively mutated if you have active Thalassemia, your red blood cells develop into malformed, or sickled, cells, thus inhibiting their affinity to bind and transport oxygen. This lower affinity can cause extreme cases of anemia. In major cases, treatments such as chronic blood transfusion therapy, splenectomy, transplantation and iron supplementation are used.

Many immunologists believe that this immunity to malaria diseases that is associated with Thalassemia is a result of Darwinian genetics. A good example of this is Africa, which has some of the highest rates of malaria in the world, as well as a Thalassemia diagnosis of approximately 40% of the entire population. Those with the recessive mutation survive malaria more effectively, and have a higher likelihood of handing such mutations down through to following generations.

On a semi-related note, a friend turned me on to this Animal Planet show called Monsters Inside Me, which is all about parasites and other fun things! Here is a short video about malaria with some neat animations of the active infection:








I’m sure I will go into more specifics about malaria in future posts, but I wanted to address the question and request that I received in a timely manner. With that being said, if you have a topic that you are dying to read about, please feel free to send me an email, and I’ll get to it!

1 comment:

  1. how can thalassemia help prevent malaria infection and work as immunity for our RBCs??

    ReplyDelete