Plasmodium falciparum in Cambodia
Introduction to Malaria
Malaria is fatal disease that infects about 515 million people worldwide and kills nearly a million people annually (1). Malaria is widespread in mostly tropical and subtropical countries because of their conditions allow the Anopheles mosquitoes to thrive.
Malaria infected individuals have symptoms such as fever, abdominal pain, chills, headaches, nausea, diarrhea, vomiting which can appear after couple of days or weeks after the infection. Also, very often malaria can lead to severe anemia, seizures, kidney failure, confusion and death if not treated on time (5).
The parasite initially enters the liver, where it multiplies and then infects the red blood cells. Here parasites still continue to multiply until eventually the red blood cells burst and the parasite appears in the plasma. Now, the parasites are free in the plasma and will infect any mosquito that bites and feeds on the host’s blood. Once the parasites enter the mosquito, they are also found in its saliva and are ready to be transferred to another individual and repeats the cycle after biting another host.
As a result of its devastating effects on the human population, many organizations (Gates Foundation) and countries (Global Fund) have banded together to find preventative measures and treatments for this global epidemic.
Description of Malaria
In Cambodia, the specific species (Anopheles dirus, A. minimus, and A. sundaicus) transmit the malaria-causing parasites (Plasmodium falciparum and P. vivax) to the host during feeding with the bite, transmitting the parasite through their saliva.
The number of infected people observed in Cambodia each year exceeds more than a million out of which about 10-15% die (5). Victims of malaria are mostly children, infants, and pregnant women because of their weaker immune system (3). Forest inhabitants, border workers and migrants are also in high risk in getting the disease because of their increased exposure to mosquito vectors. Due to global warming, the increasing temperatures, humidity, and rains may all favor the spread of malaria as mosquito habitats spread (4).
Description of the Plasmodium falciparum
Plasmodium falciparum is species of the genus Plasmodium, which of the Eukaryote domain and Plasmodiidae family. Plasmodium are much more complex than simple bacteria because of a “genetic complexity five times greater” (1). Their complex genome allows them more flexibility in various environments where simple bacteria can’t survive. Aside from having a complex genome, Plasmodium possesses various invasive stages for targeting specific host.
Infection/Polymorphism/cycle
Plasmodium possesses various forms, the most prominent being sporozoite, merozoite, and ookinete. These various forms of a plasmodium are directly tied to the cycle of infection. Sporozoite enters the human body via the saliva of mosquitoes during a blood meal. Sporozoites infect the hepatocytes (liver cell) within 30 minutes. From the hepatocyte, the parasite reproduces asexually into merozoites until they are released from the liver and enter the bloodstream. Merozoites then invade the erythrocytes (red blood cells) within 10 minutes. The merozoites continue proliferation in infected erythrocytes and also infect other uninfected erythrozytes. In an erythrocyte, merozoite can also differentiate to become gametocyte where they can be carried off by female mosquitoes after a blood meal. The gametocytes travel to the mosquitoes’ guts where they differentiate into male and female cells for fertilization. A zygote or ookinete is ultimately formed. The ookinete develops into sporozoites and venture into the saliva of the mosquitoes where they can further infect other human (1).
This cycle ties human and mosquitoes directly in the transmission and infection of malaria. In this relation, anopheline mosquitoes act as a vector and aid in spreading the infection. However, not all mosquitoes can be vectors. Only 68 out of 460 Anopheles can be vectors. Moreover, only female mosquitoes can take up gametocytes and transmit sporozoites as they are the only mosquitoes that bite.
Reasons for Symptoms
Symptoms of malaria are caused by the effects of merozoites interfering with the red blood cells' ability to carry oxygen. In infected erythrocytes, the cells are found to be deformed and stiff. Hemoglobins also function as food and nutrients for the merozoites. Infected red blood cells are more prone to rosetting and sequestration. Rosetting is when red blood cells attached to other red blood cell. With malaria, this occurs at a higher rate to allow for further infection of other red blood cells. Sequestration is the attachment of infected blood cells to the endothelial layer by rolling. The site of sequestration also prompts more infected cells to attach resulting in a buildup. Sequestration hinders oxygen delivery to organs and tissues. The effects of sequestration can lead to coma symptoms in severe cases of malaria. The combined effect of rosetting, sequestration, and consumption of hemoglobin by merozoites play a strong role in hindrance of oxygen delivery. This leads to the flu like symptoms of malaria (2).
Prevention
Malaria preventive measures can be approached in various ways. Simple preventative measures can be vector control or protection from mosquitoes bites via mosquito nets or the use of bug sprays containing DEET. Anti-malaria drugs can be combined with vector control or bit prevention to lower the risk of infection. Unlike typical diseases, vaccination is not a viable solution due to the disease's complexity.
Why is this disease a problem in Cambodia?
What is being done to address this problem
Include anything being done by the local government or groups as well as efforts by non-local groups.
What else could be done to address this problem
Are there solutions that could be successful but haven't been implemented due to political or economic reasons? Are there successful efforts in other countries? Are there reasons why these efforts may or may not be successful in the country you've focused on? etc. etc.
References
1. “Genome of Parasite that Causes Relapsing Malaria Decoded.” 2009. ScienceDaily. 9 Oct. 2008.
2. Pierce, Susan K., Miller, Louis H. World Malaria Day 2009: What Malaria Knows about the Immune System that Immunologists Still Do Not. 2009. The Journal of Immunology. 5 March, 2009.
3. “Drug-Resistant Malaria Has Emerged in Cambodia.” 2009. Science Daily. 13 Aug. 2009.
4. “Is Global Warming Likely to Cause an Increase Incidence of Malaria?” 2009. Libyan Journal of Medicine. 13 Feb. 2009.
5. "Fewer Malaria Cases in Cambodia.” 2009. Population Reference Bureau. Dec. 2002.
6. "Epidemiological Profile of Cambodia" World Malaria Report 2008. Geneva : World Health Organization , ©2008. p.51-54.
Edited by [Betsy Chiem, Ben Cho, Chuong Do, Katherina Leu, Albert Luong and Lusine Minasyan], students of Rachel Larsen
