Team:JMU Wuerzburg/Introduction Malaria
Short introduction
Malaria is an infectious disease that affects 200 million people a year and lead to 400 000 deaths in 2017. It is spread worldwide with a concentration in subtropical and tropical areas. Malaria is caused by the parasite that is conducted through the bite of a mosquito. 1
Systematic classification
Plasmodium are pathogenic blood and tissue protozoa that infect humans. To date, five different Plasmodia have been recorded which cause different types of Malaria in humans.2
| pathogen | disease |
|---|---|
| Plasmodium falciparum | Malaria tropica |
| Plasmodium vivax | Malaria tertiana |
| Plasmodium ovale | Malaria tertiana |
| Plasmodium malariae | Malaria quartiana |
| Plasmodium knowlesi | Different kind of Malaria |
Symptoms
The incubation period in most cases varies from seven to 30 days. Shorter periods are observed most frequently with P. falciparum and longer ones with P. malariae.
Uncomplicated Malaria: This type lasts six to ten hours. Patients show following symptoms: a cold stage (sensation of cold, shivering), a hot stage (fever, headaches, vomiting; seizures in young children) and finally a sweating stage (sweats, return to normal temperature, tiredness).
Severe Malaria: This type causes serious organ failures or abnormalities in the patient’s blood or metabolism. The manifestations of severe malaria include for example cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities, severe anemia due to hemolysis (destruction of the red blood cells), Hemoglobinuria (hemoglobin in the urine) due to hemolysis etc. 7
Uncomplicated Malaria: This type lasts six to ten hours. Patients show following symptoms: a cold stage (sensation of cold, shivering), a hot stage (fever, headaches, vomiting; seizures in young children) and finally a sweating stage (sweats, return to normal temperature, tiredness).
Severe Malaria: This type causes serious organ failures or abnormalities in the patient’s blood or metabolism. The manifestations of severe malaria include for example cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities, severe anemia due to hemolysis (destruction of the red blood cells), Hemoglobinuria (hemoglobin in the urine) due to hemolysis etc. 7
Medication
Medical treatment depends on already existing drug resistance, as well on the Plasmodium causing Malaria.
Different medication is applied whether the patient needs prophylactic treatment, “stand-by” therapy (emergency self-treatment in absence of a physician with existing symptoms) or a standard therapy and is also adjusted to the patient’s age and weight. 2
Table: Summary of the most commonly used antimalarial drugs in monotherapy
Different medication is applied whether the patient needs prophylactic treatment, “stand-by” therapy (emergency self-treatment in absence of a physician with existing symptoms) or a standard therapy and is also adjusted to the patient’s age and weight. 2
Table: Summary of the most commonly used antimalarial drugs in monotherapy
Drug resistance
Drug resistance to antimalarial drugs has occurred in three of the five malaria species known to affect humans until today: P. falciparum, P. vivax and P. malariae.
P. falciparum has developed resistance to nearly every kind of antimalarial drugs currently available, such as chloroquine, sulfadoxine/ pyrimethamine, mefloquine, halofantrine, and quinine. Artemisinin-based drugs are the exception here. Although, recently a low-grade resistance to artemisinin-based drugs has emerged in parts of Southeast Asia.
P. vivax is chloroquine resistant. 3
It has been observed that patients with sickle cell anaemia and other globin abnormalities have a hereditary partial resistance against Malaria infections. It is still unknown how exactly this preexisting conditions affect Malaria infections, but it has been resolved that they interfere in the development cycle of Plasmodia. 4
P. falciparum has developed resistance to nearly every kind of antimalarial drugs currently available, such as chloroquine, sulfadoxine/ pyrimethamine, mefloquine, halofantrine, and quinine. Artemisinin-based drugs are the exception here. Although, recently a low-grade resistance to artemisinin-based drugs has emerged in parts of Southeast Asia.
P. vivax is chloroquine resistant. 3
It has been observed that patients with sickle cell anaemia and other globin abnormalities have a hereditary partial resistance against Malaria infections. It is still unknown how exactly this preexisting conditions affect Malaria infections, but it has been resolved that they interfere in the development cycle of Plasmodia. 4
Drug resistance tests
In response to the development of drug resistances in Plasmodium, an in vitro micro-test for the assessment of the response of Plasmodium falciparum to chloroquine, mefloquine, quinine, sulfadoxine/pyrimethamine, and amodiaquine as well as an in vitro assessment of antimalarial drugs against P. vivax has been established. 6
Life Cycle
The life cycle of Plasmodium spp. is quite complex. While asexual reproduction occurs in vertebrates, sexual reproduction occurs in female Anopheles mosquitos. In the following, the development in humans will be the main theme: When the female mosquito takes its blood meal, it injects the sporozoites into the dermis (A, B in figure 1). They then attain the vascular system and thus the liver, where they leave the sinusoids behind and enter the hepatocytes (B). At this point they start schizogony, a form of asexual reproduction, forming tens of thousands of merozoites in merosomes. In this form, they leave the hepatocytes and return to the bloodstream (B). With the infection of erythrocytes by merozoites, the asexual reproductive cycle begins: They enter an erythrocyte, form the ring stadium, the trophozoite and finally the schizont. Then the erythrocyte bursts and dismisses the merozoites into the bloodstream and the cycle starts again (C). A few merozoites are reprogrammed to form gametocytes, erythrocytes with precursors of the gametes. Within 15 days they reach the periphery, where they are absorbed by a mosquito during a meal (D). This is where the mature gametes occur, which unite to form the zygote, which becomes a dividing sporozoite. (E, F) The sporozoites can then be injected into a human again.8
Regular diagnosis for Malaria
Malaria is usually diagnosed by microscopic identification of Plasmodium parasites in a blood smear or with immunochromatoraphic rapid diagnostic tests (RTDs).
These RTDs are lateral flow immuno-chromatographic antigen-detection tests working with small amounts of patient’s blood. Malaria parasites producing antigens differ from every species of Plasmodium.
A drop of blood is added to hole A, while some drops are added to hole B. Inside the cassette is a strip made of filter paper and nitrocellulose. The buffer carries the blood along the length of the RDT. If certain antigens of the parasite are visible they bind to specific antibodies which are connected to the nitrocellulose strip. A labelled antibody then can bind them so a visible band together with a test band shows a positive result. 9 10
These RTDs are lateral flow immuno-chromatographic antigen-detection tests working with small amounts of patient’s blood. Malaria parasites producing antigens differ from every species of Plasmodium.
A drop of blood is added to hole A, while some drops are added to hole B. Inside the cassette is a strip made of filter paper and nitrocellulose. The buffer carries the blood along the length of the RDT. If certain antigens of the parasite are visible they bind to specific antibodies which are connected to the nitrocellulose strip. A labelled antibody then can bind them so a visible band together with a test band shows a positive result. 9 10
Plasmodia in culture used in the lab
We used the genomic DNA of the following laboratory-cultured strains for our experiments:
Plasmodium falciparum FCR3: isolated in Gambia, resistant to chloroquine and sensitive for pyrimethamine. 11
Plasmodium falciparum 3D7: isolated in the Netherlands, sensitive for chloroquine and pyrimethamine. 11
Plasmodium falciparum HB3: isolated from Honduras, sensitive for chloroquine and resistant to pyrimethamine. 11
Plasmodium falciparum Dd2: isolated in Indochina, resistant to chloroquine and resistant to pyrimethamine. 11
Plasmodium falciparum Mali2K
Plasmodium falciparum FCR3: isolated in Gambia, resistant to chloroquine and sensitive for pyrimethamine. 11
Plasmodium falciparum 3D7: isolated in the Netherlands, sensitive for chloroquine and pyrimethamine. 11
Plasmodium falciparum HB3: isolated from Honduras, sensitive for chloroquine and resistant to pyrimethamine. 11
Plasmodium falciparum Dd2: isolated in Indochina, resistant to chloroquine and resistant to pyrimethamine. 11
Plasmodium falciparum Mali2K
List of References
1 http://www.who.int/malaria/media/world-malaria-report-2017/en2 Duale Reihe Medizinische Mikrobiologie, Hof H, Dörries R, Hrsg. 6., unveränderte Auflage. Stuttgart: Thieme; 2017. doi:10.1055/b-004-140256
3 http://www.who.int/malaria/areas/treatment/drug_efficacy/en/
4 https://www.symptoma.com/de/info/malaria
5 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4778180/table/T1/?report=objectonly
6 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3385227/
7 https://www.cdc.gov/malaria/about/disease.html
8 Cowman, Alan F., Healer, Julie, Marapana, Danushka and Marsh, Kevin: Malaria: Biology and Disease, Cell 167, October 20, 2016, http://dx.doi.org/10.1016/j.cell.2016.07.055 Text about Lifecycle: written with the help of deepL.com
9 http://www.who.int/malaria/areas/diagnosis/rapid-diagnostic-tests/en/
10 http://www.who.int/malaria/areas/diagnosis/rapid-diagnostic-tests/about-rdt/en/
11 Volkmann, Sarah K. et al.: A genome-wide map of diversity in Plasmodium falciparum, Nature Genetics volume 39, 2007, pages 113–119 (2007), Supplementary Table 1, https://media.nature.com/original/nature-assets/ng/journal/v39/n1/extref/ng1930-S4.pdf (Abruf: 13.10.18)