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How Is Malaria Transmitted?

Last Updated: 02.04.20

 

Malaria is a nasty disease which affects both humans and animals. It is transmitted through mosquito bites, and that is why using the best mosquito repellent is so important. There is only one species that can provoke this condition, but it is best to avoid them all.

 

What is malaria?

Most of us have heard about malaria and we can associate it with a medical condition. However, if you are lucky enough not to live in an area where this disease is common, you may not know so many things about it. 

As mentioned earlier, malaria is a mosquito-transmitted disease. It produces symptoms that usually include fever, headaches, tiredness, and even vomiting. In severe cases, it can cause seizures, yellow skin, coma, and death. These symptoms typically occur between ten and fifteen days after being bitten by a mosquito that is infected. 

If it is not treated properly, recurrence of the disease may happen months later. For individuals who have survived the infection, reinfection generally causes lighter symptoms. This disease is widespread in the tropical and subtropical zones. 

The human-populated areas that are mostly affected are Sub-Saharan Africa, Latin America, and Asia. There were 216 million cases of malaria reported in 2016, worldwide, followed by approximately 445000 to 731000 deaths. Almost 90% of these cases occurred on the African continent. 

This disease is usually associated with poverty and generates a huge negative effect on economic development. Due to increased healthcare costs, limited ability to work, and negative effects on tourism, Africa is estimated to lose around US$12 billion per year. 

 

 

How is malaria transmitted?

Malaria parasites belong to the Plasmodium genus, otherwise known as phylum Apicomplexa. Plasmodium falciparum, malariae, ovale, vivax, and knowlesi are known to cause malaria in humans. In order to understand how this disease is transmitted, it is important to look at the life cycle of Plasmodium. 

Thus, a female from the Anopheles species, which is the definitive host, transmits a motile infective form, called the sporozoite, to a vertebrate host, which is the secondary host. This is called a transmission vector. The sporozoite moves through the blood vessels straight to the liver cells, hepatocytes, where it reproduces asexually. 

This process generates thousands of merozoites. These microorganisms infect new red blood cells and then begin a series of asexual multiplication cycles. This is called blood schizogony and it can generate 8 to 24 new infective merozoites. At this point, the cells split and a new infective cycle begins, over and over again.

There are other merozoites that develop into juvenile gametocytes. These are the precursors of male and female gametes. Therefore, when a fertilized mosquito bites a person that is infected, the gametocytes are also taken with the blood and then mature in the mosquito’s gut. The male and female gametocytes combine and create an ookinete, which is a fertilized motile zygote.

These ookinetes grow into new sporozoites which travel to the mosquito’s salivary glands. From this point on that insect is ready to infect another new vertebrate host. The sporozoites are injected into the skin through the saliva, while the mosquito enjoys its blood meal. It is only the female mosquitoes that feed on blood and can transmit the disease. 

Male mosquitoes feed on plant nectar and are basically harmless. Females from the Anopheles species usually feed at night. They start foraging for food at dusk and continue until they succeed. It is also important to know that malaria can also be transmitted through blood transfusions. This is a rare situation, however.

 

Prevention

As you can see, this is a vicious circle. Any infected mosquito can transmit the disease to a human host, and any human that is infected can give the pathogen to a healthy mosquito that can later infect a new host. You cannot tell which insect is healthy or not, so the best way to stay safe is to avoid getting bitten as much as possible.

In order to prevent malaria, various methods are being used such as medications, mosquito elimination, as well as prevention of bites. Unfortunately, there is no vaccine for this disease. 

The existence of malaria in a certain area requires a combination of high Anopheles mosquito population, a high human population density, as well as high rates of transmission from humans to mosquitoes and vice-versa. In case any of these is lowered sufficiently, the parasite will disappear eventually. 

This is what happened in Europe, North America, and some parts of the Middle East. Still, unless the parasite is eliminated from the entire world, there is always a risk of it re-establishing where conditions return to a combination that could favor the parasite’s multiplication. There is also the cost per person which grows with a decreasing population density. 

This makes the process economically unfeasible in certain areas. It is true that the prevention of malaria is more cost-effective than treatment in the long run, but the primary costs needed are out of reach for the world’s poorest populations.

Unfortunately, in countries where malaria is common, children under five years old frequently suffer from anemia which is often due to malaria. Offering these children preventive antimalarial medication leads to improved red blood cell levels. However, it does not decrease the risk of death or the need for hospitalization. 

 

Mosquito control

Reducing the levels of transmission by mosquitoes are methods used to decrease malaria often referred to as vector control. When it comes to individual protection, the most effective mosquito repellents are based on DEET or picaridin. 

Other ways to prevent malaria, especially where this disease is common, include insecticide-treated mosquito nets or ITNs, as well as indoor residual spraying. Fast treatment of confirmed cases using artemisinin-based combination therapies or ACTs can also help reduce transmission.

There are other methods that have been used in order to reduce mosquito bites. Efforts have been made to decrease mosquito larvae by reducing the availability of open water where they are known to develop. 

Also, adding substances to limit their spread proved to be effective in certain locations. There are also the electronic mosquito repellent devices which generate high-frequency sounds. They are supposed to keep mosquitoes away, but their effectiveness is not as powerful. 

 

 

Treatment

This disease is usually treated with antimalarial medications. The exact ones that need to be used are in accordance with the type as well as the severity of the condition. Although medications against fever are generally used, their exact effects on the outcome are not really clear. 

Uncomplicated or simple malaria can be treated with oral medications. For infection with the P. falciparum, the most effective treatment is with artemisinins combined with other antimalarials. This is known as artemisinin-combination therapy or ACT. This type of treatment reduces the resistance to any single drug component. 

ACT is usually 90% effective when used to treat simple malaria. When it comes to treatment during pregnancy, it is recommended to use quinine plus clindamycin in the first trimester. ACT should be used only in the later stages, like the second and third trimesters. Unfortunately, in the 2000s, malaria with some resistance to artemisinins developed in Southeast Asia. 

The severe or complicated form of malaria is most of the times caused by infection with P. falciparum. Since mortality rates are high, in the range of 10% and 50%, severe malaria is a medical emergency. 

The worst neurological symptoms occur in the case of cerebral malaria. The recommended treatment is intravenous antimalarial medications. In the case of severe malaria, parenteral artesunate is superior to quinine in both adults and children. 

The treatment for complicated malaria includes supportive measures that are best performed in a critical care unit. This involves handling high fevers and seizures that might occur as a result. Monitoring poor breathing effort, low blood sugar and potassium are also common when managing this condition.

 

Drug resistance

Unfortunately, drug resistance poses a developing problem in the 21st-century treatment of malaria. Resistance is presently common against all classes of antimalarial medications except for artemisinins. 

Therefore, the treatment of resistant strains became more dependant on this class of drugs. The bad news is that the cost of artemisinins borders their use in developing countries. For example, malaria strains found on the Thailand-Cambodia border are resistant to therapies that involve artemisinins. Therefore, these strains can become untreatable. 

 

Conclusion

Malaria is a serious business! Although treatments are available, it is best to avoid being bitten as much as possible. If you are about to travel to a country where malaria is common, it is advisable to equip yourself with the best insect repellent you can find and to inquire your medical specialist if there are any preventive vaccines available.

 

 

 

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