The parasites in mosquitos that spread malaria belong to the Plasmodium genus. Over 100 types of Plasmodium parasite can infect a variety of species. Different types replicate at different rates, changing how quickly the symptoms escalate, and the severity of the disease.
Five types of Plasmodium parasite can infect humans. These occur in different parts of the world. Some cause a more severe type of malaria than others.
Once an infected mosquito bites a human, the parasites multiply in the host's liver before infecting and destroying red blood cells.
In some places, early diagnosis can help treat and control malaria. However, some countries lack the resources to carry out effective screening.
Currently, no vaccine is available for use in the United States, although one vaccine has a license in Europe.
In the early 1950s, advances in treatment eliminated malaria from the U.S. However, between 1,500 and 2,000 cases still occur each year, mostly in those who have recently traveled to malaria-endemic areas.
Doctors divide malaria symptoms into two categories: Uncomplicated and severe malaria.
Malaria is passed on by the Anopheles mosquito.
A doctor would give this diagnosis when symptoms are present, but no symptoms occur that suggest severe infection or dysfunction of the vital organs.
This form can become severe malaria without treatment, or if the host has poor or no immunity.
Symptoms of uncomplicated malaria typically last 6 to 10 hours and recur every second day.
Some strains of the parasite can have a longer cycle or cause mixed symptoms.
As symptoms resemble those of flu, they may remain undiagnosed or misdiagnosed in areas where malaria is less common.
In uncomplicated malaria, symptoms progress as follows, through cold, hot, and sweating stages:
- a sensation of cold with shivering
- fever, headaches, and vomiting
- seizures sometimes occur in younger people with the disease
- sweats, followed by a return to normal temperature, with tiredness
In areas where malaria is common, many people recognize the symptoms as malaria and treat themselves without visiting a doctor.
In severe malaria, clinical or laboratory evidence shows signs of vital organ dysfunction.
Symptoms of severe malaria include:
- fever and chills
- impaired consciousness
- prostration, or adopting a prone position
- multiple convulsions
- deep breathing and respiratory distress
- abnormal bleeding and signs of anemia
- clinical jaundice and evidence of vital organ dysfunction
Severe malaria can be fatal without treatment.
Treatment aims to eliminate the Plasmodium parasite from the bloodstream.
Those without symptoms may be treated for infection to reduce the risk of disease transmission in the surrounding population.
The World Health Organization (WHO) recommends artemisinin-based combination therapy (ACT) to treat uncomplicated malaria.
Artemisinin is derived from the plant Artemisia annua, better known as sweet wormwood. It rapidly reduces the concentration of Plasmodium parasites in the bloodstream.
Practitioners often combine ACT with a partner drug. ACT aims to reduce the number of parasites within the first 3 days of infection, while the partner drugs eliminate the rest.
Expanding access to ACT treatment worldwide has helped reduce the impact of malaria, but the disease is becoming increasingly resistant to the effects of ACT.
In places where malaria is resistant to ACT, treatment must contain an effective partner drug.
The WHO has warned that no alternatives to artemisinin are likely to become available for several years.
There are several ways to keep malaria at bay.
Research to develop safe and effective global vaccines for malaria is ongoing, with the licensing of one vaccine already having occurred in Europe. No vaccine is yet licensed in the U.S.
Seek medical attention for suspected symptoms of malaria as early as possible.
Advice for travelers
While malaria is not endemic to the U.S., travel to many countries around the world entails a risk.
The Centers for Disease Control advise travelers to take the following precautions:
- find out what the risk of malaria is in the country and city or region they are visiting
- ask their doctor what medications they should use to prevent infection in that region
- obtain antimalarial drugs before leaving home, to avoid the risk of buying counterfeit drugs while abroad
- consider the risk for individual travelers, including children, older people, pregnant women, and the existing medical conditions of any travelers
Travelers to places where malaria is prevalent should take precautions, for example, using mosquito nets.
- ensure they will have access to preventative tools, many of which are available to purchase online, including insect repellants, insecticides, pre-treated bed nets, and appropriate clothing
- be aware of the symptoms of malaria
In emergency situations, local health authorities in some countries may carry out "fogging," or spraying areas with pesticides similar to those used in household sprays.
The WHO points out that these are not harmful for people, as the concentration of pesticide is only strong enough to kills mosquitoes.
While away, travelers should, where possible, avoid situations that increase the risk of being bitten by mosquitoes. Precautions include taking an air-conditioned room, not camping by stagnant water, and wearing clothes that cover the body at times when mosquitoes are most likely to be around.
For a year after returning home, the traveler may be susceptible to symptoms of malaria. Donating blood may also not be possible for some time.
Malaria happens when a bite from the female Anopheles mosquito infects the body with Plasmodium. Only the Anopheles mosquito can transmit malaria.
The successful development of the parasite within the mosquito depends on several factors, the most important being humidity and ambient temperatures.
When an infected mosquito bites a human host, the parasite enters the bloodstream and lays dormant within the liver.
The host will have no symptoms for an average of 10.5 days, but the malaria parasite will begin multiplying during this time.
The liver then releases these new malaria parasites back into the bloodstream, where they infect red blood cells and multiply further. Some malaria parasites remain in the liver and do not circulate til later, resulting in recurrence.
An unaffected mosquito acquires parasites once it feeds on a human with malaria. This restarts the cycle.
Early diagnosis is critical for recovery from malaria.
Anyone showing signs of malaria should seek testing and treatment immediately.
The WHO strongly advise confirmation of the parasite through microscopic laboratory testing or by a rapid diagnostic test (RDT), depending on the facilities available.
No combination of symptoms can reliably distinguish malaria from other causes, so a parasitological test is vital for identifying and managing the disease.
In some malaria-endemic areas, such as sub-Saharan Africa, the disease's severity can cause mild immunity in a large proportion of the local population.
As a result, some people carry the parasites in their bloodstream but do not fall ill.