Malaria is a life-threatening blood disease caused by parasites transmitted to humans through the bite of the Anopheles mosquito. Once an infected mosquito bites a human and transmits the parasites, those parasites multiply in the host's liver before infecting and destroying red blood cells.
The disease can be controlled and treated if diagnosed early on. Unfortunately, this is not possible in some areas of the world lacking in medical facilities, where malaria outbreaks can occur.
Researchers are working hard on improving the prevention of malarial infection, early diagnosis and treatment, with just one malaria vaccine close to being licensed so far.
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You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on malaria
Here are some key points on malaria. More detail and supporting information is in the main article.
- Malaria was first identified in 1880 as a disease caused by parasitic infection1
- The name of the disease comes from the Italian word mal'aria, meaning "bad air"
- Malaria is transmitted to humans through bites by infected mosquitoes
- The most common time for these mosquitoes to be active is between dusk and dawn
- Worldwide, there were an estimated 198 million cases of malaria in 2013 and 584,000 deaths
- Malaria occurs mostly in poor, tropical and subtropical areas of the world
- Malaria was eliminated from the US in the early 1950s, but the mosquitos that carry and transmit the malaria parasite still remain, creating a constant risk of reintroduction
- Reported malaria cases in the US reached a 40-year high of 1,925 in 2011
- A malaria vaccine for humans is close to being approved for use in Europe
- An estimated 3.4 billion people in 106 countries and territories are at risk of malaria - nearly half of the world's population10
- Annual funding for malaria control in 2013 was three times the amount spent in 2005, yet it represented only 53% of global funding needs2
- Malaria incidence rates are estimated to have fallen by 30% globally between 2000 and 2013 while estimated mortality rates fell by 47%
- The World Health Organization (WHO) has set out to reduce all malaria cases and deaths by 90% by 2030.3
What is malaria?
Derived from the Italian word for "bad air," it was originally thought swamp fumes in Rome were the cause of malaria, as outbreaks were a regular occurrence there.4
If left untreated, malaria can be fatal due to the fast reproduction of the parasite within a host's bloodstream.
There are more than 100 types of Plasmodium parasites,5 which can infect a variety of species. Scientists have identified five types that specifically infect humans,6 they are:
- P. falciparum - located worldwide in tropical and suburban areas, but predominately in Africa. An estimated 1 million people are killed by this strain every year. The strain can multiply rapidly and can adhere to blood vessel walls in the brain, causing rapid onset of severe malaria including cerebral malaria.
- P. vivax - located in Latin America, Africa, and Asia, it is arguably the most widespread due to the high population of Asia. This strain has a dormant liver stage that can activate and invade the blood after months or years, causing many patients to relapse.
- P. ovale - located mainly in West Africa, it is biologically and morphologically very similar to P. vivax. However, unlike P. vivax, this strain can affect individuals who are negative with the Duffy blood group, which is the case for many residents of sub-Saharan Africa. This explains the greater prevalence of P. ovale (rather than P. vivax) in most of Africa.
- P. malariae - located worldwide and the only human malaria parasite to have a three-day cycle. If left untreated, P. malariae can cause a long-lasting, chronic infection that can last a lifetime and which may cause the nephrotic syndrome.
- P. knowlesi - located in Southeast Asia and associated with macaques (a type of monkey). This strain has a 24 hour cycle and can, therefore, multiply rapidly once a patient is infected, causing an uncomplicated case to become serious very quickly. Fatal cases of infection with this strain have been reported.
Causes of malaria
Malaria is caused by the bites from the female Anopheles mosquito, which then infects the body with the parasite Plasmodium. This is the only mosquito that can cause 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. For the next 5-16 days, the host will show no symptoms but the malaria parasite will begin multiplying asexually.7
The new malaria parasites are then released back into the bloodstream when they infect red blood cells and again begin to multiply. Some malaria parasites, however, remain in the liver and are not released until later, resulting in recurrence.
An unaffected mosquito becomes infected once it feeds on an infected individual, thus beginning the cycle again.
The video below from the Howard Hughes Medical Institute visualizes how a single bite from an infected mosquito can quickly turn into the life-threatening disease.
Symptoms of malaria
According to the Centers for Disease Control and Prevention (CDC), malaria symptoms can be classified in two categories: uncomplicated and severe malaria.
Uncomplicated malaria is diagnosed when symptoms are present, but there are no clinical or laboratory signs to indicate a severe infection or the dysfunction of vital organs. Individuals suffering from this form, can eventually develop severe malaria if the disease is left untreated, or if they have poor or no immunity to the disease.
Symptoms of uncomplicated malaria typically last 6-10 hours and occur in cycles that occur every second day, although some strains of the parasite can cause a longer cycle or mixed symptoms. Symptoms are often flu-like and may be undiagnosed or misdiagnosed in areas where malaria is less common. In areas where malaria is common, many patients recognize the symptoms as malaria and treat themselves without proper medical care.
Uncomplicated malaria typically has the following progression of symptoms through cold, hot and sweating stages:
- Sensation of cold, shivering
- Fever, headaches, and vomiting (seizures sometimes occur in young children)
- Sweats followed by a return to normal temperature, with tiredness.
Severe malaria is defined by clinical or laboratory evidence of vital organ dysfunction. This form has the capacity to be fatal if left untreated. As a general overview, symptoms of severe malaria include:
- Fever and chills
- Impaired consciousness
- Prostration (adopting a prone or prayer position)
- Multiple convulsions
- Deep breathing and respiratory distress
- Abnormal bleeding and signs of anemia
- Clinical jaundice and evidence of vital organ dysfunction.
On the next page, we will look at the tests, diagnosis and treatments for malaria.