Malaria

The Basics

What is malaria?

Where does malaria occur?

The occurrence of malaria depends on where the Anopheles mosquito is able to survive, breed, and transmit the Plasmodium parasite.

"At temperatures below 20°C (68°F), Plasmodium falciparum (which causes severe malaria) cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted" (CDC, 2010). 

Typically, cooler regions will have less intense and more seasonal malaria transmission (CDC, 2010b).  The map below shows the countries of the world where malaria occurs.  Notice that malaria occurs in most of Central and South America, most of Southern Africa, and much of South East Asia.    

The map below shows the countries of the world where the Anopheles mosquito, the malaria vector, is found. 

Much of the world's malaria occurs on the continent of Africa.  The following are some facts about malaria in Africa:

- 90% of the world's malaria occurs in sub-Saharan Africa (Blumberg, 2005)

- At least 90% of malaria deaths occur in sub-Saharan Africa and primarily amongst young children (Blumberg, 2005)

- There is malaria in every country in Africa, except Lesotho, but some areas are more endemic than others (Blumberg, 2005)

The map below shows where malaria occurs in Africa.  Notice that much of malaria occurs in the central parts of Africa, whereas the northern countries of Africa, where the Sahara desert covers much of the land, has very little or no malaria. 

Organizations such as the Red Cross are working in Africa to combat malaria.  Click HERE for a video about the Canadian Red Cross' work called Campaign Against Malaria in Africa.

Asia

When the mosquito bites a host, if the mosquito is carrying the malaria parasite, it is transmitted in the saliva of the mosquito.  The parasite can also be transmitted from an infected host, the infected human, to a female Anopheles mosquito (CDC, 2010c).      

     Once the parasite has multiplied enough that the liver cell bursts/lyses, the parasite then moves out of the liver, and into the blood stream, where it can find red blood cells/erythrocytes.  Once in an erythrocyte, the malaria parasite continues to grow and multiply (CDC, 2010c). 

     These are known as blood stage parasites.  While in the erythrocyte, the parasite will ingest and degrade approximately 80% of the hemoglobin.  The parasite also ingests the host cell's cytoplasm as it develops (CDC, 2010c).  

The above video shows how malaria is transmitted.  

       A red blood cell will eventually burst from an overload of parasite, as well as waste products such as hemozoin pigment and other toxins (CDC, 2010d), and then release the merozites, or daughter parasties into the blood, where they invade other red blood cells and continue the cycle of infection (CDC, 2010c).  The hemozoin pigment and other toxins like glucose phosphate isomerase are also dumped into the blood stream when the red blood cells bursts/lyses.  These toxins activate the body's immune system macrophages, which then produce cytokines and other products, that then cause the human body's fever, and possibly other symptoms of malaria (CDC, 2010d).

     Once the malaria parasites have migrated to the red blood cells in the human blood, these gametocytes, can be picked up by an Anopheles mosquito during a bite and blood meal.  Inside the mosquito, also called the vector, the malaria parasites continue to multiply, and will be ready to infect a human after 10-18 days, when they are sporozites in the salivary glands of the mosquito.  These sporozites will be  injected into the human when the mosquito's saliva is also injected.  The cycle of infection will be repeated when the malaria parasites reach the liver of the human (CDC, 2010c).  

Fast Fact:  The CDC also lists blood transfusions, mother to fetus transmission, needle sharing, and organ transplantation as modes of transmitting malaria (CDC, 2010e).

What are the symptoms of malaria? 

     Once an individual is bitten by an infected Anopheles mosquito, the incubation period between the time of the bite and the onset of symptoms can vary from 7 to 30 days (CDC, 2010d).  Plasmodium falciparum is typically associated with a shorter incubation period.

     Blumberg also agrees that malaria symptoms can present as early as seven days, but 10-21 days after being bitten is much more commonly seen in infected individuals (Blumberg, 2005). 

     An infected individual can present malaria symptoms in a wide range of severity, from no symptoms at all (asymptomatic) to extremely severe symptoms, and also death.  Malaria is typically labeled as either uncomplicated or complicated/severe malaria (CDC, 2010d).  The World Health Organization warns that, "if not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs" (WHO, 2011).   

     According to Blumberg, the symptoms of severe malaria include:  impaired consciousness, convulsions, respiratory distress, pulmonary edema, jaundice, bleeding, and shock.  Blumberg also notes that renal impairment, acidosis, hepatic impairment, hypoglycemia, and hypoxia may be evident in a patient afflicted with severe malaria (Blumberg 2005).   

The CDC says that "in general, malaria is a curable disease if diagnosed and treated promptly and correctly" (CDC, 2010d).  

Uncomplicated Malaria

Severe Malaria

     According to the CDC, "severe malaria occurs when infections are complicated by serious organ failures or abnormalities in the patient's blood or metabolism" (CDC,2010d).  It is also almost exclusively caused by the Plasmodium falciparum parasite, and rarely by P. vivax or P. ovale (Trampuz, 2003).   

     In areas of Africa where there there is a high endemic rate of malaria as well as a stable transmission rate (Tanzania, Malawi, Mozambique), severe malaria is more common in children under 5, and in pregnant women.  This is because adults and older children have acquired a partial immunity to malaria because of repeated exposures.  Areas in Africa with low endemic rates have higher rates of severe malaria in adults and older children because of their fewer exposures to the disease (Blumberg, 2005). 

     Factors that contribute to more severe cases of malaria include a delay in diagnosis and adequate medications.  The adherence of infected red blood cells to blood vessel walls/endothelium can also compromise blood flow in tissues, and can also contribute to cerebral malaria (see below) (Blumberg, 2005).   

Severe malaria in a patient may cause: 

     - cerebral malaria:  abnormal behavior, seizures, coma

           - severe anemia

     - blood in the urine

     - ARDS:  Acute Respiratory Distress Syndrome

     - impaired coagulation of the blood

     - low blood pressure

     - kidney failure

     - hypoglycemia

     - convulsions

     - Respiratory Distress Acidosis

     - jaundice

 Cerebral Malaria

     It is thought that cerebral malaria, an encephalopathy, is caused by Plasmodium falciparum-infected red  blood cells adhering to the walls of blood vessel walls in the brain, and then not freely circulating in the blood.  Cerebral malaria is associated with a high mortality rate for malarial infection (CDC, 2010d), and is associated with altered mental status and coma in affected patients, and is also more commonly seen in older children and adults (Newton, 2000).   

 Above:  a brain infected by cerebral malaria

 Relapse

 Other Complications

1.  Palsy, speech difficulty, deafness, blindness, and trouble moving/ataxia following severe malaria.

What are the statistics of malaria?

"In 2008, malaria caused nearly one million deaths, mostly among African children."

"Malaria can decrease gross domestic product by as much as 1.3% in countries with high disease rates."

"In 2008, there were 247 million cases of malaria and nearly one million deaths – mostly among children living in Africa."

"In Africa a child dies every 45 seconds of Malaria, the disease accounts for 20% of all childhood deaths."

"The long lifespan and strong human-biting habit of the African vector species is the underlying reason why more than 85% of the world's malaria deaths are in Africa."

"In 2008, malaria was present in 108 countries and territories."

Is malaria still a threat in the United States?

According to the CDC, there are about 1,500 cases of malaria in the United States each year.  Eradicated from the United States in the early 1950s, most of the cases diagnosed are found in travelers and immigrants from areas where malaria is found, such as in Africa and South Asia. 

The mosquitoes that transmit malaria, the Anopheles mosquitoes, are still found in the United States.  So there is a constant threat of malaria reappearing in the U.S. as a problem because of the amount of travelers and immigrants that arrive in the United States from malaria-endemic areas.

(CDC, 2010e)   

Fast Fact: 

While carrying the malaria parasite Plasmodium, the mosquito does not experience any malaria symptoms (CDC, 2010c). 

"In recent years, some human cases of malaria have also occurred with Plasmodium knowlesi – a monkey malaria that occurs in certain forested areas of South-East Asia" (WHO, 2011b).