Malaria
Malaria
Malaria is a serious, sometimes fatal, disease caused by a parasite. There are four kinds of malaria that can infect humans: Plasmodium falciparum (plaz-MO-dee-um fal-SIP-a-rum), P. vivax (VI-vacks), P. ovale (o-VOL-ley), and P. malariae (ma-LER-ee-aa).
In Africa, a child dies of Malaria every 30 seconds. It kills 1 in 5. Malaria plays a big role in deaths from other diseases too. This is called comorbidity. Being sick with one thing makes it more likely to get sick with another, both drain the body, in effect, they both kill. Malaria is a lynchpin for child survival and economic development for Africa. Malaria causes poverty. Malaria makes people sick, kills children, burdens hospitals, and saps the economy. It drains energy from individuals and the whole system. Malaria halts progress.
What are the signs and symptoms of malaria?
Symptoms of malaria include fever and flu-like illness, including shaking chills, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhea may also occur. Malaria may cause anemia and jaundice (yellow coloring of the skin and eyes) because of the loss of red blood cells. Infection with one type of malaria, Plasmodium falciparum, if not promptly treated, may cause kidney failure, seizures, mental confusion, coma, and death.
See what the CDC says about Malaria: Overview and Parasite lifecycle.
Malaria and Mosquitoes
Mosquitoes transmit malaria. Mosquitoes are known as 'vectors' of the disease. We know that mosquitoes carry diseases from the recent outbreaks and spread of West Nile Virus across the United States. A few curious facts help us understand why the malaria campaigns focus on providing Insecticide Treated Nets, or ITN's, also known as bednets.
Mosquitoes cannot pass the malaria parasites on to their offspring. Each mosquito must obtain the parasite on her own. I use 'her' because only female mosquitoes can transmit the parasite. Female mosquitoes of certain anopheles species, to be more precise.
Each mother mosquito seeks out humans (or juicy plants or animals) to obtain a 'bloodmeal' for her eggs. If she bites humans that have no parasites, she cannot become infectious. She can only obtain the parasite from an infected human. (No mosquitoes share infected needles that I have ever heard of).
Hence the human reservoir of the malaria parasite plays a big role in malaria transmission. No human reservoir, no malaria. That's why Europe and the US have few cases of malaria, most of which originates in tropical countries and is carried in. Every year or two some person who has never traveled out their county comes down from malaria, probably from some mosquito that survived the trip to the US, or that bit an infected visitor and then passed the parasite on, but that's rare.
As an aside, malaria also infects birds, apes and even lizards. The types of malaria do not jump species. So you're safe if the birds or apes or lizards have malaria so long as the local humans do not.
| The USA, USSR, southern Europe and most Caribbean Islands achieved malaria eradication by 1960. Parts of Asia and South America were not far behind. Africa, though, did not eradicate malaria, and its people continue to suffer from the deadly disease. |
Interrupting Transmission
The reason sleeping under insecticide treated nets works so well is that mosquitoes bite their victims mostly between 9 pm and 3 am. Insecticides repel the mosquitoes by making them feel sick so that they fly away. If the mosquito touches the net, she will probably die. Even if she doesn't die, if she touches a net she usually will fall to the ground and be eaten by other insects or get crushed underfoot. The life of mosquitoes is perilously short.
The other key fact is that mosquitoes that have dined on infected blood are not immediately infectious. The parasite must stay in the gut and salivary glands of the mosquito for 10 days before it can pass on to another human being. The 10 day period includes at least 5 and perhaps as many as 50 bloodmeals. This is the 10-day rule. If a single one of those feedings includes a meaningful encounter with a treated net, the mosquito dies before she becomes infectious.
The mathematically gifted analysts tell us that this 10 days/ 5+ feedings means that not everyone must sleep under a mosquito net to interrupt transmission. I haven't gotten a straight answer from any such analyst, but coverage of 50% of the people is enough, according to most studies, to lower the rates of malaria dramatically.
Likewise, getting malaria from a single infected bite or a couple of bites probably gives a lighter case of malaria than a heavier one. A single bite is different from getting it from 100 or 1000 infected bites, as happens in the areas of highest transmission. Furthermore, education about malaria and its symptoms can lead those who do get malaria to seek rapid treatment.
Whether covering exactly 50% or 38.2% of a given population with nets is the magic number to interrupt transmission we may never know. What we do know is that at some point of coverage, we interrupt transmission completely. Is that point 68% or 73% or 92%? We do not know. The point may vary with local conditions. Infected mosquitoes can always blow in from the neighboring village or country on a storm. The ITNs could kill enough mosquitoes early enough to stop reinfection completely.
Burn Out
The other key to understanding malaria transmission is that the parasite, if not reintroduced to the human, will usually 'burn itself out' in 120 days, plus or minus a few. We are talking about the deadly plasmodium falciparum variety of malaria in this case. What does that mean? If we can keep a group of people from getting or transmitting malaria for a few months, perhaps a malaria season, if transmission is seasonal, there may be no more parasites in the human reservoir to go around in the first place.
last updated 25 May 2006