How Much Time Between Mosquito Bite and Malaria Symptoms?

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QUESTION

If a mosquito carrying malaria is biting you, do you get sick the next day?

ANSWER

No.  There is a delay called the incubation period, which usually is between 7 to 30 days (depending on the malarial parasite the anopheles mosquito is carrying). The shorter periods are observed most frequently  from P. falciparum and the longer ones with P. malariae.

Antimalarial drugs taken for prophylaxis by travelers can delay the appearance of malaria symptoms by weeks or months, long after the traveler has left the malaria-endemic area. (This can happen particularly with P. vivax and P. ovale, both of which can produce dormant liver stage parasites; the liver stages may reactivate and cause disease months after the infective mosquito bite.)

Such long delays between exposure and development of symptoms can result in misdiagnosis or delayed diagnosis because of reduced clinical suspicion by the health-care provider. Returned travelers should always remind their health-care providers of any travel in malaria-risk areas during the past 12 months.

Malaria Prevention

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QUESTION

How can I protect myself from being infected with malaria?

ANSWER

There are many ways to prevent from getting infected with malaria. Some methods are more appropriate if you live in a malarial area, others are more for travellers to malarial areas, who are not staying long term. MALARIA.com has a comprehensive page dedicating to malaria prevention and protection.

Malaria in Australia and Bali

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QUESTION

Is Australia, Bali or Tasmania in the malaria affected area?

ANSWER

While malaria used to be endemic in parts of Australia (not Tasmania—it is too cold), the country was declared to be free of malaria transmission in 1981. However, several hundred cases are reported in Australia every year, mainly brought back by travellers returning from other regions, such as south-east Asia and Africa.

The tropical northern region of Australia, i.e. Northern Queensland and particularly the Torres Strait area, is climatically very suitable for malaria transmission, and some local outbreaks may occur. Similarly, Bali is climatically very suitable for malaria, and some transmission does occur, though not high levels. For both Bali and northern Australia, it is not usually considered necessary to take anti-malarial medication while visiting the region, but precautions should be taken against getting mosquito bites, as this is how malaria is transmitted. Such precautions include sleeping under an insecticide-treated bednet, wearing long-sleeved clothing in the evenings and at night, and wearing insect repellent on exposed skin.

Is there malaria in North America?

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QUESTION:

Are there malaria-infected mosquitoes in North America?

ANSWER:

North America is usually defined as including Canada, the United States and Mexico. Of these, Mexico has known regions of regular malaria transmission; specifically the regions bordering Guatemala and Belize in the south (Chiapas, Quintana Roo and Tabasco), rural areas in the tropical lowlands slightly further north (parts of Oaxaca, Nayarit and Sinaloa) and a very localised section of northern Mexico, located across the states of Chihuahua, Sonora and Durango. Travellers to these areas are recommended to take measures to prevent against malaria infection, such as minimising mosquito bites or taking prophylactic medication. Both P. falciparum and P. vivax are known to be transmitted in Mexico, so you should consult with a travel physician before deciding which form of preventative (prophylactic) medication to take, depending on the length of your stay, your budget and the type of malaria most commonly found in the area to which you are travelling.

Malaria was once also widespread in the southern USA, though a concerted public health campaign that started in 1947 (mainly consisting of reducing the number of mosquitoes through insecticide spraying and control of stagnant water bodies) greatly reduced transmission and led to the disease being considered eliminated by the 1950s. Occasionally, small pockets of transmission will be reported, though stringent diagnosis and treatment quickly places these outbreaks under control once more.

However, there are additional cases of malarial mosquitoes occasionally also reported even from northern parts of the United States and Canada; these are when mosquitoes are accidentally transported from malarial regions, for example in airplanes, in luggage or in shipping containers. These mosquitoes almost never transmit the disease to people, and in most temperate regions, do not live long enough to be a public health threat or to enable the persistance of the disease.

Does malaria spread from a person to another?

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QUESTION:

Can malaria spread from one person to another?

ANSWER:

Usually, no. In most cases, the malaria parasite has to first pass from a human host into a mosquito as the mosquito takes a blood meal, and then from the mosquito into another human via the mosquito’s saliva. This severely limits the amount of person-to-person transmission that exists. In fact, the only mechanisms for direct transmission between humans are when malaria parasites are passed between a mother and her unborn child via the placenta (congenital transmission) and through unscreened blood transfusions.

Congenital malaria is the more common type of human-to-human transmission; across various surveys of newborns in West Africa, between 8-24% were found to be infected with malaria parasites.

All four main species of human malaria (P. falciparum, P. vivax, P. ovale and P. malariae) have been implicated in congenital transmission. Infection with malaria during pregnancy not only puts the mother at greater risk of severe disease episodes (probably through reduced immunocompetence during pregnancy) but may also negatively impact the baby; although in endemic areas it is rare for babies to be symptomatic for malaria when acquired congenitally, even if they have parasitaemia, they have been shown to have a higher mortality rate than non-infected newborns. In non-endemic areas, babies with congenital malaria often display symptoms, which usually manifest themselves between 2 and 8 weeks after birth. Both quinine and artemisinin-based therapies have been successfully used to treat congenital malaria.

Malaria infection as a result of blood transfusion was first identified in 1911 and is one of the most common illness transmitted via transfusion, although the risk of being infected, particularly in non-endemic countries, is very low.

As it is difficult to screen blood directly for malaria infection, a number of standards have been put in place by blood-collection services to reduce the risk of obtaining blood containing malaria parasites. For example, in many places, you will not be allowed to donate whole blood if you have visited an endemic malarial region in the last three months, nor should you donate if you have previously had malaria unless you have been symptom-free for at least three years.

Due to the longevity of Plasmodium malariae in the blood, you are unlikely to be able to donate blood if you have ever been confirmed as positive for P. malariae. Serological screening of blood for malaria antibodies has recently been shown to be a sensitive method for testing for malaria in blood, although it is expensive and therefore not cost-effective for screening every sample, especially in non-endemic countries. However, it can be effective and efficient to avoid wastage when employed together with a travel-based questionnaire to ascertain donors who are high-risk for malaria.

It is worth mentioning that transmission of malaria via plasma only is very uncommon, and so frequent travellers or residents in malarial areas, who may be denied the right to donate whole blood, should ask about the possibility of donating plasma instead.