Transmission of Malaria from Person to Person

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QUESTION

I was in Lagos, Nigeria and i was bitten. I had stomach ache and diarrhea for a day then back to normal. Just for precaution I checked my blood and the doc said that I have a mild malaria in my blood and he gave me a medicine. If i have malaria can I affect or transmit the malaria to other people like my friends or my wife by the saliva or by any means?

ANSWER

No, you cannot directly transmit malaria to other people. It can only be transmitted via the bite of an infected mosquito; as such, while you are recovering from malaria, you should take care not to be bitten by any mosquitoes, because if these mosquitoes then went on to bite someone else, they might get infected with malaria.

Since malaria infects the blood, if large amounts of blood are transferred between people, for example during a blood transfusion, organ transplant or during childbirth, then malaria can sometimes also be transmitted. But under normal circumstances, you can not directly transfer malaria to another person.

Malaria Hosts

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QUESTION

Which are malaria hosts and how does malaria have an effect on one of them?

ANSWER

The parasite which causes malaria (called Plasmodium) requires two different hosts—a vertebrate intermediate host, such as a human, and an insect definitive host, also known as the vector. For the types of malaria which infect humans and other mammals, the vector is always a mosquito of the genus Anopheles.

However, there are other types of malaria which infect birds and reptiles, and these can use other genera of mosquito as their vectors, and some parasites closely related to Plasmodium can even use sandflies and other types of insects as their vectors too.

In humans, malaria usually causes disease, characterized by high fever, chills, aches and nausea. However, the presentation of symptoms and their severity depends on a number of factors, such as the type of Plasmodium (P. falciparum is the most dangerous to humans), the immune status of the host and the infective dose received from the vector.

Many mammals are also susceptible to malaria, such as macaque monkeys, and with them as well the effect of the parasite depends on a number of factors. For example, for macaques in south-east Asia, many will be co-infected with several different types of malaria simultaneously, though none appear to cause disease. However, if macaques from other parts of tje world, such as the Himalayas, are experimentally infected with these same types of malaria, they will get sick and possibly even die. As such, evolutionary history also plays a part in terms of how severe malaria will be in a particular host.

For the insect vector, infection with malaria parasites does not appear to have a strong deleterious effect, though some studies have shown reduced survival in mosquitoes infected with malaria. Also, changes in behavior have been observed. For example, some studies have shown that mosquitoes which are infected with malaria are more likely to continue seeking for food (i.e. through biting a host) even if they have recently fed than mosquitoes which are uninfected, or infected with non-transmissable life stages of malaria. This suggests that in some way the malaria parasite is manipulating the vector’s behavior in order to increase its own chances of being passed on to a new host.

Hereditary Malaria

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QUESTION

Can malaria be passed on through heredity?

ANSWER

In the vast majority of cases, malaria is only transmitted via the bite of an infected mosquito.

However, if a pregnant woman becomes infected with malaria, she can pass the parasite to her unborn child via the placenta, or via blood transfer during childbirth. An infection in a newborn child, caused by infection in the mother during pregnancy, is known as “congenital malaria”. Otherwise, a child cannot “inherit” malaria from their parents, apart from the above case of congenital malaria.

Malaria Socio-Economic Issues

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QUESTION

What are the socio-economic issues on the spread of malaria?

ANSWER

Malaria transmission requires the presence of Anopheles mosquitoes; as such, conditions which favor the growth and persistence of these mosquitoes will also be hotspots for malaria transmission, provided the climate is also sufficiently warm for the development of the parasite within the mosquito.

Rural areas without sophisticated water and sanitation systems often utilize streams or ponds for everyday water needs; if these produce stagnant patches of water, they can be an ideal location for the development of mosquito larvae.

Similarly, if rural farmers dig canals or ditches to irrigate their fields, these can become breeding areas. Urban areas tend to have less standing water, apart from cisterns, so in many cases transmission is less prevalent in urbanized locations.

As a further socio-economic factor, preventing mosquitoes from entering the house and biting people is  key way to prevent infection. Rich people in malarial areas may be more able to have fully screened houses, possibly even with air-conditioning, which will prevent mosquitoes from establishing in the house. They may also be more likely to have access to a long-lasting insecticide treated bednet, which further reduces mosquito bites, and also access to accurate diagnostic screening and treatment, if they do happen to get infected.

All of these factors contribute to making malaria burden highest in some of the world’s poorest areas, with the highest levels of mortality in sub-Saharan Africa.

Is Malaria a Mosquito STD?

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QUESTION

Is Malaria a type of STD for mosquitoes?

ANSWER

No. Mosquitoes pick up the malaria parasite from feeding on the blood of infected humans. Since only female mosquitoes feed on blood (the males feed on nectar), male mosquitoes never get infected with the malaria parasite. The life cycle of malaria in the mosquito is also completely different than in humans, and mosquitoes have a completely different physiology and immune system to humans, so it cannot be said that they get the same disease as we observe when people get infected with malaria.

Malaria and Employees

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QUESTION

I have a domestic employee that has malaria. I also have a 1 year old baby at home. Is it safe to keep her in employ or should I grant her leave until she is fully recovered?

ANSWER

Malaria cannot be transmitted between people directly. It is transmitted via the bite of an infected mosquito. As such, the only way your baby could get malaria from your employee is if a mosquito bit the employee, then directly bit your infant. Therefore, the best way to prevent transmission of malaria in this case is to make sure both your employee and your child sleep under long-lasting insecticide treated bednets.

You should also make sure your windows and doors are screened, to prevent the entry of mosquitoes that could carry malaria. These mosquitoes feed mainly at night and in the evenings and early mornings, so during these times, you should take extra precautions against getting bitten, such as wearing long sleeved clothing and covering exposed skin in insect repellent. If you have air conditioning, having this on at night can also prevent mosquitoes from entering rooms. You should also make sure your employee gets appropriate treatment for malaria and takes the full course of medication.

Pathophysiology of Malaria

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QUESTION

What is the pathophysiology of malaria?

ANSWER

Malaria causes disease through a number of pathways, which depend to a certain extent on the species. Malaria is caused by a single-celled parasite of the genus Plasmodium; there are five species which infect humans, beingPlasmodium falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi.

All these species are introduced into the human blood stream through the bite of an infected mosquito; the life stage of malaria at this point is called a “sporozoite”, and they pass first to the liver, where they undergo an initial stage of replication (called “exo-erythrocytic replication”), before passing back into the blood and invading red blood cells (called “erythrocytes”, hence this is the “erythrocytic” part of the cycle). The malaria parasites that invade red blood cells are known as merozoites, and within the cell they replicate again, bursting out once they have completed a set number of divisions. It is this periodic rupturing of the red blood cells that causes most of the symptoms associated with malaria, as the host’s immune system responds to the waste products produced by the malaria parasites and the debris from the destroyed red blood cells. Different species of malaria rupture the red blood cells at different intervals, which leads to the diagnostic cycles of fever which characterise malaria; P. vivax, for example, tends to produce cycles of fever every two days, whereas P. malaria produces fever every three.

In addition, Plasmodium falciparum produces unique pathological effects, due to its manipulation of the host’s physiology. When it infects red blood cells, it makes them stick to the walls of tiny blood vessels deep within major organs, such as the kidneys, lungs, heart and brain. This is called “sequestration”, and results in reduced blood flow to these organs, causing the severe clinical symptoms associated with this infection, such as cerebral malaria.

More details on the exact biochemical mechanisms for sequestration and its effect on the pathology of the infection can be found on the Tulane University website.

What year was the cause of malaria discovered?

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QUESTION

When did they find out that a bug bite caused malaria, and what year was that?

ANSWER

In 1880, Charles Louis Alphonse Laveran observed that malaria was caused by a parasite in the blood; it wasn’t until 1897-1898 that Ronald Ross, a British Army medical doctor, discovered that the parasite could be transmitted between hosts (he used birds for his experiments) by mosquitoes.

Persistent Antibodies to Malaria?

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QUESTION

I had malaria as child, more than 30 years ago. It was successfully treated with no relapse. I have since travelled to malaria- endemic countries, but the last time was over 3 years ago. No symptoms. I recently donated blood and routine screening has detected malaria antibodies. How long do the antibodies persist?

ANSWER

Based on your experience, I would say at least three years! While I doubt your antibodies would persist since your infection as a child, it is more likely that in your more recent trips to malarial areas you have been re-exposed to the parasite, but for whatever reason, the infection didn’t progress into a full-blown episode of malaria. This could well be due to some residual immunity from childhood, or you just received a light enough infection that your general immune system was able to fight off. Either way, this would have produced new antibodies against malaria, which were picked up by the blood screen.

The length of time antibodies persist is important information in the control of malaria, since serological tests (which detect antibodies) can be used for screening of populations in low-transmission environments, but their efficacy is reduced in locations where people have been treated for malaria but their antibodies persist. Also, understanding how antibodies are created and maintained in the body is necessary for gaining an appreciation of how preventive measures, such as bednets, might potentially leave populations more vulnerable to malaria later on, through lack of acquired immunity.

Malaria in the United States, Years Later

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QUESTION

For years, I have questioned what sickness I got years ago after a series of bug bites in a bayou in New Orleans. I’ve just read the symptoms described here and they fit everything I was suffering with. I even had problems with my liver, but I was never tested for Malaria because I had immediately left New Orleans for Italy. I never thought of mentioning it. This mysterious illness cropped up in different forms over the years and really I was never the same after it. It has been almost 12 years, and I still suffer from recurring illness which antibiotics help for a while, but it always comes back. Could it be that I have had Malaria in my system all this time?

ANSWER

While malaria was officially eradicated from the US in the 1950s, certainly the swamps and bayous of Louisiana and the rest of the Gulf were a key habitat and a major source of transmission prior to eradication. I just found a news report in the New York Times from October 1883 which reported 16 deaths due to “malarial fever” in the previous week alone!

While these days, virtually all of the 1,500 or so cases of malaria observed in the US every year are attributed to overseas travel, in 2002 a handful of cases of malaria in northern Virginia were believed to be due to local transmission. Prompt treatment, personal protective measures (such as screening houses) and vector control quickly quelled that mini-outbreak.

Given this history along with your symptoms, and particularly your recurrent episodes of fever, I would not rule out malaria, obtained in Louisiana, as a possibility! You should talk to your doctor about the possibility of a serological test for the antibodies against malaria—if positive, you should try to have a blood test done next time you have the recurrence of symptoms. If malaria is confirmed, you should report your case to the Centers for Disease Control (CDC) Domestic Malaria Unit, which monitors all malaria cases in the US.