Testing for Dormant Malaria

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QUESTION

When malaria is dormant in the body can it be detected in a blood test?

ANSWER

Not directly, no. A normal malaria blood test consists of a thick or thin smear, which is often stained and then looked at under a microscope; with these tests, you would not be able to see any sign of the malaria which is lying dormant in the liver. However, there is another type of blood test, known as serology, which looks for the body’s antibodies against malaria. These are proteins produced by the immune system when the patient becomes infected with malaria. These antibodies are specific to the type of malaria the person was infected with, and can persist for many months and even years. As such, if a patient was infected with one of the types of malaria which can become dormant (i.e. P. vivax and P. ovale), a serology test might be able to tell whether the patient had ever been infected with one of these two types, and then suggest that they might continue to have a dormant infection.

Recurrent Malaria

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QUESTION

can malaria represent itself after 50 years?

ANSWER

There are two types of malaria which can lay dormant for long periods of time, though I don’t personally know of more than a handful of cases where the relapse was a matter of decades after the initial infection. These two types are P. vivax and P. ovale, so if you know you were infected with one of these types a number of years ago, it is possible that you could experience a relapse many years later, though as mentioned above, it is rare for the time lapse to be as long as 50 years.

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.