Malaria treatment now a breath away
How sweet are the words, “ Malaria count as at September 26, 2017 is 39”, especially to a Parasitologist whose professional life has been dedicated to the study of malaria and teaching young doctors-to-be about this scourge of the tropics. This statement appeared in the September issue of the SLMA News and continued with the news that all these cases were indeed imported (not acquired inside the island), ending with a very appropriate plea to keep Sri Lanka malaria-free.
The most used test for malaria is the examination of a blood smear (taken from a fingertip) after staining with an appropriate stain under a microscope. This is the current ‘gold standard’. This seemingly simple and inexpensive diagnostic tool extensively used in malaria endemic countries has its own disadvantages. The test requires the services of a trained, efficient technician to stain the smears and to detect and differentiate the parasite species.
A good microscope with at least the power of magnifying the parasites at least a thousand times is also needed. Therefore the test is severely disadvantaged in the field set-up particularly in remote and resource poor areas such as sub-Saharan Africa where thousands die of the infection. Human error associated with the performance of the test leads to serious consequences to the patient as well as for the prevention of the spread of the infection.
A false positive diagnosis will result in the treatment of an uninfected person and expose them unnecessarily to the side effects of the drugs. False positives also will bias the statistics collected by the health workers with serious consequences. Similarly, a false negative result will expose the patient to a lethal outcome particularly in the high-risk groups such as infants, pregnant mothers and debilitated people while providing an active reservoir of infection for the mosquito transmission of the infection.
The introduction of the RDT (Rapid Diagnostic Test) overcame much of these disadvantages. Trained technicians are not needed to perform the test. Health workers can perform and read the test results straightaway in the field set-up. The RDT is widely used to detect malaria due to Plasmodium falciparum, the parasite species that causes dangerous cerebral or brain malaria. The RDT is based on the detection of a protein – HRP2 (histidine rich protein) produced by the falciparum parasite.
The origins of the Plasmodia or the group of human- infecting malaria parasites go back to antiquity. Evolved over the millennia to survive and multiply inside the cells of another, these parasites are capable of evading whatever defensive mechanism put forward by the human host. They are able to hoodwink the host by changing the surface antigens so that the development of degree of immunity hopelessly hindered or by producing liberating into the host blood stream an array of soluble antigens against which the body produces antibodies that are non-lethal to the parasites.
Recent research has shown yet another trick by the parasite in this dangerous game between it and the human host. The alarming news is that the parasite has learnt to produce less HRP2, thus hoodwinking the humans searching for an accurate diagnostic tool. This literally means that, in the near future, RDT is becoming less reliable. The latest research presented and discussed at the American Society of Tropical Medicine and Hygiene (ASTMH) show that there is light at the end of the tunnel, once again scientists getting back into the competition with the parasites.
Malaria is transmitted by a mosquito and it is not an air-borne infection and it is intriguing that the breath – the exhaled air of a malaria patient could provide a way of diagnosing the infection. The expired air of malaria patients has also been shown to attract mosquitoes preferentially so that the parasite is able to ensure its perpetuity in the game of its survival. Odom Jones and her team of the University of Washington have compared the molecular compounds in the breath of malaria infected children with that of those who were uninfected. Odom John’s group was able to detect at least six compounds whose contents in the expired breath were varied significantly between the two groups. By measuring the values of the above compounds in the expired air the researchers are now capable of making a diagnosis of malaria in patients.
This novel diagnostic tool has been able to make a definite diagnostic in the majority of their test samples (83%). It is certainly less sensitive and specific currently at this stage compared to the blood smear examination and the RDT. The refinement of the test is almost certain to make it a simple, inexpensive diagnostic test that could be used in remote rural set-ups where malaria lurks.
In the same investigations the researchers found that the expired breath of malaria children also contained compound related to terpines. This is a compound associated with the aroma of plants and is a good attractant to mosquitoes. The higher levels of terpines in the breath of malaria infected children show that once again the parasite has demonstrated another defensive strategy to attract more mosquitoes for feeding thus, ensuring its spread leading to the continuation of the transmission cycle.
President of the ASTMH, Patricia Walker quite aptly commented at the conference that the malaria parasite has been outwitting human interventions for thousands of years. The new test is undergoing clinical trials and we certainly see a very bright light at the end of the tunnel in the quest for searching for a reliable diagnostic test for malaria.