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Explained: Plasmodium ovale and other types of malaria

The soldier in Kerala is believed to have contracted Plasmodium ovale during his posting in Sudan, from where he returned nearly a year ago, and where Plasmodium ovale is endemic.

Written by Anuradha Mascarenhas | Pune | Updated: December 13, 2020 8:44:16 am
Malaria is caused by the bite of the female Anopheles mosquito, if the mosquito itself is infected with a malarial parasite. (Source: Wikimedia Commons)

A not very common type of malaria, Plasmodium ovale, has been identified in a jawan in Kerala. The soldier is believed to have contracted it during his posting in Sudan, from where he returned nearly a year ago, and where Plasmodium ovale is endemic.

Types of malaria

Malaria is caused by the bite of the female Anopheles mosquito, if the mosquito itself is infected with a malarial parasite. There are five kinds of malarial parasites — Plasmodium falciparum, Plasmodium vivax (the commonest ones), Plasmodium malariae, Plasmodium ovale and Plasmodium knowlesi. Therefore, to say that someone has contracted the Plasmodium ovale type of malaria means that the person has been infected by that particular parasite.

In India, out of 1.57 lakh malaria cases in the high-burden states of Odisha, Chhattisgarh, Jharkhand, Meghalaya and Madhya Pradesh in 2019, 1.1 lakh cases (70%) were cases of falciparum malaria, according to a statement by the Health Ministry on December 2. In 2018, the National Vector-borne Disease Control Programme (NVBDCP) estimated that approximately 5 lakh people suffered from malaria (63% were of Plasmodium falciparum); researchers writing in the Malaria Journal of BMC felt the numbers could be an underestimate. The recent World Malaria Report 2020 said cases in India dropped from about 20 million in 2000 to about 5.6 million in 2019.

Plasmodium ovale

Scientists said P ovale rarely causes severe illness and there is no need for panic because of the case detected in Kerala. Dr V S Chauhan, emeritus professor at the International Centre for Genetic Engineering and Biotechnology, New Delhi, said P ovale is very similar to P vivax, which is not a killer form. Symptoms include fever for 48 hours , headache and nausea, and the treatment modality is the same as it is for a person infected with P vivax. P ovale is no more dangerous than getting a viral infection, he said.

It is termed ovale as about 20% of the parasitised cells are oval in shape. Distinguishing between P vivax and P ovale may be tricky, Dr Chauhan said, but a good-quality lab should be able to differentiate between the two. 📣 Follow Express Explained on Telegram

Cases in India

According to scientists at the National Institute of Malaria Research (NIMR), the Kerala case could be an isolated one and there are no recorded cases of local transmission so far. Previously, too, isolated cases were reported in Gujarat, Kolkata, Odisha and Delhi. However, no local transmission has been recorded — which means these cases have been acquired.

The jawan had returned to India from Sudan in January this year and was in Delhi. A month ago, he went to Kerala and shortly after, he began experiencing fever and other symptoms. After Covid-19 tests returned negative, he was tested for malaria.

“And on the slide, we could see the parasite inside the red blood cell sample. In Kerala, we usually see malaria types like Plasmodium falciparum and Plasmodium vivax. So we did a rapid antigen test to detect the strain and we found that it was negative for both types. When we investigated further, we diagnosed it as Plasmodium ovale,” said Dr Rajeevan, medical superintendent at the district hospital in Kannur where the jawan was treated.

Dr Rajeevan said it was possible for the parasite to remain in the spleen or liver of the body for a long time, even years, after the mosquito bite, and the person could become symptomatic later.

Africa and elsewhere

P ovale malaria is endemic to tropical Western Africa. According to scientists at NIMR, P ovale is relatively unusual outside of Africa and, where found, comprises less than 1% of the isolates. It has also been detected in the Philippines, Indonesia and Papua New Guinea, but is still relatively rate in these areas.

In a 2016 study on the China-Myanmar border, it was found that P ovale and P malariae occurred at very low prevalence, but were often misidentified. In another study, carried out in China’s Jiangsu Province, indigenous malaria cases decreased significantly over 2011-14, but imported cases of P ovale and P malariae had increased, and were often misdiagnosed.

— Inputs from Vishnu Varma in Kochi & ENS in New Delhi

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