Plasmodium knowlesi

Malaria is due to infection of with a Plasmodium parasite. Five species of Plasmodium regularly infect humans, Plasmodium falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi.

Of the five species, P. falciparum is the most severe and is responsible for most deaths. However, in recent years, P. knowlesi is increasingly giving cause for concern because it too can cause severe illness.

P. knowlesi is a natural parasite of macaque monkeys found in Southeast Asia and is classed as a zoonotic infection. So far there have been no recorded cases of P. knowlesi anywhere that macaques are not found.

Since 2004, there have been increasing reports of P. knowlesi in Malaysia, Thailand, Philippines, Vietnam, Indonesia and Myanmar and it is now the most common type of malaria found in Malaysia and Western Indonesia, countries that are nearing the elimination of malaria due to decrease in P. falciparum and P. vivax.

The mainstay of prevention of P. knowlesi is the same as for all other forms of malaria and is based around the A, B, C, D of malaria prevention advice. For travellers going to countries classed as ‘malaria free’ but where P. knowlesi is reported (Brunei and Singapore), antimalarials are not currently advised, but awareness of risk, bite avoidance and prompt investigation of fever are important.

Further information can be found on the TRAVAX (for health professionals) and fitfortravel (for the general public) websites.