Clinical
Two possible modes of transmission to humans have been proposed: either from an infected monkey to a human or from an infected human to another human.
Symptoms typically begin approximately 11 days after an infected mosquito has bitten a person and the parasites can be seen in the blood between 10 – 12 days after infection. The parasite may multiply rapidly resulting in very high parasite densities that may be fatal.
Although the current infection rate with Plasmodium knowlesi is relatively low, one risk it presents is misdiagnosis with other forms of malarial parasites such as P. malariae especially when microscopy is used. P. knowlesi can only be accurately distinguished from P. malariae using PCR assay and/or molecular characterization.
Symptoms of P. knowlesi in humans include headache, fever, chills and cold sweats. Singh et al. (2004) showed clinical symptoms in 94 patients with single species P. knowlesi infection at Kapit Hospital, Sarawak, Malaysian Borneo. Symptoms included fever, chills, and rigor in 100% of patients, headache in 32%, cough in 18%, vomiting in 16%, nausea in 6%, and diarrhea in 4%. Asexual cycle of the parasite in humans and its natural host macaque is about 24 hours. Hence the disease may be called quotidian malaria, in concert with designation of tertian malaria and quartan malaria. In addition to a lab diagnosis using PCR assay, knowlesi malaria may also present itself with elevated levels of C-reactive protein and thrombocytopenia.
This parasite causes non-relapsing malaria due to lack of hypnozoites in its exoerythrocytic stage.
While infection with this organism is normally not serious, life threatening complications or even death may occur in a minority of cases. The most common complications are respiratory distress, abnormal liver function including jaundice and renal failure. Mortality in one series of cases was about 2%.
Read more about this topic: Plasmodium Knowlesi