**2.7 Plasmodium knowlesi**

*P. knowlesi* is the only human malaria parasite that can naturally cause malaria in humans and other non-human primates (NHP) such as macaque monkeys [59, 60]. *P. knowlesi* is closely related to *P. vivax* and other Plasmodium species that infect non-human primates [61].

The parasite exists in South East Asia [62]. *P. knowlesi* rarely reported from areas outside South East Asia because its vector (the mosquitoes it infects: *Anopheles hacker* and *Anopheles latens*) are restricted to South East Asia [63, 64]. *P. knowlesi* has three subspecies which includes *P. knowlesi edesoni, P. knowlesi sintoni*, and *P. knowlesi arimai* [65, 66].

In humans, the parasite can cause both sever and uncomplicated malaria [67]. Uncomplicated *P. knowlesi* malaria is manifested by fever, chills, headaches, joint pain, malaise, abdominal pain, diarrhea, and loss of appetite [67]. In contrast to the other human malarias, *P. knowlesi* malaria has daily or quotidian malaria (a fever that that spike every 24 hours) [67, 68]. Like that of *P. vivax*, *P. malariae* and *P. ovale*, Chloroquine is also highly effective against *P. knowlesi* malaria [55].

### **2.8 Zoonotic malaria parasites**

In addition to *P. knowlesi*, other Plasmodium species have also reported to cause zoonotic malaria [69, 70]. Macaques has been reported to be reservoir of six Plasmodium species, namely *P. knowlesi, P. inui, P. cynomolgi, P. coatneyi, P. fieldi* and *P. simiovale* in Sarawak in Malaysian Borneo [71]. From these six Plasmodium species, *P. cynomolgi* has been shown to naturally cause human infection [72], and *P. inui* can cause infection in experimental condition [73], suggesting that these species might became the next Plasmodium species that may affect human health in the future.

Zoonotic malaria has also been reported from other parts of the world. Zoonotic malaria that are caused by *P. simium* [74] and *P. brasilianum* [75], that naturally infect platyrrhine monkeys have been reported in South America. *P. simium* and *P. brasilianum* are closely related with *P. vivax* and *P. malariae*, respectively [76].
