In the 1960's, it was suggested that mosquitoes of the Anopheles leucosphyrus group, may provide a link between humans and monkeys and that if simian malaria is transmitted to man in nature, it is likely to be in areas where these mosquitoes are common . This has been confirmed by the current study where An. latens has been incriminated as the vector of P. knowlesi in nature in the Kapit division  where a large focus of naturally acquired P. knowlesi infection in humans was reported . Aside from being the most predominant anopheline mosquitoes caught biting humans in Kapit, An. latens was observed to be attracted to both human and monkey hosts. In the monkey-baited net traps, it was also observed that a significant number of An. latens were collected at the higher levels compared to those caught at ground level showing an acrodendrophilic behaviour. This is important as the natural monkey host is arboreal in nature. In order for this malaria parasite to be maintained in nature and for transmission to man to occur, the vector needs to be highly simio-anthropophagic in nature. If the vector for P. knowlesi is highly simiophagic, as in the case of Anopheles hackeri in Peninsular Malaysia , transmission in the natural hosts may be maintained, but transmission to humans will be rare .
The fact that An. latens is attracted to monkeys in the canopy and humans on the ground indicates that both humans and monkeys could be exposed to infection from each other. Data from this study area indicate that the zoonotic parasite, P. knowlesi, is being transmitted to both humans and macaques by An. latens. Thus, in Kapit, humans get the infection when their forest associated activities, such as farming, logging, or hunting exposes them to An. latens. Throughout the course of this study infected mosquitoes were not obtained from the longhouse and the number of anophelines caught there were also small.
Like all members of the Leucosphyrus group, An. latens is mainly a forest breeding mosquito associated with dense jungle and forest fringes [21, 33]. In the current study, nearly 90% of the total An. latens were collected at either the farm (40%) or the forest (50%) and were consistent with earlier studies conducted in other areas of Sarawak. In addition, only 126 An. latens (10%) were collected in the longhouse, and of these 71% were collected outdoors. Entomological studies conducted in other areas in Sarawak [18, 19] showed that An. latens were commonly found in farming zones that were located at the forest fringe rather than in villages, and the density of An. latens decreases in relation to distance away from the jungle.
It is known that multiple factors determine the prevalence of malaria and one of these is the intensity of malaria transmission which is defined as the rate at which people get inoculated with malaria parasites from mosquitoes . In the current study, only An. latens were found to be infective, and the average number of infectious bites by these mosquitoes in both the farm and the forest during the entire duration of the study was 11.98 and 14.1 per year respectively, which is higher compared to the rates in many Asian countries . When considering the risk of acquiring P. knowlesi in Kapit, the intensity of transmission has been shown to be comparable for both ecotypes, hence the risk of acquiring P. knowlesi in either the forest or the farm is the same. In Sarawak, the forests and their surrounding areas are recognized focal points for malaria transmission whenever An. latens is present in large numbers .
Although An. latens has been incriminated as the vector of P. knowlesi in Kapit, the role of other anopheline species as a possible vector for P. knowlesi in Kapit needs further assessment. This is especially true for An. pujutensis, An. introlatus, and An. macarthuri, all of which were caught in small numbers and were not dissected. They have been reported to be simiophagic and have either been suspected or been incriminated as vectors of simian malaria parasites in other localities in Peninsular Malaysia [32, 35, 36]. To determine if they are vectors of P. knowlesi, intensive entomological surveys have to be carried out in many parts of the forest and in other parts of the Kapit Division. With the advancement of molecular techniques it is possible to identify the sporozoites to species level and thus vectorial status can be determined.
Anopheles watsonii, a forest species, was caught in large numbers, but only in the forest, where it was found to be attracted to both human and monkey hosts. Previously, a small numbers of this species were also obtained in hill forest in Peninsular Malaysia at night with human and monkey- baited traps . They obtained more mosquitoes in the canopy than at ground level, but all were negative by dissection. Thus earlier workers did not consider An. watsonii as a vector of human malaria. In the current study, oocysts were found by dissection and the numbers in each gut ranged from 7–90. However, none were positive for sporozoites by dissection. Since they are attracted to humans and non human primates, further studies should be conducted on this species before any definitive conclusions can be inferred about their vectorial status.
With large tracts of forest being cut down, non-human primates are coming close to the human environment. Human cases of P. knowlesi have been reported not only in Sarawak, but also in Thailand , Manymar  and in Peninsular Malaysia [8, 9, 39]. Thus control strategies for malaria in Southeast Asia may have to change to include this zoonotic aspect of the transmission.