Malaria epidemiology, the of malaria involves several interacting factors which facilitate transmission. The important factors include the mosquito vector, which is normally the Anopheles, the plasmodia parasite, the human host and the environment. Now let's look at the vector. Concerning the vector, species efficiency is important. Where you have good efficient malaria vectors, where normally transmission will be efficient, and this is very much affected by longevity. The period that the the mosquito is able to survive. She has to be able to survive during the sporogony period, which is normally two weeks. And then vector abundance. In terms of densities. We normally have mosquito densities related to the transmission cycle. So where you have a got a higher density of mosquitoes, then of course transmission is normally high. Behavioral patterns of the vector species, in terms of feeding and resting. Normally, the most efficient vectors are those ones, which are, that, are less likely to feed on and those are the ones which have the tendency to rest close to human habitations. The plasmodia parasite species distribution is important. As we know, they are put that malaria with the species. And all of these vary in terms of species distribution with plasmodia vivax and falciparum are common all around the world. But of course we have got other species like [INAUDIBLE] which have localized distribution. The virulence then and the tendency to relapse like we have in Vivax or the tendency to deliver resistance as it's now becoming apparent. Plus falciparum, all this contributes to maintain transmission. The human host vector becomes important. And this is translated in terms of protection. The ability of the human to protect themselves against mosquito bites. So in areas where the mosquito nets are used or scaled out the ability then of the population to afford the nets. And the [INAUDIBLE] to use the nets becomes important. So net usage as well as availability of the nets becomes important in protecting against mosquito bites, and therefore in preventing the transmission of malaria. Another factor linked to human behavior is the ability and tendency to be able to afford and access prompt treatment. The age structure is important in that in high transmission areas, children are the ones who normally have high parasite densities. In particular children between 6 and 59 months. Endemicity levels therefore that is for large geographical areas can be defined traditionally in terms of spleen and parasite rate in young children. And we have four classifications, but we normally refer to the first two as being low endemic, the hypoendemic and mesoendemic are the low endemic areas, and those areas with parasite rate of less than 50%. The high transmission area that is the hyperendemic and holoendemic, these are the areas which have got a high parasite densities, over 75%. Malaria can be defined also as stable or unstable. Stable malaria is when you have gotten parasite is normally endemic and this is common in areas with high vector populations. The unstable or epidemic prone areas, where we have gotten seasonal transmission and in these such areas, all groups are affected and due to low immunity in the population. The environment becomes important, particularly in terms of rainfall. A neutral transmission cycle is normally very much linked with the rainfall season pattern. Because rainfall then offers an adequate breeding areas for mosquitos. Irrigation activities, particularly during the transplantation and weeding. It also contribute to the transmission. So then the transmission cycles out so linked to such irrigation activities. Temperature, optimal temperature for the breeding of mosquitoes and to some extent, for the development of parasite in the human bodies between 20 and 30 degrees centigrade. With upper limits 16 and up to 33 degrees centigrade and lower limit of 16 degrees centigrade. When it come to altitude, this is very much related to temperature because at high altitude, normally low temperatures. So in a lot of geographical areas, we don't have malaria transmission altitude above 2,000 meters above centigrade. Relative humidity linked also to the rainfall irrigation activities. In areas of high rainfall, it has a high relative humidity. Conditions which are conducive for the survival of a lot of efficient mosquito vectors. Housing conditions become important. The type of house, screened houses located far away from the. These are likely to attract mosquitoes and therefore in such areas, transmission is likely to be low. Transmission intensity, in general, varies across geographical areas with varying levels of infective bites by year. And with the current global decline in transmission and clinical burden of malaria, heterogeneity in infection is becoming more pronounced. Another focus now is to target hot spots when it comes to intermission. Spatial heterogeneous transmission is affected by variation in climate and ecological factors as we have seen, and these affect the distribution and density of the vector population.
