The lecture today will be on trypanosomiasis vectors, which mainly include the tsetse fly. We shall look at the vectors, the epidemiology, and control. The major vector is the tsetse fly, which comes out of the genus Glossina. And this is mostly restricted to the African continent. There are two major groups of medical importance, these include the Glossina palpalis and the Glossina morsitans. When we look at the distribution, we have Glossina palpalis associated in the western part of Africa. And most of the time, which occupies the whole of Africa, of course, south of Sahara, including overlaps with areas of palpalis. Glossina palpalis which is mainly found in the forest areas of West Africa, as well as areas in riverine vegetation. It is an important vector of human sleeping sickness. Important Glossina palpalis species include Glossina palpalis palpalis, Glossina gambiensis, Glossina fuscipes fuscipes and Glossina tachinoides. Now, let's look at the Glossina morsitans. Which as we have said, is most widespread in West Africa, then, as well as in East and Southern parts of Africa. Unlike the palpalis, which is common in forest areas, the morsitans is common in savannah bushy thickets. And it's very much associated with game, which actually are the primary vectors of Rhodesian sleeping sickness and nagana. Important species then of medical importance include Glossina morsitans, Glossina pallidipes, Glossina swynertoni and Glossina austeni. This is the, the way the tsetse fly look. We can gauge the size by looking at the thumb. This is the thumb, and this is the tsetse fly. It's like one-fifth of the thumb. It's likely normal than a bigger house fly. So it's medium to large size and brownish to grayish in color. It has long wings as you can see. Which extends beyond the tip of abdomen. Let's look at the life history. Like in other Dipterans, which includes mosquitoes, Glossina have complete metamorphosis with four larval stages. They have a pair of spermathecae, which is used for the storage of sperms acquired from single mating early in life. Unlike other Dipterans, the Glossina has viviparous reproduction, which involves production of one egg at a time. And this is retained and nourished until delivery as third stage larva. Single larvae develops in the uterus and nourished from uterine milk glands. Each female has a potential to produce eight to ten larvae. So it is going to take very long to production potential. After about two weeks the, the mature third stage larva, this is a pregnant tsetse fly. The third stage level they're final excruded, extruded by the mother in this form. This is the third stage larva, which has got a puparium shape. Then, within an hour, then the larva develops into dark barrel-shaped puparium with typical two prominent lobes. Which we can see here on the posterior end. Within the puparium, two moults take place. The first one to produce the pupa and the second one the imago or the pale teneral fly. This matures into an adult within 48 hours. Emergence takes place during the afternoon and evening hours. That is within a few hours of daily maximum temperature. The life span of the female adult is two to three months. But, exceptionally, can survive for seven months. Males have a shorter life span. About their behavior, both sexes feed on blood and can transmit parasites equally. This is quite different from other blood sucking Dipteran species. Males feed less frequently only because they don't require so much food. So much source. They hunt by sight and by scent using their antenna. And sight and scent, it become important at close range. But at distance they detect movement. So they fly then wants to detect the movement, it will fly them to investigate. The attraction is limited by carbon dioxide emitted by the animal. As well as octanol can also be used, aceton and urine, urine as attractor, attractants. These habits, animal used in effective for development of effective [INAUDIBLE] as we shall see. Consider, con, consider attraction of color is important. Especially blue, black, and white. And again, these color patterns are taken into behavior. Will concer, con, constructing traps for the tsetse flies. It has diurnal activity pattern. Unlike the mosquito, which has nocturnal or night activity pattern. It has limited movement. And rest on topside of leaves of trees at night. But they do in the daytime, it rests on the wood part of vegetation, so that it can have a clear view of its prey. It can fly long distances, even up to 21 kilometers. But then, in most cases, the flight activity is limited to only short hunting distances, to suitable blood source. And it normally comes back to its habitat, a kind of homing behavior. One of the tsetse fly control method is by using bi-conical traps like this one in front of me. This takes advantage of the habits of the tsetse flies. Which are merely attracted by dark colors and also smear. And this trap is constructed in such a way that tsetse fly will be attracted by the dark colors and also by the urine, cattle urine. It will be attracted by the urine and also the color. And then when it reaches here then it can start to explore the inside of this trap. And finally, it will move upwards until it is trapped in the top here. Sometimes we use an insecticide to kill the tsetse flies which are being trapped. But also when exposed to the sunlight they can also be killed. Let's look at the epidemiology. There are three interrelated factors. Which are important for trypanosoma brucei gambiense transmission. These include the parasite, the vector, and climatic conditions. The parasite and vector are especially important. The species distribution, as you are seeing for the vector. As well as for the parasite quite variable with trypanosoma brucei gambiense in West Africa. And trypanosoma morsitans in Eastern South Africa. And these are associated with different specific vector species as well as ecological conditions. As you saw during the introductory part. Trypanosoma gambiense, the parasite. Transmission is site associated, with particular sites near riverine vegetation and also to water or collection points. In humid areas, peridomestic Glossina palpalis are associated with domestic animals and human population living close to or within villages. But in the more humid part of the vegetation the fly becomes more widespread. And therefore, the transmission is less well localized, but then you have less vector human contact. The vector has less, less intense transmission. But the vector then has higher infectivity, due to the increased longevity under this favorable condition. Trypanosoma rhodesiense, which is normally found in the western part and in the eastern and southern part of Africa, causes the acute form of sleeping sickness. This is associated with woodland savannah, the preferred habitat for the strongly zoophilic vectors, which are Glossina morsitans type species. The reason, the reservoir hosts in this case domestic animals and a variety of given animals. So specific groups of people therefore are more at risk of becoming infected. Usually those whose activities or occupations bring them into more frequent contact with the vector. Such groups then include the hunters, honey collectors, tourists who might adventure deep into the forest to contact the victims. So during their epidemics, other groups of the population are affected including children. So where have children infected, women who in most cases won't venture into the bush than this green alum for an epidemic. Climatic conditions. Favorable conditions are temperatures and rainfall which then determine the transmission as you have seen. The temperature plays an important part in determining the infectivity rates in the fly. As well as the duration of the developmental cycle of the parasite in the insect host. Climate also is important in relation to the degree of contact between man and fly. As we said earlier during dry conditions the vector will come close to the human population. Particularly, in the West Africa parts where we've got palpalis. Intense transmission at the end of the dry season then this is common when the vector then human contact is most frequent
