Now, let's now zero in on the lymphatic filariasis. 90% of infections are caused by Wuchereria bancrofti and the remainder Brugia malayi. Humans are the exclusive hosts of infection with Wuchereria bancrofti. Certain rare species like Brugia malayi can also affect some animal species. And this has been quite useful when it comes to laboratory experiments where we have a human host that can be used, an animal host that can be used. Wuchereria bancrofti is transmitted by Culex species. This is because of urban and semi-urban areas. Anopheles species in rural areas, and in some of the Pacific islands you have got Aedes species, which also is possible for the transmission. Brugia malayi and Brugia timori are transmitted by Anopheles, in some areas also by Mansonia species. Now let's look at the distribution. About 146 million people in tropical and subtropical regions are infected with lymphatic filariasis. With the main symptoms being hydroceles and elephantiasis. Hydroceles mainly in the eastern Africa region and elephantiasis in the India subcontinent. We also have Wuchereria bancrofti, one which is widely distributed in sub-Saharan Africa as well as in Asia. And also eastern parts of Latin America. Brugia malayi there is restricted to Southeast Asia. The parasite itself, there that's inhabit human lymphatic vessels and lymph nodes. The nodes are formed by the coiling of the other parasite. And usually the sexes are coiled together. And I've said, the female is normally larger than the male, about twice the size. The macro of Wucheria bancroft is sheathed. And this is quite a useful feature which is used when it comes to separating from. All the three species are similar, but Wucheria bancroft is female largest. The last one of the adults is about 18 years. But that one of Microfilaria can be about one year. The parasite has got a unique behavioural characteristic named periodicity. This involves fluctuation of densities in peripheral blood according to a 24 hr cycle. In Africa, Wucheria bancrofti exhibit nocturnal periodicity, whereby the microfilaria appear in blood during the daytime. Of course, during the nighttime they are said to occupy the vessels around the lungs. Periodicity that corresponds very well with mosquito biting habits. High densities are normally coordinated with a high density period of the vector. This is said to be caused by biological rhythm. Which is inherent in microfilaria, but to some extent also influenced by circadian rhythm of the host. Now, let's look at the epidemiology of filariasis. Determinants of transmission include that parasite in that the species and type of strains determines the intensity of the transmission. Periodicity, of course, plays a part in the sense that well have got vectors that do not bite at the time when the microfilaria densities are highest in the peripheral blood. Then the transmission then they'll not be able to be picked up by the host. So the number of circulating mf densities in peripheral blood at the time when the vectors also biting in high densities. This determines the rate of transmission. Vector-efficiency, this is important. The vectors supporting the microfilaria development differ in their levels of efficiency. For example, anopheles are is one of the least efficient vectors, because of having amateur structures in the mouth, which cause obstruction to the microfilaria. But worse are the genetic factors which interfere with the efficiency. The two species of anopheles mosquitos and Culex is responsible for the transmission. And we find that in case of Africa, the anopheles species, which are efficient in the transmission of the malaria parasite, are also efficient when it comes to the transmission of lymphatic filarias. But then this is mainly restricted to rural areas where conditions favor the breeding of Anopheles. In rural areas of Culex, which is less efficient. But because of the high numbers, then they will become important in urban areas, which offer conducive conditions for their survival. Human prevalence and intensity of microflora are important, and here we look at the age factors. As I said, it takes about one year for the to develop in the human host, which is the through host. And refer to that, usually micro falidia, that is related to the age. So the maximum period of densities is around ten years. But after 15 years when the symptoms start to form, when the adult has established itself in the body then they offer a kind of immunity which prevent other new infections. So the older population with symptoms is less likely to contribute. To the transmission of this disease. Again of course, we have other factors which relate to the prevention or to the protection, such as evidence of areas which have got high density population or suitable which can minimize the bites of the fly. Climatic and geographical conditions are important, because the black flies breed in water. And during times of drought, and then the breeding conditions are not easily available, and therefore this again reduces the rate of transmission. But in general we can say that fluorescent transmission is quite an effective mechanism that requires several bites for microfilaremia when you compare with malaria where a single bite can cause infection, this is not the case with filariasis. It requires several, several bites. The limited multiplicative stages, you have got a maximum of 10,000 microfilaraemia in blood. But then would come to the numbers of effective stages which are produced by the mosquito. They are normally less than four with an average of 1.5. Now let's go back to the life cycle we'll see where we have problems. The first problem is during passage in the vector mouth where for some species, you have got destruction. Destruction the pharyngeal cibarial aperture. But also there are cases when they are passed down to the So this reduces the [INAUDIBLE]. Then you have penetration through a tough membrane. A lot of micro film are trained to penetrate this membrane. And then this contributes to the reduction of the number of wins. And then they center themselves in the most difficult area in the wing muscles, which have got quite a lot of the flight muscles. And therefore we have a lot of mechanical destruction during the action of flight. A lot of worms then are lost in this way, in the flight muscles. And then I've got those which I'd like up to the infective stage. Then there's a problem also. Before getting to the proboscis, they wind around in the body in the Before settling in their heterogen and in the proboscis. In the proboscis there's a problem that can be lost during blood feeding. And let's look at the way in which the worm is passed through the body. This is the blood vein, and the one is deposited here covered with the [INAUDIBLE], the blood of the mosquito. Then it's up to this one to look for the puncture in order to penetrate. I'll [INAUDIBLE] which are injected directed to the bloodstream. The worm has to find its way. So depending on the humidity, this worm can undergo desiccation. For example, to locate this wound. And in fact, this solution of Filariasis, is very much linked with relative humidity. So where does under less humid conditions that problem is that the worms will not be not able to penetrate and therefore the left cycle continues to become an inefficient system. And finally in the other they also immune, like we have said. That in the adult population, which order of the adults, the chances are that there's immunity, which prevents the infective stages from developing to adult. To the inefficiency of the whole transmission system. Which in a way is good for us. Let's look at the prevention and control. The most effective method of controlling for us is now is chemotherapy which involves mass treatment. This treatment is mostly effective against microfilaria with minimum effect on the adult. About ten years ago, the drug of choice was diethylcarbamazine, which had some adulticidal effects, but now what is common for both nephatixoxis and labortoxis is labartine. I don't know in combination with albendazole. When the scent control method if for vermin which protect host brain, also the commitment for the control of the Anopheles species which can transmit arasis, And control measures for Culex quinquefaciatus which also involves targeting breeding sites like latrines and cesspools Also important. Environmental management is quite also important, which includes application of expanded polystyrene beads in latrines as well as larvicide with bacillus spharicus. Mansonia is species which Also take part in the transmission of brugia malayi. Filariasis can be eliminated by destruction of the plants. As we said, this species normally breed in areas where there are floating plants. Seem they love attaching themselves to the roots of such plants
