Anopheles mosquito

“ Reed's attention had been drawn to the possibility of the mosquito as a transmitter of disease by the then recent work of Ronald Ross, of the British Indian Medical Service, in demonstrating that the Anopheles mosquito carried the plasmodium causing malaria between birds, while Sir Patrick Manson demonstrated that the bite of an infected mosquito could cause malaria in man. ”

“ Anyone desirous of working out for himself the metamorphosis of the filaria in the mosquito can readily do so, even in the absence of a suitable human subject, by setting Anopheles mosquitoes to bite filariated dogs. ”

“ No one ever slept in the tent, and I never found Anopheles bite in the day-time.
The best way of ‘downing’ mosquitos is to prevent the imago hatching, and this, as has been indicated, can be done by killing the larvae and the pupae, which is effected by brushing oil on the water in which they live. The petrol or crude mineral oil should be renewed from time to time as it evaporates. When once the mosquitos are hatched, every effort should be made to keep them outside dwelling-houses by means of wire screens, but if that be impracticable mosquito-nets should be used at nights. ”

“ There seems small wonder that the carnivorous feeder and spirituous drinker from a chilly latitude should fall a victim in the East to malarial and other fevers: and this without any assistance from Lady Anopheles or her sister mosquitoes. To her a meed of praise would seem due, for where the mosquito exists there is proof of a need of drainage, clearance, and general sanitary attention. But man, who has stoned the prophets throughout the ages, equally execrates the insects that come as warnings. ”

“ So it is ten or twelve days or sometimes as much as eighteen or twenty days from the time an Anopheles bites a malarial patient before it is dangerous or can spread the disease. On the other hand, the sporozoites may lie in the salivary gland alive and virulent for several weeks. It does not give up all the parasites at one time, so that three or four or more people may be affected by a single mosquito. ”

“ If there were trees and shrubs and bushes every few yards, the anopheles mosquito might travel very long distances and not be much exposed to either the sun or the wind. But if an area of two hundred yards around each building is kept clear, she will not often be able to cross such a zone without destruction, either by sun or wind. Clearing this zone exposes the ground to both sun and wind, and by these forces alone many of the smaller pools will be dried up and made unfit for mosquito breeding. ”

“ The existence of the parasite is maintained by a vicious interchange between its alternate hosts, mosquitoes and man, each infecting the other. If the cycle be broken at any point the parasite must die out, assuming that it has no other origin or mode of existence. The most effective step would obviously be the extermination of the Anopheles mosquito. A great deal may be done towards this end by suppressing their breeding-places, which means the drying of the ground. ”

“ It cannot be too strongly insisted upon that we absolutely know that the statement just made is correct, and that avoiding the diseases referred to becomes as a consequence entirely a matter of preventing the entrance of mosquitoes into houses. [Pg 42]
The Anopheles mosquito, which is the one that transmits malaria, often exists in localities where the more common varieties do not occur, and on account of the habits of this insect their presence is liable to be overlooked. ”

“ Knowing the cause, we can now guard against malaria; mosquito-nets and wire-protected windows and doors are a sufficient check on the access of Anopheles to man. If the mosquito and man could only be kept permanently apart, we might hope for the disappearance of the parasite from our fauna. In relieving man from this world-wide pest, all genuine lovers of animals will rejoice that we are also relieving the far more serious lesions of one of the most delicate and beautiful insects that we know. ”

“ A sanitary inspector, when malaria is rife, has to be thoroughly familiar with the life history of the mosquito, and particularly with the life history of the anopheles. There are some six or seven hundred species of mosquitoes, and many [Pg 192] of these differ widely in their habits of flight. The stegomyia mosquito is one of the feeblest species in its ability for flight, and it is at once blown away and destroyed when it gets into a breeze. It therefore seldom wanders from the house in which it is bred. ”

“ As far as we know, the parasite of malaria exists only in infected man and in infected mosquito. Perpetuation of the disease is due to the perpetuation of the cycle, man to mosquito, mosquito to man. If the parasite is destroyed in man or the Anopheles is not allowed to breed, the disease disappears. ”

“ Generally, in any one locality, there are only three or four species of mosquito occurring in any abundance, so that when the inspector has learned to differentiate these, he is pretty well educated for work in that particular locality. Each species usually has some prominent trait; the anopheles, for instance, has the hind legs very much longer than the fore legs, which gives her when at rest the appearance of standing on her head. ”

“ It required about 150,000 gallons of mosquito oil a year to keep down the mosquitoes. There are 50 known breeds of these insects on the Isthmus and perhaps some 20 species more which have not been identified. Of the 50 or more species of mosquitoes 11 belonged to the malaria-producing family—anopheles. Their cousins of the yellow-fever-producing family—the stegomyias—boast of only two species. What the other 40 or more kinds are doing besides annoying suffering humanity has not been determined. The mosquito is comparatively easy to exterminate. ”

“ These germs, it is found, pass from malarial patients to others through the agency of a variety of mosquitoes known as Anopheles. In sucking the blood of a malarial patient, the mosquito first infects her own body.131 In the body of the mosquito the germs undergo an essential stage of their development, after which they are injected beneath the skin of whomsoever the mosquito feeds upon. For the spreading of malaria, then, two conditions are necessary: first, there must be people who have the disease ”

“ The case of the anopheles and his little contribution to human suffering is very different. Whereas the victim of yellow fever either dies or gets better and quickly ceases to be a source of infection to the mosquito, the victim of malaria seldom dies of the disease, but he remains infectious to the anopheles for three years. The disease does not simply attack new-comers or white people. Natives of the isthmus and the West Indies are subject to it, and, indeed, seem to be in a chronically malarious condition. ”

“ The only protection employed against mosquito-bite and fever by the experimenters who occupied this hut was mosquito-netting, wire screens in doors and windows, and, by way of extra precaution, mosquito-nets round their beds. Not a grain of quinine was taken. They go about the country quite freely—always, of course, with an eye on Anopheles—during the day, but are careful to be indoors from sunset to sunrise. ”

“ These spores, or merozoites, enter new blood cells and repeat the process (auto-infection) . When taken into the stomach of the mosquito Anopheles, the parasites become much larger, some develop male gametes (o, p, q) on the Polymitus form {p) ; others, female gametes (r—u) . These conjugate (v) in the stomach of Anopheles, and the copula (w) penetrates the epithelial lining of the stomach and ultimately lies suspended in the body cavity (x—zz) . When mature, the parasite forms spores (A) , which form, in turn, naked sporozoites (B) . ”

“ Some observers maintain that Anopheles does not “sing,” like the common mosquito, and its bite is much less irritating. Only the females suck blood; the act is believed to be necessary for fertilization and reproduction. Anopheles rarely bites by day, and then only in dark places. ”

“ When a gnat or mosquito sucks blood, all phases of the parasite in the peripheral circulation at that point may succeed in passing into the insect. If this occurs all trophic and schizogonic phases are forthwith digested, and the survival of the sexual phases depends entirely upon whether the insect is a gnat or mosquito. Only in the latter case can further development of the gametocytes go on; in other words, only the genus Anopheles, and not the genus Culex, furnishes specific hosts for the malarial parasites. ”

“ The old genus Anopheles (characterized by the palpi being long in both sexes) is now divided into a number of genera according to the character and shape of the scales on the different regions of the body and on the wings. These genera make up the sub-family Anophelinae, and together include over 100 species. The genus Culex, from which the family takes its name, though it has been similarly split up, is still in its restricted sense larger than any other, and some 200 species are comprised in it alone.
Mosquitoes are found in all parts of the world. ”

“ That rats convey plague to man is certain; whether fleas act as an intermediary remains somewhat uncertain.
The Mosquito family (Culicidæ) has been found to be an important if not the sole means of spreading certain serious diseases to man. To this family belong all true gnats or mosquitoes; but the only two genera which have been proved to be able to cause disease are Culex and Anopheles. ”

“ The stegomyia likes clean rain water such as is found in cisterns and water barrels. As these collections are found principally around the dwellings of man in towns and cities, this mosquito [Pg 193] is known as a town mosquito. The larvæ of the anopheles, the malarial mosquito, also likes clear, clean, fresh water, but it requires algæ and grass for its protection. These conditions are best furnished by the edges of ponds and running streams. This mosquito is, therefore, essentially a country mosquito. ”

“ They are often found in the blood some time after all symptoms of fever have disappeared, and are associated with the malarial cachexia which follows an attack of æstivo-autumnal fever. When blood containing these crescents is ingested by a mosquito of the genus Anopheles the following very remarkable transformations occur: Some of the crescents are transformed into hyaline flagellate bodies having active movements; others are changed into granular spheres. The flagella break away from the hyaline bodies and, approaching the granular spheres, appear to seek energetically to enter these bodies. ”

“ In 1900, Sambon and Low, and Grassi, conducted in the most malarious sections of Italy careful experiments which proved to the world that malaria is transmitted to man through the bites of the malarial mosquito, Anopheles maeulipennis. These experiments have since been duplicated and the results confirmed by many others in different parts of the world.
Mosquitoes breed only in water,-and the malarial mosquito will breed in almost any pool where other kinds flourish, but is never so abundant as the rain-barrel mosquito, Culex pipiens, or the salt-marsh mosquito, Culex sollicitans. ”

“ During a warm spell in the winter or if the room is kept warm they may come out for a meal almost any time.
THE YELLOW FEVER MOSQUITO
Ranking next in importance to Anopheles as a disseminator of disease and in fact solely responsible for a more dreaded scourge, is the species of mosquito now known as Stegomyia calopus. While this species is usually restricted to tropical or semi-tropical regions it sometimes makes its appearance [Pg 95] in places farther north, especially in summer time, where it may thrive for a time. The adult mosquito (Fig. 104) is black, conspicuously marked with white. ”

“ Any one who is ill with malaria or yellow fever should be carefully protected from mosquitoes, for, should a person be bitten by an Anopheles, the malarial mosquito or Stegomyia fasciata, the yellow fever mosquito, at this time, there would be great danger that the insects might fly away and bite some one else and thus spread these diseases. Screens for both doors and windows form the best protection against mosquitoes at all times ”

“ Fortunately, only a small proportion of the number of [Pg 380] mosquitoes in the world are capable of nourishing the malaria parasite. Under ordinary conditions about 5 per cent of all mosquitoes found are malarial, and a particular name has been given to those capable of transmitting the disease. The ordinary mosquito is known as the "culex," while the malarial kind is known as "anopheles." Figure 78 shows the characteristic attitude of the two kinds by which the one can be distinguished from the other when resting on a wall or ceiling. ”

“ The presence and growth within the blood-cells result in the destruction of the latter, a very serious thing to the patient if the organisms be at all numerous. If the spores be sucked up by an Anopheles, they undergo a complex change, and ultimately{160} reproduce an incredible number of minute spores or ‘blasts,’ each capable of infecting man again if it can but win entrance into his body.
Under normal circumstances, for each Filaria larva which enters a mosquito, one Filaria issues forth, longer, it is true, and more highly developed, but not much changed. ”