Anopheles

ANOPHELES, a genus of mosquitoes, subfamily Anophelinae, family Culicidae. Many species of Anopheles are capable of transmitting the malaria parasite, which determines their enormous medical significance. Several species of Anopheles live in the USSR; the most important among them are: A. maculipennis Mgn.—the common malaria mosquito, distributed from the extreme north to the south; A. maculipennis var. sacharovi Favre (A. elutus Pjdw., Crimea, Transcaucasia, Turkestan); A. bifurcatus Lin.—the forest malaria mosquito (from the Luga district southward); A. nigripes Staeg.—the black-legged malaria mosquito, the larvae of which breed exclusively in water bodies in tree hollows (Caucasus, Kharkov); A. superpictus Grassi—the speckled malaria mosquito (Turkestan and Caucasus); A. hyrcanus Pall.—Pallas's malaria mosquito (the south of the USSR, starting from Dnepropetrovsk, the Caucasus, Turkestan, and the Maritime Province); A. pulcherrimus Theo.—the beautiful white malaria mosquito (Turkestan, eastern Transcaucasia); other species are rare. The Anopheles fauna of the USSR is still insufficiently studied. The various species of Anopheles are distinguished by wing venation and spotting, the shape and color of scales and hairs, the shape of the femurs, and other subtle features (for example, the structure of the male genitalia), which can be recognized only under a magnifying glass with a magnification of at least 10 times; for minor features, microscopic examination is necessary. A. bifurcatus and A. nigripes have no spots on their wings; A. maculipennis bears four dark spots on each wing (accumulations of scales); in A. superpictus, the wings are very spotted with whitish and black elongated spots along the front margin. In A. hyrcanus, only two white spots lie along the front margin of the wing closer to the apex, and the femurs of the front pair of legs are noticeably thickened. On the rear corners of abdominal segments 2–8, densely covered with white scales, A. pulcherrimus has protruding tufts of white or yellowish-brown scales; its wings are also spotted. Domestic or semi-domestic species can be considered to be A. mac., A. super., and A. pulch.; A. hyrcanus rarely flies into human dwellings and stays in reeds and thickets; A. bifurcatus and A. plumbeus fly in parks, gardens, and forests. During the day, A. mac. sits quietly in shaded corners of rooms, under beds, in entryways, courtyard-type outdoor toilets, livestock barns, etc. Its posture at normal summer temperatures: the abdomen and rear pair of legs are raised at an angle to the surface on which it sits. At the low temperatures of wintering sites, however, A. mac. keeps its abdomen lowered, resembling the posture of Culex. A. mac. does not fly further than 2 km from its breeding site. Spreading from the hatching site, A. mac. populates human dwellings, domestic animal enclosures, etc., along the way. The topography of the place and the arrangement of buildings in relation to flight paths explain the uneven distribution of A. mac. (and malaria) across the blocks of a settlement. Practically important is the ability of A. mac. for passive distribution over long distances—on steamboats, trains, carts, etc. Thus, infected mosquitoes can be imported into a non-malarial area and become the cause of malaria cases there. A. mac. usually does not rise higher than 15 m; the higher the floor, the fewer Anopheles there may be, although along bushes and climbing plants they can rise to a great height. In the mountains, A. mac. lives at an altitude of up to 4,000 m above sea level. Only female Anopheles are blood-suckers, and they can also feed on plant juices. Males have a reduced piercing apparatus; they cannot pierce the skin and are content with plant food. Therefore, only female Anopheles have epidemiological significance in malaria and filariasis (Filaria bancrofti). Preparing to drink blood, the female places the tip of her proboscis against the skin of a human or animal and, under the control of the terminal lobes of the proboscis, begins to immerse the complex of piercing mouthparts into the skin, consisting of: a) the upper lip (labrum), b) a pair of maxillae, c) the tongue (hypopharynx), and d) a pair of mandibles. The lower lip (labium) remains outside the entire time, but as the mouthparts are immersed, the proboscis bends and finally folds in half. The salivary canal passes through the tongue of Anopheles, communicating with the excretory duct of the salivary glands. Saliva flows from the tip of the tongue into the punctured thickness of the skin tissues, enters the blood, and causes local irritation, the intensity of which depends on the species of mosquito and the degree of individual human sensitivity. Usually, Anopheles attacks humans from sunset to sunrise, but sometimes it also sucks blood in the middle of the day in full light. Anopheles drinks the blood not only of humans but also of domestic animals. In some localities (Denmark), it has been noticed that Anopheles feeds exclusively on the blood of cows or other animals. In this regard, attempts were made to distinguish two races of A. mac.—zoophilic, feeding on livestock blood, and anthropophilic, feeding on human blood. But apparently, the difference in mosquito feeding is explained not by their belonging to different races, but only by surrounding conditions—the presence and quantity of livestock, the arrangement of stalls, the timing of livestock staying outside the home, etc. The causes of "anophelism without malaria" must be investigated in each individual case. A female Anopheles consumes up to 3 mg of blood at a time; blood feeding is necessary for the maturation of eggs, which are laid repeatedly in batches of up to 350 pieces. After laying eggs, a new blood meal is necessary, and so on. Only fertilized female Anopheles overwinter (mosquito mating occurs in flight). Anopheles overwinters in cellars, basements, underfloors, barns, stables, and other places possessing a certain degree of humidity and a stable temperature independent of sharp external fluctuations, and lacking drafts and light. Mosquitoes do not settle down for the winter immediately, but during warm spells, they can leave buildings and even attack humans in the middle of winter. The start of wintering for female Anopheles varies in the USSR depending on latitude and the onset of cold weather. In 1923 in Moscow, the start of wintering was September 12; in Izyum in 1924, wintering began on August 7–8 at a minimum temperature of +12°. Further south, the start of wintering is correspondingly delayed. In winter in cool and cold rooms, Anopheles sit in a torpid state. In the same house, the emergence of Anopheles from the attic and from the basement can differ for a given spring by a month. The destruction of Anopheles in their winter quarters is the most rational method of combating them. Having flown out of winter quarters, female Anopheles drink blood and, after the eggs mature, lay them in water. For this purpose, Anopheles choose predominantly illuminated water bodies with clean (oligo- or $eta$-mesosaprobic) standing or slowly flowing water, with submerged plants. If Anopheles larvae are found in a water body without plants, this means that there is algal microflora in it, serving as food for the larvae. The suitability of a water body for the life of Anopheles larvae depends on the water composition, the reaction of the environment, the general character of the water body, plant and animal communities in it, etc. The active reaction of the environment ($ ext{pH}$) influences Anopheles larvae mainly indirectly, preventing or favoring the life of algae and other organisms serving as food for the larvae. A lack of $ ext{O}_2$ entails a lack of food. Anopheles larvae can live in water with a salt content of 0.9–1.5%. Being sensitive to water pollution by organic substances, Anopheles larvae are nevertheless also found in polluted water bodies, but only in the presence of green plants submerged in the water. Anopheles breed not only in permanent water bodies but also in temporary accumulations of water—puddles, spring pools, barrels, buckets, tin cans, and many others. Anopheles lay eggs singly; the eggs have swimming devices in the form of lateral chambers or a swimming fringe. Thanks to this, the boat-shaped Anopheles eggs stay on the very surface of the water. The hatched Anopheles larva goes through four larval stages in the water, separated from each other by molting. After each molt, the larva moves to the next age stage (instar). After the fourth molt, a pupa emerges. The differences between the larvae of different Anopheles species are insignificant; the identification of larval species is carried out according to the hairs on the front edge of their head and some other microscopic features. The Anopheles pupa looks like a giant comma. It does not feed, but moves energetically, working with its abdomen, usually tucked under the thick front part housing the head and thorax (with their appendages) of the future mosquito. Like the larvae, Anopheles pupas breathe atmospheric air with the help of special tubes, for which they rise to the surface. Figure 1. External morphology of a mosquito of the family Culicidae: a—proboscis (lower lip—labium); b—head (caput); c—thorax, showing mainly the mesonotum forming an upwardly convex hump; on the left between the bases of the middle and rear legs, a pin-shaped haltere is visible, which is a rudiment of the second pair of wings; d—abdomen (abdomen), consisting of segments; at the rear end of the abdomen, two single-jointed tubercles—cerci, or tail appendages, are visible; e—maxillary palps (palpi maxillares), while the mandibles and maxillae are hidden in the proboscis; the relative length (compared to the proboscis) of the palps is important for distinguishing Culicinae from Anophelinae; f—antenna (consisting of 15 segments); short-haired antennae are characteristic of female mosquitoes; t—five-jointed tarsus (tarsus). Figure 2. Scutellum—an appendage of the mesothorax, top—entire-margined, typical of mosquitoes of the subfamily Anophelinae; bottom—three-lobed (characteristic of Culicinae). Figure 3. Heads of mosquitoes from the side.

o-compound eye; i-probos-cis (labellum) with terminal lobes (labellulae); p-maxillary palps; s-antenna; a-head of a male A. maculipennis (male mosquitoes in general are characterized by densely hairy antennae), palp equal in length to the probos-cis, the last two segments of the palp club-like and swollen; b-head of a female A. maculipennis, antenna sparsely hairy, palp equal in length to the probos-cis; c-head of a female Culex, palp more than three times shorter than the proboscis (antenna not drawn). Figure 4. Mouthparts of a female common malaria mosquito; all mouthparts removed from the sheath formed by the trough-shaped lower lip (proboscis); a-antenna; an-faceted (compound) eye; cl-clypeus; pmx-maxillary palps; lb-lower lip (proboscis); lr-elongated and pointed upper lip (labrum); mn-spear-head-like upper jaws (mandibulae); mx-saw-like serrated lower jaws (maxillae); hp-hypopharynx («tongue»). Figure 5. Wing of the common malaria mosquito. Spots and scales not depicted. Only wing venation visible, c-costal vein (costa), sc-subcostal vein (subcosta); R₁, R₂, R₃, R₄+₅-radial veins (radius), R₂ and R₃ form the «anterior fork» of the wing; M₁+₂, M₃-medial veins (media), forming the «middle fork» of the wing; Cu₁ and Cu₂-cubital veins (cubitus), forming the «posterior fork» of the wing. Between R₄+₅ and M₁+₂ runs the radio-medial (transverse) vein; between M₃ and Cu₁ runs the medio-cubital transverse vein. The wing venation of Anopheles is characterized by the extension of vein R₄+₅ beyond the radio-medial vein into the wing cell lying medial to it. Figure 6. Egg of A. maculipennis: a-from above, b-from below. Float chambers are visible on the sides of the egg. Figure 7. Eggs of malaria mosquitoes from above. a-A. nigripes, b-A. bifurcatus, c-A. hyrcanus and d-A. pulcherrimus. Figure 8. Larva of the common malaria mosquito from above. The widest part of the body-the thorax is not subdivided into segments. The thorax, like the first abdominal segments, bears feathered hairs on the sides. Figure 9. Mosquito larvae-on the left of the subfamily Culicinae, on the right of the subfamily Anophelinae in breathing posture at the surface of a body of water. The larva of Culicinae hangs at an angle to the surface by its respiratory siphon; the larva of Anophelinae lacks a respiratory siphon and therefore stays parallel to the surface of the body of water. Figure 10. Typical resting posture of mosquitoes: a-Anopheles, b-Culex. Figure 11. Pupa of the black-legged malaria mosquito (A. nigripes). The thickened part contains the head, thorax, and its appendages of the future mosquito. On this part from above, the respiratory siphon is visible, by which the pupa hangs during breathing from the surface of the body of water. Figure 12. Structure of a female malaria mosquito, side view; the entire body is shown in optical section; the head bears antennae (a), palps (b), and proboscis (c), part of the piercing mouthparts complex (h) is partially protruded; in the head, the supra-esophageal nerve ganglion is visible (shown by dotted lines), beneath it runs the esophagus and salivary duct; in the thorax from above are shown the flight muscles (m), the crop sac (s-left) and the complex of thoracic ganglia of the ventral nerve chain (c); between e and o lies the three-lobed salivary gland; in the abdomen dorsally lies the heart in the form of a tube consisting of several chambers; beneath it lie the stomach (i) and the ovary (o), whose eggs are still underdeveloped; s (right)-long sac or bladder of the «crop»; beneath it lie the abdominal ganglia of the nerve chain. Figure 13. Clypeus hairs in larvae of various Anopheles species; a-A. nigripes, b-A. superpictus, c-A. maculipennis and d-A. bifurcatus; p-marginal or corner hair, o-median hair. surface of the body of water. The duration of metamorphosis of Anopheles depends on temperature, food abundance, nature of the body of water, and properties of the egg itself. Normal periods of metamorphosis according to Martini: temperature, egg, larva, pupa, total development in water: 24-27°: 2 days; 20-21°: 3 days; 16-19°: 5 days. In some species of Anopheles, such as A. bifurcatus and A. nigripes, the larva overwinters. Hatching of the mosquito occurs on the surface of the body of water. The abdomen of the pupa bulges horizontally. The skin of the dorsal side of the thickened part of the pupa cracks, and the head and thorax of the mosquito gradually protrude from it. The skin of the pupa serves as a little boat for the hatching insect. Until its legs are removed from the sheaths and straightened, at the slightest disturbance water can swamp the little boat-and the mosquito dies. In the northern zone of the USSR there are up to two generations of A. maculipennis per year, in the middle zone 3-4, in the southern zone 5-6. Calendar boundaries between them cannot be established, because the emergence of Anopheles from wintering sites occurs asynchronously; therefore, the period of both egg-laying and transformation phases is prolonged, which blurs the boundaries of generations. In localities inhabited by various species of Anopheles, the relative abundance of individuals of one or another species is timed to different parts of the season. In Turkestan, A. bifurcatus and A. maculipennis predominate in spring; A. superpictus and A. pulcherrimus are late species, A. hyrcanus is a poly-seasonal species. In addition to malaria, Anopheles transmit filariasis-elephantiasis (Filaria Bancrofti), as well as F. immitis and Dirofilaria repens of dogs. Consultation on the identification of Anopheles is provided by the permanent commission at the Zoological Museum of the Academy of Sciences of the USSR (Leningrad) and at the Tropical Institute (Moscow).

E. Pavlovsky.

ANOPHTHALMIA, anophthalmos (from Greek a- privative particle, and ophthalmos - eye), anophthalmy, absence of an eye or eyes (whatever the causes of this condition may be). - Acquired anophthalmia in rare cases is the consequence of direct exposure to harmful agents, and more often is the result of surgical intervention for diseases or injuries. In acquired anophthalmia, the eyelids appear sunken, do not open voluntarily, between them is a more or less wide fissure leading into the cavity of the conjunctival sac of individually varying depth. The mucous membrane is always slightly irritated due to entering dust particles, which is caused by a mechanical disorder of the function of the tear-evacuating apparatus. The depth of the orbit cavity is occupied by adipose tissue, a shrunken Tenon's capsule, and muscles attached to it, retaining their nerve pathways, which is why when the remaining eye moves, the posterior wall of the conjunctival sac also moves, on which in the center a radiant scar is usually noticeable - the trace of the conjunctival incision during surgery. - Congenital unilateral anophthalmia is rarer than bilateral (according to Schöppeler 23 : 64) and is usually accompanied by various malformations of the other eye or other organs (cleft palate, syndactyly, ear deformity, etc.). To the group of true anophthalmia should belong only those cases in which careful clinical examinations do not allow palpation in the depth of the orbit of the presence of even a small nodule (rudimentary eye), and in the thickness of the lower eyelid - a cyst-like formation; but even here patho-anatomical examination sometimes points to an underdeveloped eye. In congenital anophthalmia, there is also a delay in the development of the orbital bones and a violation of proportionality between parts of the face. The eyelids are usually formed correctly, but there is a slight entropion of them, and the palpebral fissure is shortened. The lacrimal apparatus is normal, the lacrimal glands are often enlarged, the conjunctival sac is greatly reduced, and its mucous membrane is usually in a state of chronic catarrh. The ocular muscles, even with the anatomically proven absence of the eye rudiment, are developed satisfactorily and terminate in the fascia lying beneath the conjunctiva. Autopsies of the cranial cavity show narrowness of the optic canals through which arteries pass into the orbit; optic nerves are absent, the chiasm and optic tracts may be present, but may also be completely absent, consequently, there will be no fibers of Gudden's commissure; lateral geniculate bodies are weakly expressed or absent entirely; in the cerebral visual centers - underdevelopment of layers. In some cases, all or some motor nerves of the eyes are absent. This malformation can appear in many family members (in two or even four children). There are indications of the possibility of hereditary transmission. Nevertheless, the main etiological factor must be considered not heredity, but diseases and intoxications of the parents. Stockard obtained this malformation experimentally by acting on the embryo with alcohol vapors. Various other congenital eye malformations in rabbits were obtained by exposing pregnant rabbits to choline or X-rays, with the help of bacterial toxins, by the action of skatole and paracresol. In amphibians, Leplat obtained anophthalmia by altering the environment in which they developed by the addition of lithium chloride. Gallemaerts considers syphilis to be the main factor in humans, but alcoholism must also be attributed here, and furthermore, clinical practice teaches that disturbance of the functions of the uterine mucosa (curettage) can lead to the occurrence of malformations in a child born (shortly after this operation).