time in order to evaluate the results of preventive measures. 



7. Efforts to have adult mosquitoes killed daily by the in- 

 habitants wliile highly desirable will usually be found imprac- 

 ticable. This measure would be too expensive for government 

 maintenance, but where full cooperation is assured it should be 

 adopted to supplement the foregoing. 



The control of filariasis in the Orient is complicated by the 

 presence of another filariid, quite recently discovered, which has 

 long been confused with IViichercria bancrofti. This species. 

 Microfilaria inalayi, was discovered in 1927 by Leichtenstein in 

 the Dutch East Indies. Leichtenstein had failed, after numer- 

 ous attempts, to infect Ciilex fatigans and other eulicine mos- 

 quitoes with microfilariae of the area, and noting the absence 

 of acute forms of the disease, although elepliantiasis of the leg 

 was common, it occurred to him that he might be dealing with 

 a new species of filaria. Brug (1927) examined Leichtenstein 's 

 material, found morphological characters distinct from Ban- 

 croftian microfilariae, and proposed the name Filaria malayi 

 for the parasite. Brug's observations have since been confirmed 

 by various workers, and the species now appears established on 

 morphological characters of the microfilariae and extensive epi- 

 demiologic studies, although the adult worms are yet to be 

 discovered. 



Thus far. Microfilaria malayi appears to be strictly oriental 

 in geographic distribution. It is known to occur in the Fed- 

 erated Malay States, Sumatra, Java, Ceylon, parts of India, 

 Indo-China and in north-eastern Chekiang Province of China. 

 It is often the dominant species of a given region and occurs 

 typically in rural districts along river or forest settlements. 

 Elephantiasis of the feet and legs is typically associated with 

 J/, malayi infection. The genitals and upper extremities are 

 rarely involved as in Bancroftian filariasis. The microfilariae 

 show nocturnal periodicity, but do not disappear entirely from 

 the peripheral blood during daytime. Mosquitoes of the genus 

 Manxotiia, subgenus Maiisonioidcs, are the principal vectors, 

 particularly M. (Monsonioides) annulifera. These are noc- 

 turnal feeders and are most active during the evening from 

 7 p.m. to S p.m. 



Recently, extensive studies have been made on the control of 

 filariasis in India, particularly in Travancore, where Microfilaria 

 malayi is chiefly concerned (Sweet and Pillai, 1937; Iyengar, 

 1938). It was demonstrated by these investigators that the 

 presence of a floating plant, Pistia stratioitcs, is essential for 

 tlie breeding of Maiismiia. The female mosquito does not or- 

 dinarily lay eggs except on the leaves of Pi.'<tia, and the larvae, 

 being structurally adapted to obtain their supply of oxygen 

 from the air cavities in the root, are not capable of living apart 

 from this particular plant. 



In experimental areas the clearance of ponds and tanks of 

 Pixtia markedly reduced the incidence of Maiifioiiia mosquitoes 

 and checked further spread of the infection. Pistia plants can 

 be cheaply and effectively removed by hand. Here we have an 

 excellent example of the suppression of a mosquito-borne disease 

 by a strictly limited S])ecies control of the carrier. 



2. ONCHOCERCIASIS 



Onchocerciasis in man is caused by Onchocerca volviihi.<< 

 (Leuckart, 1893), the adult forms of which are characteris- 

 tically found in prominent, subcutaneous, fibromatous tumors. 

 The microfilariae aiipcar in large numbers in the skin, especial- 

 ly in the skin in the vicinity of the tumor, the eyes, the con- 

 .iuMctivao and the cornea, and in the central portion of the 

 tumor with the adult worms. They do not appear in the cir- 

 cnlation but may rarely occur in the deeper tissues and viscera 

 (Rodhain, 1937). When seen in fresh sections of the epidermis 

 or conjunctiva they are actively motile and possess no sheath. 

 Two types are clearly distinguished. It has been suggested 

 that the smaller forms with a more compact arrangement of 

 the nuclei may represent male, and the longer ones female 

 microfilariae. 



It is believed that the tumor results from the irritation pro- 

 duced by the presence of the adult worms and the products 

 of their metabolism. Unencapsulnted adult worms have, how- 

 ever, been noted (Sharp, 1927; van den Berghe, 193li). The 

 microfilariae have been considered to be a cause of an erysipela 

 tons condition of the face and head and of disturbances in 

 vision, iritis, punctate keratitis and total lilindness. The part 

 tliat these microfilariae play in the production of these condi- 

 tions is not clear. 



Onchocerciasis is very common along the west coast of Africa 

 from Sierre Leone to the Congo liasin and extending eastward 

 through the Congo into I'ganda, Anglo-Egyptian Sudan and 

 Kenya. It also occurs endemically in southern Mexico and 

 Guatemala upon the Pacific or southern slopes of the volcanic 

 ranges at altitudes between 2,000 and 4,500 feet (Caldernn, 

 1920). The parasite in Central America was discovered by 

 Robles in 191.5 and named Onchocerca cacculieiif: by Brumpt 



in 1919, who considered the American form distinct since, in the 

 great majority of cases, the tumor was located upon the scalp or 

 in the region of the face, whereas the tumor in African cases 

 was generally found on the body. Further, the disease in America 

 was observed only in areas mainly inhabited by native Indians 

 and into which regions the negro, apparently, had never been 

 introduced. Later studies by Strong and associates (1934) 

 have shown that the Central American form cannot be sep- 

 arated from the African form on either morphological charac- 

 ters or on biological criteria. The two forms are now gen- 

 erally regarded as belonging to the same species, 0. volvulus. 



Blackloek (1926) demonstrated that the black-fly Simulium 

 (lamnosum is particularly concerned in the transmission of 

 onchocerciasis throughout tropical Africa. S. ncavci, however, 

 is said to be the chief, if not the only carrier of the parasite 

 in the Lubilash-Sankuru region in the Province of Lusambo 

 (Kasai). S. metaUicum, S. caUidum and S. ochraceum are the 

 vectors in endemic regions of Mexico and Guatemala (Strong 

 et al, 1934). The development of the parasite in these flies 

 and its transmission to man are essentially the same as the 

 development and transmission of W uchercria bancrofti in and 

 liy mosquitoes. 



The control of onchocerciasis in Africa is exceedingly diffi- 

 cult due to its widespread distribution and the general topog- 

 raplo' of the country, dense vegetation or forests and running 

 streams, ideal environments for the breeding of Simulium. 

 Vegetation is usually cleared only in the vicinity of the vil- 

 lages and plantations. This limited clearance of vegetation is 

 probably of little value in control since these flies are capable 

 of fl.ying great distances. The people are attacked by the flies 

 most frequently while defecating at the edges of streams (a 

 common and usual practice), while collecting water for drinking 

 jiurposes or while engaged in agricultural pursuits, rice, cotton 

 or coffee cultivation which bring them into the immediate 

 environment of the fly. 



Measures of individual protection against the bites of these 

 flies, such as wearing of fly-proof clothing and masks, proper 

 screening of houses and bed nets, the use of smudges and re- 

 pellents, are to be recommended, but are usually not practical 

 and are rarely applied by native populations. It is obvious 

 that effective control of onchocerciasis rests in the eradication 

 of Simulium flies but, as yet, there is no practical method 

 known to destroy their eggs, larvae or pupae which abound 

 under stones in the swiftly-flowing streams of the endemic 

 areas. 



In Central America attempts Imve been made to control the 

 human carriers which infect the flies. Surgical removal of the 

 tumors containing adult worms has been a public health proce- 

 dure of importance, and where a systematic attempt has been 

 made to eradicate the disease in sharply circumscribed areas, 

 the late of infection has been greatly reduced. It is recom- 

 mended (Strong et al, 1934) that, under local conditions as in 

 Guatemala, periodic microscopic examinations should be made 

 in each individual after operation to detect the number of 

 microfilariae which may persist and, if large numbers of micro- 

 filariae are present, the patient should be regarded as a dan- 

 gerous carrier and be isolated, or removed to a region where 

 Simiiliitm does not occur, until the parasites disappear. 



Dracunculus medinensis 

 W. W. C. 



Although the guinea worm, Dracunculus nicdini iisis, has 

 been known since ancient times nothing was understood of its 

 life cycle until Fedtschenko (1871) implicated Cyclops in its 

 transmission. Since that time various species of cyclops have 

 been infected experimentally and recently Moorthy (1938) has 

 given an adequate account of the developmental stages in this 

 liost. Leiper (1907) re])orted the experimental infection of a 

 monkey and the finding of two immature males, and recently 

 experiments with dogs (Issajev, 1934a; Moorthy and Sweet, 

 1936 & 1938) have made possible the adequate description of 

 the male (Moorthy, 1937) and added nmch to our knowledge 

 of all the stages in the definitive host. The researches of 

 Fairley and Listen (1924a), Fairley (1924), and others have 

 served to give a picture of the pathology and symptomatology 

 of dracontiasis and numerous and widely scattered publications 

 have given the present conception of its geographical distri- 

 bution, epidemiology, and control. In spite of numerous sug- 

 gestions no treatment of real value is yet known. Although the 

 extent of the studies on this parasite is impressive, much more 

 needs to be done to bring our knowledge even up to the level 

 of that of the other important human helminths. 



Natural infections with worms identified as D. medinensis 

 have been reported from a number of mammals including dog, 

 horse, cattle, jackal, wolf, leopard, monkey, deer, baboon, rac- 

 coon, mink, and fox (Leiper, 1910; Turkhud. 1920; Chitwood, 



320 



