Chief Vector Research Articles

Filariasis in melanesia: Observations at Rabaul relating to incidence and vectors

1. (1) The following microfilaria rates were recorded: 427 adult males from various districts of New Guinea and adjacent islands … … … 19·4 per cent. 131 adults, both sexes, Makada Island … … 35·1 ; 188 adults, both sexes, Matty Island … … 32·9 ; The incidence of elephantiasis was low. 2. (2) The suggestion that non-periodic filaria exists in New Guinea is discussed and shown to be without foundation. Some data supporting the accepted view that the filaria in this region is nocturnal are recorded. 3. (3) Some unpublished findings relative to vectors of W. bancrofti in the Rabaul district are given. The evidence supporting the incrimination of anophelines, and in particular A. punctulatus farauti, as the chief vectors in Melanesia, is discussed. 4. (4) Anopheles annulipes was shown to be a good experimental host of W. bancrofti.

Mosquitoes and Yellow Fever in the Sudan

Dr. J. Lewis, of the Stack Medical Research Laboratories, has discussed the relationship of mosquitoes and yellow fever in the Sudan (Bull. Ent. Res., 3, pt. 4; 1947). It appears that most of the southern half of the Sudan is a yellow fever area in the sense that people immune to the disease have been found in many parts of that territory. The chance of the disease spreading to parts hitherto free is liable to be increased by such outbreaks as the great Nuba Mountains epidemic of 1941. It is noteworthy that several towns in the Sudan lie on important air, rail and water routes leading to countries free from yellow fever. Some 140 species of mosquitoes are known from the Sudan, and, of these, twelve kinds are known to be capable of transmitting the yellow fever virus, while several other kinds are suspected in this connexion. Two further species are able to retain this virus throughout life without apparently possessing the ability to transmit the disease by their blood-sucking habits. The object of the present paper is to record information on the occurrence and distribution of mosquitoes in the Sudan. The Anophelines are only briefly considered because they are unlikely to transmit yellow fever. Among the Culicines that affect man and frequent human habitations, Aedes taylori is believed to be one of the chief vectors in the case of the Nuba Mountains epidemic. As regards Aedes cegypti, it appears that mosquito control measures have had the effect of rendering urban yellow fever epidemics, carried by this species, virtually impossible, and the disease has been exterminated from Khartoum. The relation of Tceniorhynchus africanus to the disease is of special interest owing to its wide range and abundance in the Sudan. While there is no evidence that this species can act as a vector, it seems likely that it can act in this way in limited epidemics about the Upper Nile area. The author concludes by discussing the measures of mosquito control in the Sudan, which greatly restrict the possibilities of the spread of yellow fever. At the same time it is evident that the control of a rural epidemic would be difficult to achieve.

The transmission of malaria in Borneo

A. maculatus has for long been regarded as the chief vector of malaria in Borneo. As a result of the work described, however, this mosquito has been shown to have little and probably no importance as a vector there. A. leucosphyrus, on the other hand, generally regarded as a more or less harmless insect, has been shown to be the most dangerous vector in North, Borneo, and, on the existing evidence, probably throughout the greater part of the island. This is important because measures which control the one may encourage the other. Thus measures directed against A. maculatus where A. leucosphyrus is the vector, may not only be ineffective, but may increase the disease they are intended to eliminate. A. leucosphyrus was found to be a very elusive insect, avoiding discovery and incrimination for nearly 2 years, until demonstrated by less conventional methods. This mosquito eluded search as a larva because it bred under dense jungle which often required to be cleared for its exposure, and because it remained submerged for abnormally long. It eluded search as an adult because it fed in the early hours of morning when its victims were asleep, and because it did not rest. in the houses. It is considered that had some more easily discovered vector been present, A. leucosphyrus would certainly have been missed. It is suggested that, since the mosquito is so elusive, it may be of wider distribution and greater virulence and importance in other countries than has hitherto, been supposed. It is pointed out that, in spite of its innocent reputation in many countries, wherever it has been examined in adequate numbers it has always proved to be a vector. Experimental measures for the control of A. leucosphyrus showed that this mosquito may be easily and permanently abolished, and by measures which are in keeping with agricultural and industrial development of the land. It is hoped to publish a full account of this work as a volume later.

Research on Tsetse Fly and Disease

THE Secretary of State for the Colonies has appointed a committee to consider and advise on the co-ordination of action, including research, directed against human and animal trypanosomiasis, and, in particular, against the tsetse fly as the chief vector. The committee, on which the Dominions Office and the Sudan Government are represented, will report from time to time to the Secretary of State for the Colonies, and on all matters affecting research its recommendations will be referred to the Colonial Research Committee for comment and advice before submission to him.

Observations on the Distribution of Diurnal Mosquitoes in a Tropical Forest

Workers in Brazil and Colombia have long felt, on epidemiological grounds, that the mosquito known as Haemagogus capricornii might be the chief vector of jungle yellow fever. Virus was isolated from wild mosquitoes of this species in Brazil in 1938 (Shannon, Whitman and Franca) and Drs. Bugher and Boshell have repeatedly found natural infections in this species in Colombia (Bugher, Boshell, Roca and Osorno, '43). Haemagogus capricornii often seemed, however, to be relatively scarce in areas where yellow fever was known to have been contracted. In 1940 in the course of epidemiological investigations, Dr. Boshell discovered that many more Haemagogus could be captured in a particular forest if a few trees were cut down; this discovery seemed especially significant in view of the frequency with which yellow fever is contracted by woodcutters or by people clearing forest for planting. Following this lead, he found that many more Haemagogus could be captured in an undisturbed forest by climbing the trees. In other words, the scarcity of Haemagogus at ground level in a forest did not mean that the mosquito was uncommon, but that it was predominantly an inhabitant of the upper forest levels. When we established field stations for the study of the ecology of forest mosquitoes, an analysis of this zonal distribution of Haemcagogus was one of our principal objects, and the present paper covers the results of the first year of observations.

A Survey of Malaria in Cyprus 1

Summary Malaria prevails to a serious degree in a large number of the villages of Cyprus. The chief vectors are A. elutus (sacharovi) and A. superpictus, which are the more dangerous on account of the small number of cattle and other domestic animals present in the villages at night. The amount of malaria seems entirely out of proportion to the extent of the water available for anopheline breeding, at least during the rainless summers. Our conclusions agree with those of Ross, that an attack on the mosquitoes is the measure most likely to give the best results. We would recommend that the work initiated by him and now in progress be continued and extended along the lines indicated in this report.