Observations on the habits and control of Culex pipiens fatigans in Guyana

Investigations in Guyana in 1961-63 showed that Wuchereria bancrofti was the only filarial parasite causing elephantiasis and that Culex pipiens fatigans was the primary vector. Mansonia titillans and Anopheles aquasalis were found to be secondary vectors. C. p. fatigans bred primarily in pit latrines and secondarily in the clean, confined water of drums and barrels near latrines. No breeding occurred in the relatively clean open water of trenches, ditches and drains. Of 21,016 mosquitos collected from houses, 39.9 percent were found resting on walls, 34.9 percent on clothing and other hanging objects, and 23.4 percent on or under furniture. Of 15,622 female mosquitos caught, 9.6 percent contained W. bancrofti parasites and 0.5 percent contained infective larvae. The flight range was found to be about half a mile (0.8 km). Control was achieved by a combination of antimosquito (spraying with gas-oil) and antiparasitic (chemotherapy with diethylcarbamazine) measures, which reduced the average infection rates in the Buxton control area from 17.7 percent to 2.2 percent. Over the same period, breeding in drums dropped from 14 percent-25 percent to 4.7 percent, even though the drums were not treated or covered.(AU)

Attack on the vector of filariasis in British Guiana

In British Guiana, during a study which began in April 1961, Wuchereria bancrofti was the only filarial parasite found to be causing elephantiasis, and Culex pipiens quinquefasciatus was determined to the primary vector. The parasite developed readily in Mansonia titillans and Anopheles aquasalis, which were found infested in nature, and ther were considered secondary vectors. No Brugia malayi was found. In the coastal Buxton control area, 11 miles east of Georgetown, C.p. quinguefasciatus bred primarily in the dirty water of pit latrines and secondarily in the clean, confined water of drums and barrels near latrines. No breeding occurred in the relatively clean, open water of trenches, ditches, and drains. In an 18-month period, about 21,000 C.p. quinquefasciatus, mostly females, were collected from houses in 28 villages. About 40 percent were found resting on walls, 35 percent ond clothing and other hanging objects, and 23.4 percent on or under furniture. On dissection of the naturally caught vectors, about 9 percent were found to have Wuchereria bancrofti parasites. About 0.5 percent had infective larvae in their bodies, but generally only one or two of these larvae were found per mosquito. C.p. quinquefasciatus, hatched in the laboratory, were coated with metallic dust and released. Their flight range was determined to be one-half mile. Resistance of the adult vector to DDT and dieldren was confirmed. Effective control was achieved by spraying 23 ounce of gas oil, as a residual larvicide, once a month on the surface of each latrine contents. Complete elimination of breeding in pit latrines resulted in an infection rated in some part of the control area was as high as 54 percent. After 1 year of larviciding, this rated dropped to 4.7 percent. (Summary)

Coastal survey of Aedes aegypti -breeding in British Guiana

An extensive survey to determine the degree of reinfestation of the British Guiana coastlands with Aedes aegypti was carried out in 11 areas during a two-month period from February to April 1963. A total of 19 148 premises were inspected in 170 villages outside Georgetowm and in nine wards within the city (each ward being considered as a village). Eighty-four (46.9 percent) of the 179 villages were positive for A. aegypti-breeding and 95 (53.1 percent) were negative. Although 200 762 water containers were examined, of which 525 (0.26 percent) had A. aegypti-breeding. The chief water-holding vessel or containers in which breeding was taking place were, in descending order of importance, ivy bowls, tins, drums, tubs, tyres, vats, pots and pans, vases, discarded car batteries, bathroom floors, buckets, tanks, barrels, and clay goblets. Practically all the breeding was taking place within the 10-mile coastal strip along a distance of about 105 miles. In the autumn of 1961, the death from jungle yellow fever of two men who had been living in the the interior of British Guiana precipitated the events that led to the survey. The possibility that other such cases may be present in the interior, and the potentiality of the spread of A. aegypti and the possible infestation of visiting ships, stress the need for an A. aegypti-eradication programme (Summary)

Natural and experimental infection of bedbugs with Wuchereria bancrofti in British Guiana

In Georgetown, British Guiana, 100 Cimax hemipterus (older nymphs and adults) were collected from a bed used by two persons who were positive and two persons who were negative for the microfilariae of Wuchereria brancrofti. Eighty-three of the bedbugs contained at least one living or dead parasite. Early first stage larvae were found in the abdomen, thorax, legs, and antennae. Eight bugs had a total of 9 sausage forms, of which 2 were dead and 3 apparently moribund. Also found were 2 sluggish second stage larvae and 3 infective larvae of which 2 were non-motile. Rupture of the stomach from overengorgement and consequent release of the parasites into the hemocoele was observed in 12 bugs. The development of W. bancrofti was studied in five lots of bedbugs fed on a human carrier having 165 to 200 microfilariae per 20 cmm of blood at the time of feeding. Little development occurred in 100 first- and second- instar nymphs, which sucked up relatively few parasites. Four lots of 50 older bedbugs were given, respectively, 0, 1, 2, and 3 non-infective meals at 4-day intervals after the infective meal. It was found that as the number of additional feedings increased, the parasites survived longer and developed further. No infective larvae had developed by the 20th day. Because the mortality of larvae was high in both natural and experimental infections, only a few developed to more advanced stages, it is concluded that C. hemipterus is not a suitable host for W. brancrofti (Summary)

Encapsulation of Wuchereria bancrofti in seven species of mosquitoes in British Guiana

Encapsulation of microfilariform and older larval stages of Wuchereria bancrofti was observed among seven species of mosquitoes in British Guiana over a 2-year period. In Mansonia humeralis and Psorophora ferox most of the microfilariform 1st-stage larvae were completely enclosed in a hard, thick dark-brown capsule 12 to 24 hours after the infective blood-meal. In P. ferox encapsulation often occurred within the inflated sheath. In Aedes taeniorhynchus, A. scapularis and A. serratus, progressive stages were found 12 hours after the blood meal, from unencapsulated to fully encapsulated microfilariform larvae, and in the latter species, also two slightly encapsulated, dead 2nd-stage larvae. In all mosquitoes encapsulation was associated with the presence of varying amounts of tiny granules, globules, plaques and flake-like debris. These were especially evident in A. angustivittatus and A. scapularis. Some encapsulated 1st-stage larvae were found, along with normal ones, in 2 (0.01 percent) of 14,405 Culex pipens quinquefasciatus of the British Guiana strain and in 10 (9.8 percent) of 102 C. p. quinquefasciatus of the Barbados (Island) strain. This species is the major host of W. bancrofti in both localities. No encapsulation was ever seen in M. titillans, a secondary vector in British Guiana. Most of the encapsulated microfilariform larvae were found in the hemocele, and fewer in the stomach. Rarely, encapsulated forms were found in the thorax, only in A. serriatus and in the British Guiana and Barbados strains of C. p. quinquefasciatus. Various stages of encapsulation are illustrated by photomicrographs (Summary)