Seasonal abundance, biting cycle and parity of the mosquito Haemagogus leucocelaenus in Trinidad, West Indies.

Adult female populations of Haemagogus leucocelaenus (Dyar and Shannon), the sylvan vector of yellow fever, were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port of Spain, Trinidad. Hg.leucocelaenus showed only diurnal landing activity, from 06.00 to 18.00 hours (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 14.00 hours. Densities of Hg.leucocelaenus during the wet season (May-November) were about double the level recorded during the dry season (December-April). Monthly parous rates averaged 53.9% (range 25-90%) and some females were up to five-pars. Retained eggs (range 2-6, mean 4/female) were found in the ovaries of 0.34% of landing females, all of which had stage 1 ovarian follicles for the next gonotrophic cycle. Therefore blood-feeding is not inhibited by egg retention. Hg.leucocelaenus vector potential is reappraised in the light of these findings.

Seasonal abundance, biting cycle, parity and vector potential of the mosquito Haemagogus equinus in Trinidad.

The mosquito Haemagogus equinus is a known vector of yellow fever (YF) in central America. Seasonal abundance, daily biting activity and the age composition of adult Hg.equinus female populations were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde Forest, Chaguaramas, 16 km west of Port of Spain, Trinidad. 2. Landing collections of Hg.equinus showed diurnal activity from 06.00 to 20.00 hours (suntime), with a single peak between 08.00 and 14.00 hours. 3. Overall, 5.6% of Hg.equinus were collected during the dry season (December-April) and 94.4% during the wet season (May-November). 4. Mean density of Hg.equinus in relation to man ranged from 0.35/man-day in February to 133/man-day in July, with averages of 2.8 in the wet season, 36.9 in the dry season and 22/man-day for the whole year. 5. Monthly parous rates averaged 62.1% (range 0-88%); 2.8% of females were 2-pars, another 2.8% were 3-pars, but no older females of Hg.equinus were found (sample size 467). 6. These age-grading data indicate that Hg.equinus females have relatively short life expectancy and hence low vector potential, which may help to explain why YF virus has seldom been isolated from this vector species.

Significant changes in gastrointestinal tract parasitic infections in children of St. Kitts over the 9-year period 1982-1991.

When 239 (1982) and 361 (1991) five- and nine-year-old children in St. Kitts were assessed for the presence of parasitic infections, there were significant reductions in the prevalence of trichuriasis from 83% to 58%, of ascariasis from 24% to 8.6% and of giardiasis from 15% to 9.4%. Anthelminthic use, which appeared to be the most important responsible intervention tool, remained roughly at the same level at 59-51%. However, the types of anthelminthics used changed over the period. Piperazine citrate, which was used by 66% in 1982, only had 35% usage in 1991. Albendazole which was not used at all in 1982 was taken by 32% of the children in 1991 and at the same time use of laevo-tetramisole increased by 20% from 14%. Suggestions are made for an island-wide mass intervention programme to manage parasitic infections.

Effects of Toxorhynchites moctezuma larval predation on Aedes aegypti populations: experimental evaluation.

Predatory larvae of the mosquito Toxorhynchites moctezuma were used experimentally to control a standing crop of larvae of the dengue vector mosquito Ae.aegypti. Each week, fifty Ae.aegypti first instar larvae were introduced to each of five water-filled drums (220 litres) of the type commonly used for domestic water storage in Caribbean dwellings. At the beginning of the fourth week, a certain number (0, 1, 2, 5 or 10) of first instar Tx.moctezuma larvae were introduced to each drum and the daily yield of Ae.aegypti adults from each drum was monitored thereafter. The experiment was repeated three times. With only one or two Tx.moctezuma larvae, predation on Ae.aegypti larvae stopped the output of Ae.aegypti adults for 1 week. Five or ten Tx.moctezuma prevented any Ae.aegypti emergence for up to 16 weeks. Cannibalism among Tx.moctezuma larvae was seldom observed and appeared not to be a hindrance in using this species against Ae.aegypti. Thus Tx.moctezuma is regarded as a good candidate for the biological control of Ae.aegypti by augmentative releases.

Suppression of Aedes aegypti by predatory Toxorhynchites moctezuma in an island habitat.

Larval populations of the mosquito Aedes aegypti were suppressed by predatory Toxorhynchites moctezuma mosquito larvae released systematically in a village on Union Island (Saint Vincent and the Grenadines) during March-December 1988. Eggs and larvae of Tx.moctezuma were transported from Trinidad and introduced into all semi-permanent and permanent water-holding containers in the experimental village at Clifton. The semi-isolated village of Ashton served as control. Base-line Ae.aegypti indices (house, ovitrap, Breteau, cistern/tank, drum/barrel, small containers) were obtained for the two villages over a 4-month period prior to the introduction of the predatory Tx.moctezuma mosquito larvae. After sustained releases of predators for 5 months, all indices of Ae.aegypti were lower in the treated village than in the untreated village during the last 3 months of the year.

Distribution and seasonality of Culex (Melanoconion) caudelli, a vector of arboviruses in Trinidad.

Seasonal and spatial distributions of the arbovirus vector mosquito Culex (Melanoconion) caudelli Dyar and Knab (Diptera: Culicidae) in the Aripo-Wallerfield forest, Trinidad, were studied by collecting mosquitoes attracted to mouse-baited traps in forest, ecotone and savannah, one day per week throughout the year, 98% of the Cx caudelli mosquitoes were collected during the wet season, with a significant positive correlation between rainfall and mosquito catch. The reverse occurred during the dry season. Cx caudelli displayed a preference for the ecotone where 67% were collected, while 32% and 1% were collected in the forest and savannah respectively.

Seasonality, biting cycle and parity of the yellow fever vector mosquito Haemagogus janthinomys in Trinidad.

1. Age composition, seasonal abundance and diel patterns of landing activity of the sylvan vector of yellow fever Haemagogus janthinomys Dyar were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port of Spain, Trinidad. 2. Landing collections of Hg. janthinomys showed only diurnal activity, from 06.00 to 18.00 (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 16.00 hours. 3. Densities of Hg. janthinomys were about 6 times greater during the wet season (May-November) than during the dry season (December-April); the annual Williams' mean landing rate on two collectors was 9.3 per day. 4. Monthly parous rates averaged 59% (range 0-86%) and some females were up to seven-pars. Retained eggs (range 1-21, mean 7.7/female) were found in the ovaries of 1.3% of landing females, all of which had stage I ovarian follicles for the next gonotrophic cycle. Hence blood-feeding is not inhibited by egg retention, which might promote transovarial transmission of virus. Implications of these findings are discussed in relation to yellow fever epidemiology.

Laboratory colonization and maintenance of Toxorhynchites moctezuma.

A colony of Toxorhynchites moctezuma was established at the Caribbean Epidemiology Centre in Trinidad in 1984. Toxorhynchites moctezuma was maintained in cages with high humidities. Eggs were deposited most frequently in a cut bicycle tire containing water. A minimum of 42 h was required for hatching, but 94% hatched between 43 and 51 h. Aedes aegypti larvae were supplied as prey. Larval development times varied with the quantity of prey offered, but when fed ad lib, peak developmental time was 18 days. Mean pupal developmental time was 5.5 days. Although only 12% of larvae survived to pupation in 3 years of production, our experience indicates this species would be a likely candidate for mass production and release.

Visceral larva migrans in seven members of one family in Trinidad.

The occurrence of the first seven cases of visceral larva migrans in Trinidad and Tobago is described. All cases occurred in children of the same family. The ELISA test was used to confirm the clinical diagnosis.

PIP: Visceral larva migrans is a syndrome caused by the extraintestinal migration of larval nematodes of wild and domestic animals through human tissues. Most cases occur in children under 5 years of age, with the common dog round worm apparently being the primary causative agent. This paper describes the occurrence of the first 7 cases of visceral larva migrans in Trinidad and Tobago. Cases occurred among siblings in the same family and were confirmed using the ELISA test. A mentally retarded 10-year old East Indian male was admitted to the Port of Spain General Hospital with a strong history of pica, recurrent wheezing, and epilepsy. Five siblings and one cousin were found living under extremely unsanitary conditions and in dire poverty. All had pica and Toxocara canis eggs were found in the dirt surrounding the dwelling. These eggs are most probably the common source of infection. Infection with Toxocara species is probably far more common than reported in Trinidad, given the large stray dog population and areas of primitive sanitary conditions. ELISA tests could be used to reveal additional infections in the country.

Seasonal incidence and diel oviposition periodicity of Haemagogus mosquitoes (Diptera: Culicidae) in Trinidad, W.I. Part III. Haemagogus celeste (Dyar and Nunez Tovar) and Haemagogus leucocelaenus (Dyar and Shannon).

The seasonal incidence and diel oviposition patterns of sylvan Haemagogus celeste and Hg. leucocelaenus in the Pt. Gourde Forest, Trinidad, were monitored weekly for 53 consecutive weeks using conventional ovitraps. During the dry season peak oviposition by Hg. celeste occurred between 10.00 and 12.00 hours, and that by Hg. leucocelaenus between 12.00 and 14.00 hours; during the wet season peak oviposition by both species occurred between 12.00 and 14.00 hours. Diurnal patterns of oviposition were observed for both species during the wet and dry seasons. The numbers of ovipositions and of eggs laid during the wet season were, for both species, significantly higher (P greater than 0.001) than those observed during the dry season.

Observations on the seasonal incidence and diel oviposition periodicity of Haemagogus mosquitoes (Diptera: Culicidae) in Trinidad, W.I. II. Haemagogus equinus Theobald.

Diel patterns of oviposition of sylvan Haemagogus equinus in the field in Trinidad, West Indies, were monitored weekly for 53 consecutive weeks using standard ovitraps. During the wet season (September to November 1981 and May to September 1982) a large well-defined unimodal peak (comprising 97% of all eggs laid and 89% of occurrences) occurred at 12.00-14.00 hours, four to six hours before sunset. During the dry season (December 1981 to May 1982), two small less-well-defined peaks occurred at 10.00-12.00 and 14.00-16.00 hours (comprising 4.9% of eggs laid and 14% of occurrences). A diurnal oviposition pattern was observed when the wet and dry season data were combined. The number of eggs and occurrences found during the wet season was significantly higher (P greater than 0.001) than that observed during the dry season.

Blastocystis hominis in two children of one family.

Two apparently healthy children from the same family were found to have moderate to heavy Blastocystis hominis in their stool samples whilst being investigated for intestinal symptoms: sporadic, painless, rectal bleeding in one and persistent diarrhoea in the other. After treatment with metronidazole, they had no further signs, and stool samples became negative. Eighteen months later, both were asymptomatic, and stool samples continued to be negative for the parasite.

Blastocystis hominis in two children of one family

Two apparently healthy children from the same family were found to have moderate to heavy Blastocystis hominis in their stool samples whilst being investigated for intestinal symptoms: sporadic, painless, rectal bleeding in one and persistent diarrhoea in the other. After treatment with metronidazole, they had no further signs, and stool samples became negative. Eighteen months later, both were asymptomatic, and stool samples continued to be negative for the parasite

Observations on the seasonal incidence and diel oviposition periodicity of Haemagogus mosquitoes (Diptera: Culicidae) in Trinidad, W.I.: Part I. Haemagogus janthinomys Dyar.

The diel oviposition periodicity of sylvan Haemagogus janthinomys Dyar in the Pt. Gourde Forest, Trinidad, West Indies was monitored weekly for 53 weeks using conventional ovitraps. During the wet season (September to November 1981 and May to September 1982) a large well-defined unimodal peak occurred six to eight hours after sunrise (comprising 94% of eggs laid and 91% occurrences). During the dry season (December 1981 to May 1982), a small less-well-defined peak occurred two to four hours before sunset (comprising 6% of eggs laid). The combined data showed a diurnal oviposition pattern with eggs laid from noon to sunset. The numbers of eggs and of used ovitraps found during the wet season were significantly (P less than 0.001) higher than those found during the dry season.

Diel biting activity of Culex (Melanoconion) caudelli in Trinidad, West Indies.

The diel biting periodicity of the arbovirus vector Culex (Melanoconion) caudelli Dyar and Knab (Diptera; Culicidae) in the Aripo-Wallerfield forest, Trinidad, was studied by collecting mosquitoes attracted to mouse-baited traps at 2-hourly intervals during eight 24 h periods. Biting females of Cx caudelli were collected during all night-time hours, 18.00-06.00 hours, with an overall unimodal pattern, i.e. one well-defined peak between 22.00 and 04.00 hours. This contrasts with previous reports that Cx caudelli is diurnally active. During the four moon phases, the period of peak biting activity varied from 22.00 to 24.00 hours at fullmoon, from 22.00 to 04.00 hours at first quarter, and from 24.00 to 02.00 hours at new moon and last quarter phases. The number of mosquitoes collected varied significantly with moon phases, the highest (152/24 h) being collected in the first lunar quarter and the lowest (71/24 h) in the last lunar quarter. Cloud cover and rainfall had no significant effect on the diel biting periodicity of Cx caudelli.

A laboratory investigation of mosquito larval predation by Toxorhynchites moctezuma on Aedes aegypti.

1. Functional responses of predatory Toxorhynchites moctezuma (Dyar & Knab) larvae feeding on Aedes aegypti (L.) larvae (Diptera: Culicidae) were found to be type II of Holling (1959) and Rogers (1972). 2. Estimates of searching rate were generally higher for later instar predators. The search rate of second instar predators declined as prey instar increased, but fourth instar Tx. moctezuma had the highest search rate for second instar Ae. aegypti. 3. Prey handling times were higher for early instar predators and late instar prey. 4. When presented with mixtures of two instars of Ae. aegypti, second instar Tx. moctezuma showed frequency independent selectivity for the early instars, whereas fourth instar predators showed frequency independent selectivity for the late instars of Ae. aegypti. There was no evidence of frequency dependent predation. Preferences appeared to be transitive. 5. Extended random predator equations, using parameters derived from the functional responses, did not adequately describe the outcome of predation in the prey mixture experiment, even when the possibility of optimal switching behaviour was accounted for.

Bancroftian filariasis in coastal north Trinidad: the effects of mass chemotherapy using spaced doses of diethylcarbamazine citrate on human microfilaraemias and vector infection rates.

The effects of a mass chemotherapy programme using spaced doses of diethylcarbamazine citrate on Wuchereria bancrofti microfilaraemias and vector infection rates were studied in an isolated rural community of 650 people in north Trinidad where a microfilaria rate of 15% had previously been recorded. A single oral dose of 6 mg/kg body weight was given at monthly intervals for one year. After 6 months, 79% (52/66) of persons previously microfilaraemic had become negative. After 12 months the negative proportion had increased to 90% (63/70). The geometric mean microfilaria density of those still microfilaraemic was reduced from 19.7 to 4.6 per 100 mm3 of blood. Of 147 initially negative persons, none had become positive following treatment. Filarial infection rates in Culex quinquefasciatus from randomly sampled houses fell from 6.4% to zero; in houses where occupants with microfilaraemia had been identified before treatment, the rate was reduced from 15.8% to zero. In a supplementary study, however, weekly collections from one initially positive house showed a rapid decline in the vector infection rate from 43% to 2% after three months but an additional 3 months elapsed before the index reached zero. There was negligible microfilarial uptake by the vectors from residual low-density microfilaraemias (less than 10 microfilariae per 100 mm3 of blood) after chemotherapy.