An outbreak of carbamate poisoning in a family from Central Trinidad, West Indies [abstract]

An outbreak of carbamate poisoning was investigated during April 1997 in Central Trinidad. Seven patients were transported via ambulance to the Accident and Emergency Unit of Port of Spain General Hospital. Upon examination, all patients showed evidence of poisoning: two were unconscious (3/15, Glasgow Coma Scale), 4 with elevated heart rates, 5 with pinpoint pupils (less than 3 mm), 2 showing excessive salivation and 6 with malaise. Upon investigation, it was revealed that all seven patients had ingested lemonade sweetened with sugar laced with the insecticide Lannate. All patients were successfully treated with atropine. It is recommended that laws should be enacted for the safe use of these insecticides and education programmes be conducted on the safe use of insecticides in the agricultural sector. (AU)

Comparative impact of intra- and extra extra-domiciliary malathion adulticidal sprays on the dengue vector and other mosquitoes in Trinidad

OBJECTIVE: To measure the short- and long-term impact of intra- and extra-domiciliary malathion sprays on adult Aedes aegypti and other mosquitoes. DESIGN AND METHODS: Caged populations of Ae aegypti and Culex quinquefasciatus were exposed within and outside homes to malathion sprays from hand-held and vehicle-mounted equipment. Short-term impact was determined by mortality of caged mosquitoes and long-term impact by the reduced oviposition by wild gravid mosquitoes. RESULTS: There was an immediate 100 percent mortality in both species of caged mosquitoes in and around homes and a reduction of oviposition by wild gravid mosquitoes twenty-four hours after exposure to malathion dispensed from hand-held equipment. Thereafter, there were significant immigration of gravid females from adjacent areas. Vehicle-mounted spraying from the streets killed 94 percent - 100 percent Cx quinquefascitus in the interior areas where mosquitoes may rest. There was little delayed effect from vehicle-mounted treatment since by day 5 wild mosquitoes had quadrupled their oviposition. CONCLUSIONS: Hand-held insecticide spraying by the householder has a short-lived impact but repeated, sustained treatments could effectively break the transmission cycle of dengue. Vehicle-mounted sprays are less effective both in the short- and long-term impact. In emergencies, there is a need for integrated physical and chemical methods for immediate and sustained vector management.(Au)

Insecticidal paint and fumigant canisters for Chagas' disease control: community acceptance in Honduras

This study assessed public acceptance for two new vectorial control techniques for Chagas' disease: insecticidal paint and fumigant canisters. The study compared the two with traditional fenitrothion insecticide spraying. An experimental field study was performed in an endemic area of central Honduras from August to November 1992, a year after the initial application of the treatments. The objectives of the study were to determine the acceptability of the tools on the part of the population whose homes were treated, and on the part of the personnel applying the treatments. The sample size was drawn up according to a uniform protocol applied in six Latin American countries. For this study a total of 651 persons were surveyed in 15 rural communities. Along with the surveys, focus groups were used to collect information to learn the reasons for accepting or rejecting particular treatments. The survey was done with heads of households. Focus groups were done with heads of households and also with the field operators who applied the treatments. The research showed that insecticidal paint had a low level of community acceptance (28.8 percent). Field operators strongly disliked the paint because of problems with its transport, application, unpleasant smell, and very low effectiveness against triatomines and pest insects. The results showed that in order to increase the public acceptance for insecticidal paint, it would be necessary to make the paint easier to transport and apply and to increase its effectiveness. Because of their very low effectiveness, fumigant canisters did not represent an acceptable alternative for triatomine vector control. A public educational effort should be a component of any new control method developed (AU)

Screening of medicinal plants from Trinidad and Tobago for antimicrobial and insecticidal properties

Antibacterial activity in 51 extracts from 29 plant species currently used in traditional medicine in Trinidad and the neighbouring Caribbean islands was tested for by the agar dilution streak method using six bacteria: Escherichia coli, Pseudomonas aeruginosa. Salmonella tophimurium, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. The extracts from eight of the plants tested showed significant activity against one or more micro-organisms and the most susceptible bacterium was Staphylococcus aureus. In the bioassays for toxicity towards the Aedes aegypti mosquito the most effective plant extracts were from Justicia pectoralis, Manihot utilissima and Stachytarpheta jamaicensis.(AU)

Spatial distribution of insecticide resistance in Caribbean populations of Aedes aegypti and its significance

To monitor resistance to insecticides, bioassays were performed on 102 strains of the dengue vector Aedes aegypti (L.) from 16 countries ranging from Suriname in South America and through the chain of Caribbean Islands to the Bahamas, where the larvicide temephos and the adulticide malathion have been in use for 15 to 30 years. There was wide variation in the sensitivity to the larvicide in mosquito populations within and among countries. Mosquito strains in some countries such as Antigua, St Lucia, and Tortola had consistently high resistance ratios (RR) to temephos, ranging from 5.3 to 17.7. In another group of countries - eg. Anguilla and Curacao - mosquitoes had mixed levels of resistance to temephos (RR = 2.5 - 10.6), and in a third group of countries, including St. Kitts, Barbados, Jamaica, and Suriname, mosquitoes had consistently low levels of resistance to temephos (RR = 1-4.6) (P < 0.05). On occasion significantly different levels of resistance were recorded from neighboring A. aegypti communities, which suggests there is little genetic exchange among populations. The impact of larval resistance expressed itself as reduced efficacy of temephos to kill mosquitoes when strains were treated in the laboratory or in the field in large container environments with recommended dosages. Although a sensitive strains continued to be completely controlled for up to 7 weeks, the most resistant strains had 24 percent survival after the first week. By week 6, 60 percent to 75 percent of all resistant strains of larvae were surviving the larval period. Responses to malathion in adult A. aegypti varied from a sensitive population in Suriname (RR = 1.3) to resistant strains in St. Vincent (RR = 4.4), Dominica (RR = 4.2), and Trinidad (RR = 4.0); however, resistance was generally not on the scale of that observed to temephos in the larval stages and had increase only slightly when compared to the levels that existed 3 to 4 years ago. Suggestions are made for a pesticide usage policy for the Caribbean region, with modifications for individuals countries. This would be formulated based on each country's insecticide-resistance profile. Use of physical and biological control strategies would play a more critical role than the use of insecticides.(AU)

Evidence for genetic hitchhiking effect associated with insecticide resistance in Aedes aegypti

Information on genetic variation within and between populations is critical for understanding the evolutionary history of mosquito populations and disease epidemiology. Previous studies with Drosophila suggest that genetic variation of selectively neutral loci in a large fraction of genome may be constrained by fixation of advantageous mutations associated with hitchhiking effect. This study examined restriction fragment length polymorphisms of four natural Aedes aegypti mosquito populations from Trinidad and Tobago, at 16 loci. These populations have been subjected to organophosphate (OP) insecticide treatments for more than two decades, while dichlor-diphenyltrichlor (DDT) was the insecticide of choice prior to this period. We predicted that genes closely linked to the OP target loci would exhibit reduced genetic variation as a result of the hitchhiking effect associated with intensive OP insecticide selection. We also predicted that genetic variability of the genes conferring resistance to DDT and loci near the target site would be similar to other unlinkded loci. As predicted, reduced genetic variation was found for loci in the general chromosomal region of a putative OP target site, and these loci generally exhibited larger F (ST) values than other random loci. In contrast, the gene conferring resistance to DDT and its linked loci show polymorphisms and genetic differentiation similar to other random loci. The reduced genetic variability and apparent gene deletion in some regions of chromosome 1 likely to reflect the hitchhiking effect associated with OP insecticide selection(AU)

A study of parasuicide among adolescent and young adult in southern region of Trinidad

This study was an attempt to determine factors which are responsible for the high suicide rate among adolescents and young adults. The census was taken from admission to a Health Institution in South Trinidad - the San Fernando General Hospital. An instrument based on the research questions was designed to yield the necessary data for completion of the research study. Seventy-five clients between the ages 9 years to 24 years were visited at home, interviewed and instruments completed by the researcher. The data was collated and analyzed with the aid of the computer programme SPSS Windows and a manual scientific calculator. The study revealed that East Indians (60 percent) were the most represented Ethnic group and they resided in the rural areas. Male to female ratio was 1:2. The risk and precipitating factors identified are family instability (40 percent) emotional problems (29.6 percent), financial difficulties (24 percent), peer pressure (22.4 percent) and conflict with parents and family members (38.4 percent). Unemployment (12 percent) and lovers quarrel (12 percent) was also prevalent. Ingestion of tablets (50.7 percent) was the most common means of para-suicide, followed by weedicide and insecticide (26.6 percent). The victims identified support from family members/significant others and counselling being the main strategy for healing.(Au)

Acaricidal and insecticidal activities of cadina-4, 10 (15)-dien-3-one

The novel assingment of 13C and 1HNMR data for cadina-4,10(15)-dien-3-one obtained from Hyptis verticillata is presented. The study revealed that cadina-4,10(15)-dien-3-one possesses chemosterilant activities against the economically important cattle tick, Boophilus microplus, and toxic action against adult Cylas formicarius the most destructive pest of sweet potato (I pomoea sp.) (AU)

A model of the transmission of dengue fever with an evaluation of the impact of ultra-low volume (ULV) insecticide applications on dengue epidemics

We have developed a deterministic susceptible, exposed, infectious, resistant or removed (SEIR) model of dengue fever transmission that enables us to explore the behavior of an epidemic, and to experiment with vector control practices. Populations of both host and vector are divided into compartments representing disease status (susceptible, exposed, infectious, and , for humans, resistant), and the flow between compartments is described by differential equations. Examination of the equilibrium points leads to a formulation of the basic reproduction rate (Zo) of the dsease. With a base set of parameters, Zo=1.9 and the model realistically reproduces epidemic transmission in an immunologically naive population. Control of adult mosquitoes by ultra-low volume (ULV) aerosols is simulated by an abrupt decrease in vector densities, followed by gradual recovery of the vector population. The model indicates that ULV has little impact on disease incidence, even when multiple applications are made, although the peak of the epidemic may be delayed. Decreasing the carrying capacity of the environment for mosquitoes, and thus the basic reproduction rate of the disease, by source reduction or other means, is more effective in reducing transmission. (AU)

A study of the use and impact of pesticides in Saint Lucia

The use of chemical for pest vector control has lead to the reduction in the incidence of several communicable diseases and improvement in food quality and production. Nevertheless, the toxic properties of these pesticides present a separate threat to human health and the health of the environment. The potential for occupational exposure is of particular concern in the Caribbean where agriculture and vector control programs employ more than 40 percent of the labour force. Within Saint Lucia alone, 1,500,000 kilograms of pesticides (insecticides, fungicides and herbicides) were imported in 1990. A multi-phasic project was developed to assess and reduce the incidence of acute pesticide poisoning and the prevalence of chronic pesticide poisoning in Saint Lucia and in Trinidad and Tobago. Collaborators in this intersectoral undertaking include the Ministries of Agriculture/Health in Saint Lucia and in Trinidad and Tobago, Caribbean Environmental Health Institute (CEHI), and Caribbean Epidemiology Centre (CAREC). This paper will summarize the results of the first phase of the project: a survey of the knowledge, attitudes, practices and beliefs (KAPB) of vector control officers in Saint Lucia and members of the Saint Lucia Banana Growers Association (SLBGA)(AU)

Serum cholinesterase levels of vector control workers in Trinidad, West Indies (1979-1987)

During 1979-1987 studies were carried out in vitro on the serum cholinesterase levels of 46 vector control workers exposed to insecticides on a daily basis but without clinical manifestations of insecticide poisoning. The results were compared with those of a control group of workers who had not been exposed to insecticides at home or at work. Cholinesterase levels of both groups were determined by a standard colorimetric method. Suppressed serum cholinesterase levels were detected in all 46 workers exposed to insecticides, 25 of whom were aged 30-39 years. Four persons from the control group showed suppressed levels of enzyme; one of these had a genetically low level, and the other three were on medication when the low levels were recorded. (AU)

Occupational carbamate pesticide intoxication in three farm workers: implications and significance for occupational health in Jamaica

The importance of occupational health practice principles in the delivery of health care to the working population is stressed by the authors' management of an incident of occupational pesticide poisoning. The clinical management of the patients involved, as well as the occupational and environmental health management of that incident, is discussed. An illustrative case report is used to describe an occurrence of carbofuran pesticide poisoning in three female farm workers in Jamaica. This report highlights the implications and significance of this incidence in terms of the sensitivity of the medical profession to similar occupational health problems (AU)

Suppression of Aedes aegypti by Toxorhynchites moctezuma in an island habitat - abstract

Dengue is endemic in the Caribbean where the mosquito vector is Aedes aegypti. This mosquito however, is becoming resistant to some of the insecticides used for its control, and householders themselves are objecting to the use of temephos (abate) placed in their drinking water. Consequently, alternative methods are being sought to control Aedes aegypti. Thus we have used the predatory mosquito Toxorhynchites moctezuma on an experimental basis to suppress Aed.aegypti in an island habitat. Toxorhynchites mosquitoes are predators in all larval stages. Tx. moctezuma, the species used in this project, was easily colonized from field-collected material in Trinidad. The trials were conducted in 2 villages in Union Island in the state of St. Vincent and the Grenadines in the Eastern Caribbean. One village, Ashton, served as the control while Clifton was the treated village. At Clifton, each permanent or semi permanent water-holding container received between 2 and 100 immature Tx. moctezuma, depending on its size. Baseline data were collected by obtaining ovitrap, house, Breteau, cistern and drum indices from the 2 villages for 4 months in 1988 prior to treatment. Impact of release of predators was evaluated by comparing the various indices and the percentage changes before and after the introduction of predators in the 2 villages. All indices were lower, and the percentage decline greater in the treatment village than in the control village. The use of Tx. moctezuma as a possible biological control agent for Aed.aegypti needs to be further evaluated (AU)

Landing periodicity of the mosquito Aedes aegypti in Trinidad in relation to the timing of insecticidal space-spraying

Diel landing periodicity (biting cycle) of domestic Aedes aegypti (L.) in Trinidad, West Indies, was monitored using human bait during January-August 1980. The periodicity of females was predominantly diurnal (95.2 percent arriving during daylight or twilight) and bimodal, with consistent peaks at 06.00-07.00 and 17.00-18.00 hours. The diel periodicities at indoor and outdoor sites were virtually identical. Larger numbers of adults were collected outside than inside houses. It is recommended that the time of insecticidal ULV adulticiding should coincide with peaks in landing periodicity of the Ae. aegypti adults. (AU)

Serum cholinesterase levels of vector control workers in Trinidad, West Indies (1979-1982)

During the period 1979-1982, serum cholinesterase levels were determined in blood samples collected from workers employed at the Insect Vector Control Division, Trinidad, W.I. A total of 1,162 blood samples were collected, of which 116 showed suppressed cholinesterase levels. Those workers with low serum cholinesterase levels included 46 residual spraymen, 66 Aedes aegypti operators and 4 controls. The difference in numbers of spraymen and Aedes operators with low cholinesterase levels was significant (p<.001). No significant differences were found in the number of Aedes operators with low cholinesterase levels from North and South Trinidad. Similarly, no differences were found in the number of residual spraymen from North and South Trinidad with low cholinesterase levels. A total of 7 Aedes operators and 4 residual spraymen had persistently low serum cholinesterase levels. It is likely that the main areas of absorption were the hands and forearms, with further absorption occurring via respiration. The need for continuous monitoring and supervision of vector control workers who handle insecticides is stressed (AU)

Preliminary trials using abate to control Kabowra flies in the Rupununi, Guyana - abstract

Control of Simulium (called Kabowras in Guyana) black flies is usually directed to the larvae which breed in fast flowing waters. The purpose of the project was to determine the effectiveness of Abate Insecticide 200E in controlling Simulium sp., in a selected river in the Rupununi Savannah, Guyana. Two bioassays were carried out on the San Jose River near Lethem, Rupununi to determine the effective distance of Abate 200E at a concentration of 0.3 ppm during August, 1979 along a 2.4 km and 3.5 km stretch of the river. River discharge rates were calculated at a point of injection of the Abate. The volume of Abate required to give a concentration of 0.3 ppm when dispensed over approximatelty thirty minutes at the measured discharge was dripped into the stream. Counts of larvae on marked vegetation were made at several points before injection of Abate and four and nineteen hours after injection. The results of the first bioassay over 2.4 km showed at 57.8 percent drop in larvae four hours after injection of larvicide and a 99.3 percent drop within nineteen hours. Larval mortality was 97 percent at 2.4 km. Larval counts after the second Abate application two weeks later at 3.5 km showed a 52.8 percent drop after four hours and 96.1 percent after nineteen hours. Larval mortality was 100 percent at 2.7 km and 9.3 percent at 3.5 km. Larval counts were very low during the subsequent four weeks. Abate 200E at a concentration of 0.3 ppn was found to be effective in killing Simulium larvae over a distance of 3.5 km with a mortality of 93 percent nineteen hours after injection of larvicide. These trials should continue using lower concentrations of the larvicide (AU)

A fatal episode of accidental methomyl poisoning

Three fatalities from the accidental ingestion of methomyl, a carbamate pesticide, are reported. The methomyl had been stored in an unlabelled tin can and was accidentally used in preparing "roti," an Indian dish. The identification of the source of the poison through animal tests and further chemical identification is described. The lethal dose of methomyl was estimated to have been between 12 and 15 mg/kg body weight. (Summary)