Impact of environmental temperatures on resistance to organophosphate insecticides in Aedes aegypti from Trinidad

OBJECTIVE

To examine the effects of increasing larval rearing temperatures on the resistance status of Trinidadian populations of Aedes aegypti to organophosphate (OP) insecticides.

METHODS

In 2007-2008, bioassays and biochemical assays were conducted on A. aegypti larvae collected in 2006 from eight geographically distinct areas in Trinidad (Trinidad and Tobago). Larval populations were reared at four temperatures (28 ± 2ºC, 32ºC, 34ºC, and 36ºC) prior to bioassays with OP insecticides (fenthion, malathion, and temephos) and biochemical assays for esterase enzymes.

RESULTS

Most larval populations reared at 28 ± 2ºC were susceptible to fenthion (>98% mortality) but resistant to malathion and temephos (< 80% mortality). A positive association was found between resistance to OP insecticides and increased activities of α- and β-esterases in larval populations reared at 28 ± 2ºC. Although larval populations reared at higher temperatures showed variations in resistance to OPs, there was a general increase in susceptibility. However, increases or decreases in activity levels of enzymes did not always correspond with an increase or decrease in the proportion of resistant individuals reared at higher temperatures.

CONCLUSIONS

Although global warming may cause an increase in dengue transmission, based on the current results, the use of insecticides for dengue prevention and control may yet be effective if temperatures increase as projected.

The control of hookworm disease in Commonwealth Caribbean countries

Like other countries around the globe where conditions existed for the parasites causing hookworm disease to thrive, this disease was a serious problem to settlers in countries of the Commonwealth Caribbean, i.e. those countries that were formerly part of the British Empire. Early in the 20th century, the Rockefeller Foundation (RF) assisted the southern United States in controlling this disease. Soon other countries requested assistance and the Rockefeller Foundation responded by creating their International Health Commission to target the problem. Guyana (then British Guiana) was the first country where work was started. Through a system of chemotherapy, sanitation with the provision of latrines and health education the RF assisted the Commonwealth Caribbean countries during the period 1914-1925 in controlling the disease. Most countries continued the programmes started by the Rockefeller Foundation and this paper provides evidence through a series of surveys to show that hookworm disease is no longer a public health problem.

Characterisation of DDT and pyrethroid resistance in Trinidad and Tobago populations of Aedes aegypti

Insecticide resistance is an important factor in the effectiveness of Aedes aegypti control and the related spread of dengue. The objectives of this study were to investigate the status of the organochlorine dichlorodiphenyltrichloroethane (DDT) and pyrethroid (permethrin and deltamethrin) resistance in Trinidad and Tobago populations of Ae. aegypti and the underlying biochemical mechanisms. Nine populations of Ae. aegypti larvae from Trinidad and Tobago were assayed to DDT and PYs using the Centers for Disease Control and Prevention (CDC) time-mortality-based bioassay method. A diagnostic dosage (DD) was established for each insecticide using the CAREC reference susceptible Ae. aegypti strain and a resistance threshold (RT), time in which 98-100% mortality was observed in the CAREC strain, was calculated for each insecticide. Mosquitoes which survived the DD and RT were considered as resistant, and the resistance status of each population was categorised based on the WHO criteria with mortality <80% indicative of resistance. Biochemical assays were conducted to determine the activities of α and β esterases, mixed function oxidases (MFO) and glutathione-S-transferases (GST) enzymes which are involved in resistance of mosquitoes to DDT and PYs. Enzymatic activity levels in each population were compared with those obtained for the CAREC susceptible strain, and significant differences were determined by Kruskal-Wallis and Tukey's non-parametric tests (P<0.05). The established DDs were 0.01 mg l(-1), 0.2 mg l(-1) and 1.0 mg l(-1) for deltamethrin, permethrin and DDT, respectively; and the RTs for deltamethrin, permethrin and DDT were 30, 75 and 120 min, respectively. All Ae. aegypti populations were resistant to DDT (<80% mortality); two strains were incipiently resistant to deltamethrin and three to permethrin (80-98% mortality). Biochemical assays revealed elevated levels of α-esterase and MFO enzymes in all Ae. aegypti populations. All, except three populations, showed increased levels of β-esterases; and all populations, except Curepe, demonstrated elevated GST levels.Metabolic detoxification of enzymes is correlated with the manifestation of DDT and PY resistance in Trinidad and Tobago populations of Ae. aegypti. The presence of this resistance also suggests that knock down (kdr)-type resistance may be involved, hence the need for further investigations. This information can contribute to the development of an insecticide resistance surveillance programme and improvement of resistance management strategies aimed at combatting the spread of dengue in Trinidad and Tobago.

Organophosphate resistance in Trinidad and Tobago strains of Aedes aegypti

Aedes aegypti larvae from 8 sites in Trinidad and 1 in Tobago were assayed against temephos, malathion, and fenthion using the Centers for Disease Control and Prevention time-mortality-based bioassay method. Resistance ratios (RRs) and resistance thresholds (RTs) for each insecticide were calculated in relation to the Caribbean Epidemiology Center reference susceptible strain. Results showed that the Haleland Park and Tobago strains were susceptible to fenthion and malathion, respectively (RRs < 1), while the San Fernando strain had a high RR (33.92) to malathion. All other strains had low-level resistance to fenthion and malathion. Resistance to temephos was more intense with 4 strains showing high-level resistance. The established RT was 60 min for fenthion, 75 min for bendiocarb, and 120 min for temephos and malathion. At the RTs, all Trinidad strains were resistant to temephos (11.50-74.50% mortality), 7 resistant to fenthion (21.25-78.75% mortality), and 5 resistant to malathion (56.25-77.50% mortality). The other strains were incipiently resistant (80-97% mortality). Despite the discrepancies between the RR levels and RT status, it is evident that the organophosphate insecticide resistance is prevalent in Trinidad and Tobago populations of Ae. aegypti. These results suggest that operational failure could soon occur and alternative strategies should be developed and implemented to reduce the probability of further selection pressure on resistant Ae. aegypti populations in Trinidad and Tobago.

Malaria and its vectors in the Caribbean: the continuing challenge of the disease forty-five years after eradication from the Islands

OBJECTIVES

Given the occurrence of autochthonous malaria in non-endemic island countries in the last 10 years, this study evaluates the risk factors for malaria transmission in the malaria "endemic and "non-endemic" countries of the Caribbean region.

DESIGN

Data on imported and autochthonous malaria for the 27-year period (1980-2006) were gathered from surveillance units in the 21 Caribbean Epidemiology Centre (CAREC) Member Countries (CMCs) via the CAREC epidemiology unit. Anopheles mosquito data were also gathered from various sources. The vector and malaria data were correlated to determine the current risk of malaria transmission.

RESULTS

Imported cases. For the 26-year period (1980-2005), there were 897 reported cases in the CMC islands. Jamaica (38.4%) > Trinidad and Tobago (19.5%) > Bahamas (15.8%) > Cayman Islands (12.5%) were mostly affected. Only the smallest CMCs eg Anguilla and British Virgin Islands reported no imported malaria. Indigenous malaria. Over the same time period, malaria was seen mainly in the three mainland countries of Guyana (514 386 cases) > Suriname (275 361) > Belize (85 313). However, for the period 1995-2005, Belize and Guyana reported reduction in case numbers of 84% and 54% respectively. At the same time, Suriname reported a cyclical pattern of reported cases resulting in 77% increase in cases between 1995 and 2005. "Non-endemic" CMCs such as Trinidad and Tobago, and Bahamas, did report autochthonous malaria. In 2006/7, Jamaica reported 340 P falciparum cases, coming just 1-2 years after a massive 505% increase in imported malaria in the region--88% in Jamaica. Anopheles spp: There was a rich diversity of Anopheles mosquitoes--29 spp. in CMCs. Mainland CMCs and nearby island countries had most spp. recorded. Smaller countries with limited ecological niches such as St Kitts, Anguilla, Turks and Caicos Islands (TCI) and Bermuda had little or no Anopheles spp. Two main Anopheles axes were identified--An albimanus in the northern CMCs and An aquasalis in the southern Caribbean.

CONCLUSION

All the essential malaria transmission conditions--vector, imported malaria organism and susceptible human host--now exist in most CMCs. A call is now made for enhanced surveillance, vector control and anti-malaria skills to be established in CMCs, in particular in: Recognizing the possible impact of climate change on the spread of anopheles and malaria transmission. Improving vector control skills for anopheles in CMCs. Strengthening malaria surveillance skills. Upgrading malaria therapy and prophylaxis. Emphasizing malaria prevention and educationfor all community and professional sectors.

Relative importance of the various environmental sources of Cryptosporidium oocysts in three watersheds

This study was conducted to guide the prioritisation of efforts to manage Cryptosporidum contamination of drinking water supplies in Trinidad, W.I. The main objective was to investigate the relative importance of three main types of sources of Cryptosporidium oocysts: urban, agriculture and wildlife. Weekly surface water samples were collected from 19 sites distributed among three watersheds, and examined for the presence of oocysts. A stratified random sampling design was used with each watershed representing one of the three main sources of oocysts listed above. Results showed a significant association between watershed and the occurrence of positive samples (chi(2)=16.523, d.f. =2, p = 0.000), indicating that land use influenced the presence of oocysts. Urban and forested lands were the two most important sources of oocysts. There was no apparent association between agriculture and the presence of oocysts, and there was no significant difference between the percentage of positive samples at sites below agricultural facilities and sites not associated with agriculture within a single watershed (chi(2)=2.45, d.f. =1, p = 0.117). We conclude that urban and wildlife are the main types of sources of Cryptosporidium contamination of surface water, whereas the contribution of agriculture is minor.

A knowledge, attitude and practices study of the issues of climate change/variability impacts and public health in Trinidad and Tobago, and St Kitts and Nevis

OBJECTIVE

To determine the level of understanding of the issues of climate change (CC)/variability (CV) and public health by populations of St Kitts and Nevis (SKN) and Trinidad and Tobago (T&T) and to find whether respondents would be willing to incorporate these values into strategies for dengue fever (DF) prevention.

DESIGN AND METHODS

Using a cluster sampling system, representative samples of the communities of SKN (227) and T&T (650) were surveyed for responses to a questionnaire document with questions on the impact of climate variability on health, the physical environment, respondents' willingness to utilize climate issues to predict and adapt to climate variability for DF prevention. Data were analyzed by Epi Info.

RESULTS

Sixty-two per cent SKN and 55% T&T of respondents showed some understanding of the concept of climate change (CC) and distinguished this from climate variability (CV). With regard to causes of CC, 48% SKN and 50% T&T attributed CC to all of green houses gases, holes in the ozone layer burning of vegetation and vehicular exhaust gases. However some 39.3% SKN and 31% (T&T) did not answer this question. In response to ranking issues of life affected by CC/CV in both countries, respondents ranked them: health > water resources > agriculture > biodiversity > coastal degradation. The major health issues identified for SKN and T&T respondents were: food-borne diseases > water-borne diseases > heat stresses; vector-borne diseases were only ranked 4th and 5th for SKN and T&T respondents respectively. There was in both countries a significant proportion of respondents (p < 0.001) who reported wet season-related increase of DF cases as a CC/CV link. Respondents identified use of environmental sanitation (ES) at appropriate times as a method of choice of using CC/CV to prevent DF outbreaks. More than 82% in both countries saw the use of the CC/CV information for DF prevention by prediction and control as strategic but only 50-51% were inclined to become personally involved. Currently, only 50% SKN and 45% T&T respondents claimed current involvement in DF vector surveillance and control in the last two days.

CONCLUSION

Despite the fact that knowledge and attitudes did not always coincide with practices of using ES for DF prevention, in both countries, even with CC/CV tools of prediction being available, it seems that respondents could be persuaded to use such strategies. There is a need for demonstration of the efficacy of CC/CV information and promotion of its usefulness for community involvement in DF and possibly other disease prevention.

Climate, mosquito indices and the epidemiology of dengue fever in Trinidad (2002-2004)

Between January 2002 and December 2004, a population-based study on the effects of climate and mosquito indices on the incidences of dengue fever (DF) and dengue haemorrhagic fever (DHF) was conducted in Trinidad, West Indies. The incidence of DF was 5.05 cases/1000 population in 2002, largely as the result of a major outbreak, but declined to 0.49 case/1000 in 2004. The monthly Aedes aegypti (L.) Breteau indices (BI) did not decline over the 3-year study period, however, but increased from a mean of 29 in 2002 to one of 36 in 2004, with seasonal variations (BI of 30-46 and 20-34 were recorded in the wet and dry seasons, respectively). No significant correlations were observed between temperature and DF or DHF incidence but rainfall was found to be significantly correlated with DF incidence, with a clearly defined 'dengue season', between June and November, in two of the study years. The apparent decline in dengue transmission since 2002 appears to be largely attributable to the development of 'herd immunity' in the general population and not to the attempts at vector control. Since the introduction of new serotypes or the fading of the herd immunity could lead to an explosive epidemic of dengue in Trinidad, there is clearly a need for continued surveillance.

Evidence for the interruption of transmission of lymphatic filariasis among schoolchildren in Trinidad and Tobago

This study was carried out to provide some evidence for the interruption of transmission of lymphatic filariasis (LF) among schoolchildren in Trinidad and Tobago. A cross-sectional survey for LF antigenaemia was performed among 63 (13.2%) of the 479 primary schools located in eight administrative (and geographical) regions of Trinidad and Tobago. From these communities, 2597 schoolchildren aged 6-12 years were sequentially selected for a survey of bancroftian antigenaemia. From each child, 100 microl (finger-prick) whole blood sample was applied to a Binax immunochromatographic card test (ICT), and read for the presence of antigenaemia. The ICT results showed a negative finding for LF antigenaemia and suggest that LF transmission has been interrupted in the survey areas.

Short communication: concomitant malaria and filariasis infections in Georgetown, Guyana

Lymphatic filariasis and malaria are endemic in Guyana, South America. To determine the prevalence of concomitant infections, we conducted a 1-year survey of febrile patients attending the malaria (day) and filariasis (night) clinics in Georgetown. In all, 1278 thick blood smears were collected: 769 for filariasis, of which 103 were positive for Wuchereria bancrofti, and three for both W. bancrofti and malaria parasites; and 509 for malaria, 21 of which tested positive for malaria and 17 for both malaria and filariasis. The age groups and sex of the infected persons with malaria and W. bancrofti are described. These results suggest that the incidence of concomitant infections in Guyana may be quite low but efforts should be made to reduce the disease burden in Georgetown, Guyana.

Seroprevalence of toxocariasis in schoolchildren in Trinidad

The seroprevalence of toxocariasis was investigated in 1997/98 in 1009 schoolchildren (aged 5-12 years) throughout Trinidad. Infection, as measured by titre, was found to be high compared to values obtained from children in other countries. Using an excretory-secretory antigen and performing an ELISA test, it was found that 62.3% of children had an IgG antibody titre of > or = 1:100, indicating exposure to the parasite, while 27.2% had a titre of > or = 1:800, indicating a current or recent infection. Relationships were explored between seroprevalence and host factors including age, sex, school location, and other risk factors including geophagia, thumb-sucking, presence of other gastrointestinal-tract parasitism and pet ownership. There was no significant relationship between age and the presence of current or recent infection (P = 0.746). Boys were significantly more commonly infected than girls as were the attendees of rural schools versus urban schools (P < 0.001). The percentage of seropositivity among children varied widely from school to school. Pet ownership and the absence of pipe-borne water in the household were found to be significantly associated with positive serology (P < 0.05). Clinical symptoms mostly associated with positive serology were eczema, seizures and chronic cough. Recommendations derived from this study include health education in order to increase the public awareness on the transmission of the disease, de-worming all dogs and cats periodically and the curbing of stray dogs and cats. Environmental sanitation measures should include keeping children away from contaminated areas and practising proper hygiene after play.

American cutaneous leishmaniasis in Guyana, South America

The 185 patients who presented at the dermatology clinic of Georgetown Public Hospital, Guyana, between 1992 and 1998, with skin ulcers indicative of American cutaneous leishmaniasis (ACL) were retrospectively reviewed. The laboratory-confirmed cases of ACL were identified and the corresponding data were analysed for risk factors such as age, gender, areas of residence and of possible exposure to the causative agent (Leishmania braziliensis guyanensis), ethnic origin, longevity of the ulcers, and treatment regimes prior to the definitive diagnosis. Eighty-one (43%) of the 185 subjects were confirmed to be infected with Le. b. guyanensis. Although 53 (66%) of the cases lived in or close to the capital city, Georgetown, most of the cases had travelled to (and probably been infected in) region X in the interior of Guyana (32%) or regions VII (23%), VIII (23%), IX (11%), VI (5%), I (3%) or III (3%), usually because they were involved in the mining (41%) or lumber (21%) industries, the army or hunting. Almost all (95%) of the cases were male and most (58%) were aged 20-39 years. In general, the cases had had their skin lesions for many days before presenting for treatment: 46% for 1-5 weeks and 3% for > 6 months. Prior to presentation at the clinic, many of the cases had attempted to cure themselves, using local herbal remedies (37%), antibiotics and antifungal remedies (39%), other creams (5%), household chemicals (9%) or miscellaneous remedies such as lead salts (especially lead sulphate) and battery acid, all without success. Recommendations are made for an epidemiological study of active ACL among forest workers, eco-tourists and residents of high-risk areas. Diagnostic centres need to be sited in the regions most at-risk, particularly in or near environments in which the main vectors - sandflies such as Lutzomyia umbratilis, Lu. anduzei and Lu. whitmani - are known to be prevalent.

Lymphatic filariasis in the Caribbean region: the opportunity for its elimination and certification

In order to support the case for a certification of elimination of lymphatic filariasis (LF) in some Caribbean countries, we compared the prevalence of circulating Wuchereria bancrofti antigen in communities in Guyana, Suriname, and Trinidad. For the study, we assayed school children in six communities in Guyana, five communities in Suriname, and three communities in Trinidad for the prevalence of circulating W. bancrofti antigen, using a new immunochromatographic test for LF. We also assayed adults in these three countries, with a special focus on Blanchisseuse, Trinidad, where mass treatment for LF elimination had been carried out in 1981. The prevalences of W. bancrofti circulating antigen found in the school children populations ranged from 1.7% to 33.2% in Guyana and were 0.22% overall in Suriname and 0.0% in Trinidad. Among adults in two Guyana communities the prevalences were 16.7% and 32.1%. The results were all negative from 211 adults in communities in the north, center, and south of Trinidad, as well as from 29 adults in Suriname. The data suggest that contrary to reports of LF endemicity from the World Health Organization, LF may no longer be present in Trinidad and may be of very low prevalence in Suriname. Trinidad and Tobago and other Caribbean nations proven negative could seek to be awarded a certificate of LF elimination. In Suriname the small localized pocket of infected persons who may serve as a reservoir of LF infection could be tested and appropriately treated to achieve LF elimination. Such LF-positive countries as Guyana should access new international resources being made available for LF elimination efforts. An adequate certification program would help identify which countries should seek the new LF elimination resources.

Ivermectin treatment of mansonellosis in Trinidad

This study was conducted to determine the efficacy and long-term effects of an intervention programme based on a single dose of Ivermectin (6 mg) administered during a double-blind placebo study of 40 persons with Mansonella ozzardi infections in Blanchisseuse, Trinidad. After four years, ivermectin reduced microfilariae levels by 82.2%. Short- and long-term effectiveness of the drug is contingent upon the initial microfilariae levels of the patient. We conclude that a single dose of ivermectin reduces microfilariae densities and provides both short- and long-term reductions in M ozzardi microfilaraemia.

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--e.g., Anguilla and Curaçao--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 strain continued to be completely controlled for up to 7 weeks, the most resistant strains had 24% survival after the first week. By week 6, 60% to 75% 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 increased 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 individual 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.

A comparison of surveillance systems for the dengue vector Aedes aegypti in Port of Spain, Trinidad

When the currently used larval surveillance system (visual inspection) for the dengue vector Aedes aegypti was compared with the surveillance for the presence of eggs by ovitrapping in Port of Spain, Trinidad, it was found that the latter (39.1%) was significantly more sensitive than the visual inspection system (10.1%). At the same time, the presence of the nuisance mosquito Culex quinquefasciatus was detected in 38.4% of the households. Both Ae. aegypti and Cx. quinquefasciatus showed preference for ovipositional attractants in ovitraps: hay infusion > yeast suspension > plain tap water. Although all the socioeconomic and geographic areas produced both mosquito species in 1996, upper middle class (UMC) areas (8.6-43.4%) produced more Ae. aegypti than did lower middle class (LMC) areas (7.8-38.8%), which produced more than working class (WC) areas (3.9-29.9%). For Cx. quinquefasciatus, the order of production was reversed with WC areas (50.1%) > LMC areas (30.0%) > UMC areas (26.0%). Change in vector surveillance strategies incorporating some ovitrapping and stratified sampling are recommended for Caribbean countries.

Evaluation of Caribbean strains of Macrocyclops and Mesocyclops (Cyclopoida:Cyclopidae) as biological control tools for the dengue vector Aedes aegypti

Fifteen Caribbean strains of copepods were assessed for their predation ability against mosquito larvae. Macrocyclops albidus from Nariva. Mesocyclops aspericornis from Oropouche, and Mesocyclops longisetus from E1 Socorro, Trinidad, were most effective against Aedes aegypti but not against Culex quinquefasciatus. Mesocyclops longisetus and Me. aspericornis prevented any mosquito survival over 25 wk of observation despite weekly challenges with Ae. aegypti. The copepods were tolerant to dosages of the insecticide temephos that are usually toxic to mosquito larvae. This indicated that copepods could be incorporated into an integrated control system. To determine whether pathogenic microbes might be introduced with copepods into drinking water, microbial studies were done on the copepods. These showed the presence of only Aeromonas sobria, Pseudomonas sp., Alcalignes sp., and gram-positive bacilli. Although none of these are highly pathogenic to humans, the application of these copepods has not yet been recommended for use in drinking water.

Resistance in some Caribbean populations of Aedes aegypti to several insecticides

Thirty-four strains of Aedes aegypti larvae from 17 Caribbean countries were bioassayed for sensitivity to temephos, malathion, fenitrothion, fenthion, and chlorpyrifos. There were fairly high levels of resistance in Tortola (10-12-fold resistance) and Antigua (6-9-fold resistance) strains to temephos and to fenthion (Tortola, 7-10-fold; Antigua, 6-10-fold resistance). Most other strains showed some resistance to malathion, fenitrothion, and chlorpyrifos, but only moderate levels. Adult populations of Ae. aegypti--Aruba, Jamaica, Trinidad, Puerto Rico, St. Lucia, and Antigua strains--also showed moderate resistance to malathion. Mosquito control field data supported the laboratory findings. Doubling the diagnostic dosage of temephos for larval Ae. aegypti was only partially effective against a more resistant strain, and even so, the chemical lost its limited efficacy over a short period of time. Integrated strategies for Ae. aegypti control to mitigate the negative effects of insecticide resistance in the Caribbean strains are suggested.

Mass chemotherapy with diethylcarbamazine for the control of Bancroftian filariasis: a twelve-year follow-up in northern Trinidad, including observations on Mansonella ozzardi

A microfilaria survey was conducted in Trinidad in 1992, 12 years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined using thick blood smears and a membrane filtration technique. They included 104 who had participated in the mass chemotherapy campaign in 1980. No Wuchereria bancrofti microfilariae were detected among 66% of the population examined. In 1980, 86 of 592 persons examined were found to be infected with W. bancrofti, 140 with Mansonella ozzardi and 44 with mixed infections, while in 1992, only M. ozzardi infections persisted despite treatment with DEC-C. Of the 104 persons reexamined 12 years later, 46 had M. ozzardi, of which five were new cases, but none had W. bancrofti. During both the 1980 and 1992 surveys, low microfilariae rates for M. ozzardi were observed among those 19 years of age or younger. Of the 302 persons newly examined in 1992, 29 were infected with significantly (P < 0.001) more males (79.3%) than females (20.9%) being microfilaremic. The combined results showed similar prevalence rates for M. ozzardi from 23.3% to 21.6% in 1980 and 1992. Nuclepore membrane filtration and thick blood films were very efficient in demonstrating the presence of microfilariae. The usefulness of these methods and spaced treatment using DEC-C are also discussed.

Microscopical and serological diagnosis of Wuchereria bancrofti

Venous blood from 292 patients attending a Filaria Clinic in Georgetown, Guyana, was assayed by ELISA for IgG and IgM antibodies and by Indirect Haemagglutination Antibody Assay (IHA) against filaria parasites. They were also assayed by microscopic methods before and after concentration procedures for microfilaraemia. Of the 41 blood samples microscopically positive for Wuchereria bancrofti microfilariae, 87.8% (ELISA IgG), 65.9% (ELISA IgM) and 73.2% (IHA) occurred in samples with sub-diagnostic serological threshold titres of < 1:32 (IgG and IgM) and < 1:128 (IHA). But indicators of value based on the standards of the presence of chronic and acute symptoms, the IgG and IgM diagnostic data gave 79.9% sensitivity, 96.4% specificity, 97.1% positive predictable value and 44.3% negative predictive value. A membrane filtration system (92.7%) was slightly better than a centrifugation technique (90.2%), but more efficient than a thick smear preparation (75.6%) for the detection of microfilariae. The filtration system was vastly superior for yields of microfilariae. However, the Knott's concentration (sedimentation) was the most economical in terms of technician time and materials. Most microscopically confirmed filaria cases were in the 20-29-year age group (25%), followed by the broad 30-69-year age groups (10-12%). Males were significantly more commonly affected by the ratio 24.2:6.0. It is recommended that skills and materials for concentration of microfilariae from peripheral blood be maintained in all Caribbean countries. In known filaria endemic countries, it is recommended that the serological tool be used as an aid in diagnosis for patients with acute and chronic symptoms.

Evaluation of methods for the laboratory diagnosis of malaria in Guyana

When 297 blood samples taken from patients attending a fever clinic in Georgetown Public Hospital were examined microscopically, after thick and thin blood films had been stained with Giemsa, one hundred and forty-two (47.8%) were microscopically positive for malaria. After processing the patient's serum, samples by the Indirect Fluorescent Antibody (IFA) technique, specific IgG and IgM antibodies were detected in 239 (81.3%) and 179 (60.1%), respectively, of the sera. Based on the microscopical findings, the IFAT gave positive predictive and negative values of 54.4% and 81.8% (IgG), and 57.5% and 67.8% (IgM), suggesting that the IgM would be more useful than the IgG in the diagnosis of current malaria. An odds ratio analysis showed that the presence of symptoms, IgG or IgM antibodies, as well as visits to endemic regions, could be good indicators of current malaria. Age and occupation were not. The microscopical method will continue to be the gold standard-the best available criterion for the validation of our tests-for diagnosis of acute malaria.

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.

Parasitic infections in young Jamaicans in different ecological zones of the island

Data are presented for the first country wide prospective study on gastrointestinal tract parasitic infections done in Jamaica. Samples from 2,947 young Jamaicans drawn from all ecological zones and from all parochial divisions of the island were analyzed. Pica was practised by 8.6%. Generally, prevalence of organisms was as follows: Trichuris trichiura (12.3%), Ascaris lumbricoides (9.5%), hookworm (2.2%), Strongyloides stercoralis (0.3%), Giardia lamblia (6.3%) and Entamoeba coli (7.7%). Several other spp. of protozoans were recorded. Prevalence of A. lumbricoides, T. trichiura and Necator americanus was significantly greater in upland than in lowland (both urban and rural), while the situation was reversed for G. lamblia-infections. Greatest variations were age-related. A. lumbricoides and T. trichiura reached peak prevalence of 15.3 and 20.5% respectively in 5-9-year-olds, while hookworm peaked later at 15-19 years of age. Suggestions are made for a national and even regional antihelminthic program for the mass treatment of pre- and primary school age children.

Infective arthritis due to Blastocystis hominis

A patient with rheumatoid arthritis taking prednisone developed Blastocystis hominis acute diarrhoea, which was associated with increased inflammation and effusion of the left knee. B hominis organisms were found in synovial fluid from the left knee. The patient responded dramatically to metronidazole treatment. B hominis may become disseminated in immunosuppressed patients with diarrhoea and may cause infective arthritis.

Sylvatic yellow fever activity in Trinidad, 1988-1989

Of a total of 18,068 mosquitoes (361 pools) collected in south-eastern Trinidad forests from December 1988 to May 1989, 47 species belonging to 14 genera were identified. Five yellow fever virus isolates were made from Haemagogus janthinomys and one from Sabethes chloropterus. All the other pools of mosquitoes examined were negative for the virus. The mosquito isolates were made in December and January. In addition, in late February and early March, 2 infected howler monkeys (Alouatta sp.) were detected. Since March, despite continued surveillance, no yellow fever virus has been detected in mosquitoes or monkeys. There has been no reported human infection.

Toxoplasmosis in young Jamaicans

Of 511 young (1-19 years of age) Jamaicans sampled for IgG antibodies to Toxoplasma by the ELISA method, there was an overall prevalence of 45 per cent. Seropositivity ranged from 24-26 per cent in the 2-year-olds, up to 54 per cent in the 5-9-year-olds. There was no significant difference in prevalence between the sexes, but there was a statistically significant difference between the rates from rural uplands (58 per cent), urban uplands (46 per cent), rural lowlands (40 per cent), and urban lowlands (32 per cent).

Biological control of insect pests affecting man and animals in the tropics

Biological control of pests affecting the health of man and animals is practiced in various forms throughout the tropics. In this paper, the use of parasitic viruses, bacteria, protozoa, predatory arthropods, and fish against pests such as various mosquitoes, tse tse flies, and screwworm flies as published in the literature are reviewed. Mention is also made of the usefulness and applicability of the sterile insect technique, genetic control by chromosomal aberrations, and the exploitation of various incompatabilities. These are reviewed against the background of the present state of technology and limited resources that exist in many tropical countries. Most authors maintain that due to the relative length of time required to get a biological control system working efficiently, and the perennial nature of most tropical pest species, there is often the need to initially reduce the pest population by conventional means. There will thus be a balance between biological and chemical control in most systems. Emphasis is placed on meeting the urgent need for the exchange of research and development information on biological control of pests affecting man and his animals in the tropics.

Endocrine studies in a pregnancy complicated by ovarian theca lutein cysts and hyperreactio luteinalis

Severe virilization developed in a pregnant woman in association with the occurrence of theca lutein cysts and hyperreactio luteinalis of the ovaries. At term, maternal serum levels of androstenedione (58 ng/mL) and testosterone (20 ng/mL) were elevated massively; estrone (24 ng/mL) and estradiol-17 beta (23 ng/mL) levels were increased moderately. Maternal serum levels of human chorionic gonadotropin (hCG) just before delivery, 22,276 mlU/mL, though twice the mean for normal women at term, were within the normal range. The levels of androstenedione (1.06 ng/mL) and testosterone (0.26 ng/mL) in umbilical cord serum of her normal newborn female infant were normal. The levels of androstenedione and testosterone in serum of this woman declined slowly, but progressively, during the first two months after delivery; the serum levels of androstenedione and testosterone increased substantially, however, after she was treated with hCG eight weeks postpartum. These results are suggestive that, for reasons unknown, markedly increased androgen production with theca lutein cysts and hyperreactio luteinalis in some pregnant women results ultimately because of increased ovarian sensitivity to hCG.

Current trends in screwworm myiasis in the Caribbean region

In a random sample of animal producers and animal health personnel, 33% of the respondents in Trinidad, 15% in Guyana, 11% in Suriname and 9% in Jamaica recalled at least one case of human myiasis due to Cochliomyia homivorax (Coquerel). During 1981, respondents in Surinam (88%), Jamaica (90%), Guyana (85%) and Trinidad and Tobago (82%) found at least one case of myiasis in their livestock, occurring mainly in cattle, pigs and dogs. Feral animals, e.g. jaguars, were also found to be infested. The initial wounds were mainly the umbilicus of neonates, and arbitrary wounds, and vampire bites were also affected. Fifty-three to 78% of all respondents examined their livestock daily for wounds and infestation by the screwworm. Annual estimates of losses (in U.S. dollars) due to surveillance and medication ranged from $4.82 to $10.71 per animal. Nationally, these losses amount to $0.30 million (Surinam), $1.02 million (Trinidad and Tobago), $4.33 million (Guyana) and $6.78 million (Jamaica). Figures for other losses, arising from failure to thrive, reduction in milk production and hide injury due to screwworm activity were not available. Most producers found that the greatest screwworm infestation occurred in the wet season, and most described it as second in importance to Boophilus spp. ticks as a pest of livestock, but of greater significance than biting flies, such as tabanids and stable flies. Eradication of the screwworm from the islands of Jamaica and Trinidad and Tobago can be recommended, but in Surinam and Guyana eradication seems feasible only on the 100-km wide coastal strips where most human and livestock populations exist.