Mosquitoes and tourism in Grenada - Poster abstract

The global public health importance of mosquitoes cannot be over-emphasised. The tourist industry relies heavily on customer satisfaction and this study examined the importance of mosquitoes as a cause of dissatisfaction amongst tourists visiting Grenada. Tourists who had spent three days or more at four popular hotels were included in the study. This study also examined the species and breeding site distribution of mosquitoes in the hotels selected. Three cross sectional surveys were carried out in both the dry and wet seasons at various time intervals and ovitraps were placed in various parts of each hotel for up to a week. Eggs collected from these traps were identified. Aedes sp were more numerous than Culex sp eggs and were more numerous in the rainy season. Of the tourists interviewed by questionaire, 87 percent had been bitten by mosquitoes during their stay; 74 percent had been bitten twice, 18 percent twenty times and 8 percent more than 20 times. Seventy-seven percent (77 percent) of tourists perceived mosquitoes as a severe biting nuisance whilst 16 percent and 7 percent perceived them as moderate or mild, respectively. Biting nuisance was most severe in the wet season and the dining room was reported as the most important site where biting took place for all hotels studied. Potential breeding sites were identified and appropriate mosquito control measures have been suggested to the hotels.(AU)

Transmission thresholds for dengue in terms of Aedes aegypti pupae per person with discussion of their utility in source reduction efforts

The expense and ineffectiveness of drift-based insecticide aerosols to control dengue epidemics has led to suppression strategies based on eliminating larval breeding sites. The present work attempts to estimate transmission thresholds for dengue based on an easily-derived statistic, the standing crop of Aedes aegypti pupae per person in the environment. We have developed these thresholds for use in the assessment of risk of transmission and to provide targets for the actual degree of suppression required to prevent or eliminate transmission in source reduction programs. The notion of thresholds is based on 2 concepts: the mass action principal- the course of an epidemic is dependent on the rate of contact between susceptible hosts and infectious vectors, and threshold theory - the introduction of a few infectious individuals into a community of susceptible individuals will not give rise to an outbreak unless the density of the vectors exceeds a certain critical level. We use validated transmission models to estimate thresholds as a function of levels of pre-existing antibody levels in human populations, ambient air temperatures, and the size and frequency of viral introduction. Threshold levels were estimated to range between about 0.5 and 1.5 Ae. aegypti pupae per person for ambient air temperatures of 28 degrees C and initial seroprevalences ranging between 0 percent to 67 percent. Suprisingly, the size of the viral introduction used in these studies, ranging between 1 and 12 infectious individuals per year was not seen to significantly influence the magnitude of the threshold. From a control perspective, these results are not particularly encouraging. The ratio of Ae. aegypti pupae to human density has been observed in limited field studies to range between 0.3 and >60 in 25 sites in dengue-epidemic of dengue-susceptible areas in the Caribbean, Central America, and South East Asia. If, for purposes of illustration, we assume an initial seroprevalence of 33 percent, the degree of suppression required to essentially eliminate the possibility of summertime transmission in Puerto Rico, Honduras, and Bangkok, Thailand was estimated to range between 10 percent and 83 percent; however in Mexico and Trinidad, reductions of >90 percent would be required.(AU)

Transmission thresholds for dengue in terms of Aedes aegypti pupae per person with discussion of their utility in source reduction efforts

The expense and ineffectiveness of drift-based insecticide aerosols to control dengue epidemics has led to suppression strategies based on eliminating larval breeding sites. With the notable but short-lived exceptions of Cuba and Singapore, these source reduction efforts have met with little documented success; failure has chiefly been attributed to inadequate participation of the communities involved. The present work attempts to estimate transmission thresholds for dengue based on an easily-derived statistic, the standing crop of Aedes aegypti pupae per person in the environment. We have developed these thresholds for use in the assessment of risk of transmission and to provide targets for the actual degree of suppression required to prevent or eliminate transmission in source reduction programs. The notion of thresholds is based on 2 concepts: the mass action principal-the course of an epidemic is dependent on the rate of contact between susceptible hosts and infectious vectors, and threshold theory-the introduction of a few infectious individuals into a community of susceptible individuals will not give rise to an outbreak unless the density of vectors exceeds a certain critical level. We use validated transmission models to estimate thresholds as a function of levels of pre-existing antibody levels in human populations, ambient air temperatures, and size and frequency of viral introduction. Threshold levels were estimated to range between about 0.5 and 1.5 Ae. aegypti pupae per person for ambient air temperatures of 28 degrees C and initial seroprevalences ranging between 0% to 67%. Surprisingly, the size of the viral introduction used in these studies, ranging between 1 and 12 infectious individuals per year, was not seen to significantly influence the magnitude of the threshold. From a control perspective, these results are not particularly encouraging. The ratio of Ae. aegypti pupae to human density has been observed in limited field studies to range between 0.3 and >60 in 25 sites in dengue-endemic or dengue-susceptible areas in the Caribbean, Central America, and Southeast Asia. If, for purposes of illustration, we assume an initial seroprevalence of 33%, the degree of suppression required to essentially eliminate the possibility of summertime transmission in Puerto Rico, Honduras, and Bangkok, Thailand was estimated to range between 10% and 83%; however in Mexico and Trinidad, reductions of >90% would be required. A clearer picture of the actual magnitude of the reductions required to eliminate the threat of transmission is provided by the ratio of the observed standing crop of Ae. aegypti pupae per person and the threshold. For example, in a site in Mayaguez, Puerto Rico, the ratio of observed and threshold was 1.7, meaning roughly that about 7 of every 17 breeding containers would have to be eliminated. For Reynosa, Mexico, with a ratio of approximately 10, 9 of every 10 containers would have to be eliminated. For sites in Trinidad with ratios averaging approximately 25, the elimination of 24 of every 25 would be required. With the exceptions of Cuba and Singapore, no published reports of sustained source reduction efforts have achieved anything near these levels of reductions in breeding containers. Practical advice on the use of thresholds is provided for operational control projects.

Seasonal abundance, biting cycle, and parity of the mosquito Anopheles Homunculus in Trinidad, West Indies

Seasonal abundance, daily biting activity, and the age composition of adult Anopheles homunculus female populations were monitored weekly during 1989-90 by human bait on the ground at Cumaca Forest, Platanal, Trinidad. Landing collections of An. homunculus showed diurnal and nocturnal activity, with a single peak between 1600 and 2000 hours. Overall, 27.7 percent of An. homunculus were collected during the dry season and 72.3 percent during the wet season. Similiar seasonal parous rates were observed in wet (58.9 percent) and dry (56.1 percent) seasons. Diel periodicities of nullipars and pars were almost identical during the wet and dry seasons (AU)

Seasonal abundance, biting cycle, and parity of the mosquito anopheles homunculus in Trinidad, West Indies

Seasonal abundance, daily biting activity, and the age composition of adult Anopheles homunculus female populations were monitored weekly during 1989-90 by human bait on the ground at Cumaca Forest, Platanal, Trinidad. Landing collections of An. homunculus showed diurnal and nocturnal activity, with a single peak between 1600 and 2000 hours. Overall, 27.7 percent of An. homunculus were collected during the dry season and 72.3 percent during the wet season. Similar seasonal parous rates were observed in wet (58.9 percent) and dry (56.1 percent) seasons. Diel periodicities of nullipars and pars were almost identical during the wet and dry seasons(AU)

Acute renal failure following multiple stings by africanized bees - abstract

From 1979 to October 1990, Africanized bees have stung 3,955 humans with 10 deaths and 1,071 animals with 715 deaths in Trinidad and Tobago. The medical records of all patients seen at the General Hospital, Port-of-Spain, who developed acute renal failure following stings by Africanized bees were included in the study. Of the 5 patients in the study, 4 were males and 1 was female. One patient was stung by just over 500 bees while the rest were stung by over 1,000 bees. All patients had grossly elevated muscle enzymes. Two of the 5 patients died within 48 hours and causes of death were acute pancreatitis with acute renal failure, and acute pulmonary failure with acute renal failure. Two of the three patients who survived were desperately ill and had to be dialyzed. Renal function in these survivors did not return to normal under 50 days. It is likely that other islands of the Caribbean will soon be presented with this syndrome (AU)

Acute renal failure due to multiple stings by Africanised bees: report of the first case in Trinidad

A case of acute renal failure in an adult who was stung by over 1,000 Africanised bees is reported. The patient has made full recovery. This is the first such case to be reported from Trinidad (AU)

The black fly (simulium) problem in the Rupununi Savannahs, Guyana - abstract

Simulium black flies (called Kabowras in Guyana) are not known to carry diseases in Guyana, but they become a serious nuisance at certain times of the year in the Rupununi Savannahs. The present project was designed to study the bionomics of the nuisance species. Of about 20 species of black flies known from Guyana, 2 are serious manbiters; Simulium incrustatum and S. sanguineum s.l. The former appears in large numbers near small creeks and rivers, while the latter seems to be associated with larger rivers such as the Takutu and Rupununi. Peak densities of the two species appear at the height of the rainy season, but drop rapidly at the onset of the dry season. A peak biting rate of 928 flies per man hour was recorded for S. incrustatum and 764 flies per man hour for S. sanguineum s.l. Data obtained so far indicate that the two species tend to stay near river banks rather than the open savannahs. Both species are diurnal; none were collected after dark. For S. incrustatum there are early morning and late afternoon peaks. S. sanguineum s.l. peaks towards mid-morning and declines in the afternoon. The diurnal activities can be affected by rainfall and cloudy conditions. S. incrustatum shows no marked preference for humans or animals, but S. sanguineum s.l. shows a marked preference for livestock, dividing its attention almost equally between a cow and a horse during a comparative study. Because of their high biting rates these flies are serious pests, sufficient to discourage people from settling and developing the area. Further, their attacks on cattle may cause severe blood loss, annoyance and subsequent loss of weight resulting in financial loss to farmers (AU)

Myocarditis from scorpion stings

This paper deals with the clinical and electrocardiographic study of 45 patients who had been stung by the common scorpion of Trinidad, Tityus trinitatis (family Buthidae). The patients were examined soon after admission, and serial 12-lead electrocardiograms were done on admission and at approximately 24, 48, and 72 hours after the scorpion sting. If the E.C.G. was still abnormal at the end of 72 hours it was repeated at the end of the week. The fasting blood sugar, urinary sugar, serum amylase, serum electrolytes, and blood urea estimations were done within 24 hours of admission. The common clinical findings were pain at the site of the sting, excessive salivation, vomiting, epigastric pain, abdominal tenderness, disturbance of heart rate and rhythm, glycosuria, pyrexia, and profuse sweating. Nine patients were shocked, and three had muscular twitchings and carpoped spasms. Thiry-four patients had electrocardiographic evidence of myocarditis that is, inversion of the T waves in several leads, significant deviation of the RST segment, prolongation of Q-Tc and conduction defects with complete restoration to normal in three to six days. Toxic myocarditis has not been previously described after scorpion stings. Death is usually ascribed to a toxic effect on the medullary centres. Myocarditis is the commonest complication following stings by Tityus trinitatis, and it would be reasonable to postulate that it is a frequent cause of death in this condition (AU)