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.

The introduction of cyclofem into national family planning programmes: experience from studies in Indonesia, Jamaica, Mexico, Thailand and Tunisia. Task force on research on introduction and transfer of technologies for fertility regulation, special programme of research, development and research

Studies on the introduction of Cyclofem into family planning programmes have been undertaken in Indonesia, Jamaica, Mexico, Thailand and Tunisia. Cyclofem is a once-a-month injectable contraceptive containing 25mg medroxyprogesterone acetate and 5mg estradiol cypionate. A total of 7927 subjects were followed in close to routine service delivery conditions in primary and secondary family planning outlets. The studies confirmed the high efficacy of the method with 12-month pregnancy rates ranging from 0 to 0.7 percent. Major differences were seen in reasons and rates of discontinuation between countries, the overall 12-month life table discontinuation rates ranging from 33.5 percent in Indonesia to 71.8 percent in Tunisia. The reasons for discontinuation in each of the five countries described, differences between countries contrasted, and service delivery issues which should be addressed further, raised (AU)

Chromatographic and spectroscopic profiles of Cannabis of different origins: Part I

High-resolutin capillary gas chromatography with flame ionization detection and mass spectrometry (GC and GC/MS) and high-performance liquid chromatography (HPLC) were used to establish complex chemical profiles (chemical signatures) of Cannabis samples of known origin. Over 100 compounds could be differentiated, including noncannabinoid (terpenes, alkanes) as well as minor and major cannabinoids and their acids. A characteristic peak pattern was found within a limited number of specimens of identical origin. Correlation studies on the basis of peak area ratios(A(x)/A(i.s.)) showed the feasibility of tracing Cannabis chemically to its country of origin. Several forensic science applications for the chromatography and spectroscopic profiles of confiscated Cannabis samples are discussed, such as detection of additive (phencyclidine),differentiation of chemotypes, and monitoring of tetrhydrocannabinol (THC) potency. (AU)

The effect of economic factors on contraceptive choice in Jamaica and Thailand: a comparison of mixed multinomial logit results

In this study the sensitivity of specific potential users and user groups to the prices charged for contraceptives was investigated. The results of the author's estimations explaining the choice to use priced contraceptive sources when free sources are available, for those who choose to purchase methods, are much hypothesized. In both Jamaica and Thailand, factors other than prices tend to dominate in determining whether a woman or her partner will purchase contraceptives, given free availability. In separate analyses for Jamaica and Thailand, the results explaining the choice of a specific method for those who choose to purchase contraceptives are consistent with expectations based on economic theory. Money prices and time costs are found to be negatively related to the choice of contraceptive method, but for several of the priced contraceptives, the effects of money prices are seen to be small in magnitude. The policy implications for these results are large and obvious. They suggest that decreases in subsidization of the money price of low elasticity contraceptives (the pill, IUD, sterilization) will not significantly alter the pattern of choice of contraceptive methods. Other methods, including condoms in both Jamaica and Thailand and injections in Jamaica, are found to be relatively sensitive to money price, and the results suggest that price increases would substantially decrease their use. (AU)

Illicit traffic and abuse of cannabis in Canada

In 1984 cannabis derivatives, in particular marijuana, hashish and liquid hashish, continued to be the most readily available drugs of abuse in Canada. Marijuana originating in Colombia decreased on the illicit marijuana market in Canada from an estimated 45 percent in 1983 to 30 percent in 1984, but it remained the largest source of marijuana supply. Marijuana originating in Thialand remained at approximately the same level (20 percent) in 1984 as in 1983, while marijuana of Jamaican origin increased its share in the illicit market from 10 percent in 1983 to 20 percent in 1984. Approximately 10 percent of marijuana on the illicit market originated in Canada, 10 percent in Mexico, and 10 per cent in the United States of America. In 1984 an estimated 85 percent of hashish on the illicit market in Canada originated in Lebanon (55 percent in 1983), 10 percent in India or Pakistan (31 percent in 1983) and 5 percent in Jamaica (2 percent in 1983). Illicit shipments in tonnes of hashish originating in Lebanon made this the dominant source of supply of the drug. Liquid hashish originating in Jamaica shared 88 percent of the illicit market of this drug in Canada during 1984, while 10 percent of the drug originated in Lebanon and 2 percent in Canada. In 1984 an estimated 40 percent of smuggled marijuana entered the illicit market in Canada by air and approximately the same by sea, while 20 percent was smuggled over land. During the same year, hashish was smuggled into Canada primarily by sea, while air accounted for 5 percent and land for 1 per cent only. Liquid hashish, in contrast, entered Canada primarily by air, and only 9 percent by land and 1 percent by sea (AU)

Routine radiographic screening of the chest in pregnant women: is it indicated?

Experience with routine antepartum chest radiographic screening from July 1, 1976, through June 30, 1977, in a city-county hospital which serves a predominantly black indigent population was reviewed. The 5422 routine screening chest radiographs produced an extremely low yield of pathology (11 cases), and only 3 of the 11 cases were not suspected from the history of physical examination. Only 2 cases of active pulmonary tuberculosis were discovered, and both patients were recent immigrants from countries with a much higher incidence of tuberculosis. This low case finding probably reflects the general decline in incidence of pulmonary tuberculosis in the United States and suggests that routine screening chest radiographs (done primarily to exclude tuberculosis) are not longer indicated in our pregnant population (AU)

Aedes aegypti strain fitness for yellow fever virus transmission

Three geographical strains of Aedes aegypti from Thailand (Amphur), East Africa (Kampala), and the West Indies (Santo Domingo) were compared for susceptibility to infection with low-passage yellow fever virus (French viscerotropic) as well as for ability to transmit virus by bite at varying extrinsic incubation periods. Santo Domingo strain appeared the most competent and Kampala the least when mosquitoes were exposed to a low level virus-infecting blood meal; at higher virus levels, a similar trend was noted but differences were less evident and in no case were the differences statistically significant. All three strains were infected with and transmitted yellow fever virus (AU)

Comparison of dengue-2 and dengue-3 virus strains by neutralization tests and identification of a subtype of dengue-3

Strains of dengue-2 and dengue-3 viruses of diverse geographic origins including southeast Asia, the Caribbean region, and Tahati were compared by plaque-reduction neutralisation tests with hyperimmune-mouse asctic fluids and human convalescent sera. The dengue-2 strains all appeared similar. The dengue-3 strains from the Caribbean and from Tahiti were similar to each other and differed significantly from the southeast Asian strains. A subtype of dengue-3 was defined (AU)

Dental manpower requirements in emerging countries

The training and use of dental auxiliaries in newly emerging countries are proposed as the solution in such countries to the prevalence of dental disease, the paucity of professional dentists and dental schools, and the competing demands on their economies. Statistically valid dental health surveys of many countries do not exist, but scattered evidence from Jamaica, Guatemala, Thialand, Senegal, and Kenya, among others, indicates that caries and periodontal infections are widespread, and malocclusion, malignant neoplasms of the mouth, and calcium defects are not infrequent. The ratio of dentists to population varies from 1 to 15,000 in Jamaica to 1 to 250,000 in Kenya. Only 130 to 150 dentists are gratuated each year from Africa's seven dental schools; half the countries of the world have no dental school and no prospects of attaining one. The cost of producing one professional dentist is prohibitive - $23,000 per dentist in Guatemala, for example. Auxiliaries can fulfil many basic dental needs of both children and adults in these countries. A program with three consecutive but overlapping phases is suggested. Phase one is to produce a small corps of superbly trained dentists. Phase two is to supplement this corps by giving existing paramedical and auxiliary health personnel 6 weeks of practical chairside training to develop specific cadres of trained dental auxiliaries. Single skill auxiliaries can be trained in 2 years. A dental surgeon and six auxiliaries can serve an estimated 25,000 persons. Multiple skill auxiliaries with 8 years of general education need 3 years of technical training, preferably in an institution where graduate dentists and dental hygienists are also prepared. The auxiliary's role is both as assistant to the dentist and, where supervision is remote, as his substitute. Producing two types of auxiliaries, one oriented to the dental care of children, and the second a curative care of adults, would permit the organization of dental health services on a rational priority basis. (Summary)