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The effect of flea control on Yersinia (Pasteurella) pestis antibody rates in the California vole, Microtus californicus, and its epizootiological implications.

The effects of flea control on the prevalence of (Pasteurella) pestis antibody rates in the California vole, Microtus californicus, were studied in San Mateo County, California, USA. In this area, which had shown antibody prevalence rates of 50% or more during epizootics in previous years, continuous flea control measures reduced the antibody rate to virtually zero and held it at that level for 12 months, although a nearby area showed an incidence of 40-80% seropositive voles for 5 months during the same period. The striking correlation between the reduction of the flea population and the decline of Y. pestis antibody rates suggests that in the area studied there is no evidence that soil, or any factor other than the flea vector, was the agent of transmission of the infective agent in wild rodents.

Animals↗

The role of the peridomiciliary area in the elimination of Triatoma infestans from rural Argentine communities.

The purpose of this study was to identify the origin of Triatoma infestans reinfestation and study its dynamics following spraying with deltamethrin inside and around 94 houses in three rural communities in northwestern Argentina. The effectiveness of the spraying was evaluated immediately after the houses were sprayed and two months later. In addition, five residual peridomiciliary foci were found and sprayed, as well as three preexisting ones that had not been sprayed. To monitor reinfestation, biosensors were placed in the houses and each family was also asked to capture triatomines and keep them in plastic bags; in addition, triatomines were searched for in and around houses, using an aerosol that dislodged them from their hiding places. Selective sprayings were carried out only where a colony of T. infestans was found. During the 30 months of follow-up, the percentage of houses in which any T. infestans were captured varied between 3% and 9%. In six houses, T. infestans were captured during more than one evaluation. The number of peridomiciliary areas found to be infested (19) was double the number of infested houses (9). Colonies of T. infestans were found only in the peridomiciliary areas, where the number of T. infestans captured was six times higher than in the houses. Chickens were the host most frequently associated with peridomiciliary foci. This area was the origin and principal source of reinfestation. To reduce the speed of reinfestation and the frequency with which sprayings are needed, the following environmental and chemical control methods must be combined in the peridomiciliary area: reduce the number of hiding places of triatomines; restrict the raising of birds to structures that cannot be colonized by triatomines; apply an insecticide that is less likely to be degraded by exposure to the elements, or perform a second spraying 6 to 12 months after the first; and employ a device for early detection of the presence of T. infestans around houses.

Aerosols↗

Studies on the control of plague in the western United States: laboratory trials of six insecticide dust formulations applied to soil for the control of the plague vector Oropsylla montana (Siphonaptera: Ceratophyllidae).

In this study, six insecticide dust formulations were laboratory-tested in soil mixtures ranging in concentration from 40 to 1,280 parts per million (ppm) against a proven vector of bubonic plague, Oropsylla montana (Baker). Pulicidal effects of the six insecticides, which included three organophosphates, two carbamates, and a pyrethroid, were compared by LD(50) values at both ambient and 75% RH. Permethrin (Pyraperm 455 dust), a pyrethroid with a LD(50) less than 40 ppm, demonstrated the most effective pulicidal action for the 13-wk trial period, followed in order by chlorpyrifos, bendiocarb, propetamphos, diazinon, and carbaryl.

Animals↗

Response of Trypanosoma vivax and Trypanosoma congolense in zebu cattle in North Cameroon to prophylactic treatment with two formulations of isometamidium.

We tested the efficacy of two formulations of isometamidium in a tsetse-infested farm in North Cameroon from 20 August 2000 to 5 January 2001. A total of 90 adult cattle were used in three groups of 30 each corresponding to two treated and one untreated control. Drug efficacies were evaluated in terms of reduction of parasite incidence in the host's blood, maintenance of packed-cell volume (PCV) and weight gains. Both drugs reduced the incidence of parasites even though re-infections 2 weeks after treatment were common. PCV values were similar in both treated groups but higher than in the untreated control. Body weight changes followed a similar trend with the control losing weight from a mean of 427+/-119kg at the beginning to 398+/-93kg in 4 months. Weights increased from 375+/-76 and 396+/-110 to 396+/-69 and 418+/-112kg in the Veridium and Trypamidium groups, respectively. Efficacy was similar between the two formulations of isometamidium in the prophylaxis of bovine trypanosomosis. However, the presence of parasites in some animals barely 2 weeks after treatment suggested that either infections were not cleared or residual drug effects were not sufficient to prevent re-infections.

Animals↗

Selective primary health care: strategies for control of disease in the developing world. XVI. Chagas' disease.

Despite much research, specific chemotherapy for Chagas' disease remains problematic, and prophylaxis by vaccination seems remote. A significant proportion of today's positive seroreactive patients will burden tomorrow's hospital services with persistent cardiac failure, arrhythmias requiring pacemaker implantation, and megasyndromes requiring corrective surgical procedures. Yet the control of transmission to humans in many endemic areas is feasible by programs of residual insecticide spraying and subsequent vigilance and, in some instances, house improvement, i.e., measures to combat domiciliated vector bugs. The success of such programs will vary, depending on the dominant bug vector and degree of development of the country's public health services. The fact that the Brazilian government voted a large sum of money in 1983 for bug control by the Ministry of Health enforces this view. Transmission of Trypanosoma cruzi to humans could decrease considerably in the next decade in Brazil as a result of this program. There is, however, still a need for research to define the cheapest ways of interrupting transmission in different epidemiologic situations so that the maximum number of people at risk can be reached with the funds available, for the children infected today may be hospital patients of the future for whom little can be done.

Animals↗

The control of Chagas' disease in Mambaí, Brazil: the initial phases.

The control of Chagas' disease depends on breaking contact between Man and vector organisms living in the house fabric; the primary method utilized is residual insecticide spraying of houses. Ministries of health in afflicted countries have elaborated standard procedures for such combat programs. The first two phases of such a program in Mambaí, Goiaś, Brazil are described. In the third phase of vigilance, community participation is necessary to detect residual organism populations in houses. A house improvement scheme applied to houses with persistent infection, is recommended as being most practical at this time.

Brazil↗

Evaluation of medium treatments for management of Frankliniella occidentalis (Thripidae: Thysanoptera) and Bradysia coprophila (Diptera: Sciaridae).

Two greenhouse experiments, each comprising two trials, were conducted to evaluate medium drenches of insect growth regulators and conventional insecticides to reduce emergence of adult western flower thrips, Frankliniella occidentalis (Pergande), and fungus gnats, Bradysia coprophila (Lintner) from the medium. In the insect growth regulator trials, diflubenzuron and pyriproxyfen provided the greatest reduction in thrips emergence, and fenoxycarb, pyriproxyfen and azadirachtin resulted in the most significant reduction of fungus gnat emergence. Treatments with the contact insecticides, methiocarb and chlorpyrifos, resulted in the greatest reduction of thrips and fungus gnat populations. These data suggest that fungus gnats are susceptible to many compounds used in commercial greenhouse production. Even though medium drenches are not currently used for thrips management, drenches with diflubenzuron, pyriproxyfen, methiocarb and chlorpyrifos could aid in reducing thrips populations in greenhouse management programs.

Animals↗

[Congenital transmission of Trypanosoma cruzi infection in Argentina].

Congenital transmission of Trypanosoma cruzi infection in Argentina has being increasing its relative importance with control of vectorial and transfusional transmission growth. It is for this reason that vertical transmission is seen, in the future, as a continuous source of infected newborns, even with vectorial and transfusional transmission completely controlled. Preventing vertical transmission of T.cruzi is not possible, but it can be precociously detected, permitting mother and child to be incorporated into the medical attention system, and so allowing the newbornś treatment with practically 100% efficacy. It is estimated that between 800 and 1700 children infected with T. cruzi by congenital transmission are born in Argentina, per year. The implementation of an early strategy of detection for an effective and opportune treatment acquires great relevance as a Public Health measure.

Animals↗

The predicted and observed decline in onchocerciasis infection during 14 years of successful control of Simulium spp. in west Africa.

In 55 villages from the well-protected central area of the Onchocerciasis Control Programme in West Africa (OCP), skin snip surveys have been carried out at regular intervals since the programme started, and the latest round of surveys was undertaken after 12-14 years of successful vector control. The observed trends in the prevalence and intensity of onchocerciasis infection in cohorts of adults were compared with the trends predicted using a host-parasite model. After 12-14 years of control the community microfilarial load (CMFL) was close to zero in all villages. During the last few years of control, the prevalence of infection declined at an accelerated rate, and this was predicted by the model. There was generally good agreement between observed and predicted trends. The predictions were based on an estimated average duration of infection of 10.4 years, which corresponds to a mean reproductive lifespan for Onchocerca volvulus of 9-9.5 years, and an upper limit of 15 years for 95% of the infections. Differences between the observed and predicted data included the trend in CMFL between the first and second surveys, which in 18 villages did not show the predicted decline. Furthermore, the observed final decline in prevalence was faster than predicted in the north-eastern part of the central OCP area. After 14 years of vector control, the level of onchocerciasis has fallen to such a low level that consideration is being given to ending larviciding.

Adult↗

Personal protection measures against fire ant attacks.

BACKGROUND: Fire ant stings lead to significant morbidity and mortality each year. Virtually no information exists in the scientific literature about the effectiveness of personal protection measures against these ants. OBJECTIVES: To quantify the level of protection from ant stings by socks and cotton tights and to evaluate the efficacy of repellents and other chemicals in preventing stings. METHODS: Commercially obtained infant socks were fitted on a plastic doll's foot, which was touched to fire ant mounds in a series of controlled experiments. Socks and cotton tights were stretched over a human finger and placed in a fire ant mound to test the ability of ants to sting through fabric. Assays were developed to screen chemical substances for their ability to stop or prevent fire ant stings. RESULTS: Socks of any type reduced the number of fire ants that reached the skin and delayed the time required for ants to reach the skin above the sock level. Fire ants were unable to sting through all socks tested. Ants successfully stung both paper towels and human skin, regardless of chemical substance or repellent applied to them. CONCLUSIONS: Socks provide some degree of protection from fire ant stings; therefore, children living in fire ant-infested areas should wear them. Fire ants appear unable to sting through many commercially available socks. Cotton tights may be useful in protecting the lower extremities of children. Fire ants are not deterred from stinging by a wide variety of insect repellents and chemical substances.

Animals↗

[Bases for control of arthropod vectors: I--Definitions, bioecology of vectors (author's transl)].

Arthropoda form the most diversified and multitudinous phyllum of the animal kingdom. In this "arthropod world", the authors give the respective position of the arthropoda: a) detrimental to crops, b) venomous and noxious for human being, but mainly those who are vectors of human diseases, say about a hundred species. Biological, ecological and environmental main features of the most important arthropod vectors of human tropical diseases are reviewed. Various factors acting on the relation between pathological agent and vector and between vector and man are considered. Importance and complexity of entomological surveys are emphasized with, as a consequence, the necessity of specialized medical entomologists to manage them.

Acari↗

Sleeping sickness in Busoga, Uganda, 1976-1983.

Between 1976 and 1983 in the Busoga Region in Uganda 10,414 male and 9,560 female patients were detected with trypanosomiasis. Prior to the onset of the epidemic, Glossina f. fuscipes, the sole vector, had broken through the tsetse control barrier and had spread to cover most of the region. The fly was further observed to be resting in Lantana plants and coffee and banana plantations which are widespread in the area. A close and regular contact was thus established between man and fly. It was observed that the young and engergetic persons first became infected, but as the epidemic unfolded the older age-groups bore the brunt. The infection was also seen in all other age-groups indicating the closeness of contact between the fly and the local population.

Adolescent↗

Field evaluation of an area repellent system (Thermacell) against Phlebotomus papatasi (Diptera: Psychodidae) and Ochlerotatus caspius (Diptera: Culicidae) in Sanliurfa Province, Turkey.

A field evaluation of a new area repellent system, Thermacell Mosquito Repellent (TMR, cis-trans allethrin), was conducted against phlebotomine sand flies and mosquitoes in Cunpolat village, Sanliurfa Province, in southeastern Anatolia, Turkey, an area historically endemic for cutaneous leishmaniasis and high sand fly populations. The objective of this study was to determine the efficacy, duration of protection, and spatial characteristics of protection (downwind distance from point of release), of the TMR. Twelve adult volunteers (nine in the treatment and three controls) made collections from ankle to knee for 25 min every hour from 2100 to 0300 on six consecutive nights in August 2002. Treatment consisted of placing a TMR unit at the middle of the village and then placing human bait collectors at 2.3, 4.6, and 7.6 m away from the repellent unit. Results from the field tests showed highly significant protection provided by the TMR from attack by Phlebotomus papatasi (Scopoli) (P < 0.001) and Ochlerotatus caspius (Pallas) (P < 0.001) for up to 4 h postapplication. In the six nights that tests were done, a total of 949 sand flies and 1095 mosquitoes were collected from the untreated control sites. Only 86 sand flies and 83 mosquitoes were collected at all distances from the places treated with TMR. These results indicated that reduction in sand fly and mosquito biting rates in treated groups ranged from 87.5 to 97.7% (mean protection 92%) and 90.2-97.4% (mean protection 93%), respectively. The percentage reduction values were maintained above 90.0% for 6 h of the assessment period. Overall, the number of bites by the cutaneous leishmaniasis vector Ph. papatasi and also Oc. caspius was reduced > 11-fold and 13-fold, respectively, by the TMR.

Animals↗

Monitoring the domiciliary and peridomiciliary invasion process of Triatoma rubrovaria in the State of Rio Grande do Sul, Brazil.

The presence of Triatoma rubrovaria in Brazil has only been confirmed in the States of Paraná and Rio Grande do Sul (RS), where it is found naturally infected with Trypanosoma cruzi. In the wild environment it occurs in rocky habitats and has an eclectic diet, feeding from cockroaches, reptiles and mammals. Data from the Chagas Disease Control Program obtained by the Fundação Nacional de Saúde, between 1975 and 1997, indicate a growing domiciliary and peridomiciliary invasion of T. rubrovaria in RS, where it has become the most frequently Triatominae species captured in this state since the control of Triatoma infestans. In order to monitor this process, we analyzed collection data derived from 22 years of control campaigns against T. infestans. Collection data for triatomines from domestic habitats show an inverse relationship, with high numbers of T. infestans and low numbers of T. rubrovaria during 1976-1987, compared to the following ten years, 1986-1997, when the number of T. infestans dropped drastically and that of T. rubrovaria increased. There are no consistent indications of intradomiciliary colonization by T. rubrovaria, since only low numbers of nymphs have been captured in the intradomiciliary ecotopes. Nevertheless, this species appears to have preadaptive characteristics for anthropic ecotopes, and should be kept under constant epidemiological surveillance.

Animals↗

Further studies on the reinvasion of the onchocerciasis control programme by Simulium damnosum s.l.: the effects of an extension of control activities into southern Ivory Coast during 1979.

During 1979 the aerial larviciding operations of the Onchocerciasis Control Programme were extended southwestwards to cover those areas with Ivory Coast where the savanna cytospecies of the Simulium damnosum complex were known to breed. This resulted in a marked reduction of the reinvasion which threatened the Programme in Ivory Coast and Upper Volta in earlier years. Previous conclusions concerning the location of sources of invading populations and consequently the direction and distance of the movements of flies were substantiated. It was confirmed that S. damnosum s. str. and S. sirbanum were the main migrant species. In this area S. Squamosum was shown to be of much less importance as a migratory vector.

Cote d'Ivoire↗

La Untadita: a procedure for maintaining washbasins and drums free of Aedes aegypti based on modification of existing practices.

Chlorine bleach and detergent are routinely used by householders in El Progreso, Honduras in the process of cleaning washbasins and drums, the two most important larval habitats of Aedes aegypti in the city. The efficacy of these materials in eliminating eggs, larvae, and pupae of Ae. aegypti was assessed under controlled conditions. The promising results obtained led to trials using a combination of chlorine bleach and detergent to apply to the walls of washbasins and drums as a method for eliminating eggs. The bleach maintained its ovicidal properties when mixed with detergent, and the detergent gave the mixture consistency so that it could be applied as a thin film to the walls. This new procedure was named the little dab (Untadita in Spanish) and allows households to direct their efforts against a stage of the mosquito life cycle that has been ignored in the past: the egg.

Aedes↗

Tsetse movement in wind fields: possible epidemiological and entomological implications for trypanosomiasis and its control.

This paper presents evidence that tsetse flies (Glossina) can be dispersed by wind. This dispersal in West Africa is suggested to be along a south-west north-east axis. The implications of wind dispersal of Glossina for chemical and genetic control operations is discussed. Field experiments necessary to test this hypothesis are recommended. A study of human trypanosomiasis foci in West Africa has revealed that foci are orientated in roughly parallel lines in a south-west north-east direction. This directionally was significant when compared with 7 other compass points. It is proposed that foci could be populated by infected flies dispersed from the south west, where denser populations exist, on the prevailing winds in the late dry/early rainy season. The significance of these ideas in relation to the epidemiology of Trypanosoma brucei rhodesiense in Ethiopia and T. evansi are discussed.

Africa, Western↗

[Chagas disease in Brazil].

This article presents the current situation for Chagas disease vectors in Brazil, based on data from the Brazilian National Health Foundation (FNS). Over the course of the last 20 years, continuous chemical control has resulted in a clear reduction of triatomine densities and Trypanosoma cruzi in Brazilian dwellings. Results have been particularly promising in relation to Triatoma infestans and Panstrongylus megistus, considered the most important species in the past. In parallel, data from school serological surveys, hospitalized patients, and mortality records show an important decrease in the disease. Nevertheless, some areas of the Brazilian Northeast and some residual foci of Triatoma infestans and Panstrongylus megistus remain as major challenges for public health authorities, requiring effective epidemiological surveillance. States and municipalities are required to assume this task at present, as the traditional Brazilian National Health Foundation is undergoing decentralization.

Animals↗