Effect of fly control on trachoma and diarrhoea

The causative agent of trachoma, Chlamydia trachomatis, has been found on flies fed on heavily infected laboratory culture media. Findings are presented from an assessment of the effect of domestic fly control upon the prevalence of trachoma and associated cases of childhood diarrhea in 2 pairs of Gambian villages. 1 pair of villages was studied in the 1997 wet season and the second pair in the 1998 dry season. For each pair, deltamethrin was sprayed for 3 months to control flies in 1 village, while the other village was used as a control. Fly populations were monitored with traps. The prevalence of trachoma was measured at baseline and at 3 months, and data were collected daily on diarrhea in children aged 3 months to 5 years. Fly control decreased the numbers of muscid flies by approximately 75% in the intervention villages compared with controls. While the prevalence of trachoma was similar at baseline between study and control villages, after 3 months of fly control there were 75% fewer new cases of trachoma in the intervention villages. There was 22% and 26% less childhood diarrhea in the wet and dry seasons, respectively, compared with controls. These findings demonstrate that muscid flies are important vectors of trachoma and childhood diarrhea in The Gambia, and that the use of deltamethrin spray can help to reduce the prevalence of both trachoma and associated diarrhea cases.     

Seasonal and altitudinal variations in fly density and their association with the occurrence of trachoma, in the Gurage zone of central Ethiopia

In the Gurage zone of central Ethiopia, the association between fly density and the occurrence of trachoma has been investigated across varying altitudes. The seasonal pattern of fly density in the area was also explored. When, over short sampling periods (10 min/child indoors and 10 min/child outdoors), hand nets were used to collect flies from the eyes of children aged 2-8 years, only Musca sorbens and M. domestica were caught. Almost all of the 13,147 'eye-seeking' flies collected came from villages at low (<2000 m; 40.7%) or mid altitudes (2200-2500 m; 58.6%) with only 0.7% of them caught in the high-altitude villages investigated (at >3000 m). Musca sorbens predominated outdoors and M. domestica indoors. Almost all (99.3%) of the eye-seeking M. sorbens collected were caught outdoors whereas most (76.7%) of the M. domestica were caught indoors (P<0.0001 for each). The median numbers of flies caught, per child, per 10-min collection, in the low-, mid- and high-altitude villages were 9.5, six and zero, respectively, for M. sorbens, and eight, three and zero, respectively, for M. domestica. The altitudinal trends in these numbers of 'eye-seeking' flies matched those in the prevalences of active trachoma among children aged 1-10 years, which were high in the villages at low (81.6%) and mid altitude (78.7%) but much lower (1.7%) in the high-altitude villages. In conclusion, trachoma is a common disease of public-health importance only in the low- and mid-altitude villages in the Gurage zone, where there are large numbers of eye-seeking flies, and not in the villages that lie >3000 m above sea level, where there is a dearth of such flies.     

Chlamydia on children and flies after mass antibiotic treatment for trachoma

There are various approaches to control trachoma. These include the elimination of the ocular strains of Chlamydia trachomatis that cause the disease and to decrease the spread of infection by other measures such as fly control. Here, we examined how these two are related (i.e., how treating children with antibiotics affects carriage of Chlamydia by flies). Flies were collected in villages that had received mass oral azithromycin distribution and were compared with flies in untreated villages. Polymerase chain reaction (PCR) was performed to detect chlamydial DNA on the flies. Conjunctival swabs were also taken to assay for chlamydial prevalence in the children. Chlamydia was found on 23% of the flies in the untreated villages but only 0.3% in treated villages. Prevalence of trachoma in children proved to be an excellent predictor of the prevalence on flies (correlation coefficient, 0.89). Thus, treating children with antibiotics may drastically reduce the role of flies as a vector.     

Review of the evidence base for the 'F' and 'E' components of the SAFE strategy for trachoma control

Community control of trachoma as a blinding disease is based on the SAFE strategy of Surgery, Antibiotic therapy, Facial cleanliness and Environmental improvement. Surgery and antibiotic therapy currently dominate most programmes. Blindness from trachoma results from frequent infections repeated over many years, so ultimate success requires the reduction of transmission. This is only likely to be sustainable through the F and E components of SAFE. Environmental improvement with access to water, enhanced hygiene and better sanitation reduces trachoma transmission and the blinding sequelae eventually disappear. Transmission routes and factors that cause this are not known and consequently no single specific tool for F and E is in place. Evidence from intervention studies shows that the promotion of face-washing gave modest gains for intense effort and a pilot study showed that trachoma transmission was reduced in the absence of eye-seeking flies. Other studies have shown that latrines and improved access to water are associated with a lower prevalence of active trachoma. There is likely to be a long-term beneficial effect of a combination of improved water supplies, provision of latrines, facial hygiene promotion through established infrastructure and control of eye-seeking flies. Each of these interventions offers additional public health and other benefits in its own right. Further research on the routes of transmission, the role of hygiene and means of sustainable fly control should be a priority.     

Prevalence of risk factors and severity of active trachoma in southern Sudan: an ordinal analysis

We aimed to investigate prevalence of potential risk factors, and associations between risk factors and active trachoma in southern Sudan. Surveys were undertaken in ten sites and children aged 1-9 years examined for trachoma. Risk factors were assessed through interviews and observations. Using ordinal logistic regression, associations between severity of active trachoma and risk factors were explored. Trachomatous inflammation-intense (TI) was considered more severe than trachomatous inflammation-follicular (TF). A total of 7,418 children were included in the analysis. Risk factors and prevalences were unclean face, 52.3%; face washed less than twice daily, 50.8%; water collection > 30 minutes, 38.1%; absence of latrines, 95.4%; garbage disposal within 20 m, 74.4%; cattle ownership, 69.2%; and flies, 83.3%. After adjusting for age and sex, unclean face, less frequent face washing, cattle ownership, and increasing fly density were found to be independently associated with severity of active trachoma. Our study suggests that facial hygiene and environmental sanitation are priority trachoma-control interventions in southern Sudan.     

上海闵行区2005～2008年蝇密度监测结果分析

采用笼诱法对闵行区2005~2008年蝇密度及其种群分布进行调查。闵行区蝇密度为0.32只/笼;优势蝇种为家蝇,构成比为41.63%;季节消长呈现5、9月两个季节高峰;农贸市场和小饭店以家蝇密度最高,居民小区和大型绿化以麻蝇密度最高。闵行区蝇密度呈现季节和区域分布特征。     

Household pit latrines as a potential source of the fly Musca sorbens--a one year longitudinal study from The Gambia

OBJECTIVES: To assess whether the trachoma vector Musca sorbens was breeding in household latrines in a trachoma-endemic part of The Gambia. METHODS: Longitudinal study of flies emerging from 16 sentinel household latrines selected at random from a list of all latrines present in four Gambian villages. Latrines were surveyed and fly traps were set over the drop hole for 24 h once per month for a year. RESULTS: All the sentinel latrines were of the 'Gambian improved household latrine' design, which has a cement slab but is not ventilated or fly-proofed. The latrines were all in regular use by a family, mean number of users per latrine 14.8 (SD 8.0, range 2-29). Of 55 351 flies caught in 192 catches 54 130 (97.8%) were Chrysomya albiceps, 690 (1.2%) Musca domestica, 466 (0.8%) Chrysomya regalis and 65 (0.1%) M. sorbens. Of the M. sorbens caught 61 (93.8%) were female. CONCLUSIONS: Gambian improved household pit latrines cannot be considered a source of the trachoma vector M. sorbens, and the promotion of pit latrines as a method to reduce M. sorbens is warranted. A large number of C. albiceps were caught emerging from the latrines, but this species is not considered to be of medical importance.     

Detection and identification of Leishmania species within naturally infected sand flies in the andean areas of ecuador by a polymerase chain reaction

The surveillance of prevalent Leishmania and sand fly species in endemic areas is important for prediction of the risk and expansion of leishmaniasis. In this study, we developed a polymerase chain reaction (PCR)-based method for detection of Leishmania minicircle DNA within individual sand flies. Using this method, we detected minicircle DNA in 6 (3.3%) of 183 sand flies, while 5 (3.5%) of 143 were positive for Leishmania promastigotes in the same areas by microscopic examination. The species were identified as Leishmania (Leishmania) mexicana by nucleotide sequencing of the cytochrome b gene. Additionally, all the Leishmania-positive sand flies were identified as Lutzomyia ayacuchensis by the restriction enzyme digestion of the PCR-amplified 18S ribosomal RNA gene fragments. Since this combined method is relatively easy and can process a large number of samples, it will be a powerful tool for the rapid identification of prevalent sand fly and Leishmania species as well as monitoring the infection rate in sand fly populations in endemic areas.     

Review: Targeting trachoma: Strategies to reduce the leading infectious cause of blindness

The World Health Organisation (WHO) estimated that in 2002, 1.3 million people were blind due to trachoma, an eye infection caused by Chlamydia trachomatis. This review examines the evidence behind current strategies to reduce the global burden of trachoma. Trachoma disappeared from most western nations before the advent of antibiotics, probably due to improvements in water, sanitation and hygiene. The current effort to target trachoma, headed by the WHO and the Alliance for the Global Elimination of Trachoma by 2020, is called the SAFE (Surgery, Antibiotics, Facial cleanliness and Environmental improvement) strategy. Surgery for trachoma is more cost effective than extra-capsular cataract surgery and can reverse trichiasis (in-growing eyelashes), but needs to be repeated every few years. A single oral dose of azithromycin can eliminate trachoma infection, but cannot be used in infants under 6 months old, and needs to be given every few years in communities with a high prevalence of disease. Improved health education and facial hygiene has been linked to a lower incidence of trachoma, but the evidence is less clear than for surgery and antibiotics. Pit latrines and spraying with permethrin insecticide may reduce the spread of trachoma via eye-seeking flies.     

Impact of fly control on childhood diarrhoea in Pakistan: community-randomised trial

Since circumstantial evidence suggests that flies are vectors of diarrheal diseases, a randomized study of the effect of insecticide spraying upon the incidence of diarrhea was conducted near the town of Peshawar, North West Frontier Province, Pakistan. 6 study villages were randomly assigned to 2 groups, with flies controlled through the twice weekly application of ultra low volume space spraying with insecticide in group A in 1995 and in group B in 1996. The insecticide used was Aqua K-Othrine, a water-based formulation of deltamethrin, applied at a dose of 0.5-1.0 g of active ingredient per hectare by Porta-Pak sprayers. In 1997, the effectiveness of baited fly traps was tested in group A villages. The incidence of diarrhea episodes was monitored in children under age 5 years through mothers' reports during weekly visits by a health worker, and fly density was monitored using sticky fly-papers hung in sentinel compounds. During the fly seasons of March-June in 1995 and 1996, the application of insecticide almost eliminated the fly population in the treated villages. The incidence of diarrhea was lower in the sprayed villages than in the unsprayed villages in both 1995 and 1996, for an overall 23% reduction in incidence. At times other than the fly season, no evidence was observed of a difference in diarrhea morbidity between sprayed and unsprayed villages. Fly density data for 1997 found the baited traps to be ineffective.     

Personal and environmental risk factors for active trachoma in children in Yobe state,north‐eastern Nigeria

Objective To determine the personal and environmental risk factors associated with trachoma in pre‐school children in Yobe state, Nigeria. Methods Total of 639 children aged 1–5 from 27 villages were examined in their households for clinical signs of trachoma. Personal and environmental risk factors were independently determined by an observer while clinical examination was being performed. Results The prevalence of active trachoma was 35.7% (95% CI; 32.0–39.6) with prevalence of disease in boys being similar to girls. The highest prevalence was in children 2–3 years of age. The presence of flies on the face (OR 4.14; CI 2.72–6.29) and lack of a toilet in the compound (OR 2.11; CI 1.38–3.23) were independent risk factors for trachoma. Conclusion The prevalence of trachoma is high. Provision and use of toilets, education on personal and environmental hygiene improvements need to be emphasized as part of the Surgery Antibiotics Facial cleanliness and Environmental improvement strategy.     

Establishment of a mass screening method of sand fly vectors for Leishmania infection by molecular biological methods

Surveillance of the prevalence of Leishmania and its vector, sand fly species, in endemic and surrounding areas is important for prediction of the risk and expansion of leishmaniasis. In this study, a method for the mass screening of sand flies for Leishmania infection was established. This method was applied to 319 field-captured specimens, and 5 positive sand flies were detected. Sand fly species were identified by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) of the18S rRNA gene, and all the positive flies were Lu. hartmanni. Furthermore, cytochrome b (Cyt b) gene sequence analyses identified all the parasites as Endotrypanum species including a probable novel species. Because the method requires minimum effort and can process a large number of samples at once, it will be a powerful tool for studying the epidemiology of leishmaniasis.     

The abundance of pathogenic African trypanosomes in the salivary secretions of wild Glossina pallidipes

Trypanosome infection rates in wild Glossina pallidipes from the Lambwe Valley, Kenya, were determined using salivation and fly dissection methods. Of the 416 flies examined by salivation, one was infected with Trypanosoma brucei, seven with T. congolense, 18 with T. vivax and three with both T. congolense and T. vivax. The fly infected with T. brucei always secreted saliva heavily infected with trypanosomes. Flies infected with T. vivax secreted saliva which contained very few trypanosomes and some of these flies produced negative saliva for several successive days. There was no significant difference between the proportions of male and female flies which were infected with any one species of trypanosome, but there were highly significant differences between the mean numbers of the different species of trypanosome in the saliva.     

Genetics of two populations of Glossina morsitans centralis (Diptera: Glossinidae) from Zambia

Glossina morsitans centralis Machado was collected from the main fly belt west of Mumbwa Zambia and from the apparently isolated 'Keembe pocket' and 11 gene-enzyme systems were examined by polyacrylamide gel electrophoresis. There were no significant differences in allele frequencies among flies collected entering a vehicle, from fly-rounds, or from F3 traps in the main fly belt. Mean heterozygosity per locus is slightly higher in flies from the main fly belt than it is in flies from the 'Keembe pocket'. Allele frequencies at loci for xanthine oxidase (Xo), aldehyde oxidase (Ao) and a thoracic esterase (Est-2) were significantly different in the two populations and it is concluded that there is little gene flow between them.     

Tolerance of house fly, Musca domestica L. (Diptera: Muscidae) to dichlorvos (76% EC) an insecticide used for fly control in the tsunami-hit coastal villages of southern India

The Directorate of Public Health (DPH), Tamil Nadu, in southern India employed spraying of dichlorvos (76% EC) for quick elimination of fly concentrations in the tsunami-hit coastal villages at the concentration of 304g (a.i.)/10,000m(2). However, nuisance of house flies remained high particularly in temporary shelters and centralized relief kitchens. Susceptibility of house fly, Musca domestica to dichlorvos was determined in the laboratory to provide information for an effective management of this pest. Various concentrations of dichlorvos (76% EC) viz., 0.1, 0.2, 0.4, 0.6 and 0.8microg (a.i.) per fly, were tested using topical application against F(1) progenies of house flies collected 12 months after insecticide applications from different habitats in the tsunami-hit coastal villages. Fly mortality was recorded at 24h post treatment. Parallel controls were maintained for comparison. Mortality of the house flies varied between 17.5% and 100% and increased with an increase in dosage of the insecticide. Mortality was >80% at 0.6 and 0.8microg (a.i.) per fly. The LD(50) of dichlorvos tested against flies collected from different villages varied from 0.218microg (a.i.) to 0.235microg (a.i.) per fly and the LD(90) varied from 0.574microg (a.i.) to 0.639microg (a.i.) per fly. House flies collected from a rural village, Thirukanur that had never been exposed for insecticide treatment in the past one decade, when tested, the mortality varied between 92.5% and 100% and increased with concentration of dichlorvos. Mortality was >90% from 0.2microg (a.i.) per fly and the LD(50) was 0.0399microg (a.i.)/fly, while the LD(90) was 0.1604microg (a.i.)/fly. The LD(90) values of the flies collected from the tsunami-hit villages were 3.5-3.9 times higher than that of the flies collected from Thirukanur. Fly abundance remained high in tsunami-hit villages with no marked reduction, suggesting that the flies had developed tolerance to dichlorvos. It is suggested that for an effective management of these resistant populations changing insecticides, application of unrelated insecticide, together with an appropriate environmental sanitation measure is necessary to keep the population under check.     

Investigations on the transmissibility of Trypanosoma congolense by the tsetse fly Glossina morsitans morsitans during its development in a mammalian host

Experiments were conducted to investigate the effect of the developmental stage of a monomorphic T. congolense IL1180 strain, in a vertebrate host, on its transmissibility by the tsetse fly Glossina morsitans morsitans Westwood (Diptera: Glossinidae). Batches of 160 male teneral tsetse flies were given a single bloodmeal on mice infected with this T. congolense strain 4, 5, 6, 7 or 10 days post-infection. The proportion of infected flies in each of those batches showed that the stage of development of the trypanosome does affect the proportion of flies that develop a mature or immature infection with immature and mature infection rates of flies infected on days 5 or 10 significantly higher. The proportion of infected flies was not affected by the parasitaemia at the moment of infection. Results show that tsetse flies can become infected at any phase of the development of the T. congolense IL 1180 strain but the ease with which trypanosomes develop in the fly depends on the phase in the parasite's development in the host. Those observations suggest that in analogy with the pleomorphic T. brucei s.l. adaptation of the monomorphic T. congolense to development in the fly may also determine the parasite's transmissibility. Moreover, the findings stress the importance of standardising experiments in which the vectorial capacity of tsetse flies is determined and compared.     

Ecology of viruses isolated from sand flies in Italy and characterized of a new Phlebovirus (Arabia virus)

A total of 84 virus strains was obtained from 16,374 male and female sand flies (Phlebotomus perniciosus and P. perfiliewi) collected in two localities of Tuscany region in Italy between 1980 and 1985. Thirty-seven (44%) were identified as Toscana virus (family Bunyaviridae, genus Phlebovirus) and 47 (56%) as a new member of the Phlebotomus fever serogroup, Arbia virus. The characteristics of this new serotype are described. The overall virus isolation rate from sand flies was 0.5 per 100 insects processed. Virus isolation rates for both viruses were similar in different years and in the two localities, suggesting that the two virus types were active in the sand fly population simultaneously. Each year, the largest number of isolates were obtained during July, corresponding to the period of maximal sand fly population density. Both viruses were repeatedly isolated from male sand flies, suggesting transovarial transmission in nature. Serologic data showed no evidence of infection among domestic and wild animals. However, a strain of Toscana virus was isolated from the brain of a bat (Pipistrellus kuhli), indicating a possible involvement of this species in the ecology of the virus. Serologic tests did not provide definitive evidence for human infection by Arbia virus.     

Sand Fly Fauna (Diptera,Pcychodidae, Phlebotominae) in Different Leishmaniasis-Endemic Areas of Ecuador,Surveyed Using a Newly Named Mini-Shannon Trap

To study the sand fly fauna, surveys were performed at four different leishmaniasis-endemic sites in Ecuador from February 2013 to April 2014. A modified and simplified version of the conventional Shannon trap was named “mini-Shannon trap” and put to multiple uses at the different study sites in limited, forested and narrow spaces. The mini-Shannon, CDC light trap and protected human landing method were employed for sand fly collection. The species identification of sand flies was performed mainly based on the morphology of spermathecae and cibarium, after dissection of fresh samples. In this study, therefore, only female samples were used for analysis. A total of 1,480 female sand flies belonging to 25 Lutzomyia species were collected. The number of female sand flies collected was 417 (28.2%) using the mini-Shannon trap, 259 (17.5%) using the CDC light trap and 804 (54.3%) by human landing. The total number of sand flies per trap collected by the different methods was markedly affected by the study site, probably because of the various composition of species at each locality. Furthermore, as an additional study, the attraction of sand flies to mini-Shannon traps powered with LED white-light and LED black-light was investigated preliminarily, together with the CDC light trap and human landing. As a result, a total of 426 sand flies of nine Lutzomyia species, including seven man-biting and two non-biting species, were collected during three capture trials in May and June 2014 in an area endemic for leishmaniasis (La Ventura). The black-light proved relatively superior to the white-light with regard to capture numbers, but no significant statistical difference was observed between the two traps.     

Serratia marcescens as a pathogen of tsetse flies.

When applied to the ears of rabbits used as hosts for tsetse flies, the bacterium Serratia marcescens produced significant mortality in populations of Glossina m. morsitans and G. pallidipes. After being ingested during the blood meal, cells of S. Marcescens multiplied in the intestine of the flies and entered the hemocoel. Using the brush method of applying the bacterium, 100% mortality of both Glossina species occurred within 10 days after application. In newly killed flies, the bacteria could be found free in the hemocoel as well as in the fat body and blood cells. The supernatant of a liquid culture of S. marcescens did not produce fly mortality when applied to rabbit ears. The results indicate that S. marcescens is able to invade the hemocoel of "normal" laboratory-reared tsetse flies.     

Sand fly feeding on noxious plants: a potential method for the control of leishmaniasis.

The sand fly Phlebotomus papatasi transmits Leishmania major, which causes cutaneous leishmaniasis, in vast regions of the Old World. In addition to blood, the sand flies feed on plants. In a study of this diet, we observed that one night of feeding on branches of Solanum jasminoides, Ricinus communis, or Bougainvillea glabra drastically shortened the life span of the sand flies. Flowering B. glabra attracted P. papatasi in the field. Nevertheless, in the region endemic for L. major in yards abounding with vector sand flies, the number of P. papatasi trapped near hedges of B. glabra was eight times less (62 versus 502 flies trapped) than in the control sites. The results imply that B. glabra affords local protection against sand fly bites and decreases the risk of leishmaniasis. We suggest that this and other ornamental plants that are harmful to sand flies can be used as a tool for this purpose.