The risk of Aedes aegypti breeding and premises condition in South Mexico.

A recent innovation instrumented for the Dengue Prevention and Control program in Mexico is the use of the premises condition index (PCI) as an indicator of risk for the vector Aedes aegypti infestation in dengue-endemic localities of Mexico. This paper addresses whether further improvements for the dengue control program could be made if the prevalence and productivity of Ae. aegypti populations could be reliably predicted using PCI at the household level, as well as medium-sized neighborhoods. We evaluated the use of PCI to predict the infestation with Aedes aegypti (breeding sites and immature productivity) in Merida, Mexico. The study consisted of a cross-sectional survey based on a cluster-randomized sampling design. We analyzed the statistical association between Aedes infestation and PCI, the extent to which the 3 components of PCI (house maintenance, and tidiness and shading of the patio) contributed to the association between PCI and infestation and whether infestation in a given premises was also affected by the PCI of the surrounding ones. Premises with the lowest PCI had significantly lower Aedes infestation and productivity; and as PCI scores increased infestation levels also tended to increase. Household PCI was significantly associated with Ae. aegypti breeding, largely due to the effect of patio untidiness and patio shade. The mean PCI within the surroundings premises also had a significant and independent explanatory power to predict the risk for infestation, in addition to individual PCI. This is the 1st study in Mexico showing evidence that premises condition as measured by the PCI is related to Ae. aegypti breeding sites and immature productivity. Results suggest that PCI could be used to streamline surveys to inform control efforts at least where Ae. aegypti breeds outdoors, as in Merida. The effect of individual premises, neighborhood condition, and the risk of Aedes infestation imply that the risk for dengue vector infestation can only be minimized by the mass effect at the community level.

Predicting the distribution of canine leishmaniasis in western Europe based on environmental variables.

The domestic dog is the reservoir host of Leishmania infantum, the causative agent of zoonotic visceral leishmaniasis endemic in Mediterranean Europe. Targeted control requires predictive risk maps of canine leishmaniasis (CanL), which are now explored. We databased 2187 published and unpublished surveys of CanL in southern Europe. A total of 947 western surveys met inclusion criteria for analysis, including serological identification of infection (504, 369 dogs tested 1971-2006). Seroprevalence was 23 2% overall (median 10%). Logistic regression models within a GIS framework identified the main environmental predictors of CanL seroprevalence in Portugal, Spain, France and Italy, or in France alone. A 10-fold cross-validation approach determined model capacity to predict point-values of seroprevalence and the correct seroprevalence class (<5%, 5-20%, >20%). Both the four-country and France-only models performed reasonably well for predicting correctly the <5% and >20% seroprevalence classes (AUC >0 70). However, the France-only model performed much better for France than the four-country model. The four-country model adequately predicted regions of CanL emergence in northern Italy (<5% seroprevalence). Both models poorly predicted intermediate point seroprevalences (5-20%) within regional foci, because surveys were biased towards known rural foci and Mediterranean bioclimates. Our recommendations for standardizing surveys would permit higher-resolution risk mapping.

Reconstructing historical changes in the force of infection of dengue fever in Singapore: implications for surveillance and control.

OBJECTIVE: To reconstruct the historical changes in force of dengue infection in Singapore, and to better understand the relationship between control of Aedes mosquitoes and incidence of classic dengue fever. METHODS: Seroprevalence data were abstracted from surveys performed in Singapore from 1982 to 2002. These data were used to develop two mathematical models of age seroprevalence. In the first model, force of infection was allowed to vary independently each year, while in the second it was described by a polynomial function. Model-predicted temporal trends were analysed using linear regression. Time series techniques were employed to investigate periodicity in predicted forces of infection, dengue fever incidence and mosquito breeding. FINDINGS: Force of infection estimates showed a significant downward trend from 1966, when vector control was instigated. Force of infection estimates from both models reproduced significant increases in the percentage and average age of the population susceptible to dengue infections. Importantly, the year-on-year model independently predicted a five to six year periodicity that was also displayed by clinical incidence but absent from the Aedes household index. CONCLUSION: We propose that the rise in disease incidence was due in part to a vector-control-driven reduction in herd immunity in older age groups that are more susceptible to developing clinical dengue.

Pupal surveys for Aedes aegypti surveillance and potential targeted control in residential areas of Mérida, México.

A mosquito larval-pupal survey was conducted in 1,160 households of the Mexican city of Mérida during the rainy season of 2003 to determine their differential productivity for Aedes aegypti. Larvae and pupae were detected in 15 broad categories of container types. All breeding sites were found in the patios (backyards) and were potentially rain filled. Ae. aegypti pupae were produced from all categories of breeding site, and no single container type was predominately responsible for pupal production. The most productive buckets comprised 42% of the pupae-positive containers and provided 34% of the total pupae collected. Pupal production in buckets, together with plastic rubbish, pet dishes and basins, utensils for cooking and washing, tires, and flowerpots, accounted for almost 87% of pupal production. However, the most important pupal producers had low infestation indices for immature forms, illustrating that the use of positive-container indices can underestimate the importance of certain breeding sites. Overall, 40% of containers that were observed harboring Ae. aegypti pupae were classified as disposable. The remaining containers were considered useful, although some were seldom used. The discussion focuses on the potential utility of the pupal survey for targeting control, and its resulting pupae-per-person entomological indicator, both for comparison with a theoretical threshold for dengue transmission and for targeting vector control in this Mexican city.

Multiple hybrid genotypes of Leishmania (viannia) in a focus of mucocutaneous Leishmaniasis.

The principal agent of mucocutaneous leishmaniasis (MCL) is the South American protozoan parasite Leishmania (Viannia) braziliensis. This organism is generally considered to be clonal, that is, it does not to undergo genetic exchange. Nevertheless, apparent hybrids between several Leishmania species have been reported in the New World and the Old World. When we characterized isolates of Leishmania (Viannia) from a single focus of cutaneous leishmaniasis (CL) and MCL, we found a remarkable phenotypic and genotypic diversity, with 12 zymodemes and 20 microsatellite genotypes. Furthermore, 26 of the 59 isolates were L. braziliensis/L. peruviana phenotypic hybrids that displayed 7 different microsatellite genotypes. A hybrid genotype was the only organism isolated from 4 patients with MCL. Thus hybrids must be included among the potential agents of MCL. Despite the propensity for clonality, hybrids are also an important feature of Leishmania (Viannia) and may give rise to epidemiologically important emergent genotypes.

Advances in leishmaniasis.

Governed by parasite and host factors and immunoinflammatory responses, the clinical spectrum of leishmaniasis encompasses subclinical (inapparent), localised (skin lesions), and disseminated infection (cutaneous, mucosal, or visceral). Symptomatic disease is subacute or chronic and diverse in presentation and outcome. Clinical characteristics vary further by endemic region. Despite T-cell-dependent immune responses, which produce asymptomatic and self-healing infection, or appropriate treatment, intracellular infection is probably life-long since targeted cells (tissue macrophages) allow residual parasites to persist. There is an epidemic of cutaneous leishmaniasis in Afghanistan and Pakistan and of visceral infection in India and Sudan. Diagnosis relies on visualising parasites in tissue or serology; culture and detection of parasite DNA are useful in the laboratory. Pentavalent antimony is the conventional treatment; however, resistance of visceral infection in India has spawned new treatment approaches--amphotericin B and its lipid formulations, injectable paromomycin, and oral miltefosine. Despite tangible advances in diagnosis, treatment, and basic scientific research, leishmaniasis is embedded in poverty and neglected. Current obstacles to realistic prevention and proper management include inadequate vector (sandfly) control, no vaccine, and insufficient access to or impetus for developing affordable new drugs.

Extinction of experimental Triatoma infestans populations following continuous exposure to dogs wearing deltamethrin-treated collars.

Dogs are domestic reservoir hosts of Trypanosoma cruzi, the etiological agent of Chagas disease. We evaluated the effect of deltamethrin-treated dog collars (DTDCs) over time on the population dynamics of Triatoma infestans, a main T. cruzi vector. Forty founder bugs of mixed life stages were allowed to colonize mud-thatched experimental huts and exposed continuously to either uncollared control dogs (N = 3) or dogs wearing DTDCs (N = 7) for a period of up to 196 days. When compared with bugs exposed to control dogs, bugs exposed to collared dogs were shown to have reduced feeding success (odds ratio [OR] = 0.40; 95% confidence interval [CI], 0.26-0.63; P < 0.001) and lower survival (OR = 0.15; 95% CI, 0.08-0.29; P < 0.001); in fact, all of the bug populations exposed to collared dogs became extinct 77-196 days after study initiation. Bugs exposed to DTDC-wearing dogs were also shown to have a lower fecundity (i.e., number of eggs produced per live female bug: OR = 0.64; 95% CI, 0.51-0.81; P < 0.001) and molting rate to first-instar nymphs (OR = 0.32; 95% CI, 0.13-0.75; P < 0.01) than those bugs exposed to control dogs. DTDCs could represent a novel tool to prevent and control canine and (hence) human Chagas disease.

Leishmania panamensis transmission in the domestic environment: the results of a prospective epidemiological survey in Santander, Colombia.

INTRODUCTION: Domestic transmission now appears to be the principal route of Leishmania panamensis infection in deforested regions characterized by the replacement of primary forest by permanent plantations, i,e coffee or cacao crops. This paper presents the results of the disease patterns in a representative population of the Opón focus, in Santander, Colombia. OBJECTIVE: The principal aims were: 1) to measure the incidence rate in a representative population of the Opón focus; 2) to identify demographic risk factors for infection; 3) to estimate the proportion of infections which cause disease; 4) to estimate the protection against disease from acquired immunity; 5) to estimate the frequency of reactivations, and 6) to estimate the risk of mucosal leishmaniasis. MATERIAL AND METHODS: A 19 month prospective survey of leishmaniasis caused by Leishmania panamensis was carried out amongst 1380 people in a cacao growing region of Santander Department, Colombia. The population was diagnosed clinically and by the Montenegro skin test (at two time points). RESULTS: The incidence rate was 0.19 infections/person-year, with 31% of infections apparently subclinical. The risk of acquiring cutaneous leishmaniasis decreased with age even in the absence of apparent previous infections. Protective immunity followed both clinical and subclinical infections, persisting for at least 10 years after a primary lesion. Mucocutaneous leishmaniasis was detected in 12% of the population with cutaneous lesions, of which 77% had mild symptoms, and 23% perforated nasal septa. The risk of mucosal leishmaniasis was greatest for males, and for people whose primary cutaneous lesion was on the head. CONCLUSION: The average age of infection in Opón, 7.7 years (1/lambda), and the absence of gender as a risk factor is highly indicative of intradomiciliary or peridomiciliary transmission.

Effect of knowledge and economic status on sandfly control activities by householders at risk of cutaneous leishmaniasis in the subandean region of Huila department, Colombia.

INTRODUCTION: Householder vector control measures can be encouraged by health promotion campaigns which take into account peoples' attitudes and focus on key gaps in knowledge. OBJECTIVES: To describe household sandfly control practices in an endemic area of cutaneous leishmaniasis in the department of Huila, Colombia, and determine how these are influenced by attitudes, knowledge and socioeconomic status. MATERIALS AND METHODS: A household questionnaire was applied to collect information on: demography, socioeconomic status, knowledge of cutaneous leishmaniasis and of sandflies and their role in transmission, and the control activities practiced. Indoor sandfly abundance was estimated by light trap collections. RESULTS: Amongst 249 interviewees, 86% knew about cutaneous leishmaniasis and 98% sand flies. 35% of interviewees who knew about cutaneous leishmaniasis practiced measures with the purpose of its control. This practice was higher amongst the 32% who knew that sand flies transmit cutaneous leishmaniasis. However, 82% of interviewees practiced sand fly control measures, and these were significantly associated with high sand fly abundance. Measures included smoke, bednets, and house spraying with insecticide or non-insecticidal substances. Householders using the high cost measures (bednets and insecticide) had the highest economic status. CONCLUSIONS: Health education programmes should note that sand fly nuisance can initiate control measures, but that knowledge of the role of sand flies in transmission could enhance activities. The socioeconomic findings indicate that targeted bednet subsidies could reduce inequities in health status amongst cutaneous leishmaniasis endemic communities.

Lessons from a national survey of Chagas disease transmission risk in Colombia.

In recent years, there has been a revitalization of large-scale programmes to control parasitic disease in developing countries. In 1997, the Governments of Colombia, Venezuela, Ecuador and Peru committed themselves to replicate the cost-effective elimination of Trypanosoma cruzi transmission achieved in the Southern Cone by using insecticides against the domestic triatomine vectors (in combination with blood-bank screening). Central American Governments launched a complementary initiative. All plan to interrupt vectorial transmission throughout the region by 2010 but specific targets are decided nationally. In this article, we highlight the novel approach taken by the Colombian Government for determining the geographic distribution of Chagas disease risk to select where to intervene first.

Chagas disease control: deltamethrin-treated collars reduce Triatoma infestans feeding success on dogs.

Dogs are domestic reservoir hosts of Trypanosoma cruzi, the aetiological agent of Chagas disease. Using an experimental set-up mimicking rural mud-and-thatch houses, we evaluated the effect of deltamethrin-treated dog collars on the feeding success and survival of Triatoma infestans, the main T. cruzi vector in Latin America. Seven collared and three uncollared control dogs were exposed to colonized T. infestans at day 0 (i.e. before attachment of collars), at 15 days, and then monthly for 3 months post collar attachment. Following overnight exposure to uncollared dogs, 96% (1473/1538) of bugs fed, of which 51% (746/1473) fully engorged. Feeding rates were significantly reduced on collared dogs for up to 1 month post collar attachment with the lowest rates of 91% (551/604) observed at day 30 (P<0.05). Amongst those bugs that fed, engorgement rates were significantly reduced on collared dogs throughout the trial, during which average rates were 31% (543/1768) (P<0.001). No collar effect on individual bug survival was observed. Although observed effects on feeding and engorgement were limited, the strong association between blood-feeding, blood meal size and T. cruzi transmission suggests that deltamethrin-treated dog collars could help to control canine (and possibly human) T. cruzi infection.

Are insecticide-impregnated dog collars a feasible alternative to dog culling as a strategy for controlling canine visceral leishmaniasis in Brazil?

In a zoonotic visceral leishmaniasis (ZVL)-endemic area in Brazil, deltamethrin-impregnated collars (DMC) were fitted to 136 dogs for 5 months and significantly reduced the odds of increasing their anti-Leishmania antibody titer during this period by 50% (95% confidence interval 29-87%, P=0.01), as compared with a population of 97 uncollared dogs with pre-intervention prevalence within the same town. Mathematical modeling suggests that under typical Brazilian ZVL-endemic conditions, the epidemiological impact of community-wide DMC application should be greater than the currently practiced dog culling strategy, but that its impact will be dependent on collar coverage and loss rate. Both interventions should have a higher proportional impact in regions of lower endemicity, but the relative advantage of DMC over culling increases with transmission rate. Sensitivity analyses indicate that the impact of either intervention is not significantly affected by variation in the biology of the sandfly vector, but is greatly influenced by variation in dog mortality and serorecovery rates.

The transmission dynamics of canine American cutaneous leishmaniasis in Huánuco, Peru.

The epidemiology of canine American cutaneous leishmaniasis (ACL) due to Leishmania (Viannia) spp. was investigated in Huánuco, Peru to 1) describe the natural course of canine L. (Viannia) infections and 2) assess the role of domestic dogs as ACL reservoir hosts. Over a three-year period 1,022 dogs were surveyed, with cumulative village L. (Viannia) prevalence being 26% (range = 0-100%). The incidence of L. (Viannia) was estimated to be 0.285 dogs/year (95% confidence interval [CI] = 0.160-0.410) using cross-sectional data and 0.291 dogs/year (95% CI = 0.195-0.387) using data from 108 dogs that were surveyed prospectively. The recovery rate was estimated to be 0.456 dogs/year (95% CI = 0.050-0.862) and 0.520 dogs/year (95% CI = 0.302-0.738), respectively. Using those findings, the basic reproduction number was estimated to be R0 approximately to 1.9; if dogs were the principal ACL reservoirs, the mean yearly effort (i.e., coverage or elimination) of a dog control intervention (e.g., collaring, culling, or vaccination) to ensure the elimination of L. (Viannia) spp. transmission would be as low as 47%.

Indoor and peridomestic transmission of American cutaneous leishmaniasis in northwestern Argentina: a retrospective case-control study.

A case-control study was carried out during 1990-1994 to identify risk factors associated with American cutaneous leishmaniasis (ACL) in Santiago del Estero, Argentina. The study subjects consisted of 171 cases and 308 controls matched by age, sex, and place of residence. The analysis was performed by conditional logistic regression. Risk factors found to be significantly associated with ACL were related to indoor transmission (few rooms in the house, dirt floor, and a permanent opening in lieu of a window); peridomestic transmission (presence of a pond or woodland within 150 m of the house and an agricultural area within 200 m of the house); and human behavior (sleeping in the backyard, collecting water, bathing, and performing agricultural activities). Most transmission appears to have occurred indoors and in the peridomicile. These environments should be included in further research and control policies.

Domestic dog ownership in Iran is a risk factor for human infection with Leishmania infantum.

One explanation proposed for the widespread failure to control zoonotic visceral leishmaniasis by culling infected domestic dogs is that wild canids or humans play significant roles in transmission. The aim of this study was to determine the importance of domestic dogs as the reservoir hosts of visceral leishmaniasis in northwest Iran. A random sample of 3,872 children and 199 dogs in 38 villages was surveyed by the direct agglutination test. Dog ownership details among these households were collected by questionnaire. Parasites isolated from 16 patients and 12 dogs were characterized as Leishmania infantum MON-1. Average seroprevalence in dogs (21.6%) was much higher than in children (7%). Child seropositivity increased significantly with village dog density in absolute terms (P < 0.001) and in relation to dog/human ratios (P = 0.028). Dog ownership within villages also was a significant risk factor for child seropositivity (P = 0.003).

Domestic dog ownership: a risk factor for human infection with Leishmania (Viannia) species.

An epidemiological study has shown that cumulative, village prevalence of Leishmania (Viannia) infection in dogs ranges from 8% to 45% in Huánuco, Peru. Using data from a prospective survey of human American cutaneous leishmaniasis (ACL) collected during 1994-98, it was shown that the village-level risk of human ACL did not significantly increase with dog abundance, neither in absolute terms (P = 0.659) nor in relation to dog:human ratios (P = 0.213). A significant positive association was observed between risk of human ACL and village dog ACL prevalence (P = 0.022). When controlled for village dog ACL prevalence, there also was an association between the average number of dogs per household and risk of human ACL (P = 0.033). The results suggest that dogs play a role in the (peri)domestic transmission of Le. (Viannia) to humans in Huánuco and indicate that a control intervention targeting dogs to control human ACL is warranted.

Leishmania (Viannia) spp. dissemination and tissue tropism in naturally infected dogs (Canis familiaris).

First evidence is presented for Leishmania (Viannia) spp. dissemination and tissue tropism in the domestic dog. Using PCR and histology, parasites were detected in the conjunctiva, lung, lymph nodes and ovaries of 2 naturally infected Peruvian dogs. The detection of parasites in the blood indicates that parasite dissemination to those organs may have been haematogenous.

A continental risk map for malaria mosquito (Diptera: Culicidae) vectors in Europe.

Although malaria was officially declared eradicated from Europe in 1975, its former vectors, mainly members of the Anopheles maculipennis (Meigen) complex, are still distributed throughout the continent. The present situation of Anophelism without malaria indicates that current socio-economic and environmental conditions maintain the basic case reproduction number, Ro, below 1. Recently, it has been speculated that predicted climate changes may increase anopheline abundance and biting rates (as well as reduce the Plasmodium parasite extrinsic incubation period), allowing the reemergence of malaria transmission in Europe. As a preliminary step toward predicting future scenarios, we have constructed models to test whether the current distribution of the five former European malaria vectors [An. atroparvus (Van Thiel),An. labranchiae (Falleroni), An. messeae (Swellengrebel & De Buck), An. sacharovi (Favr) and An. superpictus (Grassi)] can be explained by environmental parameters, including climate. Multivariate logistic regression models using climate surfaces derived from interpolation of meteorological station data (resolution 0.5 x 0.5 degrees) and remotely sensed land cover (resolution 1 x 1 km) were fitted to 1,833 reported observations of the presence and absence of each species across Europe. These relatively crude statistical models predicted presence and absence with a sensitivity of 74-85.7% and specificity of 73.4-98.1% (with climate a significantly better predictor than land cover type). A geographically independent validation of the models gave a sensitivity of 72.9-88.5% and a specificity of 72.7-99.6%. This allowed us to generate risk maps for each species across Europe. Assuming that high risk equates with the potential for high abundance, these models should permit the development of risk maps for European mosquitoes under future climate scenarios. These techniques would be equally useful for estimating the risk of reemergence in other nonendemic areas such as the United States and Australia, as well as changes to risk within endemic areas.

Controlling malaria using livestock-based interventions: a one health approach.

Where malaria is transmitted by zoophilic vectors, two types of malaria control strategies have been proposed based on animals: using livestock to divert vector biting from people (zooprophylaxis) or as baits to attract vectors to insecticide sources (insecticide-treated livestock). Opposing findings have been obtained on malaria zooprophylaxis, and despite the success of an insecticide-treated livestock trial in Pakistan, where malaria vectors are highly zoophilic, its effectiveness is yet to be formally tested in Africa where vectors are more anthropophilic. This study aims to clarify the different effects of livestock on malaria and to understand under what circumstances livestock-based interventions could play a role in malaria control programmes. This was explored by developing a mathematical model and combining it with data from Pakistan and Ethiopia. Consistent with previous work, a zooprophylactic effect of untreated livestock is predicted in two situations: if vector population density does not increase with livestock introduction, or if livestock numbers and availability to vectors are sufficiently high such that the increase in vector density is counteracted by the diversion of bites from humans to animals. Although, as expected, insecticide-treatment of livestock is predicted to be more beneficial in settings with highly zoophilic vectors, like South Asia, we find that the intervention could also considerably decrease malaria transmission in regions with more anthropophilic vectors, like Anopheles arabiensis in Africa, under specific circumstances: high treatment coverage of the livestock population, using a product with stronger or longer lasting insecticidal effect than in the Pakistan trial, and with small (ideally null) repellency effect, or if increasing the attractiveness of treated livestock to malaria vectors. The results suggest these are the most appropriate conditions for field testing insecticide-treated livestock in an Africa region with moderately zoophilic vectors, where this intervention could contribute to the integrated control of malaria and livestock diseases.

Triatoma dimidiata infestation in Chagas disease endemic regions of Guatemala: comparison of random and targeted cross-sectional surveys.

BACKGROUND: Guatemala is presently engaged in the Central America Initiative to interrupt Chagas disease transmission by reducing intradomiciliary prevalence of Triatoma dimidiata, using targeted cross-sectional surveys to direct control measures to villages exceeding the 5% control threshold. The use of targeted surveys to guide disease control programs has not been evaluated. Here, we compare the findings from the targeted surveys to concurrent random cross-sectional surveys in two primary foci of Chagas disease transmission in central and southeastern Guatemala. METHODOLOGY/PRINCIPAL FINDINGS: Survey prevalences of T. dimidiata intradomiciliary infestation by village and region were compared. Univariate logistic regression was used to assess the use of risk factors to target surveys and to evaluate indicators associated with village level intradomiciliary prevalences >5% by survey and region. Multivariate logistic regression models were developed to assess the ability of random and targeted surveys to target villages with intradomiciliary prevalence exceeding the control threshold within each region. Regional prevalences did not vary by survey; however, village prevalences were significantly greater in random surveys in central (13.0% versus 8.7%) and southeastern (22.7% versus 6.9%) Guatemala. The number of significant risk factors detected did not vary by survey in central Guatemala but differed considerably in the southeast with a greater number of significant risk factors in the random survey (e.g. land surface temperature, relative humidity, cropland, grassland, tile flooring, and stick and mud and palm and straw walls). Differences in the direction of risk factor associations were observed between regions in both survey types. The overall discriminative capacity was significantly greater in the random surveys in central and southeastern Guatemala, with an area under the receiver-operator curve (AUC) of 0.84 in the random surveys and approximately 0.64 in the targeted surveys in both regions. Sensitivity did not differ between surveys, but the positive predictive value was significantly greater in the random surveys. CONCLUSIONS/SIGNIFICANCE: Surprisingly, targeted surveys were not more effective at determining T. dimidiata prevalence or at directing control to high risk villages in comparison to random surveys. We recommend that random surveys should be selected over targeted surveys whenever possible, particularly when the focus is on directing disease control and elimination and when risk factor association has not been evaluated for all regions under investigation.