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Clive R Davies

Publications and source records attributed to Clive R Davies.

18 recordsLinked to original sources
PubMed2006

Could the Chagas disease elimination programme in Venezuela be compromised by reinvasion of houses by sylvatic Rhodnius prolixus bug populations?

The Andean Pact Initiative (1997) committed Andean countries to eliminate vectorial transmission of Chagas disease by 2010 via widespread residual insecticide spraying. In Venezuela, this aim could be compromised by reinvasion of houses by palm tree populations of the major vector Rhodnius prolixus. To test this hypothesis, a multivariate logistic regression was undertaken of risk factors for triatomine infestation and colonization in 552 houses and 1068 peri-domestic outbuildings in Barinas State. After adjusting for other risk factors, including palm roofs, R. prolixus infestation and colonization of outbuildings (and, to some extent, houses) was significantly associated with proximity to high densities of Attalea butyracea palm trees. House infestation and/or colonization was also positively associated with bug density in peri-domestic outbuildings, the presence of pigsties and nests. Hence, R. prolixus populations in ineffectively sprayed outbuildings could also provide an important source of house re-infestations. The secondary vector Triatoma maculata was mainly found associated with the presence of hens nesting both indoors and outdoors.

Animals↗
PubMed2006

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.

Animals↗
PubMed2005

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.

Animals↗
PubMed2005

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.

Animals↗
PubMed2004

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.

Animals↗
PubMed2004

Predicting geographic variation in cutaneous leishmaniasis, Colombia.

Approximately 6,000 cases of cutaneous leishmaniasis are reported annually in Colombia, a greater than twofold increase since the 1980s. Such reports certainly underestimate true incidence, and their geographic distribution is likely biased by local health service effectiveness. We investigated how well freely available environmental data explain the distribution of cases among 1,079 municipalities. For each municipality, a unique predictive logistic regression model was derived from the association among remaining municipalities between elevation, land cover (preclassified maps derived from satellite images), or both, and the odds of at least one case being reported. Land cover had greater predictive power than elevation; using both datasets improved accuracy. Fitting separate models to different ecologic zones, reflecting transmission cycle diversity, enhanced the accuracy of predictions. We derived measures that can be directly related to disease control decisions and show how results can vary, depending on the threshold selected for predicting a disease-positive municipality. The results identify areas where disease is most likely to be underreported.

Colombia↗
PubMed2003

Malaria in Britain: past, present, and future.

There has been much recent speculation that global warming may allow the reestablishment of malaria transmission in previously endemic areas such as Europe and the United States. In this report we analyze temporal trends in malaria in Britain between 1840 and 1910, to assess the potential for reemergence of the disease. Our results demonstrate that at least 20% of the drop-off in malaria was due to increasing cattle population and decreasing acreage of marsh wetlands. Although both rainfall and average temperature were associated with year-to-year variability in death rates, there was no evidence for any association with the long-term malaria trend. Model simulations for future scenarios in Britain suggest that the change in temperature projected to occur by 2050 is likely to cause a proportional increase in local malaria transmission of 8-14%. The current risk is negligible, as >52,000 imported cases since 1953 have not led to any secondary cases. The projected increase in proportional risk is clearly insufficient to lead to the reestablishment of endemicity.

Agriculture↗
PubMed2003

Evaluation of PCR as a diagnostic mass-screening tool to detect Leishmania (Viannia) spp. in domestic dogs (Canis familiaris).

Several studies have suggested that the PCR could be used in epidemiological mass-screening surveys to detect Leishmania (Viannia) spp. infection in human and animal hosts. Dogs from an area of Leishmania braziliensis and Leishmania peruviana endemicity were screened for American cutaneous leishmaniasis (ACL) infection by established PCR-based and enzyme-linked immunosorbent antibody test (ELISA) protocols. PCR detected Leishmania (Viannia) infection in a total of 90 of 1,066 (8.4%) dogs: 32 of 368 (8.7%), 65 of 769 (8.5%), and 7 of 42 (16.7%) dogs were PCR positive by testing of whole blood, buffy coat, and bone marrow aspirates, respectively. ELISA detected infection in 221 of 1,059 (20.9%) tested dogs. The high prevalence of Leishmania (Viannia) detected by PCR and ELISA in both asymptomatic (7.5 and 19.2%, respectively) and symptomatic (32 and 62.5%, respectively) dogs is further circumstantial evidence for their suspected role as reservoir hosts of ACL. However, the low sensitivity of PCR (31%) compared to ELISA (81%) indicates that PCR cannot be used for mass screening of samples in ACL epidemiological studies. Unless more-sensitive PCR protocols were to be developed, its use should be restricted to the diagnosis of active (canine and human) cases and to the parasitological monitoring of patients after chemotherapy.

Animals↗
PubMed2003

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.

Adolescent↗
PubMed2003

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%.

Animals↗
PubMed2002

Rapid detection of Leishmania infantum infection in dogs: comparative study using an immunochromatographic dipstick test, enzyme-linked immunosorbent assay, and PCR.

Current zoonotic visceral leishmaniasis (ZVL) control programs in Brazil include the culling of Leishmania infantum-infected reservoir dogs, a strategy that has failed to prevent a rise of canine and human ZVL cases over the past decade. One of the main reasons this strategy has failed is because of a long delay between sample collection, sample analysis, and control implementation. A rapid, sensitive, and specific diagnostic tool would be highly desirable, because it would allow control interventions to be implemented in situ. We compared an immunochromatographic dipstick test to enzyme-linked immunosorbent assay (ELISA) and PCR for detecting L. infantum infections in dogs from an area of ZVL endemicity in Brazil. The dipstick test was shown to have 61 to 75% specificity and 72 to 77% sensitivity, compared to 100% specificity for both ELISA and PCR and 71 to 88% and 51 to 64% sensitivity for ELISA and PCR, respectively. Of the field samples tested, 92 of 175 (53%), 65 of 175 (37%), and 47 of 175 (27%) were positive by dipstick, ELISA, and PCR, respectively. The positive and negative predictive values for the tested dipstick were 58 to 77% and 75%, respectively. Efforts should be made to develop a more specific dipstick test for diagnosis of leishmaniasis, because they may ultimately prove more cost-effective than currently used diagnostic tests when used in mass-screening surveys.

Animals↗
PubMed2002

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.

Animals↗
PubMed2002

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).

Adult↗
PubMedDate not supplied

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.

Animals↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

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.

Adolescent↗