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Biomedical subjects

C Dye

Publications and source records attributed to C Dye.

88 records · Page 5Linked to original sources
PubMed1988

The epidemiology of canine visceral leishmaniasis in southern France: classical theory offers another explanation of the data.

This paper describes a compartmental model incorporating biological details of the transmission of canine visceral leishmaniasis in southern France. In contrast to earlier, empirical models (Jolivet, 1977; Rioux, Croset & Lanotte, 1977) the new model (1) predicts a threshold density of sandflies below which transmission cannot be sustained, (2) suggests that, until better data become available, the maximum prevalence of infection obtained at high sandfly density should be considered an unknown quantity.

Animals↗
PubMed1987

The life expectancy of phlebotomine sandflies: first field estimates from southern France.

1. A field study of Phlebotomus ariasi Tonnoir, the vector of Leishmania infantum Nicolle in southern France, addressed the following questions: Is it possible to estimate reliably the life expectancy of this sandfly; can spatial or temporal variation in the life expectancy be detected, and is such variation significant for disease transmission? 2. Life expectancy was estimated by examining follicular relics in the ovaries of more than ten thousand females caught in light traps at seven sites in the Cévennes and the Garrigues, throughout their active period in 1985 and 1986. Whilst the distinction between nulliparous and parous flies was easily made, assessments of the number of times a parous fly had laid eggs were unreliable. Best estimates of life expectancy were therefore calculated from the parous rate. 3. Large samples collected from one site in the Cévennes in both years gave very similar estimates of life expectancy. 4. There was also no significant difference between estimates obtained from the Cévennes and the Garrigues, despite their distinct vegetation and climates. Therefore, large regional differences in sandfly population size and the prevalence of canine leishmaniasis cannot be explained by a difference in adult survival rate. 5. With no systematic annual or regional variation, a useful mean life expectancy can be calculated from the data collected at all sites in both years. It is 1.54 (SE 0.04) ovarian cycles. However, this estimate is sensitive to the assumption that survival rate is a discrete rather than a continuous variable. 6. Local variation in the parous rate may be associated with the proximity of traps to P.ariasi emergence sites.

Age Factors↗
PubMed1986

Population dynamics of mosquito-borne disease: effects of flies which bite some people more frequently than others.

The consequences of non-homogeneous mixing (non-random contact) between vectors and hosts for the persistence, prevalence, and hence control, of any mosquito-borne disease are explored. When mosquitoes concentrate on certain hosts, the basic reproductive rate, R, of the disease (a measure of persistence) and the vectorial capacity are both greater than or equal to their values under homogeneous mixing. Field data suggest that R could be more than two and a half times as large as it would be under homogeneous mixing. Our calculations underestimate the importance of heterogeneity by ignoring mosquito patchiness and stochastic effects. Host selection limits the dependability of predictions, made from population models which assume homogeneous mixing, about the success of disease control (vaccines, chemotherapy, vector control). In particular, eradication or the maintenance of low prevalence will be more difficult than expected, unless localized control makes the distribution of infective bites on a community more nearly uniform. Age may explain most of the variability in biting in small communities (e.g., rural villages), in which case models incorporating age-specific biting will be appropriate tools in control programmes.

Anopheles↗
PubMed1986

Vectorial capacity: must we measure all its components?

Following attack on an insect vector-perhaps with insecticide or by removing breeding sites-we need to know what reduction in disease can be expected. In general, reliable predictions of the epidemiological consequences of any entomological change are highly desirable. Such predictions require a measure of the capacity of an insect population to transmit disease. A popular approach is to try to quantify all the entomological components of transmission, in isolation from the parasitological components, and then calculate the maximum daily reproductive rate of the disease-known as the Vectorial Capacity. But to measure accurately all the entomological components is technically demanding. In this article, Chris Dye argues that epidemiological predictions could be made by including only the dominant entomological variables in an index-a streamlined Vertical Capacity-which can then be fine-tuned by closely matching entomological and parasitological observations.

Journal Article↗
PubMedDate not supplied

Zoonotic cutaneous leishmaniasis in Saudi Arabia: results of a preliminary epidemiological survey in Al-Ahsa oasis.

This paper reports the results of a cross-sectional survey of lesions (active cases) and scars (past cases) of zoonotic cutaneous leishmaniasis (ZCL) carried out in 1986 in 2 villages in the eastern region of Al-Ahsa oasis in Saudi Arabia. The epidemiological pattern of ZCL was strikingly similar in both villages. Overall, 2.8% residents were found to have lesions. Only 3.7% were found with scars, presumably due to under-recording. The age distribution of lesions was bimodal, the number of cases being highest in the age-groups 0-3 and 24-27 years. The sharp fall between 3 and 15 years in the number of persons with lesions is typical of an active endemic infection which induces long-lasting immunity. The exceptional number of active adult cases were predominantly non-Saudi males. Infected non-Saudis also contributed substantially to statistically significant clustering of case in households and influenced the sex ratio of cases. More active cases were found in males than in females, and more active cases were male than were past cases. In 1985, residents reported a broad peak in the monthly discovery of lesions--from July to February. Interpretation of the available information was limited because it was not possible to standardize the data for age and sex.

Adolescent↗
PubMedDate not supplied

Evidence for a long-term increase in the incidence of Leishmania tropica in Aleppo, Syria.

We report the results of a short study of the epidemiology of Leishmania tropica in the Sheikh Maksoud District of Aleppo, Syria. The present and past status of infection in a community of about 100,000 people are assessed from prevalence and incidence data obtained by active and passive case detection, and from a skin test survey. L. tropica has apparently been endemic for at least 2-3 human generations in Aleppo, and incidence has increased over the past decade. The current estimated force of infection is 0.174/year, the incidence is about 5%, and the average age of infection is 14 years. L. tropica has the essential characteristics of a cyclic infectious disease, and the recent rise in incidence could be part of a long period cycle. A survey of leishmanial scars seriously underestimated the fraction of persons immune, as scar surveys usually do. We estimate that a passive case registration scheme, which has been established in response to growing concern about leishmaniasis in Aleppo, succeeds in recording and treating about one in 4 cases.

Adolescent↗
PubMedDate not supplied

Approaches to vector control: new and trusted. 5. The epidemiological context of vector control.

This paper discusses 2 prominent, contemporary issues in the epidemiological context of insect vector control: (i) the magnitude of the control problem, and (ii) non-linear processes influencing vector control. It concludes that we still cannot reliably measure the scale of some important control problems; e.g., there is considerable uncertainty about the basic reproduction number of malaria. The emergence of new concepts such as strain-specific immunity, and a growing emphasis on disease control as distinct from infection control, mean that some quantitative problems are being redefined more quickly than they are being solved. Population biologists have urged exploration of density-dependent processes which may help or hinder new methods of vector control. This brief review of non-linear phenomena such as facilitation and limitation finds little evidence that they will significantly influence, e.g., the introduction of some novel refractory mechanism into a vector population.

Animals↗
PubMedDate not supplied

The fall and rise of Andean cutaneous leishmaniasis: transient impact of the DDT campaign in Peru.

A retrospective analysis was carried out on census data collected from house-to-house surveys during 1991-1992 in 4 areas endemic for Andean cutaneous leishmaniasis (uta) in the Department of Lima, Peru. Major changes in mean annual incidence in susceptible persons have taken place in these sites during the last 60 years. In particular, there is strong support for the hypothesis that, from the 1950s to the 1970s, the transmission rate was temporarily suppressed, largely as a by-product of the DDT house spraying campaign against malaria. These results are consistent with (i) anecdotal evidence, contemporary with the spraying campaign, and (ii) the official Ministry of Health records for the annual number of uta cases in the Departments of Lima and Ancash.

Adolescent↗
PubMedDate not supplied

Tuberculosis.

Tuberculosis (TB) is a disease of antiquity, caused by Mycobacterium tuberculosis, which principally affects the lungs. It is a major public-health problem, with around 9 million new cases and 2 million deaths estimated to occur each year. Patients with pulmonary TB whose sputum is smear-positive for M. tuberculosis form the main source of infection in communities. About 5%-10% of infected individuals are likely to develop symptomatic TB during their lives but the risk of developing the clinical manifestations of the disease is greatly increased by HIV co-infection. The strong association between HIV and TB in sub-Saharan Africa is responsible for the massive increase in the incidence of TB observed in that region in the last 20 years. Diagnosis of TB in resource-poor countries is largely based on sputum-smear microscopy and chest radiography, although these methods lack sensitivity or specificity, especially when used on HIV-infected patients. Effective treatment has existed for 40 years but TB-attributable mortality remains high among HIV-infected patients in Africa, who are also particularly likely to develop TB again after receiving drug treatment for the disease. In Eastern Europe it is drug resistance in the local M. tuberculosis that makes the treatment of TB relatively ineffective. The approach to TB control that is now internationally recommended is the DOTS ('directly-observed treatment, short-course') strategy, which aims to prevent the transmission of M. tuberculosis, and the related illness and death, by using combinations of anti-TB drugs to treat patients with the active disease. Unfortunately, countries in sub-Saharan Africa are falling short of the World Health Organization's targets for case detection and treatment. This failure is, in turn, making the achievement of the Millennium Development Goals for TB--to ensure that the incidence of TB is falling by 2015 and to halve the prevalence of TB and the annual number of TB-attributable deaths between 1990 and 2015--less likely. To improve the performance and impact of TB-control programmes, in the face of HIV co-infection and other constraints on DOTS, the World Health Organization has launched the revised 'Stop TB Strategy'. The new strategy, to be implemented via the Global Plan to Stop TB (2006-2015), includes intensified TB-case finding, treatment of latent TB infection with isoniazid, prevention of HIV infection, cotrimoxazole preventive therapy, and antiretroviral therapy.

AIDS-Related Opportunistic Infections↗