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ABSTRACT |
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Leishmania infantum is the only species of Leishmania found in Spain. Its principal reservoir is the dog, and it is transmitted to humans by the bites of female diptera of the genus Phlebotomus.4,5 As in other European countries, the last few years have brought about a radical change in human epidemiology of leishmaniasis in Spain. Transmission by its vectors has decreased, but transmission has increased among intravenous drug users and patients infected with human immunodeficiency virus (HIV).1–3 This latter change has caused an increase in the incidence of leishmaniasis since the mid 1980s, in addition to its spread to previously infection-free areas.3 However, the actual prevalence of leishmaniasis in Spain is unknown. The fact that clinical cases represent only a fraction of those infected with Leishmania sp. and that there is marked under-reporting of these cases are critical for understanding the epidemiology of this disease.6
Leishmaniasis has not been an officially reported disease in Spain since 1997.7 In addition, few studies have been conducted on the prevalence of infection with Leishmania sp. in the general population, and published reports have almost always used leishmanin (Montenegro) skin tests.4,5,8 Most studies on the prevalence of leishmaniasis have been carried out in HIV-infected patients.2,9,10 However, the prevalence of antibodies to Leishmania in these patients does not reflect the true situation in general population.
The objective of this study was to determine the prevalence of leishmaniasis in the general population, intravenous drug users positives for antibodies to HIV in Castilla-Leon, Spain. Prevalence was determined by detection of IgG antibodies to L. infantum with an enzyme immunoassay (EIA).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Serum samples were taken in public blood sample extraction centers of the Outpatient Health Care Network over a one-year period (1996) and were stratified by province and health area (rural/city) (Table 1). Age and sex were controlled by quotas. Individuals were randomly selected from those who came to health centers for follow-up visits or for medical examinations. All individuals included in the study were given an explanation of its purpose and informed consent was obtained from all participants. Individuals with fevers or suspected of having leishmaniasis were excluded from the study. The study was reviewed and approved by the Ethical Committee of Research of the Faculty of Medicine of the University of Valladolid (Valladolid, Spain).
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The presence of IgG antibodies against L. infantum was studied in each serum by an EIA.9 The antigen used was a soluble antigen from L. infantum strain LEM-75 (SLA), zymodeme 1, MHOM/FR/78/LEM75, which was isolated according to a modified version9 of the method of Scott and others.11 A pool of sera positive for Leishmania by an indirect immunofluorescence test (IFT) was used as the positive control. The negative control consisted of the 14 blood donor samples negative for Leishmania by the IFT. The EIA positivity threshold was calculated for each plate as the average of the absorbances of the 14 negative control sera plus two standard deviations.
Results were analyzed with SPSS statistical software (SPSS Inc., Chicago, IL) using Pearson’s chi-square test and 95% confidence intervals (CIs) for proportion analysis.
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RESULTS |
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Table 2 shows the seroprevalence of L. infantum by age groups. The prevalence of IgG antibodies against L. infantum significantly increased with age (P = 0.001), ranging from less than 4% in individuals less than 31 years old to more than 7% in those greater than 60 years old.
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Determination of the prevalence of IgG antibodies to L. infantum in HIV-infected intravenous drug users showed that 139 (64.0%) of the 217 patients studied were antibody positive. This prevalence was significantly higher than that of the general population in Castilla-Leon (64.0% versus 4.9%; 95% CI = 52.58–65.64, P < 0.001).
There were no statistically significant differences between the seroprevalences found for women and men (65.2% versus 63.5%; 95% CI = –12.1–15.5, P = 0.808). Similarly, there was no significant association between seroprevalence and age.
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DISCUSSION |
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Few seroepidemiologic studies on healthy populations have been conducted in Spain. All show serious biases because the number of sera studied have been small and were selected from population groups that do not represent the general population.9,14 None of these studies found seropositive cases in healthy people. In contrast, in our study the seroprevalence of L. infantum was 5%, ranging from 6.0% in the rural population to 3.4% in the urban population (P < 0.001).
Several factors explain the differences between our results and those obtained by the other investigators who used the leishmanin skin test.4,5 First, this test is more sensitive (approximately three times greater) in detecting leishmaniasis than serologic testing. Second, when an individual shows a positive result on this test, it remains positive throughout the individual’s life.15,16
Conversely, from an epidemiologic point of view, geographic and climatic conditions greatly influence the prevalence of leishmaniasis because they affect the life cycle of the sand fly vector. These conditions in Castilla-Leon are different from those in the Mediterranean regions in southern and eastern Spain where the previously mentioned studies were carried out.4,5,8 The greater frequency of individuals with positive leishmanin skin test results found in these two regions coincides with a high prevalence of human cases.7 Using 1996 as an example (the same year in which Acedo and others4 and Morillas and others5 conducted their studies), the incidence of human cases in Spain was 0.19 cases/100,000 inhabitants. In southern Spain, Malaga and Granada had more than 0.37 cases/100,000, while in eastern Spain, Cataluña had an incidence of 0.44 cases/100,000.7 These data contrast sharply with those from regions in northern and western Spain, where Castilla-Leon had an incidence of 0.04 cases/ 100,000 (one case) that same year, the Basque region had 0.1/100,000, and Galicia, Asturias, and Cantabria did not report any cases.7 The climate of southern and eastern Spain, with an average annual temperature of 17°C (ranging from 1°C to 42.5°C) favors the development of the sand fly vector and constitutes one of the main epidemiologic factors. In contrast, the average annual temperatures are much lower in Castilla-Leon (11.5°C, ranging from -10°C to 38.6°C), which makes vector development difficult and partially explains the much lower incidence of leishmaniasis.
As reported by other investigators,4,8 our study shows that there are no differences in the prevalence of leishmaniasis between men and women. The seroprevalence of antibodies to L. infantum increased with age, from 3.96% in those less than 21 years old to 7.2% in individuals more than 60 years old. This increased prevalence indicates greater exposure to Leishmania in older individuals because seropositivity against Leishmania decreases with time, especially during the first year post-exposure.17 A higher risk of infection in older individuals apparently does not exist in the region we studied. However, it must be remembered that until the 1940s and 1950s leishmaniasis was a severe public health problem in Spain, with an increased incidence of the disease.6 Conversely, although seroprevalence was not studied in children less than 14 years old in our study, most reports indicate that seroprevalence in this group is similar or slightly lower than that in those 14–20 years old.16,18
Since 1950, the incidence of leishmaniasis has progressively decreased in Spain. The use of pesticides in agriculture and the campaigns to kill insects carried out in the 1940s and 1950s to eliminate malaria in Spain undoubtedly have played a part.6 However, since the mid 1980s, an increase in the incidence of leishmaniasis has been observed. Most studies carried out before 1980 showed that more than 60% of all the cases of leishmaniasis reported in Spain occurred mainly children.2,4,5 However since 1990, a decrease incidence in children and an increase incidence in adults has been observed.2 In the latter case, most patients presented with various states of immunodeficiency (transplants, cirrhosis, etc.), especially infection with HIV, mostly in intravenous drug users. Our study, which was carried out in a region with low incidence of infection with Leishmania, showed that 64.0% of HIV-infected intravenous drug users had IgG antibodies against L. infantum. This result was similar to that observed by other investigators in regions with a much higher prevalence of leishmaniasis than in Castilla-Leon.10,14 These data confirm the existence of an anthroponotic cycle of leishmaniasis transmission through syringes shared among HIV-infected intravenous drug users.3
Received July 8, 2003. Accepted for publication October 1, 2003.
Acknowledgments: We thank the doctors at the Primary Health Centers in Castilla-Leon and the epidemiologists at the Epidemiology Service of the Junta de Castilla y Leon for their help. Special thanks are given to M. Fe Muñoz for the statistical analysis of the results. We acknowledge the following contributors to this study from the Servicio de Epidemiología de la Junta de Castilla y Leon: M. J. Rodríguez-Recio, H. Marcos, J. M. Sendra, J. L. Yánez, I. Carramiñana, J. Ramos, A. C. Berjon, C. Andrés, L. C. González, T. Muñiz, J. A. Gomez de Caso, E. Dodero, M. Morquecho, Clara Berbel, and M. S. Martínez.
Financial support: This project was supported by the Consejería de Sanidad y Bienestar Social of the Junta de Castilla y Leon.
Authors’ addresses: José I. Garrote, M. Purificacion Gutiérrez, Raúl López Izquierdo, M. Ana I. Dueñas, Miguel A. Bratos, and Antonio Rodríguez-Torres, Área de Microbiología. Facultad de Medicina, Valladolid, Spain. Pilar Zarzosa and Ana Almaraz, Unidad de Inves-tigación, Hospital Clínico Universitario de Valladolid, Valladolid, Spain. Carmen Cañavate and M. El Bali, Servicio de Parasitología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain. Clara Berbel, Servicio de Epidemiología y Servicio de Protección de la Salud. Consejería de Sanidad y Bienestar Social. Junta de Castilla y León, Valladolid, Spain, Antonio Orduña Domingo, Área de Microbiología, Facultad de Medicina, Avenida Ramon y Cajal no. 7, 47005 Valladolid, Spain, and Unidad de Investigación, Hospital Clínico Universitario de Valladolid, Valladolid, Spain, Telephone: 34-983-423-063, Fax: 34-983-423-066, E-mail: orduna{at}med.uva.es.
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This article has been cited by other articles:
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  C. Riera Observations on "seroepidemiology study of Leishmania infantum infection in Castilla-Leon, Spain". Am J Trop Med Hyg, August 1, 2005; 73(2): 231 - 231. [Full Text] [PDF]
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