versión impresa ISSN 0716-0720
Parasitol. día v.22 n.1-2 Santiago ene. 1998
TRABAJO DE INVESTIGACION
PREVALENCE OF Rhipicephalus sanguineus INFESTATION
IN DOGS IN CUERNAVACA, MORELOS, MEXICO
CARLOS CRUZ VAZQUEZ * ZEFERINO GARCIA VAZQUEZ ** y MANUEL MORALES SOTO **
The study was conducted in the urban municipality of Cuernavaca, Morelos, Mexico. From two private veterinary clinics a sample of 1742 dogs during a three year period (1993-1995) were examined to detect the presence of Rhipicephalus sanguineus ticks in any parasitic stage, collecting and identifying the ticks found. The prevalence rates were calculated by month and year and their distribution by age and gender. Chi square tests were used to compare proportions of positive and negative dogs to tick infestation. The prevalence of dog infestation with R. sanguineus was 20% in the period studied and there was no significant difference (P 0.05) between years. Tick specimens were collected throughout the years of the study. The climatic conditions in the study area and the continuous presence of the host favoured the parasite life cycle and 2.5 generations were estimated for each year. There were no significant differences (P 0.05) in the presence of R. sanguineus infestation in dogs by dog age, gender or by year. The main factors influencing the dog tick infestation in this study were probably due to the domestic life habits and the environment of the dogs studied.
Key words: Tick, Rhipicephalus sanguineus, prevalence, dogs.
* Instituto Tecnológico Agropecuario N° 20. (D.G.E.T.A. S.E.P.).Apdo. Postal 1439, C. Camionera. CP. 20270. Aguascalientes, Aguascalientes, México.
** Facultad de Ciencias Agropecuarias, Universidad Autónoma del Estado de Morelos. Av. Universidad 1001. CP. 62210. Cuernavaca, Morelos, México.
The brown dog tick, Rhipicephalus sanguineus , is the most cosmopolitan tick species and is found in all continents between 50° N and 35° S; in the Americas it is present from Canada to Argentina. Its specific-host is the dog, but it can also infest other domestic and wild species and even the human beings.1, 2
R. sanguineus is an efficient vector of Ehrlichia canis and Babesia canis, the causative agents of canine ehrlichiosis and canine babesiosis respectively.3, 4 In humans it is the confirmed vector of many diseases, such as Rocky Mountain Spotted fever.1
In Mexico, R. sanguineus is present, widely distributed and in some places the dogs have heavy infestations of this tick and are a constant nuisance to the owner; Despite its frequency, little is known about its epidemiology in the dog in Mexico. The objective of the present study was to describe the prevalence of the infestation with R. sanguineus in dogs in the urban municipality of Cuernavaca, in Morelos State, Mexico.
MATERIALS AND METHODS
Study site: The municipality of Cuernavaca is the urban capital of the State of Morelos, located in the central part of Mexico; an altitude of 1560 m above sea level, annual mean precipitation of 1200 mm with rainfall in summer and a subtropical climate.
Dogs: From two private small animal veterinary clinics sample of 1742 dogs during a three year period were examined by the senior author, from january 1993 to december 1995, for a six hours period once a week, all dogs were examined thoroughly to detect the presence of ticks. Dogs were presented to the clinics for a variety of reasons, including various infectious as well as non infectious diseases, traumatic injuries, grooming and health certification. The dogs in the study were of different ages and gender from the urban area and all were pets with owners that could be identified.
Information of each examined dog on age (determined by questioning the owner and examining the dentition) and gender was recorded; Three categories were made regarding age, £ 2 year-old, 2 to 4 year-old and more than 4 year-old respectively.
Specimen collection: Tick specimens were obtained from each positive dog. The dog was examined beginning from the head, followed by the neck, dorsum, trunk, limbs and tail and all ticks stages were collected in a glass vial containing alcohol (70%) for later identification. The tick specimens were taken to the laboratory and taxonomic identification was carried out by the senior author.5
Statistical analysis: The Chi-square test was used to compare proportions of positive and negative tick infested dogs according to age and gender and between years in these variables. A P value of £ 0.05 was considered significant.
From the 1,742 dogs examined the overall prevalence of dog infestation with R. sanguineus was 20 %. The annual prevalence is shown in Table 1. There was no statistical significant difference (P 0.05) in the prevalences among years.
The higher prevalence rates were found from march to august and in october and november, 20% or more. The lower prevalence rates were recorded from december to february and in september, 17% or less (Table 2).
Dogs 2-4 years old, showed the highest prevalence of tick infestation with R. sanguineus, 29% and dogs <2 years old the lowest 17% (Table 3). There was no statistical significant difference (P 0.05) between years and age groups, or years and gender variable (Table 4).
Tick specimens were collected throughout the year during the study.: adult stage from december to february and from may to september, nymph stage from march to july and november, and larvae stage in march, june and october. The three stages were found in june, larvae and nymph stages in march and adult and nymph stages in july.
R. sanguineus is widely distributed in the world, and it is very important the presence of the specific-host, the dog, for understanding its distribution Thus tick can be peri or intra-household because of the dog's domestic life habits.1, 6
In the study, R. sanguineus ticks were found along the year during the three years. The differents ticks stages were present in strategical times, perpetuating its life cycle. The prevalence rates were high throughout the year and the peaks were found in april, july and november, the lower prevalence were 12.76% in january (winter season). The climatic conditions in the study area and the continuous presence of the host favoured the parasite development along the year, calculating 2.5 tick generations per year.
In general our observations in prevalence study are similars with other studies carried out by other authors in different climatic conditions. In those studies the peak population of ticks were always related with climatic conditions in the area studied.7-10
The different variables considered in this study such as age and gender were not associated with the presence of R. sanguineus infestation in dogs. The main factors influence the dog tick infestation in this study were probably due to the domestic life habits of the dogs studied, since most of them visit public gardens or live they in private or common houses with gardens, which increases the possibility of contact with the ectoparasite 6.
Adults dogs, more than 2 years old, showed higher tick infestations than young dogs (<2 years old) which have less opportunity of visiting public gardens and the owners probably give them more attention to them than to adult dogs. The high prevalence observed in all ages confirms previous report that dogs do not develop resistance to tick infestation by R. sanguineus even if they have continuous reinfestation.11
This study showed the general characteristics of the tick infestation in dogs by R. sanguineus, in Cuernavaca, Morelos, Mexico. However, it is necessary to analize the tick seasonal fluctuations in the dogs and its relation with the dog enviroment with the object of designing an integrated control program of this important ectoparasite in veterinary and human health.
El presente estudio se realizó en el área urbana de la Cd. de Cuernavaca, Morelos, México. Durante un periodo de 3 años (1992-1995), una muestra de 1742 perros de dos clínicas veterinarias, fueron examinados para detectar la presencia de garrapatas Rhipicephalus sanguineus en cualquier estado parásito, éstas fueron colectadas e identificadas. Las tasas de prevalencia fueron calculadas por mes y año y se distribuyeron por edad y sexo. La prueba de Chi cuadrada (p < 0.05) se utilizó para comparar las proporciones de perros positivos y negativos a la infestación. En el periodo, la prevalencia a la infestación fue del 20%, no existiendo diferencias entre años (P 0.05); se colectaron especímenes durante todo el periodo de estudio. Las condiciones climáticas del área y la presencia continua del huesped favoreció el ciclo de vida del parásito, calculando 2.5 generaciones por año. No existieron diferencias (p 0.05) entre edad y sexo o año. En este estudio, los factores que probablemente mas influenciaron la prevalencia fueron los hábitos de vida doméstica y el medio ambiente en que viven los perros.
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Acknowledgements. The authors would like to thanks D.V.M's Magdalena Parada and Eduardo Castro for allowing acces to their patients.