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Research in Veterinary Science 85 (2008) 35–38

Characterization of sex, age, and breed for a populationof canine leishmaniosis diseased dogs

Sonia Miranda a, Xavier Roura b, Albert Picado c, Lluis Ferrer a, Antonio Ramis a,*

a Departament de Medicina i Cirurgia Animals, Facultat de Veterinaria, Universtitat Autonoma de Barcelona, 08193 Bellaterra, Spainb Hospital Clınic Veterinari, Universtitat Autonoma de Barcelona, 08193 Bellaterra, Spain

c Centre de Recerca en Sanitat Animal, Barcelona, 08193 Bellaterra, Spain

Accepted 5 September 2007

Abstract

Our study of a large canine population investigated whether the development of symptomatic canine leishmaniosis revealed any pre-dilection for sex, age, or breed. Included in the study were 390 leishmaniosis-affected dogs that had been treated at the Hospital ClınicVeterinari attached to the Universitat Autonoma de Barcelona. Of the diseased dogs, 238 were male (61%) and 152 were females (39%),whereas percentages for males and females in the overall reference population of dogs treated at this unit were 53% and 47%, respectively,(P < 0.05). Age distribution was bimodal, with the highest prevalence of the disease occurring at 2–4 years of age and a secondary peakoccurring at seven years or over. The over represented breeds were the German shepherd (13.6% versus 6.35%, P < 0.001), the Rottweiler(13.1% versus 3.0%, P < 0.001), and the Boxer (7.9% versus 4.7%, P = 0.002), whereas the underrepresented breeds were the Yorkshireterrier (0.5% versus 6.5%, P < 0.001), and the Poodle (0.3% versus 3.0%, P < 0.001).� 2007 Elsevier Ltd. All rights reserved.

Keywords: Leishmaniosis; Dog; Sex; Age; Breed; Epidemiology

1. Introduction

Leishmaniosis is an endemic zoonosis in countries in theMediterranean basin, where the dog is the main speciesaffected. In this region, canine leishmaniosis prevalenceand seroprevalence range between 2% and 5% and between10% and 30%, respectively, and as many as 50% or more ofall dogs may be infected (Ferrer, 2002).

Since most of the epidemiological data available is basedon serological studies performed in specific geographicareas, results are varied and often even contradictory.Some authors have reported that a higher proportion ofmale dogs are affected (Denerolle, 1996; Ciaramella et al.,1997), whereas others observe no sex differences in diseasedpopulation numbers (Amusategui et al., 2003). There is

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doi:10.1016/j.rvsc.2007.09.003

* Corresponding author. Tel.: +34 93 581 3144; fax: +34 93 581 3142.E-mail address: antonio.ramis@uab.es (A. Ramis).

also little agreement in regard to the breeds most affected,although the German shepherd, Doberman, and Boxer arethe most frequently mentioned breeds (Abranches et al.,1991; Denerolle, 1996; Sideris et al., 1996). As for age,some authors have concluded that leishmaniosis tends toaffect younger animals (Moretti and Piergili Fioretti,1995), other authors have found adults to be primarilyaffected (Fisa et al., 1999), while a third group of authorshave reported older animals as being more susceptible tothe disease (Cardoso et al., 2004; Mohebali et al., 2005).It has also been postulated that the age distribution foraffected animals is bimodal, with a first peak formed byanimals aged around three years and a second less evidentpeak representing animals aged around eight years (Ferrer,2002; Alvar et al., 2004).

Such contradictory results can be attributed to a varietyof possible causes. First of all, the confusion between theterms of infection, seroprevalence and disease, make many

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0-1 5-6 =>7

Age

Cas

es

2-4

Fig. 1. Age distribution in the population of dogs diagnosed withleishmaniosis in the HCV-UAB in the period 1998–2002. HCV-UABrefers to the Hospital Clınic Veterinari attached to the UniversitatAutonoma de Barcelona.

Table 1Breeds for which significant differences (P < 0.05) were observed in acomparison of the leishmaniosis population (n = 390) and the referenceHCV-UAB population (n = 12159) for the period 1998–2002

Animals withleishmaniosis (%)

Total HCV-UABpopulation (%)

P-value

German shepherd 13.6 7.5 <0.001Rottweiler 13.1 3.8 <0.001Boxer 7.9 5.3 0.002

Yorkshire terrier 0.5 6.5 <0.001Poodle 0.3 3.0 <0.001

HCV-UAB refers to the Hospital Clınic Veterinari attached to the Uni-versitat Autonoma de Barcelona.

36 S. Miranda et al. / Research in Veterinary Science 85 (2008) 35–38

authors treat seroprevalence as disease, and this fact wouldlead to an overestimation of disease incidence (Abrancheset al., 1991). Secondly, most studies evaluate sex, age,and breed characteristics for the affected animals in termsof percentages for the evaluated animals rather than foran entire population of dogs susceptible to contractingthe disease (Amusategui et al., 2003). Finally, differentserological techniques—e.g., the indirect fluorescentimmunoassay, the enzyme-linked immunosorbent assay(ELISA), the direct agglutination test—are used by differ-ent authors, with a variety of positive cut-off values (Fisaet al., 1999; Koutinas et al., 1999; Cardoso et al., 2004;Zivicnjak et al., 2005). The aim of this study was todescribe sex, age, and breed characteristics for dogs withleishmaniosis in comparison with dogs in a reference pop-ulation, for a largely urban setting (Barcelona, Spain).

2. Material and methods

Our study population included dogs that had receivedveterinary care at the Hospital Clınic Veterinari attachedto the Universitat Autonoma de Barcelona in the period1998 through 2002. Animals were classified as having leish-maniosis if they presented two ore more signs of the char-acteristic clinical picture of the disease described by Ferrer(1992)—skin lesions, anemia, localized or generalizedlymphadenopathy, ocular lesions, kidney failure, chronicdiarrhoea, liver failure, epistaxis and lameness—and ifthey simultaneously had a positive ELISA titer accordingto the technique described by Riera et al. (1999). On thebasis of these criteria 390 animals were identified, forwhich three variables—sex, age, and breed—were deter-mined. The reference population was 12 159 dogs treatedat the University Veterinary Clinic over the same timeperiod.

The sex variable was evaluated by comparing the per-centage of males and females in the diseased and referencepopulations using the v2 test. In order to evaluate the agevariable, the diseased population was grouped into fourage brackets—pups (0–1 years), young adults (2–4 years),adults (5–6 years) and older adults (P7 years)—and thenumber of individuals in each interval was quantified witha view to analyzing distribution. To analyze the breed var-iable, within each breed, the percentage of diseased dogswas compared to the percentage of the same breed in thereference population using the v2 and Fisher’s exact test.Mixed breeds and breeds with a percentage lower than1% in the reference population, were not included. Finally,for the breeds with high rates of disease, a combined anal-ysis of variance (ANOVA) was performed to compare themean ages of dogs in each of these breeds with the meanage of individuals in all the remaining breeds in the dis-eased population. Statistical significance was consideredat P < 0.05. The statistical packages Epidat version 3.0(OPS/OMS, Santiago de Compostela, Spain) and SPSSfor Windows version 12 (SPSS Inc., Chicago, IL, USA)were used.

3. Results

The population of diseased animals (n = 390) was 61%(238) male and 39% (152) female, whereas the correspond-ing percentages in the reference population (n = 12159)were 53% (6471) and 47% (5688), respectively. The propor-tion of males in the diseased population was significantlyhigher than the proportion of females (P = 0.002).

Ages in the diseased population ranged between sixmonths and 13 years. Once individuals were grouped intothe four age brackets described above, a bimodal age distri-bution could be observed; disease incidence peaked amongyoung adult dogs (171/390) and a second less evident peak(92/390) represented older adults (Fig. 1).

A total of 52 breeds were represented in the populationof dogs with canine leishmaniosis, of which 17 were evalu-ated. In comparing percentages for the diseased and refer-ence populations, there were significant differences for theGerman shepherd (P < 0.001), Rottweiler (P < 0.001) andBoxer (P = 0.002). It was also observed that the percent-ages for two other breeds (Yorkshire terrier, 0.5%; Poodle,0.3%) were significantly lower (P < 0.001) with respect tothe same breeds in the reference population (Table 1).

ANOVA was run with a view to comparing the meanage of disease onset in the German shepherd, Rottweilerand Boxer breeds and also to compare onset for thesebreeds with onset for the remaining breeds taken as a single

Others German sh. Boxer Rottweiler

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00A

ge a

t dia

gnos

is

Fig. 2. Box plots comparing ages for the most frequent dog breeds in theleishmaniosis population with ages for all the remaining breeds takentogether. The boxes represent values between the first and third quartile,the horizontal lines within the boxes indicate medians, and each end of thevertical lines marks a maximum or minimum value.

S. Miranda et al. / Research in Veterinary Science 85 (2008) 35–38 37

group. Results showed that the Boxer developed the dis-ease at an earlier age than all the other breeds and, further-more, that the difference in mean age was significant incomparison with the German shepherd (P < 0.001) andwith all the remaining breeds together (P = 0.02) but notin comparison with the Rottweiler (P = 0.08). No signifi-cant differences were observed for the mean age of diseaseonset in the Rottweiler and German shepherd with respectto all the remaining breeds together (Fig. 2).

4. Discussion

In this study we analyzed sex, age, and breed variables ina population of dogs diagnosed with canine leishmaniosis,and compared the data to a reference population. In thediseased population we observed a significantly higher pro-portion of males compared to females, significantly higherproportions of dogs belonging to the German shepherd,Rottweiler and Boxer breeds, and significantly lower pro-portions of dogs belonging to the Yorkshire terrier andPoodle breeds. A bimodal age distribution was observedfor disease onset, with a primary peak among young adultsaged two to four years and a secondary peak among olderanimals (P7 years).

In regard to sex, it is difficult to compare our results withthe results described in the literature, as male/female pro-portions in diseased populations were not compared tototal populations of animals susceptible to developing thedisease in the published studies. Nonetheless, Denerolle(1996) and Ciaramella et al. (1997) reported that more malethan female dogs appeared to suffer from leishmaniosis.

As for sex, no studies in the literature have comparedthe percentages of breeds in an affected population withthose in a reference population for the same geographicarea and time period. Some authors reject the hypothesis

that certain breeds are more frequently affected than others(Fisa et al., 1999; Leontides et al., 2002; Amusategui et al.,2003), while others indicate a greater or lesser prevalence ofcertain breeds. Consistent with our results is the fact thatthe German shepherd is mentioned in the literature as abreed that is over represented, both in studies evaluatingonly seropositive dogs (Abranches et al., 1991; Amelaet al., 1995) and in studies quantifying diseased dogs(Ciaramella et al., 1997). The Boxer is another breedreported to have a high incidence of both seropositivity(Franca-Silva et al., 2003) and leishmaniosis clinical signs(Denerolle, 1996). The Rottweiler, however, does not fea-ture among breeds observed to be especially affected.Finally, from our results it may also be deduced that theYorkshire terrier and Poodle are breeds with a lower ten-dency to develop leishmaniosis, as indicated by the signifi-cant differences between the percentages of animalsrepresenting these breeds in the diseased compared to thereference populations (Table 1); some authors attribute thisto the fact that these animals largely live indoors (Ozonet al., 1995; Ciaramella et al., 1997).

With regard to age as a predisposing factor for thedevelopment of leishmaniosis, bimodal distributions havebeen reported too in other studies—although only in stud-ies evaluating seropositive infection (Abranches et al.,1991; Amela et al., 1995; Alvar et al., 2004). One possibleinterpretation of this bimodal distribution is that certainanimals that are inherently more sensitive to the diseasewill develop it at an early age, whereas other more resistantanimals may become infected at an early age but will notdevelop over disease until they are older (when theirimmune system declines, when a concomitant infection ispresent, or in the context of other as yet unknown risk fac-tors) (Ferrer, 2002; Alvar et al., 2004). There are, in fact, anumber of studies that describe leishmaniosis associatedwith other processes (ehrlichiosis, lymphoma, hemangio-sarcoma, pemphigus foliaceous, etc.) (Ginel et al., 1993;Margarito et al., 1994), although it is difficult to determinewhether there is a causal relationship with leishmaniosis(Ferrer, 2002). On the basis of the aforementioned interpre-tation, the fact that Boxers tend to develop the disease atan earlier age than other breeds (Fig. 2) may will beexplained by a particular sensitivity of Boxers to leishman-iosis. The second peak referring to older dogs (Fig. 1) maybe attributed to the large numbers of associated illnessesobserved: 32 of the 70 dogs represented by the second peakhad associated illnesses most of them were infectious dis-eases and neoplasias.

Finally, it should be pointed out that since we only ana-lyzed the sex, age, and breed variables in terms of statisticalpatterns, it cannot be concluded that a direct relationshipexists between these variables and leishmaniosis. Giventhat it has been demonstrated that some breeds—such asthe Ibizan hound—have developed resistance to the disease(Solano-Gallego et al., 2000) and that the resistance seemsto be genetically based (Altet et al., 2002), we are of theopinion that the data compiled in our study may be of

38 S. Miranda et al. / Research in Veterinary Science 85 (2008) 35–38

use in terms of selecting, for in-depth study, factors thatindicate a predisposition to developing leishmaniosis orfactors that confer resistance.

Acknowledgments

The first author was supported by a grant from the Min-isterio de Educacion y Ciencia. Funding for this study wasprovided by the Spanish Comision Interministerial deCiencia y Tecnologıa (National Plan for Scientific Researchand Technological Development), Project BFI2002-01448.We thank A. Maher and M.E. Kerans for their assistancein translating the manuscript. And also to the Departmentde Farmacologia, Terapeutica i Toxicologia, UniversitatAutonoma de Barcelona, for let us to use their ELISAdiagnostic data base.

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