The Veterinary Record, May 29, 2004 693 The liver and gall bladder were obtained and cut into 1 cm slices, and the bile ducts were mechanically expressed to expel any flukes present (Rodríguez and others 1994). This proce- dure was done using a sieve of 0·038 mm (No 50) to collect the flukes. The flukes were transported to the parasitology laboratory of the Faculty of Veterinary Medicine and Animal Science, Universidad Autonoma de Yucatan, where they were counted and identified. Identifications were made using the keys of Yamaguti (1971) and Bielsa and Greiner (1985). The prevalence and abundance of liver flukes were deter- mined using the formulae described by Maryolis and others (1982): Prevalence = Number of cats with P concinnum x 100 Number of studied animals Abundance = Number of flukes found in cats x 100 Number of positive cats All the positive cats were classified as having a low fluke burden if fewer than 125 liver flukes per animal were found, or a high burden if more than 125 flukes were found (Foley 1994). Three variables (sex, age and body condition score) were analysed by means of a logistic-binomial regression model of fixed-effects, using Statistix version 1.0 (Analytical Software 1996). This program provided exact regression esti- mates, 95 per cent confidence intervals (CI), odds ratios (OR), and P values. The logistic-binomial regression was used to control possible confounding variables. Forty-five of the 100 cats examined harboured P concin- num in their bile ducts; there was a mean count of 110·4 P concinnum flukes per cat. However, there was a large varia- tion in the number of flukes found in the liver of different cats, ranging from one to 843 flukes per animal. Eleven of the 45 positive cats (24·4 per cent) had a high fluke burden of P concinnum (Table 1). Table 2 shows the logistic regression analysis of the stud- ied variables. Female animals and animals older than two years were more likely to be positive for P concinnum. There was no association between body condition score and infec- tion status. In many countries P concinnum has been reported as the most significant liver fluke in cats (Foley 1994, Reis and oth- ers 1999). The prevalence of the parasite in cats in tropical and Short Communications Veterinary Record (2004) 154, 693-694 R. I. Rodriguez-Vivas, DVM, MVSc, J. J. Williams, DVM, MSc, PhD, A. G. Quijano-Novelo, DVM, G. M. E. Bolio, DVM, PhD, J. F. J. Torres-Acosta, DVM, MSc, PhD, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autonoma de Yucatan, Km 15, Carretera Mérida-Xmatkuil, CP 97100 Mérida, Yucatan, Mexico Prevalence, abundance and risk factors of liver fluke (Platynosomum concinnum) infection in cats in Mexico R. I. Rodriguez-Vivas, J. J. Williams, A. G. Quijano-Novelo, G. M. E. Bolio, J. F. J. Torres-Acosta Platynosomum concinnum is the hepatic fluke which causes the most concern in domestic cats (Bielsa and Greiner 1985, Sherding and Johnson 1994). P concinnum infection was first described at the beginning of the 20th century; it has also been referred to as Dicrocoelium concinnum, Platynosomum planicip- itus and Platynosomum fastosum (Purvis 1931, Foley 1994). Adult P concinnum usually inhabit the bile ducts and gall blad- der (Hitt 1981, Foley 1994, Tams 1994). The fluke can parasitise civet cats, opossums, ferrets and white mice (Foley 1994); it needs an intermediate host (terrestrial snails, lizards, toads and terrestrial isopods) (Young and others 1977, Foley 1994) to complete its life cycle. Infected cats show a large variety of clin- ical signs, such as jaundice, anorexia and hepatomegaly, although many cats show no signs at all (Hitt 1981, Tams 1994). The prevalence of P concinnum infection in cats is 79 per cent in Puerto Rico (Bielsa and Greiner 1985), 85 per cent in the Bahamas and 37 per cent in Brazil (Reis and others 1999). There are indicators that P concinnum is frequent in tropical and subtropical countries (Foley 1994). In Mexico, the pres- ence of P concinnum has been reported by Cárdenas and oth- ers (1990). However, there are no epidemiological studies describing the features of P concinnum infection in Mexico. The aim of this study was to determine the prevalence, abun- dance and risk factors associated with the presence of P concinnum in a cross-sectional survey of cats in Mérida, in the Yucatan region of Mexico. The climate in this area is sub- humid tropical, with a rainy season in summer. The mean temperature is 26·6°C, and relative humidity ranges from 65 to 95 per cent (mean 80 per cent), with an annual rainfall of 950 mm (Instituto Nacional de Estadística Geografía e Informática 1994). One hundred stray cats (aged six months or older), obtained from different parts of Mérida, were studied. Among them, 68 were female and 32 were male. All the cats were to be euthanased as part of a programme coordinated by the Animal Protection Association of Mérida. The following information was recorded about each animal: its sex, age (two years or older, or younger than two years, calculated by den- tal examination) (Hoskins 1990), and body condition score (good or poor) (Wills and Simpson 1995). All the cats were individually identified and euthanased by an approved injection, they were then examined postmortem. Fluke burden Number Prevalence (%) of cats among positive cats Low (≤125 flukes per animal) 34 75·6 High (>125 flukes per animal) 11 24·4 Total 45 TABLE 1: Burden of Platynosomum concinnum flukes in the liver of 100 domestic cats from Mérida, Yucatan, Mexico Number 95 per of cats Positive (%) OR cent CI P Sex Female 68 40 (59) 8·5 2·8, 26·2 0·002 Male 32 5 (16) 1·0 Age ≥2 years 53 30 (57) 2·8 1·1, 6·9 0·02 <2 years 47 15 (32) 1·0 Body condition Good 90 40 (44) 0·5 0·1, 2·6 0·41 Bad 10 5 (50) 1·0 OR Odds ratio, CI Confidence interval TABLE 2: Logistic regression analysis to determine factors associated with Platynosomum concinnum infection in cats of Mérida, Yucatan, Mexico