Seroprevalence of feline heartworm disease in Tuscany

M. Magi, DVM, B. Sebastiani, DVM, MSc, P. Bandecchi, Prof, Dipartimento di Patologia Animale, Profilassi ed Igiene degli Alimenti, Universita degli Studi di Pisa, Italy M. C. Prati, Scuola Normale Superiore di Pisa, INFN Sezione di Pisa, Italy V. Guberti, DVM, Istituto Nazionale per la Fauna Selvatica, Ozzano Emilia (BO), Italy FELINE heartworm disease caused by Dirofilaria immitis is a clinical problem of which veterinary surgeons are increasingly becoming aware. It may cause acute signs, often followed by death, or it may be chronic and asymptomatic (Atkins and others 2000). The disease is present mainly in cats living in zones where it is endemic for dogs, which are the reservoir of the disease. The cat is not an effective reservoir because microfilariaemia is transient (one to two months) or absent. Female mosquitoes propagate the disease by ingesting microfilariae in the blood of an infected dog. In Italy, the main vector for the cat is Culexpipiens (Di Sacco and others 1992, Genchi and others 1992b), but many other species of mosquito can act as vectors of the infection (Cancrini and Kramer 2000). Canine heartworm disease is present in all European countries in the Mediterranean area, the largest endemic area being the Po river valley in Italy where the prevalence among untreated dogs is estimated to be between 50 and 80 per cent (Genchi and others 1998b). The disease spreads due to several factors such as changing climatic conditions, caused by global warming and pollution, favourable for the vectors, the increased number of pets and the increased mobility of people and, as a consequence, their pets. Several cases of canine heartworm disease have been recognised in northern European countries such as Austria, Germany, the Netherlands and northern France and even the UK is at risk, due to the presence of potential vectors (Byrne and Nichols 1999). Recently, various diagnostic tests specific for feline heartworm disease have been developed. Antibody tests, which can detect patent, prepatent and occult infections, are useful in estimating the percentage of cats exposed to the infection (Genchi and others 1998a, Watkins and others 1998). The antibody seroprevalence in cats is important as it allows an estimation of the risk of infection for the cats living in the area of interest. It is not directly correlated to a high prevalence of the disease in dogs because the most important factor for the diffusion of the infection is the abundance of vectors (Dye 1990). In Italy, feline heartworm disease was first recognised in the district of Pisa in 1989 (Sassetti 1989, Sassetti and others 1998) and in northern Italy in 1990 (Di Sacco and others 1990). In 1996, the disease had been recognised only in four districts; however, by 2001, 21 districts were affected by the disease. The regions involved were Tuscany and Emilia Romagna in central Italy, Piedmont, Lombardy, Veneto and Friuli in northern Italy (Genchi and others 1992a, 1998b, 2001, Sassetti and others 1998, Falconelli 1999). The aim of the present study was to evaluate the antibody seroprevalence of feline heartworm disease in Tuscany, which is an endemic zone for canine heartworm disease. Some preliminary results were given by Magi and Sebastiani (1999). It is very difficult to estimate the actual prevalence ofcanine heartworm disease in Tuscany. Almost all dogs going to veterinary practices with their owners are under preventive therapy, so that among them the prevalence should be low. There are, however, some large kennels where stray dogs are collected and no prevention is carried out; the prevalence there should be very high. The possible association between feline heartworm disease seropositivity and the breed, sex, age, living place, lifestyle, feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) status of the cat was also investigated. From November 1998 to April 2000, 349 serum samples from cats living in Tuscany were tested for antibodies against feline heartworm disease using the test ASSURE/FH (Synbiotics), according to the manufacturer's instructions. The test can detect antibodies as early as six to eight weeks after infection with the L4 larval stage of the parasite. The sensitivity and specificity of the test are 98 per cent and 99 per cent, respectively (Bestul and others 1998). The sample of cats was chosen randomly from among the animals taken for normal checks or routine operations to veterinary clinics. For every cat examined the veterinary surgeon filled out a standard form with the following data: name of the owner; living place; age, sex and breed of the animal; its lifestyle; and the presence of a dog in the same house. The living places of the animals in each district were classified into three zones according to climatic and environmental factors as follows: coast, flat hinterland, hinterland hills. Canine filariasis is endemic in all three zones (Magi and others 1989) and mosquitoes are abundant throughout, due to the mildness and humidity of the climate. The cats were divided into three groups based on their lifestyle: living always inside the home, living always outside the home, living partly inside and partly outside the home. One hundred and ninety-eight serum samples were also tested for antibodies against FIV using ViraCHEK/FIV (Synbiotics) and 180 samples were tested for antibodies against FeLV using ViraCHEK/FeLV (Synbiotics). In order to verify any association between feline heartworm disease and the breed, sex, age, living place, lifestyle, FIV and FeLV status of the cat, chi-squared tests were performed. A logistic regression analysis was also performed (stepwise method) using SPSS 7.5 (spss), with feline heartworm disease seropositivity as the dependent variable. Positivity for FIV and FeLV were considered as interactive terms. From the output of the logistic regression the odds ratio (OR) of being positive to feline heartworm disease for cats with different lifestyles was calculated as stated in Hosmer and Lemeshow (2000). The P value for significance was 0*05. The 349 serum samples came from cats living in the dis-