Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated

Parasites & Vectors Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated Donato Traversa 0 Angela Di Cesare 0 Gary Conboy 1 0 Department of Comparative Biomedical Sciences, University of Teramo , Teramo , Italy 1 Department of Pathology and Microbiology, Atlantic Veterinary College , Charlottetown, PEI , Canada Cardiopulmonary nematodes of dogs and cats cause parasitic diseases of central relevance in current veterinary practice. In the recent past the distribution of canine and feline heartworms and lungworms has increased in various geographical areas, including Europe. This is true especially for the metastrongyloids Aelurostrongylus abstrusus, Angiostrongylus vasorum and Crenosoma vulpis, the filarioid Dirofilaria immitis and the trichuroid Eucoleus aerophilus (syn. Capillaria aerophila). The reasons of this emergence are little known but many drivers such as global warming, changes in vector epidemiology and movements in animal populations, may be taken into account. The purpose of this article is to review the knowledge of the most important heartworm and lungworm infections of dogs and cats in Europe. In particular recent advances in epidemiology, clinical and control are described and discussed. - Background Nematodes affecting the cardiopulmonary system of dogs and cats have recently become the focus of increased attention from the scientific community due to their emergence in several European countries and the spread into previously non-endemic regions. This has been particularly the case for the metastrongyloids Aelurostrongylus abstrusus, Angiostrongylus vasorum and Crenosoma vulpis, the filarioid Dirofilaria immitis and the trichuroid Eucoleus aerophilus (syn. Capillaria aerophila). Indeed, the importance of infection with the heartworm (A. vasorum and D. immitis) and lungworm (A. abstrusus, C. vulpis and E. aerophilus) parasites in companion animals is heightened by the pathogenic potential of these nematodes, the challenges involved in diagnosis and (for some) their zoonotic potential. The reasons for the apparent emergence of cardiopulmonary parasitoses in pets are unknown but several factors such as global warming, changes in vector seasonal population dynamics and movements in animal populations, may play a role in the recent rise in reports of infection in the various countries of Europe. Most of these parasites have an indirect life cycle, thus requiring an intermediate host (i.e. biological vector) for their development. This is true for the gastropod-borne A. abstrusus, A. vasorum and C. vulpis and for the mosquito-transmitted D. immitis. Conversely, E. aerophilus may develop either directly in the environment or in earthworms acting as facultative intermediate hosts. Consequently, the likelihood for a dog or a cat becoming infected by a cardiopulmonary nematode depends not only on the presence of the vector(s) but also by their abundance and the prevalence of the infection. The occurrence of canine and feline heartworms and lungworms in different geographical areas is mainly influenced by the presence of competent gastropod and culicid species, with the exception of E. aerophilus, whose presence is guaranteed by the ubiquity of the earthworms and by the direct life cycle. Therefore, the interaction between the parasites, their hosts and the environment plays a central role in the apparent increase in exposure risk of these infections and is the basis for a new recognition of the relative importance of these parasites as aetiological agents in cardiopulmonary disease in companion animals. As a consequence, in the past few years several publications mainly related to distribution, epidemiology and control have appeared, although several aspects on biology, pathology and diagnostics still need to be elucidated. Therefore the present paper aims to review the current knowledge on cardiopulmonary nematodes of dogs and cats with a focus on their epidemiological patterns in Europe, on the pathogenic impact they have and on the new avenues and perspectives for diagnosis and control. Distribution in Europe: changing patterns, certainties and dilemmas The development and survival of the gastropod and insect vectors is mainly influenced by temperature, moisture and water availability, thus one of the most important factors currently favouring the dispersal and spread of vector-borne pathogens is global warming [1]. Specifically, given that rates of physiological processes in most invertebrates depend greatly on environmental temperature, the distribution and development rates of vector-borne diseases would be greatly influenced by a rise in temperature [2,3]. These environmental changes may play a causative role in the expansion of the geographic distribution of the heartworms, D. immitis (canine heartworm) and A. vasorum (French heartworm). Population dynamics and activity of culicid and gastropod intermediate hosts are highly sensitive to temperature and moisture, and the development of nematode larvae in vectors is also known to be temperature-dependent [4]. Both D. immitis and A. vasorum have a huge range of competent vector species and their canine definitive hosts are distributed worldwide. As a likely consequence of these factors, the most recent papers report a trend in the geographic spread of both of the heartworms, D. immitis and A. vasorum, into previously free areas [5-9]. Transmission of D. immitis by mosquitoes is strictly dependant on a suitable climate allowing the larval development in the vectors, thus environmental temperatures are the main factors favoring the life cycle of this parasite [5,10,11]. Some climate-based models have been developed to investigate the possible changes that may occur in terms of distribution and seasonality for D. immitis in response to global warming [5,12,13]. These studies clearly demonstrated that Dirofilaria infections in Europe have seasonal transmission patterns with peak activities in the summer months and that warm climates facilitate larval development in the intermediate hosts. Therefore, changes in climate are likely to have a strong impact on parasite distribution, development and transmission patterns. The current trend of increasing temperatures will probably allow the spread of the nematode in several countries [5]. With regard to A. vasorum, there is clear evidence of both an increase in the number of cases reported within known endemic foci (e.g. France, Denmark and UK) and the appearance of new foci in several regions previously free of infection [6,9,14,15]. There is great interest in understanding the reasons for the spread of French heartworm and to elucidate the factors, global warming or other(s), that may be involved. The major hindrance for such studies on A. vasorum is the lack of detailed information on key biological features of the nematode, e.g. influence of climatic factors on development and transmission in the vectors and th (...truncated)