Vet Times The website for the veterinary profession https://www.vettimes.co.uk INCREASING THREAT TO UK DOGS OF ANGIOSTRONGYLUS VASORUM Author : HANY ELSHEIKHA Categories : Vets Date : July 14, 2008 HANY ELSHEIKHA discusses a parasite that can cause fatal respiratory and circulatory problems in dogs CANINE angiostrongylosis is a snail-borne infection caused by a metastrongylid nematode known as Angiostrongylus vasorum. Adult worms live in the heart and pulmonary arteries of domestic dogs and wild canids, causing severe respiratory and circulatory distress, often ending in death. The spread of this parasitic infection beyond the range of endemic areas has become an increasing cause of concern for veterinarians and dog owners. Reports of individual cases have increased worldwide over the past decade. A feature of A vasorum epidemiology that has attracted attention in Great Britain is the northwards expansion of infection to nonendemic areas. Parasite life cycle Avasorum hasanindi - rect life cycle that requires an intermediate gastropod (such as slugs and snails) and/or paratenic (such as amphibians, lizards, mice and rats) hosts for the development of first stage larvae (L1) into the infective third stage larvae (L3). Dogs become infected by ingesting the intermediate or paratenic hosts containing L3 (Morgan et al, 2005). This infective stage penetrates the gastrointestinal wall. Young nematodes follow a lymphatic-hepatic-cardiopulmonary migratory route until they reach the right ventricle of the heart and pulmonary arteries, where sexual reproduction and oviposition take place. Eggs laid by the female worms are transported to the pulmonary capillaries, where they hatch into L1. These penetrate the capillary and alveolar 1 / 9 walls to the airways, reach the pharynx by coughing, are swallowed and excreted into faeces. The intermediate or paratenic hosts become infected through ingestion of L1. Clinical features A wide range of clinical signs have been reported that are associated with A vasorum (Curry and Lima, 1996; Garosi et al, 2005; Morgan et al, 2005; Manning, 2007). However, two clinical syndromes prevail: • respiratory disease and fibrosis caused by the inflammatory response to eggs and migrating larvae; and • the haemorrhagic diatheses caused by coagulopathy (Chapman et al, 2004). The most challenging clinical aspect of A vasorum infection is to define the pathomechanisms leading to coagulopathies, as this is the most important factor causing mortalities. A vasorum has even been found in erratic sites, such as within the pericardial sac, lumen of the bladder, kidney, and femoral artery - often with fatal consequences in infected dogs (Oliveira-Júnior et al, 2004). Veterinarians should be aware of the potential for severe outcomes, and take steps to reduce both the risk of disease and resultant complications. The uses of fenbendazole, levamisole, ivermectin and milbemycin for the treatment of A vasorum have been reported with variable degrees of success. Fenbendazole and moxidectin were found to be effective against A vasorum infections in naturally infected dogs. Supportive treatment (especially with corticosteroids), to reduce chronic lung disease, remains subjective. Even so, prophylactic anthelmintic treatment may be considered before moving a dog to an area where A vasorum is not yet established. Diagnosis Detection of A vasorum infections in dogs can be accomplished based on history, clinical signs and laboratory investigation. The latter includes detection and morphologic identification of L1 in multiple faecal samples using the Baermann technique or faecal fl oatation, cytological examination of samples collected from tracheal wash or bronchoalveolar lavage, blood profile, serological assays and PCR. However, PCR and serological assays are not commercially available. Epidemiological attributes 2 / 9 Originally reported in France in the early 19th century, A vasorum h as a worldwide distribution in a wide range of hosts covering tropical, subtropical and temperate regions in Africa, the Americas and Europe. It has a patchy distribution (characterised by isolated endemic foci) in France, Ireland, England and Denmark, with occasional cases outside endemic areas (Curry and Lima, 1996; Morgan et al, 2005). We do not know the exact geographic range of A vasorum i n foxes or dogs and we do not know how it is transported from one location to another. The mechanisms behind the range expansion of this parasite in foxes, and how this may impact co-occurring counterpart species in dogs, is poorly understood at large, spatial scale. Some insights have been gained through small-scale studies in mainland Europe and Great Britain. However, our knowledge of the factors that determine the distribution of A vasorum infection undoubtedly has many lacunae. These lacunae have generated some speculations, among which the hypotheses provided by Tomlinson et al (2006). These attributed the spread of canine angiostrongylosis to increased opportunities for the transmission of A vasorum between foxes and dogs (because of the recent increase in fox populations). Carnivores present unique opportunities and challenges to A vasorum. They are wideranging animals that can move rapidly and frequently, potentially interacting with each other and with many other animal species. Canids are a highly diverse, yet closely related, group of carnivores that share a high degree of ecological overlap. Thus, the presence of A vasorum i n foxes is of major concern in urban and suburban areas, where dense populations of both foxes and dogs live close together (Koch and Willesen, 2008). For this reason, the shared distribution range of A vasorum in dogs and sympatric wild canids warrants careful monitoring. In a prospective study performed in Great Britain, prevalence of A vasorum in foxes was found to vary widely between regions, from zero to three per cent in Scotland and northern England to 23 per cent in southeast England. This pattern was consistent with the occurrence of disease in dogs, which is more prevalent in the south-east than in the north. Likewise, in the midlands, where angiostrongylosis has been reported in dogs, prevalence in foxes was 4.8 per cent (Morgan et al, 2008). These findings show the positive correlation between habitat overlap and A vasorum pervasiveness. If cross-species transmission plays any role in the dynamics of A vasorum infections, then abundance and prevalence of the parasite should also grow, with increasing levels of habitat overlap among hosts. Hence, given that A vasorum is transmitted and carried by multiple hosts, it is no surprise that increasing habitat overlap among host species was associated with increased parasite occurrence. Therefore, the differences in parasite prevalence rates probably refl ect heterogeneity in parasite transmission levels across habitats. 3 / 9 The transmission of A vasorum i nfections between wild and domestic hosts and its persistence in new areas seems to be complex. The present picture suggests horizontal or environment-mediated transmission by the interactions between a wide range of factors, such as climate change, immune status, reservoirs (for example, wild canids) or the abundance of intermediate and definitive hosts. It is likely that interactions between climate and intermediate and definitive host densities infl uence the chances of parasite establishment in new areas. In this perspective, climate change and associated alterations in slug and snail phenology could affect the ecological distribution of A vasorum and the risk of infection for foxes and dogs. Very few studies have focused on the impact of climatic conditions in the spread of the infection (Torres et al, 2001; Jeffery et al, 2004). Unfortunately, too little is known about the parasite’s climatic and biological requirements to make sensible predictions about areas at risk from range expansion. Mathematical models that take into account climatic changes in temperature and rainfall, as well as conditions for intermediate hosts, are needed. While the importance of fox population density in enabling the parasite to become established is still a controversial subject, other effects - such as immuno-suppression - could exacerbate parasite spread. In Great Britain, the pressure of concurrent infection (such as sarcoptic mange) was found to enhance the susceptibility of foxes to A vasorum, which coincided with the emergence of A vasorum in dogs. Additional reports from European countries indicated areas that have experienced outbreaks of sarcoptic mange in foxes also have a high prevalence of A vasorum. A vasorum is a generalist parasite and has an extraordinary capacity to exploit a wide range of intermediate and definitive hosts in diverse climatic conditions. This may be important for the ability of the parasite to be established on new hosts when introduced into new geographical niches. The intermediate host range of A vasorum is broad and northern parts of Great Britain certainly harbour suitable slug and snail vectors. However, it is not clear whether northern areas are relatively inappropriate for transmission, or whether they could sustain a parasite survival but have yet to be invaded. Further studies are needed to determine the importance of the different intermediate hosts and the paratenic host spectrum. Because A vasorum infects multiple definitive host species, cross interactions among sympatric hosts potentially play an important role in parasite transmission dynamics in canid communities. To evaluate