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Angiostrongylus vasorum has been recognised as a cause of respiratory and circulatory distress among dogs in southwestern France for more than a decade, and the nematode now appears to be of increasing importance in the British Isles and Denmark. The aim of this review is to give a concise account of present knowledge of this intriguing parasitosis.

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Experimental concurrent infection with two or more parasite species in mammalian host models may result in heterologous antagonistic and synergistic interactions ranging in magnitude from reduced/enhanced growth and fecundity to blockage/enhancement of establishment/expulsion. With some exceptions only, there is a reasonable correlation between the levels of interaction monitored by parasitological and by clinico-pathological parameters. Heterologous antagonistic interactions mediated by functional and specific immunological cross-reactivity occur between closely related parasite species exhibiting a marked immunobiological similarity. In contrast, antagonistic interactions between antigenetically more remote species of helminths, protozoan-induced resistance to helminth infection and helminth-induced suppression of concurrent protozoan infection generally appear mediated by immunologically non-specific factors like macrophage activation and inflammatory reactions. Synergistic heterologous interactions between helminths, helminth-induced enhancement of concurrent protozoan infection and interference with the development and maintenance of resistance to helminth infection in response to concurrent protozoan infection are generally thought to be mediated by non-specific parasite-induced immunosuppression. Concurrent experimental infection is very complex. There are problems and limitations in extrapolating from experimental studies on concurrent infection in laboratory animals to natural polyparasitism. This fact, coupled with the complex influence of ecological factors on the pattern and frequency of concurrent natural infection means that major consequences of natural concurrent parasite infection have not been definitively demonstrated. Appropriately planned and controlled field studies and further laboratory experiments on primate and domestic animal models are imperative for elucidation of the importance of heterologous interactions in concurrent parasite infection for the disease pattern in man and domestic stock. Experimental studies hitherto conducted on concurrent parasite infection pointing to natural heterologous interactions may be a valuable starting point for further studies.

A cross-sectional study was carried out to determine the prevalence of gastrointestinal (GI) nematodes and flukes (Fasciola and amphistomes) infection in communally grazed traditional cattle, zero-grazed small-scale dairy cattle and intensively grazed large-scale dairy cattle through examination of helminth eggs in faeces. Results indicated that the type of management, especially the grazing habit, has a significant influence on the prevalence and intensity of GI nematodes and flukes. The prevalence of GI nematodes in traditional, large-scale dairy and small-scale dairy cattle was 67%, 44.4% and 37%, respectively, with the highest faecal egg counts in calves. The overall prevalence of Fasciola gigantica in traditional, large-scale dairy and small-scale dairy cattle was 63.8%, 46.2% and 28.4%, respectively. The prevalence of amphistomes was 81.9%, 55.5% and 41.1% in traditional, large-scale dairy and small-scale dairy cattle, respectively. The high prevalence of flukes in the traditional system was attributed to communal grazing and watering management practices. Stomach flukes recovered in examined cattle at the abattoir were Calicophoron microbothrium and Cotylophoron jacksoni. About 42.1% of infected animals had both Fasciola and amphistomes. The prevalence of both GI nematodes and flukes varied greatly among villages and farms. The prevalence of both Fasciola and amphistomes was higher in adults (58.5%, 75.2%) than in yearlings (36.5%, 51.5%) or calves (24.9%, 47.2%). The variation in the prevalence of both GI nematodes and flukes among management and age groups within systems can be used as an entry point towards rational use of anthelmintics for each management system. More studies on seasonal transmission pattern of all these parasites are required in order to design rational, economic and locally sustainable parasite control programmes.