Felid Cardiopulmonary Nematodes: Dilemmas Solved and New Questions Posed

Abstract

In the past decade cardiopulmonary nematodes affecting felids have become a core research topic in small animal parasitology. In the late 2000s, an increase in studies was followed by unexpected findings in the early 2010s, which have stimulated research teams to start investigating these intriguing parasites. Prolific scientific debate and exchanges have then fostered field and laboratory studies and epi-zootiological surveys. New data have improved basic and applied knowledge, solved dilemmas and posed new questions. This article discusses the past and present background to felid cardiopulmonary nematodes after the last few years of intense scientific research. New data which have demonstrated the key role of Aelurostrongylus abstrusus and Troglostrongylus brevior in causing respiratory infections in domestic cats, and on the nil to negligible current importance of other species, i.e., Troglostrongylus subcrenatus, Oslerus rostratus and Angiostrongylus chabaudi, are presented. Biological information and hypothesized alternative routes of infection are analysed and discussed. Novel identification and taxonomical data and issues are reported and commented upon. On the whole, recent biological, ecological and epi-zootiological information on felid meta-strongyloids is critically analysed, with the aim to answer outstanding questions, stimulate future studies, and underline new research perspectives.

Keywords: cardiopulmonary nematodes; domestic cats; wildcats.

Figure 1

Schematic representation of the Troglostrongylus brevior spillover from the European wildcat (Felis silvestris) to the domestic cat (Felis catus).

Figure 2

Geographic distribution of Troglostrongylus brevior in Europe and Middle East. The geographic distribution of Troglostrongylus brevior in domestic cats (red triangles) [6,7,16,17,18,19,20,21] reflects the distribution area of wildcats (in grey) [22]. Troglostrongylus brevior has been sporadically reported in touristic spots where wildcats are absent or undetected (blue triangles) [1,6,7]. Green triangles indicate reports of Troglostrongylus brevior in wildcats [23,24,25,26,27,28]; areas where the nematode has been not found in absence [29,30,31,32,33] or presence [16] of wildcats are indicated by red and blue circles, respectively.

Figure 3

Migration, travels and islands suitability. (A) Complete annual migration routes, indicated in different colors, of bird species between Europe and Africa. Part of Figure 2 from [65] under the terms of the Creative Commons Attribution 4.0 International License [66]; (B) Statue of the famous Greek poet Nikos Kavadias (1910-1975), Argostoli harbour, Kefalonia, Greece (courtesy of Anna Votsi [67]); (C) Tourist travelling with her cat on a ferry boat; (D) Cat on a boat travelling with its owners on holiday and moving between touristic spots (courtesy of Instagram @miss_rigby_boatkitty); (E) Snails in a cat feeding station in Mykonos Island, Greece.

Figure 4

Hypothesized phenomena contributing to the biology of felid cardiopulmonary metastrongyloids. An experiment suggested that metastrongyloid third stage larvae (L3) may be released in the environment [83], but it has never been demonstrated if this happens in natural conditions. If so, infected molluscs drowned in a cat bowl or mingling in cat food (A) may be a potential source of infection. Another laboratory study proposed the “intermediesis”, i.e., the snail-to-snail transmission of L3 [84], which is not known whether it occurs in the field. Regardless, it would be worth investigating if similar phenomena, e.g., gastropod cannibalism and interspecific predation (B), may also occur.