Respiratory mites infesting pinnipeds as neglected parasites

Mites of the genera Halarachne and Orthohalarachne have evolved an uncommon and at the same time fascinating lifestyle: they parasitize the respiratory tract of semiaquatic marine mammals, especially eared seals, earless seals, and walruses. Their larvae inhabit the nasal cavity and are transmitted through direct nose-to-nose contact between the animals and through sneezed nasal mucus. The fast-crawling larvae then migrate into the nostrils of the new pinniped host and develop via nymphal stages into the adult parasites, which, depending on the exact species, reside in the nasopharynx or even deep in the lower respiratory tract. Over many decades, respiratory mites have been neglected, and today, they represent one of the least studied parasites of pinnipeds worldwide. Infestations can be asymptomatic, however, cases of severe respiratory disease and even associated deaths have been described. In wild pinniped colonies, these parasites can be widespread, and in recent years, our research group has detected them in various pinniped species in science-based zoological gardens in Europe. Today, we face several challenges: the diagnosis of respiratory mite infestation is very challenging due to the uncommon microhabitat of the parasites. The vast majority of research studies detected them during post-mortem examinations. Preliminary results obtained by our group, however, demonstrated for the first time that the collection of sneezed pinniped nasal mucus represents a gentle and promising detection method. Furthermore, the exact pathogenic potential of these mites to their hosts is largely unexplored. In this research project, we focus on three major aspects: 1) We will develop, adapt, and establish non- and minimally-invasive techniques to sample animals in the wild and in zoological gardens without the need of anesthesia. (2) The potential impact of mites on the respiratory system of their hosts will be examined using histological and molecular methods. In this context, we will also analyze the specific microbiome of different respiratory mite species. (3) Using imaging techniques, such as X-ray microCT, we will investigate the understudied parasitic reproductive and respiratory systems. With the planned development of non- and minimally-invasive diagnostic methods, we aim to establish a new gold standard for detecting these parasites. Such methods are urgently needed in zoological medicine to accurately evaluate the infestation status without anesthesia risk. At the same time, these methods will greatly facilitate research on these parasites in the wild. Our research findings will further deliver novel insights into the role of respiratory mites during disease processes, helping to unravel their pathogenic potential in both zoological gardens and in free-ranging populations.