There and back again – The return of the nasal mite Halarachne halichoeri to seals in German waters

Abstract

The nasal mite Halarachne halichoeri (Acari; Halarachnidae) is adapted to live in the marine environment with pinnipeds as its primary host and can cause different levels of upper respiratory disease in both harbour seals ( Phoca vitulina ) and grey seals ( Halichoerus grypus ). Historical reports of H. halichoeri occurring in seals from German waters date back to the end of the 19th century. However, with the disappearance of the grey seal from German waters as a consequence of human over-exploitation, the mite vanished from the records and the fauna found in Germany for more than a century. Although a stranding network has been monitoring marine mammal health along the German coasts since the mid 1980s with extensive post-mortem investigations, this study reports the first and subsequent findings of H. halichoeri in grey and harbour seals from the North and Baltic Sea from 2014 onwards. The re-emergence of this endoparasitic mite in North and Baltic Sea habitats seems to have occurred simultaneously with the recolonisation of its primary host, the grey seal. During the course of its recolonisation, it was probably transmitted to harbour seals sharing the same haul-out sites. Molecular analyses showed a high similarity of rDNA sequences with H. halichoeri collected from sea otters ( Enhydra lutris ) in the USA. However, more thorough analyses of additional gene loci are required to fully assess the exchange and diversity of this parasite between geographically isolated regions and species.

First report of a severe nasopulmonary acariasis caused by Orthohalarachne diminuata Doetschman, 1944 (Acari: Halarachnidae) in a captive South American sea lion (Otaria flavescens Shaw, 1800)

“…Mesostigmatid mites of the genera Halarachne Allman, 1847 and Orthohalarachne Newell, 1947 belonging to the family Halarachnidae Oudemans, 1906 constitute obligatory endoparasites infesting the respiratory tract of different semiaquatic marine mammals. Thereby, representatives of the genus Halarachne parasitize pinnipeds of the family Phocidae Gray, 1821 (earless seals) and sea otters ( Enhydra lutris Linnaeus, 1758), while the genus Orthohalarachne occurs in pinnipeds of the order Otariidae Gray, 1825 (eared seals) and Odobenidae Allen, 1880 (walruses) ( Kim et al, 1980 ; Rolbiecki et al, 2018 ; Seguel et al, 2018a ; Reckendorf et al, 2019 ; Pesapane et al, 2021 ). Within the genus Orthohalarachne , two species (with various synonyms) have been described: O. attenuata Banks, 1910 infesting nasopharyngeal mucosa, and O. diminuata Doetschman, 1944 parasitizing in parts of the upper and the lower respiratory tract ( Kim et al, 1980 ; Rolbiecki et al, 2018 ).…”

Nasopulmonary mites (Halarachnidae) of coastal Californian pinnipeds: Identity, prevalence, and molecular characterization

“…The 16S rDNA region of H. halichoeri from harbor seals is nearly identical to that of H. halichoeri collected from southern sea otters ( Table 2 ). This region appears to be highly conserved within H. halichoeri across hosts and geographic regions as H. halichoeri obtained from grey seals in Germany shared 99% homology with mites from southern sea otters ( Reckendorf et al, 2019 ). Halarachne miroungae obtained from northern elephant seals demonstrated high homology with H. halichoeri, which is not unexpected, considering these are closely related, but distinct species.…”

Nasopulmonary mites (Acari: Halarachnidae) as potential vectors of bacterial pathogens, including Streptococcus phocae, in marine mammals

“…Notably, many mite species demonstrate relatively low host specificity. Halarachne halichoeri infestations have been reported in eight marine host species [ 15 , 119 , 120 ] and Orthohalarachne attenuata in fourteen marine host species [ 15 , 119 ], suggesting broad exchange of halarachnid mites among proximate marine mammal populations [ 2 , 13 , 120 ]. As a result, NPM could mechanically or biologically vector bacteria and other pathogens within and between mammalian host species.…”

“…phocae and other bacterial pathogens of marine mammals. Given that NPMs are globally distributed and relatively abundant across marine mammal populations [ 12 , 16 , 119 , 120 ], including imperiled species like the southern sea otter and the Guadalupe fur seal ( Arctocephalus philippii townsendi ) [ 2 , 15 ], the potential for transmission of opportunistic bacterial pathogens is concerning. This potential for pathogen spread between animals should be considered for animal translocation programs, and co-housing of animals in rehabilitation facilities, zoos, aquaria, and oil spill response settings.…”

“…Collectively our findings contribute to an improved understanding of the host-parasite microbial community which can inform veterinary treatment, captive animal care, and animal conservation and translocation efforts. Prior captive care is a risk factor for NPM infestation in wild sea otter populations [ 13 ], and NPM parasitism can be very high in captivity without regular acaricidal treatment [ 1 , 4 , 121 ], and NPM are found in marine mammals worldwide [ 15 , 119 , 120 ]. As a result, our work has important implications for preventing pathogen transmission during captive care, oil spill response, and animal reintroduction efforts globally.…”