High prevalence of chigger mite infection in a forest-specialist frog with evidence of parasite-related granulomatous myositis

A review on trombiculiasis: An underreported parasitosis that affects humans and animals, including world distribution, clinical findings, associated pathogens, prophylaxis and identification methods

Chigger mites comprise three families: Trombiculidae, Leeuwenhoekiidae and Walchiidae, with over 3,000 species worldwide. Their life cycle includes six stages, and the larvae are parasites, while the other stages are free-living predators. Once attached to a host, the larvae spend several days feeding on the host's epithelial tissue, forming the stylostome. An inflammatory reaction can be formed during larval feeding, known as trombiculiasis or trombiculosis. In this study, we provide a literature review using 123 scientific articles on the cases of trombiculiasis in animals and humans reported in different biogeographical regions, including 29 countries and 30 different chigger species, with all the information compiled in the Supplementary material. This review aims to increase the visibility of this disease and group of mites, so that physicians and veterinarians can become more aware of the disease and include the causative agent in differential diagnoses. We also offer knowledge on mounting and control methods in order to improve mite identification for future research. Lastly, the prophylaxis and control methods in cases of infestations and associated pathogens are mentioned.

Review of Mites Found on Various Animal Hosts and at Different Localities in Malaysia

Mite biodiversity and distribution in Malaysia is currently understudied. Most previous works on Malaysian Acari have focused on pest organisms of medical, veterinary, and agricultural concern, with a few recent studies centered on mites in forensic contexts. Previous literatures have targeted collection sites in forest reserves and/or mountains in either Peninsular or Malaysian Borneo, though the state of Sarawak had the least publications related to mite species descriptions despite having the highest number of nature parks of any state in the country. Most publications focused on the three states Selangor, Pahang and Sabah. Most of the mite species reported were from mammals (66.3%), with fewer species from birds (21.7%), arthropods (11.2%), and reptiles (0.8%). We believe that further work on the systematic documentation of mite species throughout Malaysia is necessary as it could generate useful tools, such as the use of mites as biogeographical markers or as forensic indicators. Therefore, this review catalogs mite species that have been documented in or on animal hosts in Malaysia and serves as a foundation for future work.

Chiggers (Acariformes: Trombiculoidea) do not increase rates of infection by Batrachochytrium dendrobatidis fungus in the endemic Dwarf Mexican Treefrog Tlalocohyla smithii (Anura: Hylidae)

Amphibian populations are globally declining at an alarming rate, and infectious diseases are among the main causes of their decline. Two micro-parasites, the fungus Batrachochytrium dendrobatidis (Bd) and the virus Ranavirus (RV) have caused mass mortality of amphibians and population declines. Other, less understood epizootics are caused by macro-parasites, such as Trombiculoidea chiggers. Infection with chiggers can affect frog behavior and survival. Furthermore, synergistic effects of co-infection with both macro and micro-parasites may lead to higher morbidity. To better understand these potential synergies, we investigated the presence and co-infection by chiggers, Bd and RV in the endemic frog Tlalocohyla smithii (T. smithii). Co-infection of Bd, RV, and/or chiggers is expected in habitats that are suitable for their co-occurrence; and if infection with one parasite facilitates infection with the others. On the other hand, co-infection could decrease if these parasites were to differ in their micro-environmental requirements (i.e. niche apportionment). A total of 116 frogs of T. smithii were studied during 2014 and 2016 in three streams within the Chamela-Cuixmala Biosphere Reserve in Jalisco, Mexico. Our results show that 31% of the frogs were infected with Trombiculoidea chiggers (Hannemania sp. and Eutrombicula alfreddugesi); Hannemania prevalence increased with air temperature and decreased in sites with high canopies and with water pH values above 8.5 and below 6.7. Bd prevalence was 2.6%, RV prevalence was 0%, and none of the frogs infected with chiggers were co-infected with Bd. Together, this study suggests that chiggers do not facilitate infection with Bd, as these are apportioned in different micro-habitats. Nevertheless, the statistical power to assure this is low. We recommend further epidemiological monitoring of multiple parasites in different geographical locations in order to provide insight on the true hazards, risks and conservation options for amphibian populations.