''Orthohalarachne attenuata'' (family:

Halarachnidae Halarachnidae is a small family of mites in the order Mesostigmata. Species Halarachnidae contains seven genera, with ten recognized species: * Genus ''Halarachne'' Allman, 1847 ** ''Halarachne halichoeri'' Allman, 1847 ** ''Halarachne laysanae ...

) is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

mite Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...

normally found in the

nasal passage The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...

s of

fur seal Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than Earless seal, true seals, and share with them external ears (Pinna (anatomy ...

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

s, and

walrus The walrus (''Odobenus rosmarus'') is a large pinniped marine mammal with discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. It is the only extant species in the family Odobeni ...

es. In seals, the mites can be both prevalent (almost every single seal has them) and abundant (more than 1000 mites per seal). Although clinical observations and gross examination indicate that O. attenuata parasitization alone is not serious, some erosion and inflammation of the nasal turbinates and nasopharynx in seals has been observed in

histological section Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visi ...

s. If concomitant parasitization with ''O. attenuata'' and ''O. diminuta'' occurs, alveolar emphysema and more serious ailments can threaten the life of the mammal.

Morphology

Mature mites are shown to be elongated in the posterior part of body to form a club-shape with the rounded posterior extremity. Ten to twelve transverse rows of 8 to 12 sharp denticules and a few rows of minute spines are present on the ventral surface of the capitulum and the posterior surface of coxa III, respectively.

Transmission

The usual mode of host-to-host transmission by ''Orthohalarachne'' is thought to be accomplished by active

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e that crawl or are

sneeze A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth a ...

d from one animal to another. Both males and females are relatively non-motile and have well-developed claws from maintaining their position in the nares.

Prevalence and pathology

There is almost 100% prevalence of infestation of the nasal mite in the

northern fur seal The northern fur seal (''Callorhinus ursinus'') is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the ...

(''Callorhinus ursinus'') on the

Pribilof Islands The Pribilof Islands (formerly the Northern Fur Seal Islands; , ) are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of Unalaska and 200 miles (320 km) southwest of Cape Newenham. The ...

. Mucosal erosion was observed in the

nasal turbinates In anatomy, a nasal concha (; : conchae; ; Latin for 'shell'), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various other animals. The conc ...

as well as the

nasopharynx The pharynx (: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates, though its ...

. Based on clinical observation, the effects of the mite are of minor impairment, however, heavy infection have been shown to lead to more serious problems, such as impairment of respiration, lesions in the lungs and secondary alveolar emphysema.

Human incidences

The first known human incidence of transmission from walrus to human happened at

SeaWorld SeaWorld is an American theme park chain with headquarters in Orlando, Florida. It is a proprietor of marine mammal parks, oceanariums, animal theme parks, and rehabilitation centers owned by United Parks & Resorts. The parks host shows st ...

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. A 35-year-old Caucasian man recalled seeing the walruses spitting and snorting, and later feeling irritation in his eye. Three days after his visit to SeaWorld, the mite specimen was discovered and recovered from the lower part of his ocular iris. Pathological changes in the affected areas by the mites were a marked abrasion of the mucosa and destruction and necrosis of the deeply placed tissues by the action of the legs, palps and chelicerae of the mites.

References

{{Taxonbar, from=Q7104782 Mesostigmata Monotypic arachnid genera Parasitic arthropods of mammals