Biomedical Engineering Reference
In-Depth Information
anaplasmosis) [78]. Tick-borne viruses include: Crimean-Congo hemorrhagic
fever, tick-borne encephalitis, Powassan encephalitis, deer tick virus enceph-
alitis, Omsk hemorrhagic fever, Kyasanur forest disease (Alkhurma virus),
Langat virus, and Colorado tick fever.
In this topic ticks are not considered infectious organisms. Basically, ticks
leave the host after collecting their blood meal. Because ticks are temporary
guests and do not actually live in humans, they will not be discussed further
in this chapter.
Chelicerata
Arachnida
Acari (includes mites and ticks)
Sarcoptiformes
Sarcoptidae
*Sarcoptes
Trombidiformes
Demodicidae
*Demodex
Cheyletidae
*Cheyletiella
There are three infectious genera of mites: Demodex, Cheyletiella, and
Sarcoptes. Genera Demodex and Cheyletiella belong to the Acari subclass
Class Trombidiformes. Genus Sarcoptes belongs to the Acari subclass, Class
Sarcoptiformes. Both of these classes contain extremely small mites that can
live on humans without being identified with the naked eye.
Genus Sarcoptes contains one infectious organism for humans; Sarcoptes
scabiei, the cause of scabies in humans and sarcoptic mange in animals. This
small mite burrows into the superficial skin. Burrows are visible to astute
searchers. Once in the skin, the mites produce an allergic reaction, producing
itching. The name scabies comes from the Latin “scabere,” to scratch.
Scabies is an exceedingly common, global disease, with about 300 million
new cases occurring annually. The organism infects humans through contact
with other infected humans and animals. Spread of the scabietic rash is
encouraged by scratching, which results in self-inoculation from one area of
skin to another. The organism prefers intertriginous sites (skin creases such
as groin, under breast, between fingers).
Scabies infestation can be particularly severe for immune-compromised
patients, particularly those with AIDS. In this circumstance, the infection can
become generalized, extending over the entire surface of the body, excluding
only the face.
Demodex is a tiny mite that lives in facial skin. Demodex folliculorum
favors the hair follicles. Demodex brevis favors the sebaceous glands. Both
mites can be found in the majority of humans, and infections seldom produce
clinical disease. It is common for pathologists to encounter these mites, on
