The Penetration of the host tissue by the harvest mite, Trombicula Autumnalis shaw

Abstract

1. The introduction refers to the fragmentary state of our knowledge on Trombiculid mites and indicates that most attention has been devoted to the taxonomy and bionomics of the group. The life cycle and general method of feeding are briefly outlined and reference is made to previous work directly concerned with the present treatise.2. The morphology of the organs related to the phenomenon of piercing and sucking in the larva of Trombicula autumnalis is described.3. The physical factors of the skin influence the choice of habitat upon the host.4. The food consists of tissue fluid and disintegrated cells of the malpighian layer partially liquefied by the action of injected saliva, a condition typical of extra-intestinal digestion.5. The mechanism of the initial piercing of the skin, which is done by the cheliceral claws, is described.6. A tubular tissue canal is gradually formed in the skin of the host and around its insoluble wall are deposited superimposed layers of keratinized protective tissue.7. The mechanism of suction is described and the factors which play a part are considered. The problem of the tissue canal serving as a duct for both the ejection of saliva and the suction of food is explained by the alternation of the two processes. The inter-relationship, between the intermittent injections of saliva, the formation of the tissue canal and the deposition of protective tissue, is elucidated.

Electron Microscopic Observations of Orientia tsutsugamushi in Salivary Gland Cells of Naturally Infected Leptotrombidium pallidum Larvae during Feeding

“…In fed larvae, however, secretory granules were found clustering in the apical cytoplasm at 12 and 24 hr, and many O. tsutsugamushi were distributed in the basal region of the cell. The apical clustering is in accordance with the observation that larval mites start secreting saliva immediately after biting to digest host epidermal tissues, and continue secretion to form stylostomes or feeding tubes (1,(4)(5)(6). It seems that O. tsutsugamushi were pushed backward to the basal region due to the apical clustering of secretory granules.…”

“…Since O. tsutsugamushi is an obligate intracellular parasite (8,21), it will be vulnerable outside host cells. It is possible the host cell membrane is protecting the O. tsutsugamushi from noxious biological substances including mite saliva, which contains lytic enzymes and anticoagulants (4,5). With mouse L-cell cultures, two different processes of removing the host cell membrane have been reported (21, 29); one is the removal from outside host cells, and the other is removal in the cytoplasm of newly infected cells.…”

Trombiculiasis in domestic goats and humans in the state of Maranhão, Brazil

“…The larvae feed on their hosts by using chelicerae to inject lytic enzymes into the upper layers of the skin and, subsequently, to ingest digested cells. After feeding and detachment, the mites molt to free-living nymphs and then to adults (JONES, 1950;SHATROV, 2000). Infestation by chigger mites causes severe itching as well as transmission of diseases like scrub typhus, which is caused by the intracellular parasite Orientia tsutsugamushi in southeastern Asia and the southwestern Pacific region (TAKAHASHI et al, 2004;CHOI et al, 2007).…”

Trombiculiasis in the Florida Black Bear

“…Eggs of trombiculid mites are usually laid singly and, following emergence, the larvae move on to ground vegetation to await passage of a suitable host. The larvae tend to prefer attachment sites where the skin is thin (Jones, 1950). Thinner skin and proximity to the ground and low vegetation probably explain the primarily ventral distribution of chiggers on bears.…”

“…The mite injects saliva into the wound, causing host tissue necrosis, and feeds on the resulting tissue fluid. This process eventually results in the formation of a stylostome or feeding tube which often penetrates to the dermis (Jones, 1950). Eutrombicula splendens larvae are light orange to red in color and range in length from 150 to 600 m depending on the degree of engorgement.…”