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Mites
Published in Jerome Goddard, Public Health Entomology, 2022
Larval stage mites in the family Trombiculidae, sometimes called chiggers (Figure 18.1a), harvest mites, or red bugs, are medically important pests around the world, primarily because they cause dermatitis and may transmit the agent of scrub typhus. Adult chiggers are oval shaped (approximately 1 mm long) with a bright red, velvety appearance, but it is only the larval stage that attacks vertebrate hosts. Chigger larvae are very tiny (0.2 mm long), round mites with numerous setae (Figure 18.2). The mites may be red, yellow, or orange in color and have a single dorsal plate (scutum) bearing two sensillae and four to six setae. Identification to the species level is extremely difficult and expert technical help is required (see Chapter 8).
Mites
Published in Gail Miriam Moraru, Jerome Goddard, The Goddard Guide to Arthropods of Medical Importance, Seventh Edition, 2019
Gail Miriam Moraru, Jerome Goddard
Larvae of mites in the family Trombiculidae, sometimes called chiggers, harvest mites, or red bugs (Figure 24.6), are medically important pests around the world (see box). Over 3000 species of chigger mites occur in the world, but only about 20 species cause dermatitis or transmit diseases such as the agent of scrub typhus. Scrub typhus, caused by Orientia tsutsugamushi, is a vector-borne zoonosis traditionally thought to only occur in the “tsutsugamushi triangle” from Pakistan to far eastern Russia to northern Australia. The disease threatens over a billion people and there are an estimated 1 million cases per year.25 Recently, scrub typhus has been detected in the Middle East and South America, leading public health officials to worry about an ever-widening impact.26,27 In addition, in northern India there is an encephalitis resulting from scrub typhus infection which affects hundreds of children every year.28 Infestation with trombiculid larvae is called trombiculosis or sometimes trombidiosis. Larval chiggers crawl up on blades of grass or leaves and subsequently get on passing vertebrate hosts. Although humans are not ideal hosts,29,30 chiggers may crawl to and attach where clothing fits snugly or where flesh is tender, such as ankles, groin, or waistline. Attachment seems to be especially common in the popliteal fossae6 (Figure 24.7). Chiggers then attach to the skin with their mouthparts, inject saliva into the wound (which dissolves tissue), and then suck up this semidigested material. They do not burrow in human skin in the strictest sense; only the chelicerae penetrate the skin of the host. Following penetration, a straw-like feeding tube, called a stylostome, is formed through which the larva sucks digested host tissue and lymph. Chiggers do not take a bloodmeal. Feeding generally lasts 2–4 days, and salivary proteins may lead to intense itching in the host.29,30 Chiggers attached to the skin may easily be removed by even the most casual scratching,31 but itching may persist for a week or two after the offending specimen is gone, primarily as a result of material injected at the site of the bite. Most U.S. pest chiggers produce itching within 3–6 hours, and the rash consists of macules and wheals. At approximately 10–16 hours, red, dome-shaped papules appear, and itching increases in severity over the next 20–30 hours (Figure 24.8).6 Not all medically important chiggers produce the familiar itch reactions; those serving as vectors of scrub typhus (central, eastern, and southeastern Asia) are not associated with itching or skin reactions.32
Scrub typhus and antibiotic-resistant Orientia tsutsugamushi
Published in Expert Review of Anti-infective Therapy, 2021
Chin-Te Lu, Lih-Shinn Wang, Po-Ren Hsueh
Adults pass O. tsutsugamushi to their offspring through transovarial transmission. Larva mites are the only parasite stage, while all other active stages are free-living; humans play no role in the Orientia mite life cycle and are dead-end hosts [9]. The occurrence of scrub typhus is frequently related to temperature, and sometimes to rainfall, with high transmission peaks before and after the rainy season in many regions of Southeast and East Asia; a regular year-round transmission is common in some tropical and subtropical regions [10–14]. Chiggers are abundant in locales with high relative humidity (60–85%), moderate temperature (20–30°C), low incidence of sunlight, and a dense substrate-vegetative canopy [11,15,16].
Diagnosis & management of alpha-gal syndrome: lessons from 2,500 patients
Published in Expert Review of Clinical Immunology, 2020
In many settings, the critical point is for the astute clinician to consider AGS as a possible cause of the patient’s symptoms and Figure 1 is included as a diagnostic algorithm. However, it is important to realize that some patients with AGS may not present with these characteristics. Despite point i) above, a significant number of pediatric cases of AGS has been reported [15] and children represent approximately 12% of subjects in one published cohort [16]. Although published data suggest that the condition in children has similar features to those of adult patients, it is not unusual for children with AGS to report a specific association with limited number of foods, predominance of GI symptoms, and particular relevance of activity (e.g. sports practice). Moreover, a study of over 200 patients with AGS found that 16% reported subjective symptom onset in less than 2 hours after consuming mammalian meat [16]. History of a tick bite, larval tick bites (e.g. seed tick bites), or ‘chigger’ bites can be supportive of AGS as a diagnosis but the absence of such a history is not uncommon. Tick bites can be painless, and about half of the people who develop a tick-borne infection may not even remember being bitten by a tick. ‘Chiggers’ is a term often mentioned in the South that has become synonymous with ‘very itchy, small, red bites’ that can occur in isolation or in large numbers. We often inquire about ‘chigger’ bites with patients to gain a history of bug bites in general and less in direct questioning of their exposure to members of the Trombiculidae family of insects. Whether Trombiculidae bites can lead to the development of alpha-gal IgE is unclear but is a research question under our investigation.