Laboratory Identification of Medically- Important Arthropod Ectoparasites Blaine A. Mathison, BS, M(ASCP) Institute for Clinical and Experimental Pathology ARUP Laboratories Salt Lake City, UT California Association for Medical Laboratory Technology Sacramento CE Sessions Sacramento, CA April 7, 2019 How are Arthropods Medically Important? • VECTORS OF DISEASE – Malaria, lymphatic filariasis, Chagas disease, Lyme disease, West Nile Virus, Dengue, Plague, African sleeping sickness, trench fever, relapsing fevers, chikungunya, yellow fever, many many others • INTERMEDIATE HOSTS FOR PARASITES – Paragonimiasis, hymenolepiasis, dipylidiasis, dracunculiasis • ECTOPARASITES – Scabies, myiasis, demodicosis, pentastomiasis • VENOMOUS and STINGING ARTHROPODS – Spiders, scorpions, bees, ants, wasps, stinging caterpillars, blister beetles 2 What is an Arthropod? • Invertebrates with a hardened exoskeleton and jointed appendages. • Development variable, may be gradual or have complete metamorphosis (e.g. egg, larva, pupa, adult) • One of the most successful groups of animals, over a million species yet relatively few of medical or public health concern • Major Groups: – Insects, arachnids, crustaceans, centipedes, millipedes 3 Arthropod Body Plan https://bugguide.net/node/view/37485/bgimage Major Groups of Arthropods Major Body Plan Legs Wings Antennae Develop- Group ment Insects 3 regions: 6 as adults; 1-2 functional 1 pair Incomplete or head, thorax, larvae often pairs or absent complete abdomen legless metamorphosis Arachnids Usually 2: 8 as adults Always absent Always absent Gradual cephalothorax (tick, mite and abdomen larvae have 6) Crustaceans Highly variable, Highly variable, Always absent 2 pairs Variable, often 2 usually at least incomplete 10 metamorphosis Centipedes 2: head and Many, 1 per Always absent 1 pair Gradual body body segment Millipedes 2: head and Many, 2 per Always absent 1 pair Gradual body body segment 5 Collection and Submission of Arthropods to the Diagnostic Laboratory • Arthropods (or parts thereof) should be transported to the lab in a liquid preservative (10% formalin or 70-95% lab grade alcohol). – Prevents desiccation that may result in the altering of morphologic features – Kills pathogens that might be associated with vectors (e.g. ticks) • Skin scrapings for scabies can be placed in vials of alcohol if the specimen is to be transported to an off-site reference laboratory. Ticks • Obligate parasitic mites. • Two medically-important families: Ixodidae (hard ticks) and Argasidae (soft ticks). • Gradual development consisting of (usually) multi-host life cycles, including a larva, one to several nymphs, and adult. • Vectors of parasitic, bacterial, viral diseases • Can cause paralysis and have been implicated in ‘meat allergy’ (alpha-gal syndrome) • Diagnosis is important regarding the genus of tick and the possible vectors in a given geographic area. – Also whether or not a tick is engorged and degree of engorgement is reported. 7 What makes a tick a tick? Haller’s organ Toothed hypostome Ixodid (hard) vs. Argasid (soft) Ticks 9 Ixodid (Hard Tick) Anatomy 10 Ticks: Long vs. Short Mouthparts Life Cycle of a Hard Tick Ixodes spp. – Medically Important US species • Ixodes scapularis-complex -commonly called black-legged tick. -vector of Borrelia burgdorferi and B. mayonii (Lyme disease); Babesia microti (babesiosis); Ehrlichia muris eausclairensis (EML); Anaplasma phagocytophilum (HGA), Powassan virus -distributed in the Northeast, upper Mid-west, and adjacent Canada. • Ixodes pacificus -commonly called western black-legged tick -vector of Borrelia burgdorferi (Lyme disease); Babesia duncani (babesiosis); hypersensitivity reactions from bites. -distributed coastally from BC to Baja California; also AZ. Ixodes spp. - Morphology • Mouthparts long, in relation to basis capituli. • Inornate dorsal shield. • No festoons or eyes. • Inverted U-shaped anal groove (may be difficult to see in engorged specimens). Ixodes spp. Ixodes spp. Ixodes spp. Ixodes – Degree of Engorgement Amblyomma spp. – Medically important US species • Amblyomma americanum -commonly called Lone Star tick -vector of Francisella tularensis; Ehrlichia chaffeensis (HME); E. ewingii (HE). -distributed central TX north and east to NY; Mexico to South America -implicated in alpha-gal syndrome • Amblyomma maculatum -commonly called Gulf Coast tick -vector of Rickettsia parkeri (tidewater spotted fever). -distributed Gulf Coast states; AZ (range expanding). Ambylomma species - Morphology • Mouthparts long in relation to basis capituli. • Festoons and eyes present. • Ornate dorsal shield in adults (nymphs and larvae usually inornate). • Round body that often keeps a round shape when engorged Amblyomma americanum Female (left); male (right) Amblyomma americanum Amblyomma americanum - nymph Amblyomma maculatum Amblyomma vs. Ixodes - Engorged Amblyomma Ixodes Dermacentor – medically important U.S. species • Dermacentor variabilis -commonly known as American dog tick -primary vector of (Rickettsia rickettsii) RMSF in the eastern U.S.; Francisella tularensis; tick paralysis -distributed throughout much of the U.S. except in parts of the Rocky Mountains; Central Canada • Dermacentor andersoni -commonly known as Rocky Mountain wood tick. -primary vector of RMSF in Rocky Mountain region; Francisella tularensis; Colorado tick fever virus; tick paralysis. -distributed western Plains and Black Hills of SD, Rocky Mountains west to Cascade and Sierra Nevada Mountains (not coastal in the West); into AZ and NM; also adjacent Canada. Dermacentor spp. - Morphology • Ornate dorsal shield in adults; nymphs and larvae may be inornate. • Mouthparts short in relation to basis capituli (longer in immature stages). • Eyes on dorsal shield. • Festoons present. • Species-level identification often requires examination of spiracular plate. Dermacentor spp. female male Dermacentor spp. Dermacentor spp. Dermacentor spp. – spiracular plates D. andersoni D. variabilis Rhipicephalus sanguineus • Commonly known as the ‘brown dog tick’. • Not an efficient vector of disease but there are reports/outbreaks of RMSF (Rickettsia rickettsii). • Laterally produced, angulate basis capituli. • Mouthparts short in relation to basis capituli. • Eyes and festoons present. • Deeply-cleft front coxae. Rhipicephalus sanguineus Rhipicephalus sanguineus Hyalomma spp. • Endemic to the Old World (Africa, Asia, southern Europe) • Vectors of Crimean- Congo Hemorrhagic Fever Virus Hyalomma truncatum (USA ex: Ethiopia) Soft Ticks • Ornithodoros spp. in North America are vectors of tick-borne relapsing fever (TBRF) spirochetes; the species name of the Borrelia is the same as the species name of the tick! • Otobius megnini (spinose ear tick) – zoonotic tick causing ear infections • No dorsal shield. • Mouthparts hidden from above. • Nymphs and adults do not reside on the host, but rather feed for short periods of time before returning to sheltered location. Complex life cycles with varying numbers of nymphs and feeding cycles. Soft Ticks Ornithodoros spp. • Tick-borne relapsing fever (TBRF) spirochetes, Borrelia sp. Otobius megnini • Commonly known as the ‘spinose ear tick’ of cattle • Only parasitic in the larval and nymphal stages • Colonizes host’s ear, causing severe pain and possibly rupture of the tympanum resulting in hearing problems Scabies caused by Sarcoptes scabiei • Caused by the scabies or itch mite, Sarcoptes scabiei. Worldwide in distribution. • Cutaneous parasites that reside in burrows under the skin but above the stratum corneum. All stages reside on the human host. • Life cycle stages including eggs, 6-legged larval, and 8-legged nymphal and adult stages. • Causes sever itching, especially upon subsequent infections. Crusted form of disease known as ‘Norwegian scabies’ seen primarily in immunocompromised patients and patients in institutionalized settings. • Highly-contagious, person-to-person contact, or sometimes via fomites. • Diagnosis is made by finding mites (and their eggs and feces) in skin scrapings and biopsy specimens. Collecting and Preparing Skin Scrapings for Scabies • Mites are more-likely to be found in skin scrapings collected at the end of burrows in nonexcoriated and noninflamed areas. Scrapings should be performed using a sterile scalpel or glass microscopy slide with a drop of mineral or immersion oil applied to the surface (the oil helps the mites adhere to the blade or slide and facilitates transfer to a slide for microscopic examination). The skin should be scraped vigorously at approximately a 90ºangle (vigorous meaning there should be some RBCs on the slide but no frank bleeding); the patient should be sampled at a minimum of six different sites. The scrapings can be pooled on a single slide or examined on individual slides; place a coverslip over the slide prior to examination. The scrapings should be screened at 40x or 100x magnification and then evaluated at 200x or 400x magnification for confirmation. • Note: Live Sarcoptes mites are highly contagious and gloves and other PPE should be used at all times during collection and examination. Life Cycle of Sarcoptes scabiei Crusted or “Norwegian” Scabies Sarcoptes scabiei Sarcoptes scabiei Sarcoptes scabiei feces (=scybala) Demodex spp. • Demodicosis caused by follicle mites in the genus Demodex; D. folliculorum (hair follicles) and D. brevis (pilosebaceous glands) most-commonly occur on the forehead, face, nose and eyelids. • Are not believed to cause disease in humans, but have been associates with skin conditions