Camelidae and Cervidae Foot Mites (Chorioptes) Study Guide

Overview and Clinical Importance

Chorioptic mange (also called foot mange, leg mange, or itchy heel) is a common ectoparasitic skin disease caused by non-burrowing surface mites of the genus Chorioptes. These mites are of significant veterinary importance in camelids (llamas, alpacas, guanacos, vicunas) and cervids (deer, elk, reindeer, moose). Unlike Sarcoptes mites that burrow into the epidermis, Chorioptes mites live on the skin surface and feed on epidermal debris, causing a generally milder but persistent form of mange that can be challenging to eradicate.

In South American camelids (SACs), chorioptic mange is increasingly recognized as the most common ectoparasite infestation, particularly affecting the interdigital spaces and lower limbs. In cervids, Chorioptes texanus specifically infests the ear canals of reindeer, while Chorioptes bovis has been documented in elk and moose populations.

Etiology and Taxonomy

Classification

Chorioptes mites belong to the following taxonomic classification:

Species of Veterinary Importance

Two primary species are recognized as valid based on morphological and molecular genetic studies:

• Chorioptes bovis - The most widespread species; infests cattle, horses, sheep, goats, camelids (llamas, alpacas), and rabbits worldwide
• Chorioptes texanus - Primarily infests ear canals of reindeer in the Canadian Arctic; also reported in cattle, goats, and elk

Additional species (C. panda, C. sweatmani, C. crewei, C. mydaus) have been described but their validity remains debated. C. sweatmani was recently confirmed as a distinct species causing ear inflammation in moose (Alces alces) in Scandinavia.

Morphology and Identification

Gross Morphology

Chorioptes mites are small (200-300 micrometers in length), surface-dwelling mites. Adult mites can just be seen with the naked eye on a microscope slide but are not visible on the animal without magnification.

Key Morphological Features

• Body shape: Circular, dorsoventrally flattened with striate cuticle
• Legs: Four pairs of moderately long, robust legs that extend past the body margin
• Pedicels: SHORT and UNJOINTED pretarsi with terminal suckers - this is the KEY diagnostic feature
• Sexual dimorphism: Males are approximately one-fourth smaller than females
• Male features: Prominent abdominal (opisthosomal) lobes with 5 setae; fourth pair of legs very short
• Female features: Transverse ovipore slit; third and fourth leg pairs more slender; third pair ends in whip-like setae

Mange Mite Comparison Table

Life Cycle

The entire life cycle of Chorioptes occurs ON the host animal. The cycle is completed in approximately 3 weeks (21-26 days), depending on temperature and humidity.

Life Cycle Stages

Environmental Survival

Chorioptes mites can survive OFF the host for a clinically significant period:

• Off-host survival: Adults can survive several days to several weeks (up to 60+ days in optimal conditions)
• Environmental factors: High humidity and low temperatures prolong survival
• Fomite transmission: Possible via contaminated bedding, grooming equipment, fences, and shared housing

Clinical Signs

Camelids (Llamas and Alpacas)

Predilection Sites

• Primary: Interdigital spaces (between the toes) - most common and characteristic location
• Secondary: Lower legs, axillary region (armpits), inguinal region (groin), perineal area, ventral tail, ventral abdomen
• Less common: Ears, face, or generalized body involvement in severe cases

Clinical Presentation

Early/Acute Signs:

• Variable pruritus (often mild to moderate; some animals show hypersensitivity reaction)
• Erythema and papules in affected areas
• Foot lesions often partially hidden by fleece; may not be obvious from a distance
• Patchy hair/fiber loss around feet and lower legs

Chronic Signs:

• Alopecia with crusting and scaling
• Lichenification and thickening of skin (hyperkeratosis)
• Splaying of toes due to tissue thickening in longstanding cases
• Secondary bacterial infections
• Foot stamping, scratching with hind feet, restlessness

Cervids (Deer, Elk, Reindeer, Moose)

Reindeer (Rangifer tarandus)

• Chorioptes texanus primarily infests the ear canals
• Head shaking, ear scratching, droopy ears
• Dark waxy discharge in ear canals
• Lesions may extend to skin of head and neck

Moose (Alces alces)

• A distinct Chorioptes species (C. sweatmani) causes inflammation of the outer ear canal
• High prevalence (up to 81%) documented in Scandinavian populations
• Dermal inflammatory infiltrate with plasma cells
• May also cause alopecic lesions on body skin

Elk/Wapiti (Cervus elaphus)

• Chorioptes texanus has been documented
• Clinical signs similar to other species: foot and lower leg lesions
• Must differentiate from Psoroptic mange (more commonly documented in elk populations)

Seasonality

Chorioptic mange shows marked seasonal variation:

• Peak incidence: Autumn/fall, winter, and early spring
• Reduced severity: Late spring and summer (apparent spontaneous improvement)
• Contributing factors: Housing/confinement during winter months increases transmission; mite populations decline on pasture in warm months

Diagnosis

Skin Scraping Technique

Definitive diagnosis requires microscopic identification of mites in skin scrapings. The technique is critical for success:

Sampling Procedure

• Select site: Scrape from the active margins of lesions (edges where healthy skin meets affected skin) - mites congregate at the periphery
• Apply mineral oil: Place drop of mineral oil on scalpel blade and skin to help mites adhere
• Scrape superficially: Unlike Sarcoptes, Chorioptes is a SURFACE mite - deep scraping until bleeding is NOT required
• Multiple sites: Sample from several areas; recommended sites include dorsal interdigital spaces and axillae
• Consider fly spray: Chorioptes mites are fast movers; applying fly spray before scraping may increase detection

Microscopic Examination

• Initial scan: Low power (4x or 10x objective) to locate mites
• Confirmation: Higher power (40x) to identify key morphological features
• Mounting media: Mineral oil, glycerine, or commercial mounting media (Hoyer's medium for permanent mounts)
• Note: Avoid potassium hydroxide (KOH) as it can dissolve mite pellets and fecal material

Differential Diagnoses

Treatment

Important Note: Chorioptic mange is notoriously difficult to eradicate from affected herds. Treatment failures are common due to: (1) surface-feeding behavior limiting systemic drug efficacy, (2) prolonged environmental survival, (3) lack of lanolin in camelid fiber limiting topical product spread, and (4) inadequate treatment protocols.

Treatment Principles

• Treat ALL animals in the group/herd - not just clinically affected individuals
• Multiple treatments required - single treatments are rarely effective
• Combine systemic AND topical treatments for best results
• Environmental decontamination is essential - remove bedding, clean housing, leave empty if possible for 3+ weeks
• Address hyperkeratotic crusts - topical products cannot penetrate thick crusts; use keratolytics first

Treatment Options Table

Supportive Care

• Remove crusts: Use chlorhexidine 3% shampoo followed by salicylic acid-containing keratolytics
• Treat secondary infections: Systemic antibiotics if bacterial pyoderma present
• Udder salve/emollients: After acaricide treatment to promote skin healing and fiber regrowth
• Nutritional support: Address any concurrent undernutrition or parasitism

Prevention and Control

• Quarantine and examine new animals: Inspect feet, interdigital spaces, and perform skin scrapings before introduction to herd
• Environmental management: Clean bedding regularly; disinfect housing; leave stalls empty for 3+ weeks between infested animals
• Segregate grooming equipment: Clean and disinfect brushes, halters, and other fomites
• Monitor herd regularly: Examine feet and interdigital spaces during routine husbandry, especially in winter
• Consider seasonal treatment: Prophylactic treatment before winter housing may reduce clinical cases

Memory Aids

"CHORIOPTES" Mnemonic:

C = Compact (short, unjointed) pedicels

H = Herbivore hosts (camelids, cervids, cattle, horses)

O = On surface (non-burrowing)

R = Requires topical treatment (systemic alone fails)

I = Interdigital predilection in camelids

O = Off-host survival (up to 60 days)

P = Persistent but not penetrating

T = Treats ALL contacts (herd-wide)

E = Environmental decontamination essential

S = Skin debris feeder (not blood)

Exam Focus - Differentiating Mange Mites: "SIP" = Sarcoptes Intense Pruritus (burrows, zoonotic), "PEL" = Psoroptes Ears and Long pedicels, "CFL" = Chorioptes Feet and Lower legs (short pedicels, not zoonotic)