Trixacarus caviae (Sarcoptic Mange) in Guinea Pigs

Bottom line

Trixacarus caviae, the guinea pig's own burrowing sarcoptic mite, is the most dramatic dermatologic emergency in the species: the intense, painful pruritus can be so severe that scratching or handling looks like a true seizure [1]. Make it your first differential for any severely pruritic cavy, diagnose with deep skin scrapings, but treat on clinical suspicion when scrapings are negative, because delay is dangerous and the pruritus-plus-pain picture is diagnostic enough on its own. Prognosis is excellent with prompt macrocyclic-lactone therapy — ivermectin 0.4 mg/kg SC every 10-14 days for four treatments, or a single topical dose of selamectin 15 mg/kg [1] — and in the only head-to-head randomized trial both regimens cleared mites (by day 40 and day 30 respectively) with pruritus resolving in every animal by day 10 [2]. Treat every in-contact guinea pig and correct the husbandry stressors that unmask disease, or it recurs.

Condition facts

Organism. Trixacarus caviae is a burrowing sarcoptid mite (family Sarcoptidae) — the guinea pig's species-specific sarcoptic-mange mite — that tunnels within the stratum corneum, creating epidermal burrows, and drives a cell-mediated hypersensitivity response, which is why the clinical picture is so out of proportion to the actual mite burden. The entire life cycle plays out in the epidermis, so infestation is perpetuated and amplified on a single host rather than requiring reinfection. Contrast it with the two far milder cavy ectoparasites you will otherwise meet: Chirodiscoides caviae, a non-burrowing fur mite that lives on the hair shaft and is frequently subclinical, and the chewing lice (Gliricola porcelli, Gyropus ovalis), which are surface dwellers that typically cause less severe, species-specific signs [1]. Only T. caviae routinely produces the seizure-on-handling emergency.

Signalment and triggers. Any age or sex is susceptible, and T. caviae infestation should be your first differential for any pruritic guinea pig [3]. Florid disease frequently erupts when a previously subclinical infestation is unmasked by stress, pregnancy, overcrowding, concurrent illness, or immunosuppression [1]. A stable cavy that suddenly turns frantically pruritic after a stressor is the classic history.

Transmission. Spread is by direct contact, and the mite completes its entire life cycle on the host. Subclinically infested carriers move it silently between animals, which is exactly why the subclinically affected in-contacts must also be treated [1].

Clinical signs and presentation

The lead sign is intense, relentless pruritus. Expect widespread alopecia, thick crusting and hyperkeratosis, and marked self-trauma — the itch is so severe it drives self-inflicted excoriation, scales, and crusts concentrated over the neck, shoulders, dorsum, back, trunk, and inner thighs before generalizing [1][4]. Chronic cases develop lichenification and frequent secondary bacterial or fungal infection, become thin and lethargic, and the disease can be fatal if left untreated [5].

Progressive weight loss and anorexia accompany severe or chronic cases, driven by the metabolic cost of the dermatitis, the pain, and the reluctance to feed in a debilitated animal. Presentation spans a spectrum: from a subclinical carrier with no visible lesions, through focal alopecia and scale over the dorsum, to the fulminant, generalized, seizuring patient.

The hallmark that separates T. caviae from every other cavy skin disease is neurologic. The scratching can be so intense that it appears the animal is having a seizure [1], and genuine convulsions resembling seizures occur secondary to the intense pruritus and debilitation [3]. Handling, restraint, or palpating an affected animal can trigger an episode. Because the convulsion can dominate the presentation, T. caviae is repeatedly misdiagnosed as primary epilepsy or metabolic/neurologic disease — always part the coat and scrape a pruritic cavy before committing to a neurologic workup.

Diagnosis

Confirm with deep skin scrapings taken from multiple sites and examined microscopically for mites and eggs [3]. The practical caveat is decisive: scrapings are frequently negative even in florid disease, because signs are driven by hypersensitivity rather than high mite numbers, so a negative scrape does not rule out the disease. Treat on suspicion. A profoundly pruritic, crusting guinea pig — especially one with seizure-like episodes on handling — warrants empiric acaricidal therapy, and a rapid clinical response is itself confirmatory. Histopathology showing chronic hyperplastic dermatitis with intracorneal mites can resolve ambiguous cases [4]. Trichography and acetate-tape preparations help identify the non-burrowing Chirodiscoides fur mite and lice, which sit on the hair and skin surface rather than burrowing. Keep the differential list open: the pruritic, crusting cavy can also have dermatophytosis (commonly Trichophyton mentagrophytes), cheyletiellosis, or pediculosis, and mixed infestations with secondary bacterial pyoderma are common — running a dermatophyte culture or PCR and coat brushings in parallel with the scrape avoids anchoring on a single diagnosis.

Treatment

First-line therapy is a macrocyclic lactone, and the two best-evidenced regimens are:

• Ivermectin 0.4 mg/kg (400 ug/kg) SC, repeated every 10-14 days for four treatments [1]. In the only head-to-head randomized trial, ivermectin at 400 ug/kg SC every 10 days for four injections rendered guinea pigs mite-free by day 40, with pruritus resolving in all animals by day 10 and no adverse reactions or recurrence [2]. A commonly cited alternative from dermatology proceedings is 0.2-0.4 mg/kg every two weeks for two to three treatments; use the subcutaneous route, because oral ivermectin is unreliably absorbed in guinea pigs [3].
• Selamectin 15 mg/kg topically as a single spot-on application [1]. In the same randomized trial, one topical dose of selamectin 15 mg/kg cleared mites by day 30 — faster than ivermectin, with equal efficacy and the convenience of a single, non-injectable treatment [2].

An isoxazoline is an emerging option: a single oral dose of afoxolaner 2.5 mg/kg (NexGard) produced complete clinical remission with full hair regrowth by four weeks in a documented pet-guinea-pig case [4]. Reserve it as an off-label alternative pending broader data. Note that essentially every acaricide used in cavies is extralabel — flag this and obtain informed consent. Whatever agent you choose, complete the full course; stopping at apparent clinical cure invites relapse from surviving mites and eggs.

Monitor at each treatment interval. Expect pruritus to fall away within the first week or so and crusts to shed over the following weeks; resolution of pruritus and lesions is the practical endpoint, and repeat scrapings can document mite clearance. If a patient fails to improve on an appropriate regimen, reassess before escalating the dose: re-weigh and re-calculate the dose, reconsider the diagnosis (dermatophytosis, mixed infestation, secondary pyoderma), and confirm that every in-contact animal was actually treated on schedule — an untreated cage-mate is the most common reason for apparent treatment failure.

Managing pruritus and seizures

The seizure-like episodes are a downstream consequence of the intense pruritus and debilitation, not primary epilepsy [3], so the definitive anticonvulsant is the acaricide — episodes abate as the mange resolves. In the interim, minimize handling, which provokes the attacks, and control the itch directly: antihistamines and NSAIDs are recommended for the severe pruritus [1], and analgesia plus a quiet, low-stress environment reduces self-trauma. Provide supportive care to the thin, debilitated patient — fluids, assisted feeding, and vitamin C supplementation, since hypovitaminosis C is endemic in cavies and compounds debilitation — and treat any secondary pyoderma. Reserve sedation for animals actively convulsing on handling.

Environment and in-contact animals

Treat every in-contact guinea pig, not just the symptomatic one. Subclinical carriers are common and will re-seed the household or colony if left untreated [5]; the professional guidance is explicit that subclinically affected animals should also be treated [1]. Concurrently correct the husbandry factors that unmask disease: relieve overcrowding, reduce stress, and address concurrent illness and nutritional deficiency. While the animal is under your care, screen for the other common husbandry-driven cavy conditions — pododermatitis and dental malocclusion — that share the same neglect-and-stress substrate. Sanitize or replace bedding and cage furniture during the treatment window. Because the mite is largely host-dependent, treating all animals through the full course plus thorough environmental cleaning usually breaks the cycle.

Prognosis and prevention

Prognosis is excellent with prompt, complete treatment: pruritus typically resolves within about 10 days and mites clear within 30-40 days on standard protocols [2], followed by full hair regrowth [4]. Untreated, the disease is progressive and can be fatal [5]. Prevent recurrence by quarantining and treating new arrivals, minimizing stress and overcrowding, maintaining vitamin C-adequate nutrition, and re-treating the whole group if any animal relapses. Counsel owners that T. caviae has zoonotic potential [1] and can produce transient, itchy, papulovesicular lesions in people handling infested animals [4]; human lesions are self-limiting once the guinea pig is treated.

Frequently Asked Questions