Abstract

The African pygmy hedgehog (Atelerix albiventris) is a nocturnal insectivore, grouped in the order Eulipotyphla along with shrews and voles. African pygmy hedgehogs should be housed in well-ventilated enclosures and provided exercise wheels. Supplemental heat may be necessary to prevent pet hedgehogs from entering a torporous state. Diet consists of a high-protein, moderate-fat kibble as the base, along with additional supplemented food items like vegetables and live insects. Physical examination and diagnostic sample collection are challenging in awake hedgehogs due to an inclination to roll into a protective ball of keratinaceous spines. Chemical immobilization is necessary for a complete physical examination in hedgehogs. Common disorders include hemorrhagic vulvar discharge, neoplasia, parasitic dermatologic disease, neurologic disease and oral cavity disease.

Introduction

African pygmy hedgehogs (Atelerix albiventris) are popular pets due to their inquisitive, often convivial nature; however, because of their unique anatomy and behavior, hedgehogs can be challenging patients. The lack of prospective research in this species forces veterinarians to rely on anecdotal information, which could lead to difficulties with diagnostics and ineffective or even dangerous treatment strategies.

Natural History and Anatomy

The African pygmy or central African hedgehog (Atelerix albiventris) is a nocturnal insectivore originating from central and eastern Africa. Hedgehogs are family Erinaceidae and were previously classified in the now obsolete order Insectivora. They are now grouped in the order Eulipotyphla that includes other small mammals like shrews and moles. The two most familiar hedgehog species are the central African hedgehog (Atelerix albiventris) and the European hedgehog (Erinaceus europaeus).

African pygmy hedgehogs are very active invertebrate predators and travel long distances at night to search for food. They are territorial, solitary animals and can enter a state of torpor in the wild during harsh environmental conditions.

The mantle is the formidable covering of the crown (head) and dorsum consisting of thousands of keratinaceous spines. There are four major muscles that function to roll the hedgehog into an impenetrable ball of spikes¹: the caudodorsalis m. and the frontodorsalis m. start the action by rolling up the spines covering the rump and head, respectively. The panniculus carnosis m. then rolls up the dorsum of the hedgehog and the orbicularis m. cinches the mantle closed around the animal, like a purse string. The mantle should be moved dorsally when performing lateral radiographic views of the thorax so as to not interfere with the lung fields. The mantle spines are not barbed and have a basal bulb connecting the spine to the follicle that makes removal of healthy spines difficult. Teeth are brachydont, and the first maxillary incisor teeth have a considerable gap between them. The tail is short and spineless.

Sexing is easily accomplished by examining the anogenital distance. In females, the vulvar opening is located immediately cranial to the anus. In males, the preputial opening is located mid-abdomen, a great distance from the anus. Males have dramatic accessory sex glands (particularly the seminal vesicles) which often fill a large portion of the caudodorsal abdomen and can be mistaken for an abdominal mass when palpating dorsal to the urinary bladder. The testicles are mobile and sit in a para-anal recess rather than a scrotal sac. Females have a tightly curled, bicornuate uterus that has a “ram’s horns” appearance. The mesometrium is short and the ovaries are small and often hidden within adipose tissue.

Husbandry

Housing should be well-ventilated and cleaned regularly, as hedgehogs produce copious amounts of soft feces. A large, high-walled, smooth-sided plastic storage container is easy to move and sanitize. Because of their active nature and propensity for obesity in captivity, a solid surface exercise wheel should be provided and cleaned daily if frequently used, due to rapid buildup of feces. Hedgehogs quickly learn to drink from either standing water or bottles. Bedding used for hedgehog enclosures varies from aspen shavings to artificial fleece material. Recycled paper bedding is easily cleaned, produces minimal dust, and a thick layer provides hedgehogs with opportunities to dig and burrow.

Insectivorous mammals are traditionally fed diets that are high in protein and have moderate fat content. Commercial hedgehog kibble or a high-quality weight management dry cat food is often used for the base diet. Vegetables may also be offered. Hedgehogs should be supplemented with live, low-fat content invertebrates for enrichment.

Physical Examination, Chemical Restraint and Analgesia

Performing a complete physical examination without chemical restraint is impossible, given hedgehog’s shy nature and propensity to curl into a protected ball. Stress level of the individual animal and poor habituation to handling probably play the largest roles as to why hedgehogs remained curled up. Even hedgehogs that are used to handling and rarely ball up for their owners may become shy and non-approachable in a strange environment. While held suspended, holding the hedgehog with its ventrum facing the ground and then tilting the balled-up hedgehog head forward may coax tractable hedgehogs to unroll. For more stubborn individuals, placing them in a shallow (<2 cm depth) dish of warm water will often cause them to rapidly unroll in order to try and exit the water. During this attempted escape from the water, a cursory abdominal palpation may be performed. Scruffing can be performed but is likely stressful. Inhalant gas anesthesia with isoflurane or sevoflurane is the most common method of chemical restraint in African pygmy hedgehogs. Induction is via use of a small anesthetic chamber and then via facemask. Intubation requires small endotracheal tubes (1–2 mm I.D.), and it is difficult to visualize the glottis in this species. In the author’s experience, a small supraglottic airway device designed for rabbits (v-gel R1, Docsinnovent Ltd, London, UK) provides improved airway support during general anesthesia when compared to a facemask and permits positive pressure ventilation.

There are few studies examining injectable anesthetic agents in this species, although use of various combinations of benzodiazepines, alpha₂-agonists, opioids, and ketamine have been anecdotally reported.² Administration of midazolam (0.5 mg/kg SC, IM; West-ward, Eatontown, NJ, USA) and butorphanol (0.3–0.5 mg/kg SC, IM; Torbugesic, Fort Dodge Animal Health, New York, NY, USA) may result in mild sedation which may permit scruffing. A combination of alfaxalone (3–5 mg/kg) and midazolam (1 mg/kg) administered deep SC into the mantle results in heavy sedation to light anesthesia useful for examination or basic, non-painful procedures like diagnostic imaging. It is partially reversed with flumazenil (0.05 mg/kg, deep SC).

While there is little information regarding analgesia in hedgehogs, a recent study^3,4 determined that a single, deep SC dose of buprenorphine hydrochloride administered into the mantle at 0.03 and 0.05 mg/kg provided analgesia for 36 and 48 hours, respectively, without apparent side effects.

Common Conditions and Presentations

Neoplasia

Neoplasia occurs commonly in African pygmy hedgehogs and is well reported in the scientific literature. Major organ systems affected include integumentary, hemolymphatic and alimentary.⁵ Oral squamous cell carcinoma is one of the most commonly reported neoplasias in African pygmy hedgehogs.^5,6 Often, more than one type of malignant neoplasia has been reported in a single individual at the time of presentation. There are no studied oncologic treatments in pet hedgehogs.

Hemorrhagic Vulvar Discharge

At the author’s institution, pet hedgehogs are commonly presented for hemorrhagic vulvar discharge. Urinalysis and abdominal ultrasound are useful tools for differentiating between two major differentials for hemorrhagic vulvar discharge: cystitis and uterine disease. Antibiotic treatment for cystitis should be based on urine bacterial culture and sensitivity. Uterine disease, often affecting the endometrium, is commonly reported in the literature,^7,8 with clinical signs including vaginal bleeding, hematuria, and weight loss. Recommended treatment for uterine disease is ovariohysterectomy.

Acariasis

Infestation with Caparinia tripilis is common in pet hedgehogs and can result in one or a combination of signs including spine or quill loss, seborrhea, pruritus, or skin erythema. Diagnosis is through skin scrapings of affected areas. Both mite sexes have three long setae on the third pair of legs and there are trilobite projections on both sides of the posterior end of male mites.⁹ Selamectin (15–30 mg/kg topically q 14–30 d; Revolution, Zoetis Inc., Kalamazoo, MI, USA) or ivermectin (0.2–0.4 mg/kg SC or topically q 14 d; Ivomec, Boehringer Ingelheim, St. Joseph, MO, USA) may be used for treatment.

Oral Disease

A complete oral examination under anesthesia is very important for this species. Gingival masses, gingival hyperplasia and recession, periodontitis, gingivitis, calculus formation, dental fractures and abscesses may be noted during an oral exam. Antimicrobial therapy may be used for cases of gingivitis.¹⁰ Dental prophylaxis may be performed as in other carnivores.

Obesity

Obesity is a common problem in captive hedgehogs. Healthy hedgehogs should be able to roll up completely, without any portion of the ventrum protruding. Obese hedgehogs may have large axillary or rump fat deposits or a decreased ability to roll up. Treatment includes eliminating high-fat foods, rationing the main diet, and increasing exercise. Hiding food in the substrate or disseminating it throughout the enclosure substrate can help promote weight loss through foraging and exercise. Weight reduction should be gradual to help prevent hepatic lipidosis, with owners monitoring their pet’s weight with an accurate scale.

Neurologic Signs

In the author’s experience, pet hedgehogs are often presented for ataxia. Wobbly hedgehog disease is a disorder of the white matter of the central nervous system leading to often progressive neurologic signs. The etiology of the disease or effective treatment options remain unknown. While “wobbly hedgehog syndrome” is an attractive differential, the author commonly encounters patients that have advanced systemic disease (e.g., severe anemia or metabolic derangement secondary to neoplastic disease) and are severely weak and stumble while ambulating, resulting in an abnormal gait that may be misinterpreted as true ataxia. Hedgehogs inadvertently allowed to enter a state of torpor may also present in a similar fashion, although the prognosis is much more favorable. Depending on the home environment, supplemental heating is often beneficial in preventing torpor by keeping temperatures in a preferred optimum range of 75 to 85°F (24 to 29°C). In southern African hedgehogs (Atelerix frontalis), torpor occurred in most animals at environmental temperatures ≤68°F (20°C).¹¹

Normal neurologic examination findings have not been reported for African pygmy hedgehogs, making interpretation of findings and neurolocalization in animals presenting for suspected neurologic disease difficult. Additionally, considering the normally defensive behavior of many hedgehogs, performing several portions of the neurologic exam may be challenging to impossible.

References

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2.  Helmer P, Carpenter J. Hedgehogs. In: Carpenter J, ed. Exotic Animal Formulary. 5th ed. St. Louis, MO: Saunders Elsevier; 2018:443–458.

3.  Doss GA, Mans, C. Antinociceptive efficacy and safety of subcutaneous buprenorphine hydrochloride in African pygmy hedgehogs (Atelerix albiventris). J Am Vet Med Assoc. 2020. In press.

4.  Doss GA, Mans C. Efficacy and safety of buprenorphine in African pygmy hedgehogs (Atelerix albiventris). ExoticsCon. 2019;8.

5.  Raymond JT, Garner MM. Spontaneous tumours in captive African hedgehogs (Atelerix albiventris): A retrospective study. J Comp Pathol. 2001;124:128–133.

6.  Gardhouse S, Eshar D. Retrospective study of disease occurrence in captive African pygmy hedgehogs (Atelerix albiventris). Isr J Vet Med. 2015;70:32–36.

7.  Chambers JK, Shiga T, Takimoto H, et al. Proliferative lesions of the endometrium of 50 four-toed hedgehogs (Atelerix albiventris). Vet Pathol. 2018;55:562–571.

8.  Mikaelian I, Reavill DR. Spontaneous proliferative lesions and tumors of the uterus of captive African hedgehogs (Atelerix albiventris). J Zoo Wildl Med. 2004;35:216–220.

9.  Kim DH, Oh DS, Ahn KS, Shin SS. An outbreak of Caparinia tripilis in a colony of African pygmy hedgehogs (Atelerix albiventris) from Korea. Korean J Parasitol. 2012;50:151.

10.  Lennox AM, Miwa Y. Anatomy and disorders of the oral cavity of miscellaneous exotic companion mammals. Vet Clin North Am Exot Anim Pract. 2016;19:929–945.

11.  Hallam SL, Mzilikazi N. Heterothermy in the southern African hedgehog, Atelerix frontalis. J Comp Physiol B. 2011;181:437–445.