Recognizing Common Signs of Illness in Pet Rodents

<<Vet Med 93[11]:981-987 Nov'98 Review Article 7 Refs

Shawn P. Messonnier, DVM
Paws and Claws Animal Hospital 2145 W. Park Blvd. Plane, TX 75075

- Diagnosing diseases in pet rodents (rats, mice, guinea pigs, hamsters, and gerbils) is essentially the same as in dogs and cats. The differential diagnoses are based on the patient's history and clinical signs as well as conditions common to each species. In this article, I describe common clinical signs in pet rodents and how to diagnose and treat the conditions that usually cause them.

How to administer fluid therapy: Fluid therapy can be vital in treating sick rodents. Fluids can be given subcutaneously, intraperitoneally, or intraosseously. Vascular access in small pet rodents makes intravenous therapy impractical. Intraosseous access is easily accomplished in anesthetized patients (use general anesthesia or local anesthesia in depressed pets) by inserting a spinal needle or a 20- to 22-ga needle into the femur through the trochanteric fossa. Fluids can be given subcutaneously or intraperitoneally at a loading dose before discharging a patient for home care. Any balanced electrolyte solution is practical;   lactated Ringer's solution can be administered at 10 ml/100 g of body weight/day for maintenance.

Collecting blood samples: Blood collection is not routinely performed in pet rodents because it is difficult to access peripheral veins in these species and because only a small quantity of blood can be safely removed from a sick rodent. Blood samples can be taken from the nail, tip of the tail, ventral tail artery, ear vein (in guinea pigs), orbital sinus (in anesthetized patients), dorsal vein of the penis (in anesthetized guinea pigs), jugular vein (in guinea pigs), cranial vena cave (in guinea pigs), or saphenous vein (in anesthetized guinea pigs; a cut-down may be needed). Orbital sinus collection has potential complications, and clipping the tail is usually unnecessary. The ventral tail artery is the vessel of choice. In pet rodents, total blood volume is about 6% to 7% of body weight (e.g. 3 to 4 ml in a 60-g gerbil). Up to 25% of this amount can be safely collected every two weeks (ea. 0.9 ml in a 60-g gerbil). Replace blood volume subcutaneously or intraperitoneally with an equal amount of a balanced electrolyte solution.

When a pet rodent dies: Most pet rodent owners are amazed that an animal that seemed healthy the night before can be semicomatose and near death the next day. When a pet rodent dies (or an owner chooses euthanasia), offer a necropsy to ascertain the cause of death and to determine whether a zoonotic disease (e.g. salmonellosis, hymenolepiasis, lymphocytic choriomeningitis), although rare, was involved. Necropsy findings can not only comfort many owners but provide useful information for practitioners.


VIN SUMMARY:

Differential diagnoses are based on history, clinical signs, and knowledge of conditions common to species.

Handling and physical examination

Pet rodents need special handling and restraint. Lift guinea pigs with one hand under the trunk, and one under the hindquarters. Pick up hamsters by cupping the hamster, holding loose skin at nape, or by gripping over the back. (Hamsters can turn and bite even when held by nape.) To restrain/pick up rats, mice, and gerbils, hold them either at the base of the tail or the nape. Large rats can be held by putting one hand over the back and ribcage and supporting the trunk with the other hand. Immediately release any rodent that struggles. Get an accurate weight, check teeth, and auscult with a pediatric stethoscope.

Common clinical signs

Skin lesions

Obtain a history, perform a complete physical examination, and obtain a skin scraping/fungal culture (especially if pruritus present). Skin biopsies (use isoflurane anesthesia) may be more cost effective and diagnostic than skin scraping/fungal culture.

Common causes are mange, ringworm, bacterial dermatitis, cervical lymphadenitis, pododermatitis, lice infestation, nasal dermatitis, and skin cancer

Demodectic mange in older pet rodents usually signifies underlying internal disorder

Type of skin lesion Animals affected Diagnosis/Treatment
Alopecia Hamsters, gerbils, guinea pigs Skin scraping, fungal culture, skin biopsy…treat for subsequent diagnosis
Scaling without pruritis Hamsters gerbils, guinea pigs Skin scraping, fungal culture, skin biopsy…treat for subsequent diagnosis
Scaling with pruritis Hamsters gerbils, guinea pigs Bathe with an antipruritic or mild antiseborrheic shampoo labeled for cats and/or give ivermectin (200 – 400m g/kg SC in two treatments 10 – 14 days apart). Ivermectin treatment may be diagnostic for mange if the lesions resolve.
Abscesses (submandibular or cervical lymphadenitis) Guinea pigs Caused by Streptococcus zooepidemicus.

Treatment: Lance abscess or remove lymph nodes; follow with systemic antibiotics (trimethoprim-sulfamethoxazole, trimethoprim-sulfadiazine, or enrofloxacin).

Mange Guinea pigs (Demodex caviae or Trixacarus caviae, a sarcoptid mite)

 

Gerbils (Demodex spp.)

Hamster (Demodex spp., Notoedres notoedres, Notoedres cati)

*Trixacarus mange: whole body lime-sulfur dips (once a week continuing for 2 weeks after a negative skin scraping) or ivermectin (200 – 400 m g/kg SC every 10 – 14 days until skin scraping is negative).

*Demodectic mange: Amitraz (Mitaban ) (250 ppm as a whole body dip, once a week, continuing for 4 weeks after a negative skin scraping).

*Notoedric mange: whole body lime-sulfur dips (once a week continuing for 2 weeks after a negative skin scraping) or ivermectin (200 – 400 m g/kg SC every 10 – 14 days until skin scraping is negative).

Ringworm

 

**Dermatophytosis in rodents is potentially zoonotic

All pet rodents (Trichophyton mentagrophytes) Dx: Fungal culture or biopsy

Whole body treatment: 2% lime-sulfur or 1% chlorhexidine, topical application

Local lesions: use topical creams (Tresaderm or Conofite )

Systemic treatment: Give griseofulvin 25 mg/kg PO SID until fungal culture is negative. (Use only if needed; do not use in pregnant animals.)

Bacterial dermatitis All pet rodents, especially those housed with other rodents Usually Staphylococcus spp.

Bite wounds; primary skin infections possible.

Treatment: Trimethoprim-sulfamethoxazole, trimethoprim-sulfadiazine, or enrofloxacin. (Avoid antibiotics with predominantly gram-positive spectrum.)

Pododermatitis Guinea pigs Staphylococcus aureus.

Enlarged, edematous, and erythematous food pads, with crusting, hemorrhage, or ulceration. Advanced cases have a poor prognosis due to difficult treatment and occurrence of systemic amyloidosis from chronic infection.

Treatment: topical antibiotic rinses (diluted chlorhexidine or diluted povidone-iodine), systemic antibiotics (trimethoprim-sulfamethoxazole or trimethoprim-sulfadiazine at 30 mg/kg PO BID; or enrofloxacin 10 mg/kg PO BID), and soft, frequently-changed bedding.

Non-infected wounds may be encouraged to epithelialize by using BioDres or Tegaderm wound dressings.

Lice Guinea pigs Direct observation of adults or nits or by acetate tape impression.

Treatment: Use pyrethrin or pyrethroid sprays (labeled safe for cats), or 2% lime-sulfur dips, or ivermectin (200 – 400 m g/kg SC every 10 – 14 days until there is no evidence of infestation).

Nasal dermatitis

(bald nose)

 

 

 

 

 

 

Staphylococcal nasal dermatitis

Gerbils

 

 

"Bald nose"

Alopecia on the nose and muzzle and no other lesions. Caused by rubbing the cage or burrowing or excess secretion or accumulation of the harderian gland secretions.

Treatment: place pet in a smooth sided cage with soft bedding (shredded newspaper), decrease humidity (normal is 40 - 50%).

Staphylococcus spp. infection

Alopecia with erythema, oozing, crusting, scaling, abscessation, fistulation, or ulceration.

Treatment: Give trimethoprim-sulfamethoxazole or trimethoprim-sulfadiazine at 30 mg/kg PO BID; or enrofloxacin 10 mg/kg PO BID

Skin cancers Rare in all pet rodents Definitive diagnosis made by biopsy.

Signs: Solid tumors or alopecia.

Tumors

Tumors are common. Rats develop tumors more often than do mice or other pet rodents.

Most common tumors seen:

Rats: mammary gland fibroadenomas

Mice: mammary adenocarcinomas

Guinea pigs: trichofolliculomas (a solitary lesion in the dorsal lumbar region with alopecic and crusted skin overlying the tumor; keratinous material or hemorrhagic exudate may come from a central pore); neoplasms of the lungs, reproductive tract, mammary glands, & hematopoietic system

Hamsters: nodal lymphosarcomas, adrenal cortical tumors, and uterine adenocarcinomas; rarely, cheek pouch neoplasia

Gerbils: squamous cell carcinomas, melanomas, and female reproductive tract neoplasms

Diagnosis of solid tumors: fine-needle aspiration & cytologic exam; excisional biopsy/surgical removal & histopathologic exam

Other diagnostic aids: blood tests, radiographic and/or sonogram examinations, biopsies, and post mortem examinations

Tumor removal is usually curative, but depends on the tumor type.

Respiratory signs

Respiratory problems are commonly noted by owners. Clinical symptoms range from mild nasal or ocular discharge to anorexia, lethargy, dyspnea, and increased respiratory sounds upon auscultation (dry or moist rales, wheezing).

Bacterial causes:

Guinea pigs: Bordetella spp. and Streptococcus spp.

Rats and mice: Mycoplasma spp.

Other rodents: Streptococcus spp., Pasteurella spp., and Corynebacterium spp.

Other causes: viruses, heat stress, allergies, pregnancy toxemia (guinea pigs only), and irritation from bedding material

Diagnosis: history, clinical signs, and radiographic exam

Treatment:

Systemic antibiotics - Trimethoprim-sulfamethoxazole or trimethoprim-sulfadiazine at 30 mg/kg PO BID

Ophthalmic drops/ointments - Tetracycline, chloramphenicol, gentamicin

Added treatments for more severe cases (dyspnea, anorexia, lethargy):

Fluid therapy - Give a balanced electrolyte solution (lactated Ringer’s solution) at 10 ml/100g body weight/day for maintenance; use subcutaneous, intraperitoneal, or intraosseous (anesthetized patients only) routes.

Warm patient in incubator warming (< 80 F)

Provide humidification/nebulization,

Give parenteral antibiotics: enrofloxacin 10 mg/kg SC BID

Supply oxygen therapy

Give supplemental vitamin C (50 – 100 mg/pet IM BID) to all sick guinea pigs

Advise owner that prognosis is guarded to poor with severe disease.

Ocular Lesions

Chromodacryorrhea (red or bronze tears from pigment in lacrimal secretions) is commonly seen in respiratory disease.

Usually seen in rats; may be seen in mice and gerbils

Caused by illness, stress, or sialodacryoadenitis virus.

Signs: red/bronze tearing, squinting, blinking, eye rubbing, sneezing

Treatment: Antibiotic (tetracycline) ophthalmic ointment

Mycoplasma spp. ocular infections

Treatment: Antibiotic (tetracycline) ophthalmic ointment

Gerbils: ocular disorder associated with inflammation, enlargement, or prolapse of the harderian gland

Treatment: surgical removal of the gland

Excessive salivation

Caused by overgrown incisors (all rodents) and/or premolars or molars (guinea pigs only)

Malocclusion of cheek teeth can be caused by hereditary factors, tooth injury, infection of the oral cavity, and severe malnutrition.

Dx: otoscopic exam; radiographic exam

Treatment: trim every 4 – 6 weeks using a dental drill, rotary tool, or rongeurs on a sedated or anesthetized patient

Chew sticks or wood pieces may help prevent overgrow incisors, but the wood may splinter and injure the oral mucosa

Prognosis is poor if malocclusion of cheek teeth is present

Diarrhea

Seen in anorexic, lethargic, and moribund patients that are terminally ill; also seen in young pet rodents, especially hamsters..

Caused by: viruses, inappropriate administration of antibiotics, intestinal parasites (usually coccidia; rarely tapeworms), Cryptosporidia spp., bacteria (Escherichia coli; Campylobacter spp.; Clostridium piliformis & other Cl. spp.).

May cause rectal prolapse, especially in hamsters and mice, and is difficult to cure.

Complete history should include whether or not pet store antibiotics have been given ("diarrhea treatments" such as tetracycline and neomycin).

Treatment: Fluid therapy (SC or IP), as needed; oral electrolytes; oral kaolin-pectin products; increased dietary fiber (hay and vegetables); cease pellet feeding; oral antibiotics (trimethoprim-sulfamethoxazole, tetracycline, or doxycycline).

Lactobacillus (yogurt) supplements may help but the benefits are unproven.

Diarrhea prevention (using antibiotics correctly, treating intestinal parasites, and avoiding dietary indiscretion) is preferred to treatment.

Urinary signs

Cystitis and urolithiasis are occasionally seen; they are more common in guinea pigs than in other rodents.

Clinical signs: hematuria, wet perineum, bloody discharge from genitalia, blood in the cage

Diagnosis: palpable urinary calculi, radiographic exam, urinalysis, and/or urine culture

Cystitis treatment: appropriate antibiotics

Urolithiasis treatment: surgical removal of calculi

Signs of vitamin C deficiency (scurvy)

Guinea pigs require exogenous vitamin C

Clinical signs: subcutaneous and joint hemorrhages, anorexia, poor hair coat, weight loss, lethargy, arthralgia, and nasal discharge. Always suspect hypovitaminosis C in any sick guinea pig.

Treatment: Vitamin C, 100 mg/guinea pig, IM or SC, daily (in hospital)

Prevention: Feed fresh pellets (guinea pig formula) and supplement the water with vitamin C

"Acute" anorexia and lethargy

"Acute" is a misnomer. Pet rodents have a well-developed preservation response and will mask signs of illness until compensation no longer is possible.

Geriatric conditions are common causes. Normal life spans are:

Guinea pig: 4 – 8 years

Gerbils: 2 – 4 years

Rats, mice, & hamsters: 1 – 3 years

Complete history, physical examination, and subsequent laboratory/clinical tests are essential for proper diagnosis and treatment.

Prognosis is grave, if pet is moribund upon presentation.

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vinid = JA013008, date1298
Journal info: ISSN 8750-7943; ID=J035, VM


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