rodents

Chapter 4 Small rodents

Small rodents are popular both as children’s (and adult) pets, but also as show animals. Rats in particular have a very enthusiastic following. Those species that are likely to be encountered in the veterinary surgery are:

• Mice (Mus musculus)

• Rats (Rattus norvegicus)

• Mongolian gerbil (Meriones unguiculatus)

Table 4.1 Small rodents: Key facts

Consultation and handling

Small rodents are prey animals and may become stressed by the presence of potential predators such as cats, dogs and unfamiliar people; this includes auditory and olfactory signals, so where possible they should be housed separately from such animals, and hands should be well cleaned to remove other species’ odours before handling.

Many small rodents move quickly and unpredictably and care should be taken to prevent unwanted escapes or potentially disastrous leaps to the floor. Gently wrapping in a towel will often help with the handling and control of an excitable rodent. A sure way to annoy a pet rat (and alienate its owner) is to attempt to grasp it by the scruff of the neck. Most are used to being gently handled and are unlikely to bite. If in doubt, use a towel. Do not attempt to pick a hamster straight from its bed; they are territorial of this and are likely to bite. Instead, gently tease or tip it out. Recalcitrant hamsters are more easily scruffed and, although this will help with an examination of the teeth, it may upset the rodent.

Hamsters are permissive hibernators and may attempt hibernation if temperatures fall consistently below 4.5°C. Poor food availability, altered photoperiod and other factors may also induce hibernation, although this varies between individuals. Hibernation is not continuous but is interrupted every 2–3 days by bouts of normal activity including foraging. During hibernation, hamsters remain sensitive to tactile stimulation and can be gently aroused. Exposure to normal room temperatures (18–22°C) and lighting (12–14 h) are unlikely to trigger hibernation. Many owners misinterpret clinical signs of illness (lack of movement and lethargy, anorexia) with hibernation, often delaying presentation to the veterinary surgeon.

Nursing care

See Nursing Care in Rabbits for general principles.

Small rodents by virtue of their size and the high risk of predation are forced to obtain most of their water from preformed (food) and metabolic sources. Dehydration can be a real issue, especially at higher environmental temperatures (Table 4.2).

Table 4.2 Small rodents: Nursing care

Fluids can be given s.c., i.p. or i.o. However, for small rodents, the intravenous route (Fig. 4.1) for fluid administration is largely impractical, but Table 4.3 gives suggested sites.

Fig. 4.1 Intravenous fluids given through the lateral tail vein.

Table 4.3 Small rodents: Sites for fluid administration

Intravenous (rat and mouse)	Lateral tail vein (helps if warm!) (Fig. 4.1)
Intravenous (hamster)	Very difficult: lateral tarsal vein, anterior cephalic vein and lingual vein
Intravenous (gerbil)	Lateral tail vein or saphenous vein
Intraperitoneal (all three species)	Hold the patient vertically downward and inject into the lower left quadrant
Intraosseous (all three species)	Under GA to insert either an intraosseous catheter or a hypodermic needle into the marrow of either the femur (via the greater trochanter) or tibia (through the tibial crest). Fluids, colloids and even blood can be i.o. if necessary.

Jugular catheterization can be attempted in all species but it is difficult and may result in respiratory embarrassment. Many of these sites may also require anaesthesia and surgical cut down, which may not be appropriate for the welfare of the patient. In hypovolaemic patients vascular access may be impossible. It is better to consider either i.p. or i.o. administration.

Hypothermia

Much endogenous body heat is generated by gut and muscle activity; sick, inactive or anaesthetized rodents are prone to hypothermia (Jepson 2004). Use a heat source, e.g. electric heat mat, plus insulation such as silver foil over the feet, pinnae and tail (reduces heat lost by conduction) and bubble wrap (reduces heat lost by convection). Maintain in warm air, e.g. incubator, or use a commercial medial warm air generator.

Nutritional status

Many small rodents are presented as emergencies after a prolonged period of ill-health that will have affected their food intake. These animals are often hypoglycaemic – testing with a commercial glucometer on a small sample of blood – and i.v. or i.p. glucose can be given to these cases once identified.

Table 4.4 Small rodents: Analgesic doses

Analgesia

Anaesthesia

Small rodents may have subclinical respiratory infections.

It is important to keep small rodents warm as they have a large surface area compared with volume, which results in significant heat loss during surgery. This also applies during anaesthesia – hypothermia acts as a general depressant and is also immunosuppressive. Merely applying insulation such as bubble wrap is often insufficient – inactive, anaesthetized rodents are not generating heat and you may be insulating it from a higher ambient temperature. Place these animals on to a heat mat, on to which is placed an absorptive towel or other material to both protect the mat from becoming wet, and reduce the slight risk of localized burns.

Use reflective foil over hairless areas where heat loss can occur, e.g. tails, feet, pinnae on mice and rats.

There is no need to starve – prolonged fasting can lead to hypoglycaemia.

Skin disorders

Syrian hamsters have large, bilaterally symmetrical hip glands; these are scent glands used for marking burrow walls and in males they can be particularly pronounced in both size and the amount of sebaceous secretion they produce. These are frequently mistaken as skin lesions. Dwarf hamsters and gerbils possess ventral scent glands visible on the abdomen.

Alopecia

• Ectoparasites (see below)

• Dermatophytosis (rat, mouse) (often asymptomatic)

• Trichophyton spp and Microsporon spp

• Barbering (usually done by dominant individual in group)

• Muzzle alopecia. Secondary to repetitive rubbing of muzzle against bars during cage-bar chewing

• Staphylococcus aureus dermatitis (gerbil). Localized alopecia and erythema around the external nares

• Nasal dermatitis (gerbil). Alopecia and pruritic reddened scabs appear first around the external nares, mainly on the upper lip. May spread over the head and to the forepaws

• Wood shaving and sawdust bedding made from treated wood

• Low protein diet (<16%) (hamster)

• Hormonal alopecia (see Endocrine Disorders)

• Cystic ovaries (see Reproductive Disorders)

• Satinization in hamsters. Individuals homozygous for the satin gene may have only a thin coating of hair.

Changes in pigmentation

• Rash (Ectromelia virus in the mouse); nickel contact allergy (mouse)

• Seborrhea (esp. older adult male rats).

Ectoparasites

• Mites: Myobia musculi (fur mite), Mycoptes musculinus (fur mite), Radfordia affinis (fur mite); Sarcoptes scabei (rare), Psorergates simplex spp (follicular mite – rare)

• Ear mites: Notoedres muris

• Lice: Polyplax serrata (sucking lice), P. spinulosa

• Fleas: Ctenocephalides felis

• Mites: Demodex meroni, Liponyssoides sanguineus (esp. Egyptian gerbils, Meriones libycus). Rarely Sarcoptes scabei and Notoedres muris

• Storage mites (Acarus farris) on cereal based foods may occasionally cause irritation.

Necrosis of extremities

• Shortening of extremities secondary to necrosis (mouse: Ectromelia virus)

• Ringtail (annular constrictions of the tail) (rats).

Investigations

1 Microscopy: examine fur pluck, acetate strips or skin scrapes to affected area and examine for ectoparasites

2 Examine teeth. Rodents with dental disease may have difficulty grooming normally

a Pododermatitis – often underlying osteoarthritis

4 Routine haematology and biochemistry

a Eosinophilia (ectoparasitism)

5 Serology for ectromelia virus

6 Bacteriology and mycology: hair pluck or swab lesions for routine culture and sensitivity

a Fine-needle aspirate followed by staining with rapid Romanowsky stains

9 Biopsy obvious lesions

10 Ultraviolet (Wood’s) lamp – positive for Microsporium canis only (not all strains fluoresce). Also porphyrins fluoresce (nasal dermatitis in gerbils)

11 Endocrine analysis: Thyroxine (see Endocrine Disorders), oestradiol

12 If barbering suspected, examine hair under microscope to see if chewed; separate from other animals; supply extra hay.

Treatment/specific therapy

• Poxviruses (including Ectromelia virus)

• No treatment; supportive only. Consider euthanasia. Rat poxvirus is a potential zoonosis

• Hamster polyomavirus (HaPV, Papova virus)

• No treatment

• Transmitted via the urine

• Cull affected and in-contact animals.

• Corynebacterium kutscheri (pseudotuberculosis)

• Appropriate antibiosis. Prevalence is variable

• Ectoparasites

• Ivermectin at 0.2 mg/kg or as topical (450 μg/tube) ‘spot on’ (Xeno450, Genitrix) weekly for 3–4 weeks

• Dust with pyrethrin powder

• For cases of severe self-inflicted trauma then NSAIDs plus prophylactic toe clipping may be necessary to reduce excoriation, plus antibiotics to control secondary infections

• Notoedres in Syrian hamsters (Beco et al 2001)

• Ivermectin at 400 μg/kg s.c. every 7 days for a minimum of 8 weeks

• Moxidectin at 400 μg/kg p.o. every 7 days for a minimum of 8 weeks

• Demodex mites

• Amitraz as wash at 100 mg/L applied topically every 7 days until resolution

• Ivermectin as for Notoedres

• Some mice may fail to respond to treatment; it is thought that some of these individuals may have inherent, genetic immune deficits whilst others may develop a hypersensitivity to mite antigen that is difficult to control

• Storage mites

• Topical fipronil spray applied with a cotton bud

• Dispose of affected foods and clean storage containers

• Ornithonyssus bacoti is a potential zoonosis (Beck & Pfister 2004)

• Surgical removal of affected part. Linked to low humidity (RH <40%) so increase to 50–70%.

• Allergic dermatitis

• Separate from all potential allergens, and where appropriate seek alternatives, including beddings, certain foods (see below), metallic objects (including caging), environmental triggers such as cigarette smoke

• For suspected dietary allergies an elimination protocol can be developed – remove all high risk triggers, e.g. sunflower seeds, peanuts, coloured dog biscuits and replace with cooked rice, maize flakes and fruits (including dried) (Richardson 2003)

• Diet-associated dermatitis

• Change food to more appropriate material (see Dietary)

• NSAIDs to control pruritus

• Abscessation

• Systemic antibiosis

• Bath wounds and apply topical antibiosis

• May require surgical removal

• Surgical removal

• Where surgery is considered non-viable, accessible cutaneous tumours can be treated by injecting cisplatin directly into the tissue mass on a weekly basis as a debulking exercise

• Staphylococcal dermatitis

• Topical and systemic antibiosis

• Environmental modification: high humidity, fighting, and trauma are thought to predispose

• Nasal dermatitis

• May be linked to focal hyperplasia of the Harderian glands and increased lachrymal secretion

• Environmental modification; may be associated with trauma from burrowing into certain beddings; provision of sand may improve the condition

• Topical ophthalmic treatment may be beneficial

• Sores on legs from wire wheel

• Treat with topical preparations and switch to a solid backed and rimmed wheel

• Treat symptomatically with appropriate shampoos.

Respiratory tract disorders

Fungal

Neoplasia

• Alveologenic carcinoma

• Pulmonary metastases from other neoplasia especially uterine adenocarcinomas.

Other non-infectious problems

• Allergic disorders, e.g. to fine sawdust

• Heart disease (see Cardiovascular and Haematological Disorders)

• High environmental ammonia levels.

Management

• A clean, well-ventilated, but not draughty, air space is necessary.

• Some of the smaller module-based rodent housing has poor ventilation which can produce areas of high humidity and high ammonia levels. Both of these can predispose to respiratory disease.

Tags: Exotic Animal Medicine A Quick Reference Guide

Aug 21, 2016 | Posted by admin in EXOTIC, WILD, ZOO | Comments Off

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