Small rodents

Small rodents are popular not only as children's (and adult's) 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 gerbils (Meriones unguiculatus)

• Hamsters

• Syrian (golden) hamster (Mesocricetus auratus)

• Russian hamster (Phodopus sungorus)

• Roborovski hamster (Phodopus roborovskii)

• Chinese hamster (Cricetulus griseus)

• Hamster species differ in their standard husbandry.

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' odors 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 up 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 among individuals. Hibernation is not continu­ous but is interrupted every 2 or 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 to 22° C) and lighting (12 to 14 hours) 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 Chapter 2 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).

Fluids can be given SC, IP, or IO. For small rodents, the intravenous route (Fig. 4-1) for fluid administration is largely impractical, but Table 4-3 gives suggested sites.

Jugular catheterization can be attempted in all species, but it is difficult and may result in respiratory embarrassment.

Fig 4-1. Intravenous fluids given through the lateral tail vein.

Hypothermia

Much endogenous body heat is generated by gut and muscle activity; sick, inactive, or anes­thetized rodents are prone to hypothermia (Jepson 2004). Use a heat source, such as an 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 medical warm air generator.

Nutritional status

Many small rodents are presented as emergencies after a prolonged period of ill health that has affected their food intake. These animals are often hypoglycemic—test with a commercial glucometer on a small sample of blood—and IV or IP glucose can be given to these cases once identified.

Analgesia

Anesthesia

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 anesthesia—hypothermia acts as a general depressant and is also immunosuppressive. Merely applying insulation such as bubble wrap is often insufficient—inactive, anesthetized rodents are not generating heat and you may be insulating it from a higher ambient temperature. Place these animals onto a heat mat, onto 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 hypoglycemia.

Premedication

1. Premedication is rarely used, but it does permit easier, smoother anesthetic induction; this should be balanced against increased recovery times where short operations are performed.

2. Suitable premedications include:

a. Acepromazine: 0.5 to 5.0 mg/kg IM or IP

b. Diazepam: 2.5 to 5.0 mg/kg IM or IP

c. Midazolam: 2.5 to 5.0 mg/kg IM or IP

3. Premedicate 45 to 60 minutes before gaseous anesthesia.

4. Mask down or use induction chamber with isoflurane. Induction is usually quick due to high respiratory rates.

Parenteral anesthesia

1. Always weigh accurately.

2. Always supply oxygen by face mask.

3. Many rodents fail to lose withdrawal reflex and may respond to surgical stimuli; therefore, you may need to use low concentration of inhalation anesthetic or infiltrate with local anesthetic.

4. There is a range of published anesthetic regimens. The author has found the following of use:

a. Ketamine: 50 to 100 mg/kg plus xylazine 2.0 to 10 mg/kg IP

b. Ketamine: 50 to 100 mg/kg plus medetomidine 0.25 to 1.0 mg/kg IP

Cardiopulmonary resuscitation

For respiratory arrest

1. Administer 100% oxygen.

2. Assist ventilation—compress thorax at around 60x/min.

3. Doxapram sublingual or at 10 mg/kg IV or IP. Note: This will increase the animal's oxygen demand.

4. If appropriate, give atipamezole.

For cardiac arrest

1. As for respiratory arrest. But also:

2. Compress thorax at around 90x/min.

3. If asystole—give epinephrine at 0.1 mg/kg IV, IO, repeat if necessary every 3-5 minutes of 1 : 10,000.

4. If ventricular fibrillation—lidocaine (lignocaine) at 1 to 2 mg/kg IV, IO, Intratracheal; repeat after

3-5 minutes if needed.

Skin disorders

Syrian hamsters have large, bilaterally symmetrical hip glands; these are scent glands used for marking burrow walls; 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.

Pruritus

• Ectoparasites (Fig. 4-2)

• Otitis externa (ear mites)

• Pyoderma (see also “Abscessation” below)

• Diet-associated dermatitis (mouse, see Nutritional Disorders)

• Allergic dermatitis

• Swollen feet, palpebral swelling, ocular discharge, and sneezing (hamsters)

• Contact allergy to nickel (mouse)—typically see inflammation on nose, feet, and tail

• Nasal dermatitis (gerbil)

Alopecia

• Ectoparasites (see below)

• Dermatophytosis (rat, mouse—often asymptomatic)

• Trichophyton spp. and Microsporum 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

Fig 4-2. Trauma from Myobia musculi infestation in a mouse.

• 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 (Sarcoptes scabiei (rare), Psorergates simplex spp. (follicular mite—rare)

• Ear mites: Notoedres muris

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

• Fleas: Ctenocephalides felis

• Hamster

• Demodex criceti and D. aurati. Infestation more common than disease

• Sarcoptes scabiei

• Ctenocephalides felis

• Ear mites: Notoedres notoedres and N. cati (but can have a more generalized distribution, including the face, genitalia, limbs, and tail)

• Ornithonyssus bacoti (tropical rat mite; Fox et al 2004)

• Gerbil

• Mites: Demodex meroni, Liponyssoides sanguineus (especially Egyptian gerbils, Meriones libycus); rarely Sarcoptes scabiei and Notoedres muris

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

Neoplasia

• Squamous cell carcinoma

• Mammary adenocarcinomas (mouse—see Reproductive Disorders)

• Melanoma

• Hemangiosarcomas

• Trichoepitheliomas (in hamsters, may be related to HaPV infection)

• Dermal lymphoma (Kubiak and Denk 2014)

Necrosis of extremities

• Shortening of extremities secondary to necrosis (mouse—ectromelia virus)

• Ringtail (annular constrictions of the tail—rats)

Other

• Anemia, debilitation (Ornithonyssus bacoti, the tropical rat mite; heavy infestations of lice)

• Note: Lice (Polyplax spp.) can be vectors for Encephalitozoon cuniculi, Eperythrozoon coccoides, and Haemobartonella muris.

• Fleas (Xenopsylla spp. and Nosopsyllus spp.) can be vectors for Yersinia pestis (plague) and Rickettsia typhus and can act as intermediate hosts for Hymenolepis spp.

(see Gastrointestinal Tract Disorders).

Findings on clinical examination

• Areas of alopecia

• Swellings, often firm consistency even if abscess. Displacement of normal outline of coat may indicate swelling.

• Cuts and abrasions

• Extreme pruritus

• Systemic signs

• Overgrown claws

• Pododermatitis—swelling and abscessation of the soles of the feet, especially the hind feet

• Areas of inflammation and excoriation around the nares in gerbils (nasal dermatitis, staphylococcal dermatitis)

• Hair loss and sores on legs of hamsters (repetitive trauma from wire wheel)

• Hair loss on one side of mouth (persistent bar gnawing)

• Seborrhea

• Multiple small lumps around neck in hamsters (with subsequent ulceration), weight loss; mortalities (can be up to 15% to 20%) (HaPV)

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.

3. Radiography

a. Pododermatitis—often underlying osteoarthritis

4. Routine hematology and biochemistry

a. Eosinophilia (ectoparasitism)

5. Serology for ectromelia virus

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

7. Cytology

8. Gram stain

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), estradiol

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

Management

1. Pododermatitis

a. Soft bedding

b. Covering antibiosis

c. Regular cleansing

d. Application of topical amorphous hydrogel dressings, such as IntraSite Gel (Smith and Nephew Healthcare Ltd), encourages secondary healing.

e. Attend to any underlying osteoarthritis with NSAIDs (e.g., meloxicam).

TreatmentZspecific therapy

• Poxviruses (including ectromelia virus)

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

• HaPV (papovavirus)

• No treatment

• Transmitted via the urine

• Cull affected and in-contact animals.

• Corynebacterium kutscheri (pseudotuberculosis)

• Appropriate antibiosis. Prevalence is variable.

• Dermatophytosis

• Griseofulvin at 25 mg/kg PO once daily for 30 to 60 days

• Miconazole/chlorhexidine (Malaseb, Leo) shampoo—bath once daily.

• Itraconazole 5 mg/kg PO s.i.d. for 30 days

• Improve ventilation.

• Ectoparasites

• Ivermectin at 0.2 mg/kg SC or as topical (450 pg/tube) spot-on (Beaphar Anti-Parasite Spot-On for Small Animals, USA, Genitrix Xeno 450, UK) weekly for 3 to 4 weeks

• Dust with pyrethrin powder.

• For cases of severe self-inflicted trauma, 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 pg/kg SC every 7 days for a minimum of 8 weeks

• Moxidectin at 400 pg/kg PO 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 while 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 and Pfister 2004).

• Ringtail

• Surgical removal of affected part. Linked to low humidity (relative humidity Tract Disorders and Ophthalmic Disorders)

• Mouse hepatitis virus (MHV—mouse; see also Gastrointestinal Tract Disorders)

Bacterial

• Pasteurella pneumotropica

• Mycoplasmosis, esp. M. pulmonis (rats and mice; forms part of rat pneumonia complex)

• Cilia-associated respiratory bacillus (CAR; part of rat pneumonia complex)

• Streptococcus pneumoniae (rats—see also Cardiovascular and Hematologic Disorders)

• Corynebacterium kutscheri (pseudotuberculosis); often subclinical (rats and mice)

• Listeriosis (bushy-tailed jirds, Sekeetamys calurus); acute pneumonitis (see also Gastrointestinal Tract Disorders)

Fungal

Neoplasia

• Alveologenic carcinoma

• Pulmonary metastases from other neoplasias, especially uterine adenocarcinomas

Other noninfectious problems

• Allergic disorders (e.g., to fine sawdust)

• Heart disease (see Cardiovascular and Hematologic Disorders)

• High environmental ammonia levels

Findings on clinical examination

• Upper respiratory signs, such as sneezing, porphyrin staining around the eyes (Fig. 4-3)

• Swollen neck and eyes; ophthalmic lesions (SDAV in rats)

Fig 4-3. Porphyrin-stained tears in a rat.

• Respiratory distress—can be severe

• Cyanosis of mucous membranes, feet, nares, and tails (rats and mice)

• Tachypnea: Estimates for the normal respiratory rates of small mammals can be achieved with the following formula:

Respiratory rate = 53.5? wt^-0∙²⁶, where wt = body weight in kg

• Dyspnea

• Marked lung sounds

• Rhinitis and nasal discharge

• Torticollis, circling, and other neurologic disorders (see Neurologic Disorders)

• Weight loss, anorexia

• Pyrexia

Investigations

1. Differentiate porphyrin staining from blood by either using blood “dipstick” tests or UV light (porphyrins fluoresce).

2. Radiography

a. Pneumonia

3. Routine hematology and biochemistry

4. Polymerase chain reaction (PCR) for M. pulmonis, Sendai virus, CAR, SDAV, MHV

5. Culture and sensitivity (including from tracheal wash)

6. Cytology from tracheal wash

7. Pleural tap and cytology

8. Culture and sensitivity

9. Mycoplasma culture

10. Cytology

a. Gram staining of discharges or effusions

11. Endoscopy

12. Ultrasonography

Management

• A clean, well-ventilated, but not drafty, 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.

TreatmentZspecific therapy

• Viral infections

• Control of secondary infections

• For SDAV, MHV, and Sendai virus, attempt removal from breeding colonies by euthanizing all unweaned and weanling young and preventing breeding for 8 weeks. This allows immunocompetent adults to seroconvert and eradicate these viruses.

• Bacterial disease, including mycoplasmosis

• Appropriate antibiosis

• M. pulmonis infections may be exacerbated by concurrent SDAV.

• Rat pneumonia complex

• Broad-spectrum antibiotics

• NSAIDs (e.g., meloxicam)

• Mucolytics such as bromhexine and N-acetylcysteine may be useful.

• Improved environmental conditions (i.e., sanitation and ventilation)

• Often cure is impractical; control of the condition is often the case.

• Allergic disease

• Often only one in a group affected.

• Consider NSAIDs or antihistamines as a control.

• Avoid suspected antigens.

Gastrointestinal tract disorders

Disorders of the oral cavity

In small rodents, the cheek teeth either grow very slowly or not at all, so dental disease involving these is rare. Gnawing in rodents involves a significant rostrocaudal movement of the lower jaw relative to the upper; therefore, the lower incisors are naturally long. True indicators of incisor malocclusion include uneven wear, sloping of the cutting edges, fractured teeth, altered pigmentation, and obvious pathological overgrowth.

The hemimandibular junction is flexible, and it is normal for the lower incisors to be able to deviate from each other during manipulation.

Permanent dental formula of a rodent

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C:⁰,

0

PM :⁰,

0

M :3

3

Dental disorders

• Incisor malocclusion—secondary to fractures, developmental problems, hereditary predisposition

• In some cage bar-chewing rodents the cutting edges of the incisors may show a slope to one side associated with uneven wear due to repetitive gnawing on vertical bars.

• Some rodents with grossly overgrown incisors may present with weight loss secondary to extreme incisor malocclusion that results in an inability to physically close the mouth for mastication.

• Dental caries can be common in rodents fed treats high in sugar and other carbohydrates or acidic foods.

• Burr back overgrown incisors. Avoid rotation of tooth during this process to reduce risk of trauma.

• Provide something to gnaw on (e.g., safe wood or dog biscuit).

• Incisor extraction: Significant risk of mandibular fracture

• Tooth root abscessation

• Surgical debridement and covering antibiosis.

Cheek pouches

Very well developed in hamsters and some other rodents (e.g., chipmunks)

• Cheek pouch impaction

• Food accumulation; may begin to autolyze and secondary infection ensues. Empty under general anesthesia (GA).

• Cheek pouch eversion/prolapse/neoplasia (Fig. 4-4)

• Some cases may respond to gentle replacement.

• Requires surgical resection

Fig 4-4. Prolapsed cheek pouch secondary to neoplasia.

Foreign bodies

• The rodent may display an apparent malocclusion, hypersalivation, and discomfort around the mouth. Require removal, possibly under GA

Differential diagnoses for gastrointestinal disorders

Coprophagy is commonly practiced by many small rodents. Hamsters have a stomach divided into two compartments: an aglandular forestomach (which allows some pregastric fermenta­tion to occur, especially of ingested feces) and the true glandular stomach.

Viral

• SDAV (coronavirus—rats; see also Respiratory Tract Disorders and Ophthalmic Disorders)

• MHV (coronavirus—mouse; see also Respiratory Tract Disorders)

• Rotavirus (mouse)

• Reovirus (mouse)

Bacterial

• Citrobacter freundii (mouse)

• Clostridium piliforme (Tyzzer disease—all rodents, especially gerbils)

• Salmonellosis, especially Salmonella enteriditis and S. typhimurium

• Listeriosis (bushy-tailed jirds, Sekeetamys calurus); disease characterized by acute deaths without clinical signs

• Proliferative ileitis or wet-tail in hamsters

• Lawsonia intracellularis

• Campylobacter spp.

• Escherichia coli

• Yersinia pseudotuberculosis

• Pasteurella (enteritis in hamsters)

Protozoal

• Rat

• Cryptosporidium parvum

• Eimeria spp. (rare)

• Giardia muris

• Spironucleus muris

• Mouse

• Cryptosporidium muris, C. parvum

• Eimeria spp., common in wild mice (E. falciformis, E. musculi, E. schueffneri, E. krijgsmanni, E. keilini, E. hindlei)

• G. muris

• Trichomonas muris

• Spironucleus muris

• Entamoeba muris

• Hamster

• Cryptosporidium spp. (see “Proliferative Ileitis” in Treatment/Specific Therapy below)

• Giardia spp.

• Balantidium coli and B. caviae

• Spironucleus muris

• Tritrichomonas muris

• Entamoeba muris

Parasitic

• Rat

• Nematodes: Aspiculuris tetraptera, Syphacia muris (pinworms), Trichosomoides crassicauda

• Cestodes: Hymenolepis nana and H. diminuta

• Mouse

• Nematodes: A. tetraptera, Syphacia obveolata, Trichuris muris

• Cestodes: H. nana, H. diminuta, and H. microstoma

• Gerbil

• Nematodes: S. muris and S. obveolata (pinworms), Dentostomella translucida (oxyurid)

• Cestodes: Hymenolepis nana

• Hamster

• Nematodes: S. obveolata (pinworms) and A. tetraptera

• Cestodes: H. nana

Nutritional

• Sudden change in dietary composition (e.g., influx of vegetable material)

Neoplasia

• Intestinal polyps

• Forestomach papillomas

• Intestinal adenocarcinoma

Other noninfectious problems

• Antibiotic-induced enterotoxicosis (often secondary to Clostridium difficile)

• Intussusception

• Rectal prolapse

• Gut stasis/impaction

Findings on clinical examination

• Diarrhea, soiling around the perineum

• Nonspecific signs of ill health (e.g., hunched posture, ruffled coat)

• Weight loss

• Rectal prolapse (C. freundii in mice)

• Death

• Cervical thickening (swollen salivary glands, lymph nodes), ocular swelling (swollen lachrimal glands), and ocular discharge (SDAV in rats)

• CNS signs (e.g., head tilt, ataxia indicate neurologic involvement such as with Clostridium piliforme)

• Testicular enlargement suggestive of salmonellosis in gerbils (Laber-Laird 1996)

• Proliferative ileitis (wet-tail) in hamsters

• Acute: Acute enteritis with profuse and often hemorrhagic diarrhea

• Subacute: Stunting, dehydration and diarrhea, palpable abdominal viscus, mortalities

• Chronic: Few overt, clinical signs; palpable ileal lesions, sudden death. This may explain some outbreaks without contact with other hamsters.

Investigations

1. Fecal examination

a. Microscopy of wet prep; flotation

2. Aspiculuris ova are symmetrical; Syphacia are asymmetrical (slightly banana shaped).

Syphacia deposits eggs around anus while Aspiculuris does not, so use acetate strip test for Syphacia.

3. H. diminuta and H. microstoma ova have polar filaments. H. nana and H. diminutia eggs have three pairs of hooks.

4. Spironucleus muris—look for cysts in feces (shaped like Easter eggs); trophozoites in small intestine (wet mounts, histology). Usually subclinical

5. Radiography

a. Intestinal obstruction (parasites, neoplasia, foreign bodies)

b. Ileus (obstruction, compromise of gut motility, dietary-induced gut disorder)

6. Routine hematology and biochemistry

7. PCR for C. piliforme, SDAV, MHV

8. Culture and sensitivity

9. Ultrasonography

10. Endoscopy

11. Biopsy

a. Wet-tail without ileal hyperplasia may be caused by E. coli.

12. Postmortem

a. Gross thickening of colon and rectum (C. freundii in mice)

b. Yellowish foci in the liver and myocardium (C. piliformis)

c. Multiple microabscessation, especially liver and spleen (Yersinia)

Management

• Fluid therapy

• In cases of severe disruption of the gut environment and its commensal flora, consider supplementation with vitamin B compounds.

• Probiotics may be of benefit.

TreatmentZspecific therapy

• Bacterial diseases, including C. freundii

• Appropriate antibiosis

• Address any stress factors (e.g., environmental temperatures and overcrowding).

• C. piliformis (Tyzzer disease)

• Appropriate antibiosis and supportive care

• Yersinia

• Appropriate antibiosis

• Strict sanitation

• Prevent access of wild rodents and birds to pet rodent food/living areas.

• Proliferative ileitis (wet-tail) in hamsters

• Fluid therapy plus good nursing care (see Nursing Care)

• Appropriate antibiosis

- Enrofloxacin at 5 mg/kg PO or SC or as 10 mg/100 mL fresh drinking water daily

- Erythromycin at 100 mg/L fresh (distilled or de-ionized) drinking water

- Oxytetracycline at 400 mg/L fresh drinking water

• Cryptosporidium: No effective treatment. Consider potentiated sulfonamides or nitazoxanide (100mg/kg PO b.i.d. for 3 days).

• Strict sanitation

• Protozoa

• Sulfamethazine at 0.2% in drinking water for 7 to 10 days

• Metronidazole at 2.5 mg/mL in drinking water

• Nematodes

• Ivermectin at 0.2 mg/kg SC or as topical (450 pg/tube) spot-on (Beaphar Anti-Parasite Spot-On for Small Animals, USA, Genitrix Xeno 450, UK) weekly for 3 to 4 weeks

• Topical emodepside plus praziquantel preparations (Profender, Bayer) at 0.004 mL/30 g body weight (Mehlhorn et al 2005a)

• Topical imidacloprid and moxidectin compound (Advocate Cat, Bayer) reduced T. muris burdens by up to 95% at a concentration of 128 mg imidacloprid and 32 mg moxidectin/kg body weight (Mehlhorn et al 2005b).

• Cestodes, including Hymenolepis spp.

• Praziquantel at 5 to 10 mg/kg PO or SC. Repeat after 10 days.

• Note: All species have intermediate arthropod hosts, but H. nana can have a direct life cycle. Zoonotic hazard, especially with H. nana, as no intermediate host required.

• Sudden dietary changes

• Switch to dried food only.

• If pronounced diarrhea, consider fluid therapy (see Nursing Care)

• Do not use antibiotics unless specifically indicated, as these may retard the reestablishment of the normal gut flora.

• Antibiotic-induced enterotoxicosis

• As for “Sudden dietary changes” above

• Cease antibiotic administration.

• Supplementation with probiotics may be useful.

• Vitamin B supplementation

• Intussusception

• Especially seen in hamsters

• Euthanasia or surgical correction

• Rectal prolapse

• May be secondary to diarrhea or intussusception

• Surgical correction

• Supportive nursing

• Gut stasis/impaction

• May be linked to systemic disease, dry foods, and foreign bodies (e.g., bedding fibers)

• Laxatives and gut motility enhancers (e.g., metoclopramide at 0.2 to 1.0 mg/kg PO, SC) may be of benefit.

• Surgical removal of foreign bodies

Nutritional disorders

• Diet-associated dermatitis (mouse), possibly linked to high sunflower and nut diet (Richardson 2003)

• Hypovitaminosis E in hamsters (see Musculoskeletal Disorders and Reproductive Disorders)

Findings on clinical examination

• Pruritus in mice (diet-associated dermatitis)

TreatmentZspecific therapy

• Diet-associated dermatitis

• NSAIDs (e.g., meloxicam)

• Place on simpler diet or proprietary pelleted mouse food.

Hepatic disorders

A gallbladder is present in the mouse, gerbil, and hamster but absent in the rat.

Bacterial

• Listeriosis (gerbils)

• Salmonellosis

Neoplasia

• Hepatic carcinoma

Other noninfectious disorders

• Amyloidosis (see Systemic Disorders)

Findings on clinical examination

• Vague signs of ill health

• Diarrhea

• Weight loss

• Jaundice

• Polydipsia/polyuria

• Poor blood clotting (hepatic lipidosis)

• Hepatomegaly

Investigations

1. Radiography

2. Routine hematology and biochemistry

3. Culture and sensitivity

4. Endoscopy

5. Biopsy

6. Ultrasonography

Management

• Fluid therapy

• Milk thistle (Silybum marianum) is hepatoprotectant; dose at 4 to 15 mg/kg PO b.i.d. or t.i.d.

• Lactulose at 0.5 mL/kg PO b.i.d.

TreatmentZspecific therapy

1. Bacterial infections

a. Guarded prognosis

b. Antibiosis

Pancreatic disorders

Diabetes mellitus (see Endocrine Disorders)

Cardiovascular and hematologic disorders

Cardiac disease is considered very common in Syrian hamsters, such that heart failure may represent a common aging-related cause of mortality (Schmidt and Reavill 2007). Rodent heart rates are fast. As a guide the normal heart rate of a rodent can be reasonably estimated with the following formula:

Heart rate = 241 ? wt^-0∙²⁵ where wt = body weight in kg

Viral

• Encephalomyocarditis virus (hamsters)

• Hamster leukemia virus

Bacterial

• Streptococcus pneumoniae (rats—see also Respiratory Tract Disorders)

• Bacillus piliformis (Tyzzer disease)

• Erysipelothrix rhusiopathiae (see Systemic Disorders)

• Septicemia (phlebothrombosis) with, for example, Salmonella spp.

• Myocarditis (suppurative)

Fungal

Protozoal

• Haemobartonella muris (rat)

• Eperythrozoon coccoides (mouse)

Parasitic

Dietary

Neoplasia

• Lymphocytic leukemia

Other noninfectious problems

• Cardiomyopathy (Syrian hamsters)

• Autosomal recessive in the Bio 14.6 strain

• Inherited dilated cardiomyopathy in Bio TO-2 strain

• Congenital cardiac and aortic anomalies (Syrian hamsters)

• Atrial thromboses (Syrian hamsters)

• Calcifying vasculopathy (Syrian hamsters)

• Myocardial fibrosis (acute and chronic)

• Polyarteritis nodosus (rat)—can cause aneurysms, thrombus formation, and stenosis of blood vessels, leading to multiple organ disruption or failure

• Anemia secondary to other causes (e.g., hemorrhage, hemolytic anemias, anemia of chronic disease, neoplasia, chronic renal disease)

Findings on clinical examination

• Anemia

• Exercise intolerance

• Heart abnormalities (e.g., arrhythmias, abnormal heart sounds)

• Exaggerated breathing postures (air hunger) and other respiratory signs

• Pulmonary edema

• Cyanosed extremities

• Splenomegaly, hepatomegaly

• Lymphadenopathy

• Sudden death (may be due to rupture of aneurysms formed in polyarteritis nodosus)

Investigations

1. Radiography

a. Pericardial effusions (S. pneumoniae)

2. Routine hematology and biochemistry

3. Culture and sensitivity

a. Gram stain effusions (S. pneumoniae)

4. Endoscopy

5. Ultrasonography

6. ECG

Management

• Supportive treatment, including vitamin B₁₂ for anemia

TreatmentZspecific therapy

• Cardiomyopathies

• Benazepril at with appropriate antibiotics, both topical and systemic. Ensure eardrum is intact before treatment.

• Otitis interna

• Appropriate systemic antibiosis depending on etiology

• If bulla osteotomy is required, swab for culture and sensitivity.

• E. cuniculi

• Co-trimoxazole at 30 mg/kg PO b.i.d. for at least 3 weeks

• Albendazole at 10 mg/kg PO s.i.d. for 6 weeks

• Fenbendazole at 10 mg/kg s.i.d. PO for 1 month

• Radiculoneuropathy

• Consider euthanasia. Small “carts” have been used to support the back-end of rats with similar disorders, thereby allowing some voluntary movement. The ethics of this should be considered carefully.

• Seizures

• Phenobarbital at 10 to 20 mg/kg PO b.i.d.

• Phenytoin at 25 to 50 mg/kg PO b.i.d.

Ophthalmic disorders

In rats, mice, and gerbils the harderian gland can produce tears rich in porphyrins when the rodent has a concurrent illness. These porphyrins can stain the fur around the eyes and external nares a reddish-brown color—this can be mistaken by owners for hemorrhage; dif­ferentiate either by exposing to UV light (porphyrins fluoresce) or by testing on a urine dipstick (Fig. 4-3).

Viral

• SDAV (coronavirus—rats)

Bacterial

• Uveitis

Parasitic

• Rhabditis orbitalis (rare)

Neoplasia

Other noninfectious problems

• Allergies

• Prolapse (especially Syrian hamsters)

• Glaucoma (possibly inherited in Campbell's Russian hamsters)

• Keratitis sicca

• Microphthalmia/anophthalmia (recessive disorder in black-eyed white, white-bellied, and dominant-spot Syrian hamsters—see Richardson 2003)

• Diabetes mellitus (Russian and Chinese hamsters)

Findings on clinical examination

• Porphyrin secretion around the eyes (SDAV in rats)

• Suborbital swelling (SDAV in rats)

• Keratitis

• Uveitis

• Cataracts (see Endocrine Disorders)

• Corneal ulceration

• Deaths in weanling rats (SDAV in rats)

• Upper respiratory tract signs and swollen neck/salivary glands (SDAV in rats—see

Gastrointestinal Tract Disorders and Respiratory Tract Disorders)

• Swollen globe (glaucoma); may prolapse and/or ulcerate

• Nematodes present on the cornea (Rhabditis orbitalis)

Investigations

1. Routine ophthalmic examination

2. Radiography

3. Routine hematology and biochemistry

4. Culture and sensitivity

5. Endoscopy

6. Biopsy

7. Ultrasonography

8. Tonometry

a. Rat: 13.9 ± 4.2 mm Hg (Lewis rats)

b. Mice: 13.7 ± 0.8 mm Hg (C3H strain); 12.3 ± 0.5 mm Hg (B6 strain);

9.4 ± 0.5 mm Hg (A/J strain); 7.7 ± 0.5 mm Hg (BALB/c strain)

TreatmentZspecific therapy

• Uveitis

• Topical ophthalmic steroid or NSAID preparations

• Topical ophthalmic antibiotic preparations plus systemic antibiosis if appropriate

• Enucleation if severe

• Prolapse/ulceration

• Tarsorrhaphy

• Glaucoma

• Enucleation (hereditary form)

• Otherwise treat as for uveitis.

• Keratitis sicca

• Topical cyclosporine A ointment

• Covering antibiosis

• Rhabditis orbitalis

• Ivermectin at 400 pg/kg SC, topically; repeat weekly as necessary.

Endocrine disorders

Neoplasia

• Thyroid neoplasia

• C-cell tumors (rats)

• Follicular cell adenomas (mice)

• Hyperadrenocorticism (Cushing disease)

• Adrenocortical adenoma/carcinoma

• Pituitary adenoma

• Insulinomas

Other noninfectious problems

• Hypothyroidism

• Diabetes mellitus (inherited in Russian and Chinese hamsters)

• Iatrogenic hyperadrenocorticism (glucocorticoid therapy)

Findings on clinical examination

• Bilateral symmetrical alopecia of flanks

• Weight loss

• Ataxia, head tilt, and other CNS signs (pituitary hyperplasia/adenomas)

• Thin skin (hyperadrenocorticism)

• Alopecia, hyperpigmentation, cold intolerance, thick skin, and lethargy (hypothyroidism in hamsters)

• Hyperpigmentation

• Polydipsia, polyuria, polyphagia (hyperadrenocorticism, diabetes mellitus)

• Cataracts, weight loss (diabetes mellitus)

• Secondary infections and parasitic infestations (diabetes mellitus)

• Intermittent weakness, collapse, seizures (insulinoma)

• Pseudopregnancy, mammary gland hyperplasia/neoplasia (pituitary hyperplasia/ adenomas in rats—see also Reproductive Disorders)

Investigations

1. Radiography

2. Routine hematology and biochemistry

a. Diabetes mellitus (Table 4-5)

b. Hyperadrenocorticism (Table 4-6). Note: Hamsters may secrete both cortisol and corticosterone, so diagnosis on cortisol levels alone may be inaccurate.

c. Hypothyroidism (Table 4-7)

3. Culture and sensitivity

4. Urinalysis

a. Ketonuria occasionally seen in diabetic hamsters

5. Endoscopy

6. Biopsy

7. Ultrasonography

a. Enlarged adrenal gland(s)

TreatmentZspecific therapy

• Diabetes mellitus

• Provide a high-fiber, low-fat diet.

• Oral hypoglycemic agents such as glyburide may prove useful in hamsters.

• The author has used the oral hypoglycemic metformin hydrochloride oral solution 500 mg/5ml at 0.1 mL b.i.d. in a rat with diabetes mellitus.

• In rats, Keeble (2001) reports that twice-daily treatment with a medium duration insulin product at 1.0 IU/kg SC can give stabilization, combined with twice daily urinary glucose monitoring.

• In hamsters, neutral protamine Hagedorn (NPH) insulin may be useful, but titration and subsequent dosage may prove difficult long term at home.

• In gerbils diabetes mellitus is associated with obesity and high sunflower intake.

• Insulinoma

• Surgical resection

• Glucocorticoid therapy may give palliative results for a period of time.

• Hyperadrenocorticism

• Pituitary hyperplasia/adenomas in rats

- Toremifene at 12 mg/kg PO s.i.d.

- Early ovariohysterectomy may prevent adenoma formation.

• Surgical adrenalectomy

• Hamsters (Keeble 2001): Metyrapone 8 mg PO s.i.d. for 4 weeks

- Mitotane 5 mg PO s.i.d. for 4 weeks

- Trilostane 2-4 mg/kg PO every 24 hours

• Palliative and supportive treatment

• Hypothyroidism

• Supplement with thyroxine (e.g., levothyroxine) at 10 pg/kg daily in divided doses.

• Thyroid neoplasia in rats

• Usually involves C-cells and, therefore, does not produce typical thyroid disease- associated signs.

Urinary disorders

Viral

• LCM virus (arenavirus—mouse, hamster)

Bacterial

• Cystitis

• Leptospirosis (wild rodents); usually asymptomatic but is significant zoonosis

Parasitic

• Trichosomoides crassicauda (bladder threadworm)

• Encephalitozoon cuniculi (rats)

Neoplasia

• Can be related to T. crassicauda infestations in the rat

Other noninfectious problems

• Glomerulosclerosis, with an interstitial fibrosis (rats)

• Glomerulonephritis

• Amyloidosis

• Urolithiasis (especially hamsters)

Findings on clinical examination

• Nonspecific signs of ill health (e.g., hunched posture, ruffled coat, reduced appetite)

• Weight loss

• Polydipsia, polyuria

• Ascites

• Fibrous osteodystrophy

• Dysuria

• Hematuria

• Preputial hemorrhage

• Uroliths may be palpable in the penile urethra of males (especially hamsters)

• Hairlike nematode visible in rat urine (T. crassicauda)

Investigations

1. Urinalysis (Table 4-8)

2. Radiography

3. Calculi (may accompany T. crassicauda infestations in the rat)

4. Routine hematology and biochemistry

a. Rats with glomerulosclerosis, biochemistry findings may show elevated urea (normal, 2.2 to 8.3 mmol/L) and creatinine (normal, 17.7 to 70.7 pmol/L).

b. Eosinophilia (T. crassicauda)

5. Serology for LCM virus

6. Culture and sensitivity

7. Endoscopy

8. Ultrasonography

9. Biopsy

Management

• Supportive care, especially fluid therapy

• Feed more natural diet; rats fed more refined foods tend to develop chronic renal disease earlier (Fallon 1996).

TreatmentZspecific therapy

• LCM virus: Potentially fatal zoonosis so consider euthanasia

• T. crassicauda

• Combination therapy (Bowman et al 2004):

- Ivermectin at 0.2 mg/kg SC weekly for 3 weeks

- Fenbendazole at 20 mg/kg PO s.i.d. for 5 days

• Thorough and repeated cage sanitation

• Urolithiasis

• Cystotomy and/or urethrotomy

• Hamsters especially prone as they naturally produce triple phosphate and calcium carbonate crystals in their urine.

Reproductive disorders

The mammary tissue in small rodents, especially rats and mice, can be quite extensive and may extend laterally up the neck, flanks, and perineum.

Viral

• Mouse mammary tumor viruses (MMTV; retroviruses)

• LCM virus (hamster, mouse—see Systemic Disorders)

Bacterial

• Mycoplasma pulmonis (endometritis, pyometra; rats—see Respiratory Tract Disorders)

• Staphylococcus aureus (preputial gland abscess—mouse, rat)

Fig 4-5. Postmortem snowing uterine neoplasm in a rat.

• Streptococcus spp.; streptococcal mastitis in hamsters

• Pasteurella pneumotropica (preputial gland abscess, pyometra—mouse, rat, hamster)

• Salmonellosis (cause of testicular hyperplasia in gerbils—see Gastrointestinal Tract Disorders)

• Mastitis

Nutritional

• Hypovitaminosis E in hamsters

Neoplasia

• Uterine neoplasia (Fig. 4-5)

• Preputial gland neoplasia

• Mammary gland adenocarcinomas and carcinomas (especially mice); may be triggered by MMTV

• Mammary gland fibroadenomas (especially rats); can grow extremely large and suffer significant abrasions

• Ovarian neoplasia

• Interstitial cell tumors and other testicular neoplasia

• Pituitary hyperplasia/adenoma (rat—see Endocrine Disorders)

Other noninfectious problems

• Uterine prolapse (mouse—rare)

• Ovarian follicular cysts (cystic ovaries)

• Pseudopregnancy

• Physiologic postestrus vaginal discharge (hamster). This is clear and should not be mistaken for a vaginitis.

• Pregnancy toxemia (see Systemic Disorders)

Findings on clinical examination

• Swollen viscus palpable in females (uterine neoplasia, pyometra, pregnancy)

• Swollen abdomen (pregnancy, phantom pregnancy, abdominal mass, ascites)

• Symmetrical alopecia (cystic ovaries)

• Bilateral swelling around penis (preputial gland abscess—mouse, rat)

• Unilateral swelling next to penis (preputial gland neoplasia)

• Single or multiple swellings of mammary tissue. Note: In rats and mice the distribution of mammary tissue can be extensive, spreading some way up the flank, neck, and perineal area.

• Mastitis

• Pseudopregnancy, mammary gland hyperplasia/neoplasia, CNS signs, hyperadrenocorticism (pituitary hyperplasia/adenomas in rats—see also Endocrine Disorders)

• Male sterility, abnormal gestation, muscular weakness, and paralysis in hamsters (hypovitaminosis E)

• Testicular enlargement

• If unilateral consider neoplasia. This appearance may be exacerbated as the other testicle may also reduce in size. Occasionally a hard mass may be palpable in an otherwise normal testicle.

• Bilateral in gerbils—salmonellosis

Investigations

1. Radiography

a. Enlarged uterus (pyometra, neoplasia)

2. Ovarian cysts

3. Routine hematology and biochemistry

4. Serology for LCM virus (hamster)

5. Culture and sensitivity

6. Endoscopy

7. Biopsy

8. Ultrasonography

a. Ovarian cysts

TreatmentZspecific therapy

• Bacterial diseases

• Appropriate antibiosis

• Bacterial infections (e.g., pyometra) may follow an outbreak of respiratory disease

• LCM virus may induce pyometra

• Preputial gland abscess

• Lance, flush, and drain. Administer appropriate antibiosis.

• Preputial gland neoplasm

• Surgical removal

• Mammary gland neoplasia

• Surgical resection

• Implantation with the GnRH-agonist deslorelin (Suprelorin) at the time of surgery may prevent or delay the recurrence of further mammary neoplasia in rats.

• Early implantation with deslorelin may prevent the formation of mammary neoplasia in rats.

• Early ovariohysterectomy may reduce incidence of mammary neoplasia in rats.

• Other neoplasia

• Surgical removal where practical

• Uterine prolapse

• Replace uterus and apply suture to retain; poor prognosis; may require ovariohysterectomy

• Mastitis

• Systemic antibiosis

• May require debriding and application of antibiotics or medications to enhance healing (e.g., topical amorphous hydrogel dressings to encourage secondary healing such as IntraSite Gel from Smith and Nephew Healthcare Ltd)

• Pseudopregnancy

• In hamsters, lasts 7 to 13 days; usually resolves spontaneously

• Ovarian cysts

• Ovariohysterectomy (treatment of choice)

• Draw fluid off by paracentesis

• Attempt hCG at 1000 IU/kg SC weekly for 1 to 3 weeks

• Hypovitaminosis E in hamsters

• Supplement with vitamin E.