Chapter3

BIOLOGY OF THE MONGOLIAN GERBIL (JIRD)

(Meriones unguiculatus)

 

 3.1 Taxonomy:

Order: Rodentia

Suborder: Myomorpha

Family: Cricetidae

Subfamily: Gerbillinae

Genus: Meriones

Species: unguiculatus

Origin: Asia (Old World)

 

3.2 General Characteristics:

Somewhat of a cross between characteristics of a rat and hamster. Long, fully haired tail, hind legs adapted for jumping, burrowing, active both day and night, curious, gentle, rarely bite, no specific dietary requirements, foot stomping when excited. More resistant to radiation exposure than other rodents. 

3.3 Anatomical Features:

Length (inc. tail):

25 cm

Weight:

males - 70-120 gms

females - 65-100 gms

Mammae:

2 inguinal, 2 thoracic

Thymus:

Thoracic, persists in adult

Adrenals:

Large

Marking gland:

large in male, on ventral abdomen

Color:

Agouti, black(rare), acromelanic albino (rare)

Body temp.

38.2 - 38.6o C (100.1o F)

Dental formula:

2 (I 1/1 C 0/0 PM 0/0 M 3/3) 

3.4 Environmental Conditions:

Contact bedding, secure cage lid, room temperature, 70-80 (range 60-80o F), humidity maintained below 50% but not less than 30%. 

 3.5 Biological Data 

Feeding:

Commercial rodent rations, avoid "treats" - will eat seeds to the exclusion of regular diet. Consume 5-7 gm feed/animal/day, consume 5 cc water/animal/day if given, or can extract all the water they need from lettuce, apples, carrots, etc.

 Maintenance:

A desert animal, very dry feces, urine output only a few drops per day. Therefore, low odor and can tolerate relatively infrequent cage changing.

 Blood Sampling:

Nail clip, orbit, heart puncture (under anesthesia, not recommended for pet animals). 

Hematology:

Serum often lipemic

PCV:

46-49 (males higher than females)

Hb:

13-15 mg/100 ml

RBC:

8-9 X 106/mm3 Reticulocytes, basophilic erythrocytes, polychromasia common (short RBC life span)

WBC:

9-14 X 103/mm3

Lymphs:

approximately 70-80%

BUN:

20 mg/dl

Protein:

7.8 mg/dl

Glucose:

95 mg/100 ml

Anesthesia:

Reproduction:

 Newborn:

Lifespan:

 

3.6 DISEASES OF THE MONGOLIAN GERBIL 

Nutritional:

Rare, only if fed other than good quality commercial diet. 

Viral:

None reported 

Bacterial:

 Parasitic:

Infrequent or isolated reports of: Demodex, Syphacia, Hymenolepis, Dentostomella 

Neoplastic:

Common, especially ovary, adrenal, marking gland, kidney, spleen"Old age related" - chronic interstitial nephritis, neoplasms, ovarian or periovarian cysts very common. 

Miscellaneous:

Starvation, water deprivation - especially in weanlings; overcrowding leads to tail denuding, rough haircoat with higher than 50% humidity; overgrown incisors - rare but possible; tail amputation; fractures; etc.

 Epilepsy:

Hereditary trait, appears after maturity, latent period 5-7 days, stimulus - novel environment, medication not recommended. No long term or adverse effect on gerbil.

 Treatment:

References:

  • 1. Marston and Chang: Lab. An. Care, 15:34-48, 1965.
  • 2. UFAW Handbook, Edinburgh, p. 263-74, 1972.
  • 3. Gerbil Digest, Tumblebrook Farm, W. Brookfield, Mass.
  • 4. Harkness and Wagner: The Biology and Medicine of Rabbits and Rodents, Lea and Febiger, 1983.

  3.6.1 GERBIL OBJECTIVES 

DISEASES OF THE MONGOLIAN GERBIL 

Spontaneous diseases are uncommon in the Mongolian gerbil (Meriones unguiculatus) as the animals are generally very healthy and hardy. However, the disease syndromes that do occur can be divided as follows:

3.6.2  NUTRITIONAL DISEASES

These are rare if the animal is maintained on a good quality rodent chow. If animals are fed a home-made diet and specific nutrients are lacking, deficiency symptoms for that particular nutrient will be the same as in other animals.

Obesity can be a problem in gerbils if overfed (recommended feeding level is 5 gm/day)

3.6.3 VIRAL DISEASES

None have been reported in gerbils to date as naturally occurring. 

3.6.4 BACTERIAL DISEASES

3.6.4.1 Tyzzer's Disease:

NOTE: Mortality due to Tyzzer's disease is greatest in 3-7 week old gerbils and can reach up to 85%.

In a recent report by Waggie et al. (Lab. Ani. Sci. 34:53-57, l984), it was suggested that Gerbils are extremely susceptible to Tyzzer's Disease, more so than any other animal.

A. Etiology:

Bacillus pillformis, a gram negative pleomorphic, filamentous intracellular organism. Forms subterminal spores and is motile by peritrichous flagella.

B. Transmission:

Occurs by contact with infected animals or their bedding via the fecal route. Predisposing factors include age (younger animals being more susceptible) and physiological stresses such as irradiation, cortisone administration, overcrowding, shipping, poor sanitation, and administration of sulfonamides.

C. Clinical Signs:

Acute, fatal, epizootic hepatoenteric disease. The first sign in a colony situation is sudden unexpected death loss. Other animals of the colony may be exhibiting depression, ruffled hair coat, and varying degrees of watery diarrhea. Emaciation is not usually seen due to the rapid course of the disease. Mortality is usually high.

D. Gross Pathology:

Multiple yellowish white foci of necrosis in the liver; varying degrees of enteritis; edema of the intestinal serosa and possible cardiac involvement.

E. Histopathology:

Foci of necrosis in the organs involved. Varying degrees of intestinal epithelial sloughing with submucosal edema and neutrophilic invasion may be seen. Definitive diagnosis is made by demonstrating the presence of the bacillus in hepatocytes bordering the necrotic foci with Giemsa, PAS, or silver stains. Silver stains are the most consistent in demonstrating the organism.

F. Treatment:

No treatment is effective once signs develop due to the Intracellular nature of the organism and the development of resistant spores. Oxytetracycline (0.1 mg/ml) in the water for 30 days has been reported to abate an epizootic.

G. Control:

Avoidance of stress and strict sanitation. 

3.6.4.2 Sore Nose:

(Nasal or facial dermatitis)

A. Etiology:

Unknown however trauma and Staphylococcus aureus Infections have been associated with sore nose.

B. Transmission:

Predisposition usually includes some type of special burrowing habits or of mechanical injury. The nose is usually involved as the animals can abrade the nose while reaching through cage bars for food and pushing bedding as the animals tunnel. Infection can spread from the nose to the legs and ventral surface of the body. Incidence is higher in weanilings than adults.

C. Clinical Signs:

Abraded nose, focal dermatitis with scab formation.

D. Diagnosis:

Culture of causative organism.

E. Treatment:

Chloramphenicol (0.08 mg/l00 ml water) or tetracycline (0.l mg/ml water) accompanied by daily dips in 0.02% nitrofurozone. Topical ophthalmic ointments may also be used as long as they do not contain streptomycin.

References:

1. Lab. An. Sci. 33:258-263, l983.

2. J.A.V.M.A. 181:1357-1377, 1982. 

3.6.4.3 Enteritis:

A. Etiology:

Salmonella enteritidis, Salmonella typhimurium; other causes can be contaminants in the food, protozoan infection, and stress associated with food deprivation in the young. 

B. Transmission:

Contact with infected individuals or soiled bedding. Salmonella typhimurium usually produces a non-fatal transient infection with recovery in a few days.

C. Clinical Signs:

Moderate to severe diarrhea, rough hair coat, weight loss, listlessness and dehydration. In some cases there is death with no prior signs.

D. Gross Pathology:

Gastrointestinal distension with fluid and gas, fibrinosuppurtive peritonitis, congested liver.

E. Histopathology:

foci of inflammation in the liver that may or may not contain calcified debris; little response in the intestinal system.

F. Treatment:

Tetracycline (0.3 g/l00 ml) or chloramphenicol palpitate (l g/L) in the drinking water.

G. Control:

Proper sanitation and husbandry, prevent food contamination

I. Public Health Significance:

Salmonella typhimurium is known to cause a transient diarrhea in humans. 

 

3.6.5 PARASITIC DISEASES 

Parasitic diseases are an infrequent problem. Some of the more common are:

3.6.5.1 Mite- Demodex Criceti and Demodex aurati

A. Etiology:

Demodex criceti or Demodex aurati 

NOTE: Demodex infection has not been reported in mice rats, guinea pig and rabbits; however, it has been reported in Hamsters.

B. Transmission:

Direct contact.

C. Clinical Signs:

Alopecia, ulcerative dermatitis, hyperemia, scabs at the base of the tail and rear legs. Clinical signs commonly occur when the health status of the animals is compromised, e.g.., old age, dietary deficiencies, or chronic infection.

D. Diagnosis:

Microscopic examination of skin scrapings for the characteristic mite. Since these mites burrow deep into the skin, deep skin scrapings must be collected for microscopic examination. Scraped material is placed on a slide with few drops of warm l0% KOH, covered and allowed to stand for l0 minutes and then examined.

E. Treatment:

Supportive nutrition, clipping hair, bathing with Phisohex or Seleen, Goodwinol ointment, or dips (Lindane-Ronnel mixture) are effective.

3.6.5.2 Pinworms:

A. Etiology:

Syphacia obvelata (mouse Pinworm) and Syphacia muris (Rat Pinworm)

B. Transmission:

Ingestion of embryonated eggs or invasion via anus by infective larve.

C. Clinical Signs:

No clinical signs are usually seen.

D. Gross Pathology:

White hair-like nematodes seen in the cecum or colon.

E. Diagnosis:

Direct examination of cecal contents, fecal flotation or perinatal tape test.

F. Treatment:

Adults may rid themselves of infection; If treatment is desired, piperazine (4-7 mg/ml) in the drinking water for 3-l0 days is effective.

G. Control:

Rigid sanitation.

3.6.5.3 Protozoa:

3.6.5.3.1 Entamoeba sp.

Incidental infection has been reported.

3.6.5.3.2 Trichomonas sp.

Incidental infection has been reported.

 

3.6.5.4 Tapeworms

A. Etiology:

Hymenolepis nana or Hymenolepis diminuta.

B. Transmission:

Hymenolepis nana and Hymenolepis diminuta can be transmitted by an indirect mode with cockroaches or beetles as intermediate hosts. Hymenolepis nana can also be transmitted by direct ingestion of hexacanth ova or by autoinfection in which the entire life cycle occurs in the small intestine without ingestion of ova (complete life cycle in l4-l6 days).

C. Clinical Signs:

Usually no external signs of infection. However, catarrhal enteritis, diarrhea, emaciation, and chronic weight loss may occur with heavy infestation.

D. Gross pathology:

Hymenolepis nana adults range from 25- 40 mm long and less than l mm wide and have an armed rostellum. Hymenolepis diminuta adults range from 20-60 mm in length and 3-4 mm wide with no hooks on the scolex. Often the tapeworms migrate up the pancreatic and biliary ducts.

E. Diagnosis:

Fecal flotation and examination for hexacanth ova, direct examination of intestine, histopathological examination of tissues.

F. Treatment:

Niclosamide at l0 mg/l00 gm body weight orally should be given in 2 treatments at 7 day intervals.

G. Control:

Cockroaches should be eliminated and infected animals treated. Strict vermin control program should be instituted.

H. Public Health Significance:

Humans are susceptible to Hymenolepis nana infection; since autoinfection can occur, a heavy parasite load may quickly develop.

 

3.6.5.5 Dentostomella:Round worm

A. Etiology:

Dentostomella translucida.

B. Transmission:

Direct contact with diseased animals or contaminated bedding.

C. Clinical Signs:

None apparent.

D. Gross Pathology:

Adults range in length from 6 to l3 mm (males) to 9 to 31 mm (females). Eggs are asymmetrically ovoid with a thin shell and granular appearing embryo.

E. Diagnosis:

Fecal flotation or examination of anterior small intestine.

F. Treatment:

None reported. The parasite has only been reported in gerbils in the Columbia, Missouri area. 

 

3.6.6 OLD-AGE DISEASES 

Old-age diseases are very common in gerbils 2 yrs old or older. Older gerbils develop a number of spontaneous neoplasms. Especially common are leiomyomas, subcutaneous fibrosarcomas, sebaceous gland adenomas, adenocarcinomas of marking gland, hemangioma (spleen), adrenal adenomas, malignant melanomas, duodenal adenocarcinomas, etc. Other old age syndromes include cystic ovaries (in 20% of the females) and interstitial nephritis. The lesions in interstitial nephritis are focal in nature with extensive scarring, glomerular atrophy and loss of renal tubular epithelium with formation of tubular casts. Clinical signs include PU/PD and progressive weight loss. The disease is chronic in nature. 

3.6.6.1 EPILEPSY 

The gerbil displays spontaneous epileptiform seizures. The seizures may be precipitated by stress such as handling or exposure to a novel environment. The incidence of seizures is 20% in the natural population. The condition appears to be inherited and both seizure resistant and seizure sensitive strains of gerbils have been developed by selective breeding. The incidence in inbred animals has been increased to near l00%.

The seizures vary in severity from mild hypnotic seizures characterized by cessation of activity and twitching of vibrissae and pinnae to severe myoclonic convulsions followed by tonic extensor rigidity. The mean duration is from 30 sec. to one minute. Death following seizures occurs in only l% of seizure prone gerbils.

The incidence of seizures increases with age and most occur at night. There is no permanent damage to the animal. Severity of seizures also increases with age then levels out after the animal is approximately 6 months old. A refractory period of up to 5 days follows the more severe seizures. Investigators have found that seizures were almost completely suppressed if animals were stimulated during the first 3 weeks of life. Frequent handling of animals from an early age may suppress seizures. Treatment is not necessary and not recommended. 

Ref.: Vincent, A.L., et al.: Lab. Ani. Sci. 29:645-651, 1979. 

 

3.6.7 MISCELLANEOUS DISEASES

3.6.7.1 Starvation:

A problem seen in overcrowding, shipping without food, and in weanlings housed in too deep a cage so that they are unable to reach food and water. Proper husbandry is the main prevention.

3.6.7.2 Water Deprivation:

Seen especially in weanlings who cannot reach the sipper tube. Again, good husbandry is the key to prevention.

3.6.7.3 Tail Denuding:

Is caused by overcrowding and improper handling of the animal.

3.6.7.4 Tail Fractures and "slipped" tail:

Are caused by improper handling of the animal. In such cases, amputation is the only cure. Many gerbils caught and lifted by the tail will slough the tail skin or may fracture the tail. Autoamputation may occur following either trauma or fighting.

3.6.7.5 Rough Hair Coat:

Is often an indicator of excessive humidity levels of the environment (> 50%). this is seen many times when gerbils are housed in aquariums with solid glass tops. The hair appears matted and damp. Prevention is merely to provide adequate air exchange for the environment,

3.6.7.6 Malocclusion:

Due to overgrown incisors, is a rare problem but will occur. Treatment is clipping incisors with nail clippers.

3.6.7.7 Alopecia:

Can occur in infant animals not yet weaned. The cause is unknown and hair will grow as the animals age. It may occur due to bacterial or mite infestations, or chewing and denuding between one another's hair.

3.6.7.8 Dihdrostrepomycin Toxicity:

Dihydrostreptomycin is very toxic to gerbils. 50 mg will cause 80-l00% mortality in 55-65 g gerbils. It causes ascending flaccid paralysis presumably due to inhibition of acetylcholine release from synaptic membranes resulting from overdue of dihydrostreptomycin sulfate.

Ref.: Wightman, S.R., et al.: Lab. Ani. Sci. 30:71-75, 1980.

3.6.7.9 Atherosclerosis:

Not very common but has been reported.

3.6.7.10 Diabetes/Obesity:

Very common in overfed gerbils. Both male and female are equally susceptible.

3.6.7.11 Periodontal disease:

Not very common but has been reported.

Ref.: Vincent, A.L., et al.: Lab. Ani. Sci. 29:645-651, 1979.

3.6.8 REFERENCES 

  • 1. Hoffman, R.A., Robinson, P. F., and Magalhaes, H., eds.: The Golden Hamster. Iowa State University Press, Ames, l968.
  • 2. Kirk R. W.: Current Veterinary Therapy VIII, p. 746-754. W.B. Saunders Co., Philadelphia, 1983.
  • 3. Nutrient Requirements of Laboratory Animals. National Academy of Sciences, 3rd revised edition, 1978.
  • 4. UFAW Handbook on the Care and Management of Laboratory Animals, 4th Ed., Williams and Wilkins Co., Baltimore, l972.
  • 5. Harkness, J.E. and Wagner, J.E.: The Biology and Medicine of Rabbits and Rodents, Lea and Febiger, 1983.
  • 6. Williams, C.S.F.: Practical Guide to Laboratory Animals. C.V. Mosby Co., l976.
  • 7. Marston, J.H. and M.C. Chang: Lab Animal Care, l5:34-48, l965.
  • 8. Gerbil Digest, Tumblerbrook Farm, W. Brookfied, MA.
  • 9. Fox, J.G. et al.: Laboratory Animal Medicine, Chapter 7, Academic Press, Inc., 1984.