Rat Diseases

1. Rat Diseases

2. Murine Respiratory Mycoplasmosis • Mycoplasmapulmonis • Very common and important! • Transmission: intrauterine and aerosol • Chronic subclinical carrier state; disease precipitated by stress andairway damage • Same as mice…

3. Nasal Discharge – Porphyrin Staining

4. Murine Respiratory Mycoplasmosis- “Cobblestone” lung

5. Streptococcosis • Streptococcus pneumoniae • Humans are primary reservoir • Transmission by aerosol and contact • Incidence of infection is low

6. Streptococcosis • Clinical signs: • URT infection that spreads to LRT • Especially effects young rats • Dyspnea, snuffling, abdominal breathing • Weight loss, hunched posture

7. Streptococcosis • Pathologic findings: • Fibrinopurulent pleuritis • Pericarditis • Otitis media

8. Fibrinopurulent pleuritis

9. Streptococcosis • Diagnosis and treatment: • Histology and culture • Oxytetracycline in water will control mortality but will not eliminate carrier state

10. Rat Bite (Haverhill) Fever • Streptobacillusmoniliformis • Commensal in nasopharynx of wild and some laboratory rats • Transmission: (rat bites, aerosol, contaminated bedding, fomites) • Zoonotic (endocarditis/DJD)

11. Rat Bite Fever • Diagnosis: • Very difficult to culture • Treatment: • Penicillin (no procaine use Pen G benzathine or Streptomycin if used in rats)

12. Tyzzer’s Disease • Etiology:  Clostridium piliforme is a gram-negative, obligate intracellular rod that produces spores • See mice….

13. Clinical Signs: •   Subclinical infection is the most common form of infection in the rat. Clinical manifestations of Tyzzer's disease include anorexia, hunched posture, distended abdomen, rough hair coat and death.  Diarrhea has not been reported in the rat. 

14. Gross Pathology: •   A "fat rat" syndrome with a flaccid segmental dilatation of the intestine (especially of the ileum) has been described.  The liver typically has multiple pale foci throughout. Circumscribed, greyish foci may sometimes be observed in the myocardium. Multiple necrotic foci in sections of  liver and myocardium are often surrounded by a pyogranulomatous cellular infiltrate

15. Staphylococcal Dermatitis • A syndrome of ulcerated to scabby skin lesions on the dorsal cervical or cranial regions occur frequently in some rat colonies .  This syndrome appears to be seasonal with most cases occurring in the spring and occasionally the fall.Trauma to the skin from fighting, scratching, etc. is thought to be an inciting factor.  • In many cases, Staphylococcus sp., including S. aureus and S. epidermidis, have been isolated from the wounds.

16. Staphylococcal Dermatitis • Combination therapy of oral benadryl (10 mg/kg) and chloramphenicol (50 mg/kg) has resulted in resolution of ulcerative lesions.    • Clipping  toenails of the hind foot has allowed healing of the wounds without antibiotic therapy • Clean with Nolvasan

17. Sialodacryoadenitis virus (SDAV) • Very common coronavirus • Highly contagious via aerosol, contact, fomites • Tropism for salivary, lacrimal, Harderian gland, and lung • Usually mild disease (strain dependent)

18. Sialodacryoadenitis virus (SDAV) • Clinical signs (transient): • Oculonasal porphyrin staining • Enlarged submaxillary salivary gland • Exophthalmus and blepharospasm (keratitis/corneal ulcers) • Photophobia • Sniffling, nasal crackles

19. SDAV- Exopthalmia

21. – Swollen edematous salivary glands – Cervical lymph node enlargement

22. interstitial pneumonia

23. SDAV- Pathology & Diagnosis • Coagulative necrosis & squamous metaplasia of gland types above • Rhinitis, tracheitis, focal bronchitis, bronchiolitis w/ neutrophil infiltrate • ELISA

24. SDAV- Treatment • No treatment available • No carrier state • Spread contamination throughout large colony so that every rat gets infected or separate out clinical cases in small colony • Cease breeding for 2 months

25. Parvoviruses (RV, H-1, RMV, and RPV-1a) • Etiology: Parvoviruses are single stranded DNA viruses. Multiple species of parvoviruses in rats include Rat Virus (RV or Kilham rat virus), H-1 (Toolan's H-1 virus), Rat Minute Virus (RMV 1a, 1b and 1c) and Rat Parvovirus 1 (RPV-1a).  Of these, RV is the only virus species reported to cause clinical disease in rats

26. Parvovirus cont.. • Transmission is primarily by direct contact or contact with fomites. • Clinical Signs: Parvovirus infections are usually subclinical. • In newly infected breeding colonies, RV causes decreased fertility, fetal resorption, small litters, and runting of pups.

27. Parvovirus cont.. • Diagnosis: Serologic assays are used for virus identification • Control: Eliminate seropositive rats and replace with parvovirus-free animals. Since parvoviruses can survive for weeks in the environment, environmental clean-up with parvovirocidal disinfectants is critical to prevent re-infection of clean rats

28. Parasites

29. Radfordia ensifera “Rat Fur Mite” • Relatively common • Transmission by direct contact • May be subclinical, or cause: • Scruffiness, pruritus, patchy alopecia, self-trauma, skin ulcerations, pyoderma, secondary bacterial infections

30. Radfordia ensifera “Rat Fur Mite” • Diagnosis: collection and examination of mites

31. Treatment: • Ivermectin at 0.2 mg/kg SQ may be effective when administered every 2 to 3 weeks for a total of 3 treatments

32. Flagellated Protozoa • Spironucleus muris and Giardia muris are protozoa that colonize the upper small intestine; Spironucelus muris dwells in the mucosal crypts of the small intestine and in the pylorus, and Giardia muris resides along the villous enterocytes in the anterior small intestine.

33. Syphaciamuris (Rat Pinworm) •  Transmission:  Syphaciamuris deposits eggs in the perianal region.  Transmission of infection occurs via ova ingestion.  The eggs are very light and have been shown to aerosolize, resulting in widespread exposure.  The incidence of infection is high.

34. Clinical Signs:  • No signs are usually seen.  It has been reported that heavy parasite loads may lead to catarrhal enteritis, or perianal irritation causing hair to be chewed off the tail base

35. Diagnosis: • Direct exam of cecal contents, fecal flotation, and tape test of the perianal region will identify adults and eggs, respectively.  The eggs are slightly smaller and more symmetrical than those of Syphacia obvelata.

36. This image shows adult pinworms found in the cecum and large intestine

37. Treatment: • If treatment is desired, piperazine (4 to 7 mg/ml water) for 3 to 10 days is effective.  Karo syrup can be added to the solution if the rats refuse to drink it.  • Fenbendazole medicated feed provided every other week for 5 weeks has been an effective treatment method. • Ivermectin at 0.2 mg/kg subQ weekly for 2 to 3 weeks or in drinking water (25 mg/liter) for 4 to 5 daily treatments 3 days apart.

38. Control: • Rigid sanitary procedures, use of filtered cage tops to prevent aerosol transmission, and regular ova examinations with treatment may control the parasitism.

39. NEOPLASTIC DISEASES

40. Mammary Fibroadenoma • Most common rat tumor • Almost always benign • Rare in males • Fast growing • Will make you a hero (easy to fix) • Surgical excision (be quick, look for “feeder vessel”, keep rat warm and well hydrated)

41. Mammary Fibroadenoma • Because of the extensive mammary tissue present in rats, tumors may be found practically anywhere--behind the shoulder blades, at the base of the tail, etc. Look mom, I can Carry my tumor!

42. Mammary Fibroadenoma With surgical removal, the prognosis is good, although recurrence in another location is common. 

43. Pituitary Chromophobe Adenoma •  This is an extremely common tumor of rats, although incidence varies with strain.  Grossly, tumors are soft with an irregular surface and may have prominent hemorrhagic areas.  They are generally well circumscribed and compress adjacent brain tissue, occasionally causing hydrocephalus resulting in depression or head tilt.  The tumors commonly secrete prolactin

44. MISCELLANEOUS  DISEASES

45. Malocclusion • Autosomal recessive trait • Incisors overgrown poorly aligned • Inanition, oral trauma, ptyalism (“slobbers”), starvation • Diagnosis- just look • Do not breed these rats • Clip w/sharp human nail clippers but avoid scissoring action. Dremmel-type dental disc every 2 to 3 months

46. Malocclusion

47. Heat Exhaustion • Rats have a limited ability to regulate body temperature with the primary thermoregulatory mechanism being tail vein dilation or constriction.  • Males also use scrotal vasculature for same purpose • Hyperemic scrotum (pathognomonic)

48. Heat Exhaustion • Predisposing factors to heat exhaustion are ambient temperatures above 28oC (85oF), high humidity (about 80%), poor ventilation and overcrowding • The rats salivate profusely to wet the hair coat for cooling, and water consumption increases (see photo).  • Death from heat exhaustion can be diagnosed from history of high temperature, lack of water (or empty water bottles), saliva soaked chins • Treatment of affected rats includes cool water baths, forced-feeding water, and subcutaneous saline or 5% dextrose administration

49. Ringtail • Low environmental humidity (<40%) • Annular constriction of the base of the tail • More common in weanlings and rats in wire-bottom cages • Tail may slough • Increase humidity and provide bedding

50. Ringtail • Tail stumps usually heal without complication. Prevention of ringtail is accomplished by providing sufficient environmental humidity, reducing drafts, and maintaining room temperatures between 70oF to 74oF.