1. Viral Arthritis (VA)
A widespread viral infection of poultry that affects the synovial membrane, tendon sheaths, tendons and myocardium of meat-type chickens, and occasionally turkeys.
Infection occur early in life (less than 2 weeks of age) but hens break down when placed in breeder house (usually slatted floors).
Roasters – over 5 lbs.

2. Comment
Signs and lesions are most often seen involving the tendons of the hocks and legs because these are weight bearing limbs.
Many times Staphylococcus becomes involved as a secondary infection of tendon sheaths.

3. Etiology
Reovirus
First recognized in 1957

4. Incubation Period
3-5 DAYS – but usually musculoskeletal disease presents much later in life.
Enteritis can start to cause nonuniformity of the flock early in life.
Maternal antibody is important in determining the incubation period. This can prevent the disease if MAT is high for the 1st 3 weeks of the broiler’s life.

5. Course of Disease
CHRONIC

6. Method of Spread Via respiratory or digestive routes.
Transovarian. This occurs when the hens are viremic.
For a period of 2-4 weeks, there may be poor chick quality and high mortality in the progeny.

7. Usually low – chronic problem
Morbidity
Frequently 100%
Mortality
Usually low – chronic problem

8. Clinical Signs
Swelling of the tendon sheaths of the digital flexor and metatarsal extensor. A knot is palpable in the tendon above the hock.
Affected birds tend to sit on their hocks and are reluctant to move.
Rupture of the gastrocnemius tendon. This occurs when birds start to jump on the slats. A large bruise may be visible above the hock.
Reovirus induced enteritis will cause diarrhea, feed passage, and poor growth and feed conversion.

9. Crippled bird

10. Swollen Tendon

11. Swollen Tendon

12. Swollen Foot Pad

13. Leg Bruise

14. Postmortem Lesions Edema of tendons.
Excessive fluid in the hock joint.
Rupture of the gastrocnemius tendon and hemorrhaging dorsal to the hock.
Erosion of articular cartilage.
Staph will often invade afterwards causing purulent arthritis.

15. Tendon Hemorrhage

16. Ruptured Tendon

17. Ruptured Tendon

18. Ruptured Tendon

19. Ruptured Tendon

20. Differential Diagnosis
Mycoplasma synovitis
Staphylococci
Trauma

21. Diagnosis
Serology – AGP & ELISA – Interpretation unclear because there are many reoviruses in chickens that do not cause this disease. Reovirus does not produce a strong antibody response.
Virus isolation – CAM of eggs. Virus infects the birds early in life but lesions develop much later so virus is not usually still present.
Histopathology – No lesions associated with viral invasion may be visible 10 weeks post infection. Staph comes in and confuses the picture.
Best is to use history of company problem and clinical signs.

22. Treatment
TLC

23. Prevention and Control
Depopulate farm and decontaminate.
Breeder hens are vaccinated.
Both attenuated and killed vaccine are available.
Must use live vaccine primer before killed vaccine. Problem breeder flocks may receive 2 live followed by 2 killed vaccines. This is very expensive.
Under certain conditions broilers are vaccinated with live vaccines. Can be given with MDV at 1 day of age S.Q.