Caprine arthritis encephalitis

Also known as Big knee and Caprine retrovirus infection


The Caprine arthritis and encephalitis (CAE) virus is a lentivirus (slow virus) in the family Retroviridae. CAE virus infection is widespread in dairy goat breeds. Most goats acquire the infection at an early age and they remain infected for life.  Only a proportion develop clinical disease months to years later. CAE is primarily transmitted through ingestion of virus-infected colostrum or milk; however horizontal transmission also occurs by direct animal contact or contaminated fomites.

CAE virus infection in kids from one to six months old may result in encephalomyelitis and includes clinical signs of posterior weakness and ataxia progressing to paralysis. Arthritis occurs predominantly in adult goats and is most noticeable in the carpal joints, giving rise to the term ‘big knee’.  Clinical signs in adult animals may include lameness, ill thrift, weight loss, viral and indurative mastitis (‘hard udder’) and chronic progressive pneumonia.

Diagnosis and tests available


Diagnosis is supported by history, clinical signs, viral serology and histopathology.

Since the majority of infected animals are subclinical, viral serology is the preferred method for detecting infection in individual goats and herds. A positive viral serology result infers infection, but does not confirm that the clinical signs are caused by CAE virus.

Histopathology can assist in providing a definitive diagnosis.

Tests available


Sample(s) required

Days of the week test is conducted

Turnaround time1

Caprine arthritis and encephalitis virus antibody ELISA

Clotted blood (red top tube)

Batch tested weekly

Up to 7 days

Histopathology examination

Fixed tissue

Monday –Friday

Up to 2 weeks for brain samples. Up to 5 days for all other sample types.

1 Turnaround times are provided as a guide only. For specific information about your submission please contact Customer Service.

Specimen requirements

Blood (without anti-coagulant)

  • 10ml of blood collected into a plain red top tube
    • Submit chilled

Fixed tissue

  • Carpal joint, brain, spinal cord, lung and mammary gland
    • Submitted fixed in neutral buffered formalin at a 10:1 ratio of formalin: tissue


  • Interpretation of viral serology:  Adult does should not be tested in the period of one month before or after kidding as inconsistent results may occur. In addition, no goat should be tested within one month of vaccination. The antibody against CAE virus is not a protective antibody, so any antibody positive animal should be regarded as infected.  Because the virus is transmitted in colostrum, a kid that has acquired antibody through colostrum is likely to be infected.  It can take up to three months, rarely up to two years, for antibodies to develop after exposure to the virus.  Suspect animals with a negative test result should be retested in a few months time to confirm their negative status.
  • For more comprehensive information on the disease, testing and control in NSW, see the Primefact, Caprine arthritis encephalitis (CAE) (PDF, 74.21 KB).
  • NSW DPI administers a CAE accreditation scheme. For information on the scheme contact