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Histopathology Service
Caprine Arthritis Enchephalitis Virus
Pythiosis in Dogs
Disseminated Intravascular Coagulation
Infectious Pancreatic Necrosis Virus
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Caprine Arthritis-Encephalitis Virus

            Caprine arthritis-encephalitis virus (CAEV) is a lentivirus in the family Retroviridae.  It is antigenically similar to ovine progressive pneumonia virus (OPPV).  The seroprevalence of CAEV in United States dairy goat herds ranges from 38% to 81%.  Both OPPV and CAEV cause life-long persistent infections in sheep and goats, respectively.  With both viruses monocytes and macrophages are the primary target cells for infection.  Generally, less than 35% of infected goats will show clinical signs, and the time from infection to clinical expression may be years.

Clinical Signs

            CAEV infection can be manifested in a variety of clinical forms; arthritis is the clinical form most commonly seen.  The most frequently affected joint is the carpal joint, but virtually all joints have microscopic evidence of infection.  The arthritic form occurs in mature goats, usually over one year of age.  The onset may be sudden or insidious.  Signs may include:  joint swelling, evidence of pain, stiffness, abnormal posture or weight loss.  Dramatic synovial hyperplasia and distention of joints by yellow fluid may be observed grossly at necropsy.  The neurologic form of CAEV is most often seen in kids 2 to 6 months of age.  Clinical signs of this form may appear as a slowly developing paresis and paralysis of the limbs.  Limb involvement may be asymmetrical.  In over 50% of cases other neurologic signs may also be seen, such as blindness, abnormal pupillary light response, nystagmus, head tremors, head tilt, circling, or cranial nerve deficits.  In the early form of the neurologic disease, kids remain bright and alert.  CAEV may also present with mammary gland involvement.  This is characterized by a firm udder and hypogalactia/agalactia in young does.  CAEV can cause a chronic interstitial viral pneumonia, which results in progressive respiratory distress and weight loss.

Transmission

            The major mode of transmission of CAEV is through ingestion of virus-infected colostrum or milk.  Antibodies to CAEV are also ingested with the virus in the colostrum/milk; however, these antibodies do not appear to be protective.  Antibodies from passive immunity are no longer detectable after 6 months of age.  Horizontal transmission between mature goats is possible, as an increase in seroprevalence with age is observed among commingled infected and non-infected animals.  Other potential routes of transmission include:  in-utero, vaginal contact during birth, dam's saliva/respiratory secretions, cross milk contamination between does, blood contaminated veterinary equipment, or venereally.  Infection of CAEV in sheep does not appear likely under natural conditions, although infection can be induced experimentally.

Serologic Diagnosis

            Serology is currently the most widely used means of detecting CAEV.  The anti-CAEV antibody AGID test is commonly employed.  Sensitivity of this test depends on the antigen used.  The CAEV gp135 surface glycoprotein is more sensitive than the CAEV p28 core protein.  The AGID test may give false-negative results, but it has a high specificity.  The ELISA tests are generally considered more sensitive, but less specific than the AGID.  Indirect ELISAs may give false-positive results, because there can be contamination of the antigen preparation with proteins that are cross-reactive.  An indirect ELISA which detects CAEV antibodies in milk has recently been developed.  However, knowing the CAEV status before lactation begins is most useful for planning any changes that might be made in kid rearing.  PCR has also been used to detect viral DNA/RNA in infected animals; however, this test is not currently available for routine diagnostics.

Current Recommendations

The following recommendations have been made to help control CAEV in goat herds.

  1. Kids should be removed from their dams immediately after birth to prevent contact with nasal secretions and nursing.
  1. Feed kids only pasteurized milk and heat treated colostrum.  CAEV can be inactivated by heating colostrum at 56 degrees C (133 degrees F) for 60 minutes.  Temperatures lower than this failed to prevent disease transfer, and temperatures greater than 59 degrees C denature immunoglobulines.  Using cow's milk and colostrum is acceptable if it is also heat treated and pasteurized to prevent other neonatal infections.
  1. Establish a serologic surveillance program.  Testing every 6 months appears sufficient in small herds with low seroprevalence.
  1. Cull or separate seropositive animals.  Separation consists of solid partitions or 2-3 m of space.  Feed bunks and waterers should not be shared between groups.
  1. Milk seropositive does after seronegative does.
  1. When possible do not breed seropositive animals to seronegative animals.
  1. Avoid iatrogenic transmission by disinfecting equipment.

 

- by Chris Cyr, Class of 1999

- edited by Marlon Rebellato, DVM

 

 

 

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