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.
- Kids should be removed from their dams immediately
after birth to prevent contact with nasal secretions and nursing.
- 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.
- Establish a serologic surveillance program. Testing
every 6 months appears sufficient in small herds with low
seroprevalence.
- 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.
- Milk seropositive does after seronegative does.
- When possible do not breed seropositive animals to
seronegative animals.
- Avoid iatrogenic transmission by disinfecting equipment.
- by Chris Cyr, Class of 1999
- edited by Marlon Rebellato, DVM
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