Update On Caprine Arthritis Encephalitis (CAE) Virus
Fall, 2008
Caprine arthritis encephalitis (CAE) is a lentiviral infection of goats
which may lead to chronic disease of the joints and on rare occasions
encephalitis in goat kids less than six months of age. The CAE virus is
intimately associated with white blood cells; therefore, any body secretions
which contain white blood cells are potential sources of virus to other goats in
the herd. Since not all goats that become infected with CAE virus progress to
disease, it is important to test goats routinely for infection by means of a
serology test which detects viral antibodies in the serum.
We have had numerous inquiries about CAE virus, how to test for it, and most
importantly, how to take steps to control the infection in goat herds. It is
important to remember that ‘goat infection status,
not clinical disease, is the element of interest in assessing risk factors
and designing control programs for CAE virus’ (Rowe & East, 1997). We have
taken some of the most frequently asked questions and presented them along
with some short answers.
1. What are the major means of spread of the virus?
The CAE virus is primarily transmitted to kids via colostrum in the first
few feedings after birth. Blood (e.g., contaminated instruments such as
needles, dehorners, etc, and open wounds) is regarded as the second most
common way of spread. Contact transmission between adult goats is considered
to be rare except during lactation.
2. May an owner sample goats and send the serum directly to the
lab?
The diagnostic laboratory provides services to veterinarians. Although we
will test goat serum samples mailed directly from an owner, we strongly
encourage goat owners to work with a veterinarian in developing a CAE
control program. We will send results to the veterinarian, and also to the
owner if requested.
3. How should I ship samples for CAE viral antibody testing?
We recommend working with your veterinarian to obtain appropriate samples.
Blood should be collected into a five or ten ml. "red-top" clot tube or
serum separator tube, and immediately sent to the lab by overnight mail. Do
not refrigerate blood before clot retraction is evident - keep at room tem.
4-6 hours or package and ship without ice packs. We do not recommend
separating the serum from the clot prior to shipment. Colostrum and milk are
NOT validated samples in this test method.
Please number the tubes consecutively to match a key sheet with the animal
names. (See
key sheet for example) Overnight package delivery should be sent to:
WSU-WADDL, 155N Bustad Hall, Pullman, WA 99164-7034. WADDL offers discounted
shipping through Federal Express (1-3 lbs. $10 in-state, $18 out of state,
over 3 lbs., actual rates). Use the WADDL account number on the air bill and
specify "Standard Overnight Service." Please call the lab for our Federal
Express Account number for discounted shipping. Shipping fees will be added
to the testing charges. The address for post office mail is Washington
Animal Disease Diagnostic Laboratory (WADDL), P.O. Box 647034, Pullman, WA
99164-7034. An ice pack is recommended if shipment is expected to take
several days in warm weather. Pack tubes in a plastic sealable bag, with
absorbent material in with the tubes, and put another plastic bag around the
first. Pack so the box can be dropped from four feet height without
breaking any tubes!
4. How long does it take to get CAE virus serology results?
CAE competitive ELISA tests are generally run once a week, on Thursday
morning, with reports going out on Friday. During busy times, the test may
be set more than one time per week. However, to be tested on Thursday,
samples must arrive by Wednesday afternoon. Results can be phoned or Faxed
to the veterinarian and/or owner upon request. At present, we are not
emailing results but are working toward using email for notification of
results in the future.
5. What does it cost for testing at WADDL?
In-state (WA) costs are a $10 accession fee per case, and $4.00 for each.
Costs for out-of-state residents are a $10 accession fee and $6.00 for each.
Please do not send payment with the samples. We will bill
the veterinarian or owner directly.
6. What does a positive or negative mean?
A positive result means the goat has been infected with the
CAE virus and has made antibodies reactive with the CAE antigens used in
this test. This goat is regarded as potentially contagious for the virus,
especially if lactating. The antibody against CAE is not a protective
antibody, and although strong antibody reactions may be detected in this
test, infectious virus can still be spread in milk and blood of this goat.
As many as 90% of positive goats may be free of clinical signs of the
disease, and remain so for years or life. A young goat which has received
heat-treated colostrum containing CAE antibodies may also test antibody
positive for several months because of passive transfer of maternal
antibodies. We recommend retesting these kids after six months of age to
determine their true status.
A negative result means that this goat is either not
infected, or has been recently infected and is producing amounts of antibody
too low to be detected. While the latter case does not appear to be common,
it is a good reason to retest all negative goats when not in a closed herd.
Goats that are negative should be periodically tested (twice a year for the
1st year, and annually thereafter). Predictability (or reliability) of a
test result is often used to assess the overall accuracy. For the CAE cELISA,
the predictability of positive and negative test results is very high.
7. Can an animal testing positive ever test negative on future
tests?
It is unlikely that a CAE virus infected adult goat which has tested
positive would ever test negative in the sensitive cELISA test. Occasionally
a very young animal, fed heat-treated colostrum containing CAE antibodies
may test positive and later negative from the decline of passively acquired
antibodies in the colostrum. In some goats, seroconversion may be delayed
for months after exposure. These "silently" infected animals test negative
for antibody until the viral infection is activated by stress or other
factors. It has not been determined whether these goats were infectious to
other goats during the time they harbored the virus but remained
seronegative.
8. Is there a difference in the types of serology tests available
for making a diagnosis of CAE virus infection?
Yes, WADDL has a validated and USDA licensed competitive Enzyme Linked
Immunosorbent Assay (cELISA) for CAE virus antibodies. This test is more
sensitive (ability to detect true positive animal) than the agar gel
immunodiffusion (AGID) test. Values for the CAE cELISA have been set by
double testing goat sera by ELISA and a very sensitive research assay,
called immunoprecipitation. The positive cutoff score for the cELISA had a
sensitivity of 100%, and specificity of 99.6%.
9. Is it okay to drink raw milk containing the infectious CAE
virus?
There is NO evidence that the CAE virus is transmissible to humans. However,
there are other serious human pathogens which have been transmitted through
raw milk. Consult your veterinarian regarding the public health hazards of
consuming raw milk.
10. Biosecurity Screen
We recommend this screen for new animals entering the herd and
animals producing milk for human consumption. This screen includes CAE, Johne's
Disease, caseous lymphadenitis and Brucella. Tests
are priced individually (see:
http://www.vetmed.wsu.edu/depts_waddl/fees.aspx#Immunodiagnostics
11. In heat treating colostrum, what times and temperature
should I use?
Colostrum from any doe may be heated to between 133 degrees and 138
degrees F (56 to 59 degrees C) and held at that temperature for one hour
to inactivate the virus. An accurate thermometer is important. It is
recommended to use a water bath or double boiler to regulate the
temperature more closely. A large batch may be heat-treated and frozen
in small feeding size portions for later use (about one pint per kid).
If heated higher than 140 degrees F, the usefulness of the colostrum
will be greatly reduced due to denaturing of proteins, including
beneficial antibodies to other infectious microorganisms.
12. How often should I test my animals?
Twice a year initially followed by annual testing is suggested for herds
which are primarily negative, with testing before kidding recommended. Any
new animals brought into the herd should be quarantined and tested twice (at
least 30 days apart) before introduction with other negative animals. In
addition to CAE infection, new goats should be tested for Johne’s disease,
and Brucellosis as a biosecurity screen (see #10). For
herds with both positive and negative animals, negative animals should be
tested more often to adjust the milking order so that negative animals are
milked first.
13. Are there other test methods on the horizon?
Yes. WADDL is working with USDA scientists in the development of a
polymerase chain reaction (PCR), which tests for CAE virus specific nucleic
acid. Current PCR assays have lower specificity (more false positives) than
the antibody assays. The PCR assay may become practical and financially
affordable enough for routine testing, especially in goats that have delayed
seroconversion.
Additional information on CAE virus and other infections of
livestock can be obtained by contacting your local veterinarian or the
diagnostic laboratory at 509-335-9696, FAX 335-7424.
REFERENCES
1. Rowe, JD and NE East: Risk factors for transmission and methods for
control of caprine arthritis-encephalitis virus infection. Vet Clinics No
Amer 13:35-53, 1997.
2. Adams, DS, et al: Transmission and control of caprine
arthritis-encephalitis virus. Am J Vet Res 44:1670-1675, 1983.
3. Vander Schalie, J, et al: Evaluation of a kinetic enzyme linked
immunosorbent assay for detection of caprine arthritis-encephalitis
virus-specific antibodies. J Vet Diagn Invest 6, 30-33, 1994.
4. Evermann, JF: Control of CAE virus takes work and periodic testing.
United Caprine News. Winter, 2002 update.
5. Steele, JH: History, trends, and extent of pasteurization. J. Am Vet
Med Assoc 217:175-178, 2000.
6. Knowles, DP Jr: laboratory diagnostic tests for retrovirus infections
of small ruminants. Vet Clinics No Amer 13:1-11, 1997.
7. Greenwood, PL et al.: Prevalence, spread and control of caprine
arthritis-encephalitis virus in dairy goat herds in New South Wales. Aust.
Vet. J. 72:341-345, 1995.
8. Nord, K et al.: Control of caprine arthritis-encephalitis virus and
Corynebacterium pseudotuberculosis infection in Norwegian goat herd. Acta
Vet Scand 39:109-117, 1998.
9. Ozyoruk, F et al.: Monoclonal antibodies to conformational epitopes of
the surface glycoprotein of caprine arthritis-encephalitis virus. Potential
application to competitive-inhibition enzyme-linked immunosorbent assay for
detecting antibodies in goat sera. Clin Diag Lab Immunol 8:44-51, 2001.
10. Cebra, C and M Cebra: Caprine arthritis-encephalitis virus infection.
In Pugh, DG: Sheep and Goat Medicine, W.B. Saunders, Co. Phil, 2002, pp
388-389.
11. DeMartini, JC et al: Comparison of a Maedi-visna virus fusion protein
ELISA with other assays for detecting sheep infected with No. American ovine
lentivirus strains. Vet Immunol Immunopathol 71:29-40, 1999.
12. Fieni, F et al.: Presence of caprine arthritis-encephalitis virus
(CAEV) infected cells in flushing media following oviductal-stage embryo
collection. Therigenol 57:931-940, 2002.
13. Rolland, M et al.: Characterization of an Irish caprine lentivirus
strain - SRLV phylogeny revisited. Virus Res 85:29-39, 2002.
14. Peterhans, E et al: Routes of transmission and consequences of small
ruminant lentiviruses (SRLVs) infection and eradication schemes. Vet Res:
35:257-274, 2004.
15. deAndres, D, et al: Diagnostic tests for small ruminant lentiviruses. Vet
Microbiol 107: 49-62, 2005.
16. Bertoni, G. Caprine arthritis encephalitis complex.
In Recent Advances in Goat
Diseases, Intl Vet infor Service, NY (www.ivis.org), 2007.
Contacts on CAE:
Dr. James Evermann or
John VanderSchalie
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