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Caprine arthritis encephalitis (CAE)

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Ratification Date: 03 Dec 2015

Policy

Caprine arthritis encephalitis should be considered by the Animal Health Committee for classification nationally as a notifiable disease. A single national eradication strategy should be developed by the goat industry groups in Australia, and veterinarians should be involved in all stages of the program.

The Goat Health Statement and National Kid Rearing Plan will function as Caprine arthritis encephalitis risk-minimisation strategies.

Background

Caprine Arthritis Encephalitis (CAE) and Maedi Visna (MV) are diseases caused by lentiviruses from the retrovirus family. Due to their similarities, these diseases have been classified together as Small Ruminant Lentiviruses (SRLV) since the early 2000’s.

CAE, also known as Caprine Retrovirus or “Big Knee”, causes chronic peri-arthritis in multiple joints of adult goats, encephalitis (mainly in kids), chronic mastitis (also called “hard udder”) and wasting.

MV can affect both sheep and goats and causes chronic pneumonia and nervous disease.

CAE is widespread in the developed world, and is present in Australia. MV is exotic to Australia. The World Organisation for Animal Health (OIE) requires 6 monthly reporting of CAE and MV incidence.

CAE is spread by body secretions and is present in blood. Infection generally occurs immediately after birth via ingestion of colostrum. Horizontal infection is also possible. CAE is a slow virus and clinical signs are usually not evident until after the first kidding i.e. between 2 and 3 years of age. A significant percentage of a herd may thus be infected before clinical signs become evident, and some carriers never develop signs, so infection rates may be under-estimated.

CAE is present in the Australian dairy goat industry; some producers have successfully eradicated it from their herds, however infected dairy goat herds remain in production.

The incidence of CAE in meat and fibre goats in Australia appears to be low and CAE has not been demonstrated in Australian Rangeland goats.1 The incidence in Boer goats is unknown, as no CAE surveys have been conducted since their release from quarantine into Australia.

Meat and fibre goats have been diagnosed with CAE when kept with CAE positive dairy goats; hence strict segregation between non CAE- accredited dairy goats and other sectors of the goat industry is important to prevent further spread.

Currently CAE is only notifiable in Victoria.

Economic impacts

CAE causes economic loss, although the extent is unknown at present. Two studies showed lower milk production in CAE positive goats.2,3 Goats with CAE have been shown to have higher somatic cell counts and are more likely to develop mastitis.4 One 12 year study showed lower levels of fat, total protein and lactose in CAE infected goats.5

Animal welfare impacts

CAE is also important from an animal welfare perspective as it can cause severe pain and suffering in affected animals. There is no treatment other than palliative care, and animals remain infected for life. It is characterised by chronic peri-arthritis, joint and leg deformities, wasting, chronic mastitis, chronic pneumonia with severe dyspnoea and nervous signs.

Risk to sheep industry

Recent international research has shown the closeness and cross infection capability of CAE in goats and MV in sheep6 and that the similarity between these two diseases warrants their simultaneous control.7,8 Direct evidence of mixed infections of CAE and MV has been found in both sheep and goats overseas, and there is evidence of cross-species transmission. Hence successful control programmes require inclusion of both species”.9,10 In dual-infected animals, viral chimeras have been detected. This means there is an increased risk that highly pathogenic variants may emerge.11 MV is not present in Australia, so the risk of this is currently low.

CAE eradication is progressing world-wide

Successful CAE eradication programs have been in place for over 30 years12,13 but there is variable support for these schemes in the Australian dairy goat industry. Switzerland has eradicated CAE and Norway is likely to be free by the end of 2014. The New Zealand Dairy Goat Cooperative has announced a set date by which all suppliers must be free of CAE. Many countries have succeeded in limiting CAE to certain zones. A single national control scheme with trace- forward and trace-backwards abilities would assist CAE eradication in Australia.

Recommendations

The various state CAE voluntary accreditation schemes which aim to contain the spread of CAE are supported, but a single national scheme would assist producers in controlling the disease. It is recommended that goat industry groups in Australia develop an eradication strategy akin to the dairy cattle Enzootic Bovine Leucosis eradication program. To this end, research into a bulk milk test for CAE in goats’ milk may be warranted. It is recommended that the Australian goat industry follows a similar plan to New Zealand and set a date by which all suppliers must be free of CAE virus. Veterinarians should be involved at all stages including development of the national program, advising goat breeders on implementation of the plan, and sample collection.

Use of the Goat Health Statement, which was introduced to minimise the risk of spread of infection between goat herds, is recommended. See: http://www.farmbiosecurity.com.au/toolkit/declarations-and-statements/)

Use of the National Kid Rearing Plan, introduced for both CAE and Johne’s disease control, is recommended. See: www.animalhealthaustralia.com.au/national/kid/rearing/plan

As CAE is transmitted in body fluids, veterinarians should observe good infection control when treating goats and encourage good biosecurity practices on goat farming establishments.

References

  1. Surman, P. G., E. Daniels and B. R. Dixon. Caprine arthritis-encephalitis virus infection of goats in South Australia. Australian Veterinary Journal 1987;64(9):266-271.
  2. Leitner, G., O. Krifucks, L. Weisblit, Y. Lavi, S. Bernstein and U. Merin (2010). The effect of caprine arthritis encephalitis virus infection on production in goats. Vet J 2010;183(3):328-331.
  3. Sølverød, L. Udder health in Norwegian goat dairy herds. Goat Milk Quality- Regional IGA Conference Tromsø, Norway, International Goat Association, 2013.
  4. Ibid.
  5. Kaba, J., N. Strzalkowska, A. Jozwik, J. Krzyzewski and E. Bagnicka. Twelve-year cohort study on the influence of caprine arthritis-encephalitis virus infection on milk yield and composition. J Dairy Sci 2012;95(4):1617-1622.
  6. Pisoni, G., A. Quasso and P. Moroni. Phylogenetic analysis of small-ruminant lentivirus subtype B1 in mixed flocks: evidence for natural transmission from goats to sheep. Virology 2005;339(2):147-152.
  7. Peterhans, E., T. Greenland, J. Badiola, G. Harkiss, G. Bertoni, B. Amorena, M. Eliaszewicz, R. A. Juste, R. Krassnig, J. P. Lafont, P. Lenihan, G. Petursson, G. Pritchard, J. Thorley, C. Vitu, J. F. Mornex and M. Pepin. Routes of transmission and consequences of small ruminant lentiviruses (SRLVs) infection and eradication schemes. Vet Res 2004;35(3):257-274.
  8. Shah, C., J. B. Huder, J. Boni, M. Schonmann, J. Muhlherr, H. Lutz and J. Schupbach. Direct evidence for natural transmission of small-ruminant lentiviruses of subtype A4 from goats to sheep and vice versa. J Virol 2004;78(14):7518-7522.
  9. Gjerset, B., C. M. Jonassen and E. Rimstad (2007). Natural transmission and comparative analysis of small ruminant lentiviruses in the Norwegian sheep and goat populations. Virus Res 2007;125(2):153-161.
  10. Pisoni, G., A. Quasso and P. Moroni. Phylogenetic analysis of small-ruminant lentivirus subtype B1 in mixed flocks: evidence for natural transmission from goats to sheep. Virology 2005;339(2):147-152.
  11. Minardi da Cruz, J. C., D. K. Singh, A. Lamara and Y. Chebloune. Small Ruminant Lentiviruses (SRLVs) Break the Species Barrier to Acquire New Host Range. Viruses 2013;5(7):1867-1884.
  12. Synge, B. A. and C. M. Ritchie. Elimination of small ruminant lentivirus infection from sheep flocks and goat herds aided by health schemes in Great Britain. Vet Rec 2010;167(19):739-743.
  13. Van Maanen, C., J. M. Brinkhof, L. Moll, B. Colenbrander and D. J. Houwers. Aspects of the epidemiology, research, and control of lentiviral infections of small ruminants and their relevance to Dutch sheep and goat farming. Tijdschr Diergeneeskd 2010;135(16):600-603.