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Bovine malignant catarrhal fever

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Bovine malignant catarrhal fever
Virus classification
Group:
Group I (dsDNA)
Family:
Herpesviridae
Subfamily:
Gammaherpesvirinae
Genus:
Macavirus
Binomial name
Alcelaphine gammaherpesvirus 1 (AlHV-1)
Ovine gammaherpesvirus 2 (OHV-2)

Bovine malignant catarrhal fever (BMCF) is a fatal lymphoproliferative disease[1] caused by a group of ruminant gamma herpes viruses including Alcelaphine gammaherpesvirus 1 (AlHV-1)[2] and Ovine gammaherpesvirus 2 (OvHV-2)[1][3] These viruses cause unapparent infection in their reservoir hosts (sheep with OvHV-2 and wildebeest with AlHV-1), but are usually fatal in cattle and other ungulates such as deer, antelope, and buffalo.[2] In Southern Africa the disease is known as snotsiekte, from the Afrikaans.[4][5]

BMCF is an important disease where reservoir and susceptible animals mix. There is a particular problem with Bali cattle in Indonesia,[6] bison in the US[7] and in pastoralist herds in Eastern and Southern Africa.[8][9]

Disease outbreaks in cattle are usually sporadic although infection of up to 40% of a herd has been reported. The reasons for this are unknown. Some species appear to be particularly susceptible, for example Pére Davids deer,[10] Bali cattle[6] and bison,[7] with many deer dying within 48 hours of the appearance of the first symptoms and bison within three days.[1][11] In contrast, post infection cattle will usually survive a week or more.[12]

Epidemiology

The term bovine malignant catarrhal fever has been applied to three different patterns of disease:

  • In Africa, wildebeests carry a lifelong infection of AlHV-1 but are not affected by the disease.[2] The virus is passed from mother to offspring and shed mostly in the nasal secretions of wildebeest calves under one year old.[13][14] Wildebeest associated MCF is transmitted from wildebeest to cattle normally following the wildebeest calving period. Cattle of all ages are susceptible to the disease, with a higher infection rate in adults, particularly in peripartuent females.[15] Cattle are infected by contact with the secretions, but do not spread the disease to other cattle. Because no commercial treatment or vaccine is available for this disease, livestock management is the only method of control. This involves keeping cattle away from wildebeest during the critical calving period. This results in Massai pastoralists in Tanzania and Kenya being excluded from prime pasture grazing land during the wet season leading to a loss in productivity.[16] In Eastern and Southern Africa MCF is classed as one of the five most important problems affecting pastoralists along with East coast fever, contagious bovine pleuropneumonia, foot and mouth disease and anthrax.[17] Hartebeests and topi also may carry the disease.[18] However, hartebeests and other antelopes are infected by a variant, Alcelaphine herpesvirus 2.
  • Throughout the rest of the world, cattle and deer contract BMCF by close contact with sheep or goats during lambing. The natural host reservoir for Ovine herpesvirus 2 is the subfamily Caprinae (sheep and goats) whilst MCF affected animals are from the families Bovidae, Cervidae and suidae.[19][20] Susceptibility to OHV-2 varies by species, with domestic cattle and zebus somewhat resistant, water buffalo and most deer somewhat susceptible, and bison, Bali cattle, and Père David's deer very susceptible.[21] OHV-2 viral DNA has been detected in the alimentary, respiratory and urino-genital tracts of sheep[22] all of which could be possible transmission routes. Antibody from sheep and from cattle with BMCF is cross reactive with AlHV-1.[18]
  • AHV-1/OHV-2 can also cause problems in zoological collections, where inapparently infected hosts (wildebeest and sheep) and susceptible hosts are often kept in close proximity.[23]
  • Feedlot bison in North America not in contact with sheep have also been diagnosed with a form of BMCF. OHV-2 has been recently documented to infect herds of up to 5 km away from the nearest lambs, with the levels of infected animals proportional to the distance away from the closest herds of sheep.[24]

The incubation period of BMCF is not known, however intranasal challenge with AHV-1 induced MCF in one hundred percent of challenged cattle between 2.5 and 6 weeks.[25] Shedding of the virus is greater from 6–9 month old lambs than from adults.[1] After experimental infection of sheep, there is limited viral replication in nasal cavity in the first 24 hours after infection, followed by later viral replication in other tissues.[1]

Clinical signs

The most common form of the disease is the head and eye form. Typical symptoms of this form include fever, depression, discharge from the eyes and nose, lesions of the buccal cavity and muzzle, swelling of the lymph nodes, opacity of the corneas leading to blindness, inappetence and diarrhea. Some animals have neurologic signs, such as ataxia, nystagmus, and head pressing. Peracute, alimentary and cutaneous clinical disease patterns have also been described.[26] Death usually occurs within ten days.[27] The mortality rate in symptomatic animals is 90 to 100 percent.[21] Treatment is supportive only.

Diagnosis

Diagnosis of BMCF depends on a combination of history and symptoms, histopathology[26] and detection in the blood or tissues of viral antibodies by ELISA[28][29] or of viral DNA by PCR.[22][30][31] The characteristic histologic lesions of MCF are lymphocytic arteritis with necrosis of the blood vessel wall and the presence of large T lymphocytes mixed with other cells.[1] The similarity of MCF clinical signs to other enteric diseases, for example blue tongue, mucosal disease and foot and mouth make laboratory diagnosis of MCF important.[32] The world organisation for animal health[26] recognises histopathology as the definitive diagnostic test, but laboratories have adopted other approaches with recent developments in molecular virology. No vaccine has as yet been developed.

Vaccine

Unfortunately a vaccine for malignant catarrhal fever (MCF) has not yet been developed.[1] Developing a vaccine has been difficult because the virus will not grow in cell culture and until recently it was not known why. Researchers at the Agricultural Research Service (ARS) found that the virus undergoes changes within the animal's body, a process known as "cell tropism switching". In cell tropism switching, the virus targets different cells at different points in its life cycle. This phenomenon explains why it has been impossible to grow the virus on any one particular cell culture.

Because the virus is transmitted from sheep to bison and cattle, researchers are first focusing on the viral life cycle in sheep. The viral life cycle is outlined in three stages: entry, maintenance, and shedding. Entry occurs through the sheep's nasal cavity and enters into the lungs where it replicates. The virus undergoes a tropic change and infects lymphocytes, also known as white blood cells, which play a role in the sheep's immune system. In the maintenance stage the virus remains on the sheep's lymphocytes and circulates the body. Finally, during the shedding stage, the virus undergoes another change and shifts its target cells from lymphocytes to nasal cavity cells, where it is then shed through nasal secretions.[33] This discovery undoubtedly puts scientists on the right track for developing a vaccine – starting with the correct cell culture for each stage of the virus lifecycle – but ARS researchers are also looking into alternative methods to develop a vaccine. Researchers are experimenting with the MCF virus that infects topi (an African antelope) because it will grow in cell culture and does not infect cattle. Researchers hope that inserting genes from the sheep MCF virus into the topi MCF virus will ultimately be an effective MCF vaccine for cattle and bison.[33] While there is much ground left to cover, scientists are getting closer and closer to developing a vaccine.

References

  1. ^ a b c d e f g O'Toole, D; Li H (March 2014). "The pathology of malignant catarrhal Fever, with an emphasis on ovine herpesvirus 2". Veterinary Pathology. 51 (2): 437–452. doi:10.1177/0300985813520435. PMID 24503439. Retrieved 21 March 2014.
  2. ^ a b c "Blue wildebeest and the aetiological agent of bovine malignant catarrhal fever". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  3. ^ Schultheiss PC, Collins JK, Spraker TR, DeMartini JC. J Vet Diagn Invest. 2000 Nov;12(6):497–502.
  4. ^ Elizabeth S. Williams; Ian K. Barker (28 February 2008). Infectious Diseases of Wild Mammals. John Wiley & Sons. pp. 157–. ISBN 978-0-470-34481-1.
  5. ^ Lee Merriam Talbot; Martha H. Talbot (1963). The Wildebeest in Western Masailand, East Africa. National Academies. pp. 52–. NAP:13180.
  6. ^ a b "PCR detection of ovine herpesvirus-2 DNA in Indonesian ruminants—normal sheep and clinical cases of malignant catarrhal fever". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  7. ^ a b "An outbreak of sheep-associated malignant catarrhal fever in bison (Bison bison) after exposure to sheep at a public auction sale". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  8. ^ "Assessing the impact of Malignant Catarrhal Fever in Ngorongoro District, Tanzania. A study commissioned by the Animal Health Programme, DFID". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  9. ^ "Maasai perception of the impact and incidence of malignant catarrhal fever (MCF) in southern Kenya". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  10. ^ "Malignant catarrhal fever in Père David's deer". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  11. ^ "Malignant catarrhal fever in a bison (Bison bison) feedlot, 1993–2000". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  12. ^ "Malignant catarrhal fever in cattle in the UK". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  13. ^ Mushi, E. Z.; Rurangirwa, F. R. (1981). "Malignant catarrhal fever virus shedding by infected cattle". Bull Anim Health Prod Afr. 29 (1): 111–2. PMID 7296019.
  14. ^ Baxter, S. I.; Wiyono, A.; Pow, I.; Reid, H. W. (1997). "Identification of Ovine Herpes Virus-2 infection in sheep". Archives of Virology. 142: 823–831. doi:10.1007/s007050050121.
  15. ^ Barnard, B. J.; Van der Lugt, J. J.; Mushi, E. Z. (1994). "Malignant Catarrhal Fever". In Coetzer, J. A. W.; Thompson, G. R.; Tustin, R. C. (eds.). Infectious Diseases of Livestock. New York: Oxford University Press. ISBN 0-19-570506-8.
  16. ^ Homewood, K. H.; Rodgers, W. A.; Arhem, K. (1987). "Ecology of pastoralism in Ngorongoro Conservation Area, Tanzania". J. Agric. Sci. Camb. 108: 47–72. doi:10.1017/S0021859600064133.
  17. ^ Boone, R. B.; Coughenour, M. B. (2001). A system for integrated management and assessment of east African pastoral lands. Balancing food security, wildlife conservation, and ecosystem integrity. Final report to the Global Livestock Collaborative Research Support Program (Report).
  18. ^ a b Fenner, Frank J.; Gibbs, E.; Paul, J.; Murphy, Frederick A.; Rott, Rudolph; Studdert, Michael J.; White, David O. (1993). Veterinary Virology (2nd ed.). Academic Press. ISBN 0-12-253056-X.
  19. ^ "Intra-nasal inoculation of American bison (Bison bison) with ovine herpesvirus-2 (OvHV-2) reliably reproduces malignant catarrhal fever". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  20. ^ "Comparison of ovine herpesvirus 2 genomes isolated from domestic sheep (Ovis aries) and a clinically affected cow (Bos bovis)". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  21. ^ a b "Malignant Catarrhal fever" (PDF). The Center for Food Security and Public Health at Iowa State University. 2005. Retrieved 2006-05-13.
  22. ^ a b Hüssy D, Stäuber N, Leutenegger CM, Rieder S, Ackermann M. "Quantitative fluorogenic PCR assay for measuring ovine herpesvirus 2 replication in sheep, Clinical and Diagnostic Laboratory Immunology 8(2001),pp.123–128". {{cite journal}}: Cite journal requires |journal= (help)
  23. ^ "Development of a management program for a mixed species wildlife park following an occurrence of malignant catarrhal fever". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  24. ^ "Long distance spread of malignant catarrhal fever virus from feedlot lambs to ranch bison". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  25. ^ "An immunisation strategy for the protection of cattle against alcelaphine herpesvirus-1-induced malignant catarrhal fever". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  26. ^ a b c OIE. OIE Manual of Diagnostic Tests and Vaccines for terrestrial Animal, fifth ed., France. pp. 570–579.
  27. ^ Carter, G.R.; Flores, E.F.; Wise, D.J. (2006). "Herpesviridae". A Concise Review of Veterinary Virology. Retrieved 2006-06-10.
  28. ^ "Development of an enzyme-linked immunosorbent assay for the detection of antibodies against malignant catarrhal fever viruses in cattle serum". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  29. ^ "A simpler, more sensitive competitive inhibition enzyme-linked immunosorbent assay for detection of antibody to malignant catarrhal fever viruses". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  30. ^ "Development of a multiplex real-time PCR for detection and differentiation of malignant catarrhal fever viruses in clinical samples". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  31. ^ "Validation of nonnested and real-time PCR for diagnosis of sheep-associated malignant catarrhal fever in clinical samples". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  32. ^ "Clinical differentiation of malignant catarrhal fever, mucosal disease and bluetongue". {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
  33. ^ a b "Figuring Out Puzzling Animal Diseases". USDA Agricultural Research Service. 2010-04-02. Archived from the original on 2010-04-05. Retrieved July 9, 2017.
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