Bovine malignant catarrhal fever

Bovine malignant catarrhal fever (BMCF) is a fatal lymphoproliferative disease caused by a group of ruminant gamma herpes viruses including Alcelaphine Herpes Virus 1 (AlHV-1)^[1] and Ovine Herpes Virus 2 (OvHV-2) ^[2] These viruses cause inapparent 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.^[1]

BMCF is an important disease where reservoir and susceptible animals mix. There is a particular problem with Bali cattle in Indonesia,^[3] bison in the USA^[4] and in pastoralist herds in Eastern and Southern Africa.^[5][6]

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,^[7] Bali cattle^[3] and bison,^[4] with many deer dying within 48 hours of the appearance of the first symptoms and bison within three days.^[8] In contrast, post infection cattle will usually survive a week or more.^[9]

Contents 1 Epidemiology 2 Symptoms 3 Diagnosis 4 Vaccine 5 References

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.^[1] The virus is passed from mother to offspring and shed mostly in the nasal secretions of wildebeest calves under one year old.^[10][11] 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.^[12] 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.^[13] 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.^[14]Hartebeests and topi also may carry the disease.^[15] 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.^[16][8] 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 Pere David's deer very susceptible.^[17] OHV-2 viral DNA has been detected in the alimentary, respiratory and urino-genital tracts of sheep^[18] all of which could be possible transmission routes. Antibody from sheep and from cattle with BMCF is cross reactive with AlHV-1.^[15]
• 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.^[19]
• 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.^[20]

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.^[21]

Symptoms

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, inappetance 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.^[22] Death usually occurs within ten days.^[23] The mortality rate in symptomatic animals is 90 to 100 percent.^[17] Treatment is supportive only.

Diagnosis

Diagnosis of BMCF depends on a combination of history and symptoms, histopathology^[22] and detection in the blood or tissues of viral antibodies by ELISA^[24][25] or of viral DNA by PCR.^[18][26][27] 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.^[28] The world organisation for animal health^[22] 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. 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. [1] 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 tofi (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 tofi MCF virus will ultimately be an effective MCF vaccine for cattle and bison. ^[29] While there is much ground left to cover, scientists are getting closer and closer to developing a vaccine.

References

1. ^ ^{a b c} Plowright W; Ferris RD; Scott GR. Nature. 1960 Dec 31;188:1167-9. 
2. ^ Schultheiss PC, Collins JK, Spraker TR, DeMartini JC. J Vet Diagn Invest. 2000 Nov;12(6):497-502.
3. ^ ^{a b} Wiyono A; Baxter SI; Saepulloh M; Damayanti R; Daniels P; Reid HW. Vet Microbiol.1994 Sept;42(1):45-52. 
4. ^ ^{a b} Berezowski JA; Appleyard GD; Crawford TB; Haigh J; Li H; Middleton DM; O'Connor BP; West K; Woodbury M. J Vet Diagn Invest.2005 Jan;17(1):55-8. 
5. ^ Cleaveland S; Kusiluka L; Ole Kuwai J; Bell C; Kazwala R. 2001 Assessing the impact of Malignant Catarrhal Fever in Ngorongoro District, Tanzania. A study commissioned by the Animal Health Programme, DFID. 
6. ^ Bedelian C; Nkedianye D; Herrero M. Prev Vet Med. 2007 Mar 17;78(3-4):296-316. 
7. ^ Reid H; Buxton D; McKelvey WA; Milne JA; Appleyard WT. Vet Rec. 1987 Sept 19;121(12):276-7. 
8. ^ ^{a b} O'Toole D; Li H; Sourk C; Montgomery DL; Crawford TB. J Vet Diagn Invest.2002 May;14(3):183-93. 
9. ^ Holliman A; Daniel R; Twomey DF; Barnett; Scholes; Willoughby K; Russell G. Vet Rec. 2007 Oct 6;161(14):494-5. 
10. ^ Mushi EZ; Rurangirwa FR. Bull Anim Health Prod Afr. 1981 Mar;29(1):111-2. 
11. ^ Baxter SIF; Wiyono A; Pow I; Reid HW. Identification of Ovine Herpes Virus-2 infection in sheep, Archives of Virology 142(1997):823-831. 
12. ^ Barnard BJH; Van der Lugt JJ; Mushi EZ. Malignant Catarrhal Fever. In: JAW Coetzer; GR Thompson; RC Tustin; Editors, Infectious Diseases of Livestock, Oxford University Press, New York (1994). 
13. ^ Homewood KH; Rodgers WA; Arhem K. Ecology of pastoralism in Ngorongoro Conservation Area, Tanzania, J. Agric. Sci. Camb. 108(1987),pp47-72. 
14. ^ Boone RB; Coughenour MB. 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). 
15. ^ ^{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, Inc. ISBN 0-12-253056-X. 
16. ^ Taus NS; Herndon DR; Traul DL; Stewart JP; Ackermann M; Li H; Brayton KA. J Gen Virol.2007 Jan;88(Pt1):40-5. 
17. ^ ^{a b} "Malignant Catarrhal fever". The Center for Food Security and Public Health at Iowa State University. 2005. http://www.cfsph.iastate.edu/Factsheets/pdfs/malignant_catarrhal_fever.pdf. Retrieved 2006-05-13. 
18. ^ ^{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. 
19. ^ Cooley AJ; Taus NS; Li H. J Zoo Wildl Med. 2008 Sep;39(3):380-5. 
20. ^ Li H; Karney G, O'Toole D, Crawford TB. Can Vet J. 2008 Feb;49(2):183-5. 
21. ^ Haig DM, Grant D, Deane D, Campbell I, Thomson J, Jepson C, Buxton D, Russell GC. Vaccine. 2008 Aug 18;26(35):4461-8. 
22. ^ ^{a b c} OIE. In:OIE Manual of Diagnostic Tests and Vaccines for terrestrial Animal, fifth ed., France,pp.570-579. 
23. ^ Carter, G.R.; Flores, E.F.; Wise, D.J. (2006). "Herpesviridae". A Concise Review of Veterinary Virology. http://www.ivis.org/advances/Carter/Part2Chap11/chapter.asp?LA=1. Retrieved 2006-06-10. 
24. ^ Fraser SJ; Nettleton PF; Dutia BM; Haig DM; Russell GC. Vet Microbiol.2006 Aug 25;116(1-3):21-8. 
25. ^ Li H;McGuire TC; Müller-Doblies UU; Crawford TB. J Vet Diagn Invest. 2001 Jul;13(4):361-4. 
26. ^ Cunha CW; Otto L; Taus NS; Knowles DP; Li H. J Clin Microbiol. 2009 Jun 3.. 
27. ^ Traul DL; Taus NS; Lindsay Oaks J; O'Toole D; Rurangirwa FR; Baszler TV; Li H. J Vet Diagn Invest. 2007 Jul;19(4):405-8. 
28. ^ Bexiga R; Guyot H; Saegerman C; Mauroy A; Rollin F; Thiry E; Philbey AW; Logue DN; Mellor DJ; Barrett DC; Ellis K. Vet Rec. 2007 Dec 22-29;161(25):858-9. 
29. ^ "Figuring Out Puzzling Animal Diseases". USDA Agricultural Research Service. April 2010. http://www.ars.usda.gov/is/AR/archive/apr10/animal0410.htm.