Quantification of foot and mouth disease virus excretion and transmission within groups of lambs with and without vaccination.

Sheep are well known to be susceptible for foot and mouth disease virus (FMDV), but it is unknown whether the infection can spread and persist in a sheep population. We therefore quantified virus transmission by performing experiments with FMD virus strain O/NET/2001 in groups of lambs. We used six groups of four lambs each, in which half of each group was inoculated and the other half was contact-exposed. To quantify the effectiveness of a single vaccination we also included six groups of four lambs each, vaccinated with O Manisa vaccine, 14 days prior to inoculation. Oropharyngeal fluid was obtained with a swab (OPF-swab), and blood samples were collected daily to determine virus excretion and serological response. We calculated the transmission rate beta (the number of new infections per day per infectious animal), and the reproduction ratio R (the number of secondary infections caused by one infectious individual). The mean daily virus excretion and the number of days the lambs excreted virus in the OPF differed significantly between vaccinated and non-vaccinated lambs. The transmission rate beta in the unvaccinated groups was 0.105 (95% confidence limit 0.044; 0.253) per day. The duration of the infectious period (T) was 21.11 (95% confidence limit 10.6; 42.1) days. With the final size of infection we estimated the reproduction ratio R in the non-vaccinated groups to be 1.14 (0.3; 3.3), and in vaccinated groups 0.22 (0.01; 1.78). Virus transmission as quantified by the final size did not differ statistically between the vaccinated and the non-vaccinated groups of lambs. In conclusion, FMDV seems able to persist in a sheep population, although the reproduction ratio was only slightly larger than one. As a consequence, vaccination might only have a small effect on transmission, in spite of the fact that virus excretion and duration of virus excretion is significantly reduced after vaccination.

[1]  R. Kitching,et al.  Transmission of foot-and-mouth disease by vaccinated cattle following natural challenge. , 1989, Research in veterinary science.

[2]  T. Kimman,et al.  Experimental quantification of vaccine-induced reduction in virus transmission. , 1994, Vaccine.

[3]  J. Salt,et al.  Emergency vaccination of pigs against foot-and-mouth disease: protection against disease and reduction in contact transmission. , 1998, Vaccine.

[4]  K. Sorensen,et al.  Differentiation of infection from vaccination in foot-and-mouth disease by the detection of antibodies to the non-structural proteins 3D, 3AB and 3ABC in ELISA using antigens expressed in baculovirus , 1998, Archives of Virology.

[5]  R. Kitching,et al.  Clinical variation in foot and mouth disease: sheep and goats. , 2002, Revue scientifique et technique.

[6]  A. Dekker,et al.  Validation of a LightCycler-based reverse transcription polymerase chain reaction for the detection of foot-and-mouth disease virus. , 2003, Journal of virological methods.

[7]  A Bouma,et al.  Vaccination of pigs two weeks before infection significantly reduces transmission of foot-and-mouth disease virus. , 2004, Vaccine.

[8]  R. Kitching,et al.  Clinical variation in foot and mouth disease: pigs. , 2002, Revue scientifique et technique.

[9]  M. D. de Jong,et al.  The effect of vaccination on foot and mouth disease virus transmission among dairy cows. , 2007, Vaccine.

[10]  E. C. Anderson,et al.  The role of sheep and goats in the epizootiology of foot-and-mouth disease in Kenya , 1976, Journal of Hygiene.

[11]  Zhidong Zhang,et al.  Quantities of infectious virus and viral RNA recovered from sheep and cattle experimentally infected with foot-and-mouth disease virus O UK 2001. , 2002, The Journal of general virology.

[12]  Valerie Mioulet,et al.  Serial passage of foot-and-mouth disease virus in sheep reveals declining levels of viraemia over time. , 2002, The Journal of general virology.

[13]  E. Domingo,et al.  Foot-and-mouth disease virus. , 2002, Comparative immunology, microbiology and infectious diseases.

[14]  W. A. Geering.  FOOT‐AND‐MOUTH DISEASE IN SHEEP , 1967 .

[15]  M. D. de Jong,et al.  Vaccination against foot and mouth disease reduces virus transmission in groups of calves. , 2005, Vaccine.

[16]  R. Burrows.  The persistence of foot-and-mouth disease virus in sheep , 1968, Epidemiology and Infection.

[17]  Kitching Rp.  Clinical variation in foot and mouth disease: cattle. , 2002 .

[18]  M C M de Jong,et al.  Within- and between-pen transmission of Classical Swine Fever Virus: a new method to estimate the basic reproduction ratio from transmission experiments , 2002, Epidemiology and Infection.

[19]  J. Sánchez-Vizcaíno,et al.  Serological evidence of FMD subclinical infection in sheep population during the 1999 epidemic in Morocco. , 2002, Veterinary microbiology.

[20]  M. D. de Jong,et al.  No foot-and-mouth disease virus transmission between individually housed calves. , 2004, Veterinary microbiology.

[21]  P. Barnett,et al.  The role of small ruminants in the epidemiology and transmission of foot-and-mouth disease. , 1999, Veterinary journal.

[22]  B. Baxt,et al.  Foot-and-Mouth Disease , 2004, Clinical Microbiology Reviews.

[23]  Kitching Rp,et al.  Clinical variation in foot and mouth disease: sheep and goats. , 2002 .