Foot and mouth disease virus transmission during the incubation period of the disease in piglets, lambs, calves, and dairy cows

K. Orsel, A. Bouma, A. Dekker, J.A. Stegeman, M.C.M. de Jong

Research output: Contribution to journalArticleAcademicpeer-review

45 Citations (Scopus)

Abstract

Transmission of foot and mouth disease (FMD) virus by infected animals may already occur before clinical signs are evident. Quantitative data for FMD transmission rates during this so-called high-risk period are currently lacking and would provide useful information to develop surveillance systems in which the number of new outbreaks is an outcome variable. In order to address this, we used experimental data to quantify transmission in cattle, swine and sheep during the non-clinical phase of the disease. Groups consisted of vaccinated or non-vaccinated animals of one species; half of each group was inoculated with FMDV, the other half was contact-exposed. We estimated the reproduction ratio Rnonclin using a mathematical SIR model. Rnonclin was defined as the average number of secondary infections caused by one infectious individual in its non-clinical phase. Animals not showing clinical signs shed lower amounts of virus than clinically affected ones. Therefore, we estimated transmission proportionally to the virus excretion. Low estimates for Rnonclin in groups with non-vaccinated and vaccinated calves; 0.30 [0.03; 3.43] and 1.03 × 10¿8 [0; ¿] respectively and 0.21 [0.02; 2.48] for the non-vaccinated and 0.16 [0.009; 2.96] for the vaccinated lambs, were observed. These results indicate that only few secondary infections are to be expected from infected calves and lambs when they are not clinically affected. In groups of non-vaccinated piglets estimates were Rnonclin = 13.20 [4.08; 42.68], and in vaccinated piglets Rnonclin = 1.26 [0.18; 8.96]. The estimate for Rnonclin for non-vaccinated dairy cows was Rnonclin = 176.65 [80.38; 388.24], whereas Rnonclin in the vaccinated groups could not be estimated. Our findings suggest that a large number of individuals might have been infected before clinical signs are noticed, especially in non-vaccinated swine and dairy herds. These findings suggest that after clinical recognition of FMD, priority should be given to trace back contacts with swine and dairy farms, as they may already have been infectious in the herd¿s incubation period
Original languageEnglish
Pages (from-to)158-163
JournalPreventive Veterinary Medicine
Volume88
Issue number1
DOIs
Publication statusPublished - 2009

Keywords

  • pseudorabies virus
  • control strategies
  • vaccination
  • epidemic
  • cattle
  • quantification
  • infection
  • sheep
  • pigs
  • netherlands

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