title: Vaccination control programs for multiple livestock host species: an age-stratified, seasonal transmission model for brucellosis control in endemic settings.
abstract: BACKGROUND
  Brucella melitensis causes production losses in ruminants and febrile disease in humans in Africa, Central Asia, the Middle East and elsewhere. Although traditionally understood to affect primarily sheep and goats, it is also the predominant Brucella species that affects cows in some endemic areas. Despite this, no licensed vaccine is available specifically for use against B. melitensis in cows. The mainstay of most control programs is vaccination of sheep and goats with a live vaccine, Rev-1. The aim of this study was to investigate how critical vaccination of cows might be, in order to control B. melitensis on a mixed sheep-and-cattle farm.
  
  
  METHODS
  A dynamic, differential-equation, age-structured, seasonal model with births and deaths, was used to investigate whether vaccination of both sheep and cattle had an impact on time to elimination of brucellosis on an individual mixed species farm, when compared to vaccination of sheep only. The model was a Susceptible-Exposed-Infectious-Recovered-Susceptible (SEIRS) model with an additional compartment for Persistently Infected (PI) individuals. Transmission parameters were fit based on a nation-wide probabilistic seroprevalence survey in Jordan.
  
  
  RESULTS
  The model predicted that it would take 3.5 years to eliminate brucellosis (to less than 0.5% of adult sheep seropositive as a result of infection) on a mixed-species B. melitensis-endemic farm with the median field-study seroprevalence, following vaccination of both sheep and cattle, assuming a vaccine effectiveness of 80%. Limiting the vaccination to sheep only, increased the time to 16.8 years. Sensitivity analysis showed that the finding that vaccination of cattle was of significant importance, was robust. Vaccine effectiveness had a strong influence on time to elimination.
  
  
  CONCLUSIONS
  In the absence of further data, vaccination of cattle should be considered essential in Brucella-endemic settings where mixed small ruminant and cattle flocks predominate. Further evidence that Brucella melitensis predominates in cattle in Jordan, as opposed to Brucella abortus, is needed in order to validate this model. The results may be applicable to other mixed-species settings with similar livestock management practices. These methods may be applied to other pathogens affecting multiple livestock species or with seasonal transmission.
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, AL9 7TA, UK. wbeauvais@rvc.ac.uk.|London Centre for Neglected Tropical Disease Research, London, UK. wbeauvais@rvc.ac.uk.
authors.forename: Wendy
authors.initials: W
authors.lastname: Beauvais
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, AL9 7TA, UK. imusallam@rvc.ac.uk.|London Centre for Neglected Tropical Disease Research, London, UK. imusallam@rvc.ac.uk.
authors.forename: Imadidden
authors.initials: I
authors.lastname: Musallam
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, AL9 7TA, UK. jguitian@rvc.ac.uk.|London Centre for Neglected Tropical Disease Research, London, UK. jguitian@rvc.ac.uk.
authors.forename: Javier
authors.initials: J
authors.lastname: Guitian
mesh_terms: D000818:Animals; D002004:Brucella Vaccine / Q000008:administration & dosage* / Q000276:immunology*; D017347:Brucella melitensis / Q000276:immunology*; D002006:Brucellosis / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary*; D002417:Cattle; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D019353:Endemic Diseases; D058751:Livestock; D015233:Models, Statistical; D012756:Sheep
chemical_list: D002004:Brucella Vaccine
references.citation: PLoS Negl Trop Dis. 2011;5(1):e944
references.pmid: 21264355
references.citation: Trop Anim Health Prod. 2011 Oct;43(7):1319-26
references.pmid: 21509455
references.citation: PLoS Negl Trop Dis. 2012;6(10):e1865
references.pmid: 23145195
references.citation: PLoS Negl Trop Dis. 2013;7(2):e2047
references.pmid: 23469294
references.citation: Prev Vet Med. 2015 Mar 1;118(4):247-59
references.pmid: 25529385
references.citation: Epidemiol Infect. 2009 Oct;137(10):1436-48
references.pmid: 19288957
references.citation: Prev Vet Med. 2004 Jun 10;64(1):41-7
references.pmid: 15219968
references.citation: Ann Rech Vet. 1989;20(1):93-102
references.pmid: 2930137
references.citation: Prev Vet Med. 2005 Jun 10;69(1-2):77-95
references.pmid: 15899298
references.citation: Lancet Infect Dis. 2006 Feb;6(2):91-9
references.pmid: 16439329
references.citation: Trans R Soc Trop Med Hyg. 2007 Jul;101(7):707-13
references.pmid: 17442354
references.citation: Prev Vet Med. 2015 Mar 1;118(4):387-96
references.pmid: 25619944