Vaccine 30 (2012) 322–328 Contents lists available at SciVerse ScienceDirect Vaccine j ourna l ho me pag e: www.elsevier.com/locate/vaccine Transmission of a live Eimeria acervulina vaccine strain and response to infection in vaccinated and contact-vaccinated broilers Francisca C. Velkers a,b,∗ , Annemarie Bouma a , J. Arjan Stegeman a , Mart C.M. de Jong b a Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80151, 3508 TD Utrecht, The Netherlands b Quantitative Veterinary Epidemiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands a r t i c l e i n f o Article history: Received 10 March 2011 Received in revised form 17 August 2011 Accepted 30 October 2011 Available online 7 November 2011 Keywords: Eimeria acervulina Vaccination Broiler Transmission Oocyst output Infection dynamics a b s t r a c t Live vaccines for coccidiosis control are infrequently used in broilers, mainly due to variability in efficacy and relatively high costs. More insight in transmission of vaccine and wild-type strains can facilitate optimization of vaccination strategies and might increase its use as an alternative for anticoccidial drugs. The aim of this study was to quantify transmission of a live Eimeria acervulina vaccine strain and to determine the degree of protection against a subsequent infection with a wild-type E. acervulina strain. An experiment was carried out with 4 groups of 22 SPF broilers. At 2 days of age, 11 birds of groups 2 to 4 were vaccinated directly by oral application of E. acervulina oocysts of the Paracox TM vaccine and 11 birds were placed in contact with these birds (contact-vaccinated). Birds in group 1 remained unvaccinated (controls) and were not exposed to vaccinated birds. At day 28 of age, 6 groups of 10 birds were formed, with 2 groups (duplo) for each treatment group, i.e. vaccinated, contact-vaccinated or unvaccinated control birds. Five birds of each group were orally inoculated with wild-type E. acervulina oocysts and five were contact-exposed. Single droppings were examined daily from days 5 to 49 of age for oocyst output and to determine the time of infection. The transmission rate of the vaccine strain was estimated to be 1.6 per day and of the wild-type strain 2.3, 8.7 and 20.8 per day for vaccinated, contact-vaccinated and unvaccinated birds, respectively. Although transmission of wild-type coccidia was not significantly reduced in vaccinated or contact-vaccinated groups, both groups were equally protected against high oocyst output after infection compared to unvaccinated groups. These results suggest that factors influencing transmission of live vaccine strains in flocks may be important targets for improvement of vaccine efficacy and warrant further research. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Coccidiosis is an economically important disease in chickens, caused by species of the protozoan parasite genus Eimeria. Prophy- lactic use of anticoccidial feed additives have been used successfully to control coccidiosis, but concerns on drug residues, legislative bans against medicated feed and increasing emergence of drug- resistant parasites have stimulated demands for alternative control strategies. The parasite is highly immunogenic and an infection may rapidly result in a protective immune response. Vaccination may therefore be a good alternative for anticoccidial drugs to protect against symptoms or production losses and is rather successfully applied worldwide in layer and breeder flocks [1,2]. Up to now, ∗ Corresponding author at: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80151, 3508 TD Utrecht, The Netherlands. Tel.: +31 30 2534447; fax: +31 30 2521887. E-mail addresses: f.c.velkers@uu.nl (F.C. Velkers), a.bouma@uu.nl (A. Bouma), j.a.stegeman@uu.nl (J.A. Stegeman), mart.dejong@wur.nl (M.C.M. de Jong). however, the use in broiler flocks is limited, most likely due to rel- atively high costs in relation to the small profit margins, doubts about the timely onset of protective immunity in birds with such a short life span and concerns about adverse effects on growth [2,3]. Improved efficacy of vaccination strategies could be helpful to increase its use as an alternative for anticoccidials. The short life of broilers makes it challenging to induce suffi- cient and timely protection of a large part of the flock to protect against infections with circulating wild-type strains. Many authors have suggested that a crucial factor for efficacy of vaccination is the uniformity of uptake of the appropriate dose of vaccine strain oocysts by a large enough proportion of birds in the flock at an early age. It is assumed that this is often not fully achieved, probably due to the mass application of live vaccines in broiler flocks [2–5]. Another crucial factor is the immunity boosting effect of multiple re-infections with oocysts from the vaccine or wild-type strain from the environment. The time at which birds are exposed to vaccine and wild-type oocysts in the flock cycle, the uniformity of uptake of (vaccine) oocysts by individuals in the flock and the occurrence of re-infections are influenced by transmission characteristics of 0264-410X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2011.10.090