F. H. Weber,*,1 K. C. Genteman,* M. A. LeMay,* D. O. Lewis, Sr.,* and N. A. Evans†
*Pﬁzer Animal Health, Veterinary Medicine R&D, 301 Henrietta Street, Kalamazoo, Michigan 49007, and †150 East 42nd Street, New York, New York 11201 ABSTRACT Immunization of chickens by in ovoinjection of infective stages of 5 species of Eimeria was investigated. Fertile Hubbard × Petersen broiler chicken eggs were injected through the air cell on d 18 of incubation with oocysts of E. acervulina, E. maxima, E. mitis, E. praecox, or E. brunetti. Injected doses of all species ranged from 1 × 102 to 1 × 106 sporulated oocysts per egg. Chicks receiving oocysts in ovo shed oocysts posthatch. After2 wk in wireﬂoored cages, birds were given a challenge infection with the homologous Eimeria species. Chicks immunized by in ovo injection of oocysts had signiﬁcantly reduced lesion scores, improved weight gain, or reduced oocyst output compared with their nonimmunized counterparts. In additional studies, eggs were injected with 1 × 105 sporozoites of E. tenella, E. maxima, or E. acervulina peregg. Sporozoites of E. acervulina were not infective for chick embryos when administered in phosphate-buffered saline, but if sporozoites were suspended in tissue culture medium when injected in ovo, hatched chicks shed oocysts with peak output occurring 3 to 4 d posthatch. Sporozoites of E. maxima and E. tenella were infective for 18-d-old embryos regardless of the vehicle. The results demonstratethat immunization of broiler chickens against several species of coccidia by in ovo injection of oocysts is feasible. The infectivity of sporozoites for 18-d-old chick embryos varied depending on the species of Eimeria and the vehicle in which the sporozoites were suspended prior to injection.
(Key words: Eimeria, immunization, in ovo, oocyst, sporozoite) 2004 Poultry Science 83:392–399INTRODUCTION
Increasing concern regarding drug resistance among the coccidia of domestic fowl (Chapman, 1997) has stimulated a renewed interest in vaccination as a means of controlling coccidiosis in poultry. The role of live vaccines in managing this disease has recently been reviewed (Allen and Fetterer, 2002; Chapman et al., 2002; Williams, 2002). Although live vaccines have been in use for manyyears for long-lived birds such as broiler breeders, more recent research has focused on application of live vaccines to broilers, which have a shorter life span. Administering live vaccines early in the life of the bird to facilitate earlier infection and therefore more rapid development of immunity is an active area of research. With the development of automated methods for injection of vaccinesin ovo (Johnston et al., 1997), a logical development is the in ovo injection of live coccidia for the control of coccidiosis. Published work in this area to date has been limited, however. Watkins et al. (1995) attempted to vaccinate broiler chickens against Eimeria maxima by in ovo injection
of live oocysts or sporocysts at 17 to 18 d of embryo incubation. Although they found evidence ofinfection in the newly hatched chicks, these birds showed no protective immunity when challenged at 10 d of age. Provaznikova and Bedrnik (1997) reported successful immunization of broilers with an egg-adapted strain of E. tenella by in ovo administration of sporozoites, although this method was unsuccessful for other species of coccidia tested. More recently, studies have demonstrated thefeasibility of immunizing broiler chickens against infection with Eimeria tenella by in ovo injection of oocysts, sporocysts, or sporozoites into 18-d-old chick embryos (Weber and Evans, 2003). The objective of the studies reported here is to expand previous results to other species of Eimeria important in the broiler industry, speciﬁcally E. maxima, E. acervulina, E. praecox, E. mitis, and E. brunetti....