The Stealth Chicken Eimeria: E. mivati - a new perspective
Steve H. Fitz-Coy
Schering-Plough Animal Health, Union, NJ 07083
steve.fitzcoy@spcorp.com
Summary: For several decades, the validity of Eimeria
mivati had been challenged and some researchers have accepted this species to be
invalid. Over the past decade or more, several field isolates that
morphologically fit the description of E. mivati, have been secured. Three of
the recent field isolates were purified and aliquots prepared for evaluations
via PCR assays to determine speciation. Thirteen samples of Eimeria including
three E. mivati were submitted blindly to an independent laboratory for PCR
evaluations. The current primers are for E. acervulina, E. brunetti, E. maxima,
E. mitis, E. necatrix, E. praecox and E. tenella. The results showed, the
samples detected were E. acervulina, E. maxima and E. tenella, but the samples
with E. mivati were undetected. Chickens not protected against E. mivati by
either pharmaceuticals or immunization may suffer morbidity and even mortality.
During 1988 and 1990, Fitz-Coy (University of Maryland Eastern Shore), secured
three isolates thought to be E. mivati from commercial broiler farms on the
DelMarVa Peninsula (DMV). Immunization and cross-immunization trials with one of
the isolates against E. acervulina showed that chickens immunized with E.
acervulina and challenged with E. mivati were not protected. However, chickens
immunized with E. mivati and challenged with E. mivati showed good protection.
Between 1991 and 2001, Fitz-Coy isolated several field isolates of Eimeria
fitting the description of E. mivati. These isolates were from broiler farms
from the state of Georgia and the DMV, three of these were selected. The
selected isolates were further studied, including species determined via
polymerase chain reaction (PCR) assay. In 2004, 13 samples of coccidia,
identified only by a numbering system were submitted to an independent
laboratory for PCR assays. Most of the samples were single species, but a few
were multiple species. The identities of the samples were unknown and blindly
evaluated. Following evaluations, the results were compared to the key to match
the results with codes. The only samples that were unidentified via the PCR
assay were E. mivati.
E. mivati is moderately pathogenic for chickens and on some occasions, has
caused mortality. In one such study, a mortality rate of 40% occurred in a group
of naïve chickens; however, there was no pathology in the hyper-immunized
hatch-mates.