THE ROLE OF E. MITIS IN CHICKEN COCCIDIOSIS: A
STUDY OF PATHOGENICITY
Luciano Gobbi and Raffaele Pezzotti
Schering-Plough Animal Health, Milan, Italy.
luciano.gobbi@spcorp.com
E. mitis is one of seven known Eimeria
species that infects chickens. Its second Latin name, “mitis,” means mild,
because investigators of this pathogen have always considered it to be of minor
significance in poultry.
E. mitis, however, is common in broilers and breeders. It affects the large
intestine, and produces large amounts of small, almost round, oocysts, but it is
hard to identify because it does not cause gross lesions. In addition, some
studies indicate that E. mitis is more pathogenic when it occurs concomitantly
with E. acervulina.
To further investigate E. mitis, a two-phase trial was conducted. In the first
phase, three groups of 14-day-old Ross 508 chickens were infected either with E.
mitis, E. acervulina or saline solution (negative control); on days 4 and 14
after challenge, oocyst shedding and bird performance were evaluated.
Oocyst counts demonstrated successful challenge with both Eimeria species; peak
numbers were hundreds of thousands oocysts per gram (OPG) for E. mitis and
millions of OPG for E. acervulina.
Compared to controls, chickens infected with E. mitis and E. acervulina had
significantly lower daily weight gain, feed intake, and water consumption,
higher feed conversion ratio, and lower final body weight. There was a numerical,
but not statistically significant difference in water and feed intake between
the two infected groups.
In the second trial, three additional groups of 14-day-old Ross 508 chickens
were challenged with E. mitis and E. acervulina, and then injected with
Pontamine Sky Blue dye, enabling evaluation of the intestinal mucosa.
Eimeria-infected chickens exhibited colour differences in the mucosal surface as
compared to controls. Permeability was determined by increased transfer of dye,
which specifically binds to serum proteins and migrates outside blood
capillaries. Dye leakage between 72 and 144 hours post-infection stained
intestinal mucosa and gut contents, confirming cell damage and increased gut
permeability due to multiplication of both Eimeria species.
Both Eimeria infections also caused a significant gut wall thickening as
measured by stereoscopic microscope due to oedema and inflammation from 72 and
144 hours post-infection.
The results indicate that E. mitis can impair chicken performance and cause
losses just like other, better known Eimeria species. Consequently, the name E.
mitis does not, in fact, reflect the real pathogenicity of this Eimeria species,
hence, nomen non est omen.