Investigation of symptoms and lesions of chickens infected with Eimeria species at low infectious doses

The study aimed to determine the prevalence, symptoms and lesions of coccidiosis in chickens experimentally infected with coccidial oocysts at low doses. Chickens (n = 40, 14 days old, coded MD02 from Minh Du company) were randomly assigned to four equal groups. Group 1, group 2 and group 3 chickens were orally inoculated with 1, 10 & 300 isolated oocysts of Eimeria species, respectively. Meanwhile, the chickens in group 4 were inoculated with phosphate-buffered saline as the control. Chickens in each treatment were raised individually. Fecal samples were collected individually every day after infection for oocysts counting. The results showed that chickens were infected with coccidial oocysts and had typical symptoms and lesions, even chickens were inoculated with one oocyst only. The prevalence of coccidiosis increased gradually with increasing levels of infectious dose, reaching 100% in group 3. The period of oocyst shedding was from 4 to 10 days post-inoculation. The number of oocysts was highest on day 6 post-inoculation. The oocyst counts were positively correlated with the infectious dose. Symptoms of anorexia, lethargy, wing drop and whitish, watery and bloody diarrhea were observed in infected chickens. The major lesions recorded were hemorrhages in the ceca (75 - 100%) and small intestines (100%).