CLINICAL COCCIDIOSIS IN BROILER CHICKS NATURALLY INFECTED AND IMMUNOSUPPRESSED WITH DEXAMETHASONE

ABSTRACT The purpose of this study was to evaluate the occurrence of clinical coccidiosis in broilers immunosuppressed with dexamethasone. Male and female broiler chickens, from 35 to 38 days old were divided into 3 groups – group I (n = 25), including chickens without coccidiosis and negative for coccidia in fecal examination; group II (n = 25), including birds with coccidiosis and positive for coccidia in fecal examination; group III (n = 25), constituted by chickens with no coccidiosis, negative for coccidia in fecal examination and immunosuppressed with dexamethasone (4 mg/kg/day for 4 days, subcutaneous route). The diagnosis of coccidiosis was achieved using the centrifugal floatation technique in sucrose solution to investigate the presence of oocystis in stools, as well as by the observation of macroscopic and microscopic changes in the gut after necropsy. The immune response was evaluated by determination of cutaneous basophil hypersensitivity (CBH) response to phytohemagglutinin (PHA) and of the weight ratio of bursa of Fabricius and spleen in relation to body weight. Broilers from group II and III presented decreased CBH reaction to PHA in relation to group I, suggesting a decrease of the immune response. In addition, chickens from group III presented a significant decrease in the weight of the bursa of Fabricius and of the spleen. The coccidian types were E. acervulina and E. maxima in chickens from groups II and III, as well as E. tenella in chickens treated with dexamethasone. Immunosuppression induced by dexamethasone increased susceptibility to natural coccidiosis in commercially raised broiler chicks.

摘要 本研究旨在评估地塞米松免疫抑制肉鸡的临床球虫病发生情况。试验选取35至38日龄的公母肉鸡，分为3组：第I组（n=25）为无球虫病且粪便检查球虫呈阴性的肉鸡；第II组（n=25）为患球虫病且粪便检查球虫呈阳性的肉鸡；第III组（n=25）为无球虫病、粪便检查球虫呈阴性且经地塞米松免疫抑制（4mg/kg/天，皮下注射，连续4天）的肉鸡。本研究采用蔗糖溶液离心浮聚法检测粪便中卵囊，并通过剖检后观察肠道的大体及显微病理变化，确诊球虫病。通过检测肉鸡对植物血凝素（phytohemagglutinin, PHA）的皮肤嗜碱性粒细胞超敏反应（cutaneous basophil hypersensitivity, CBH），以及法氏囊（bursa of Fabricius）、脾脏重量与体重的比值，评估其免疫功能。结果显示，第II、III组肉鸡对PHA的CBH反应较第I组降低，提示其免疫功能下降；此外，第III组肉鸡的法氏囊及脾脏重量显著降低。第II、III组肉鸡的球虫虫种为堆型艾美耳球虫（E. acervulina）与巨型艾美耳球虫（E. maxima），经地塞米松处理的第III组肉鸡还检出柔嫩艾美耳球虫（E. tenella）。地塞米松诱导的免疫抑制可增强商品肉鸡对自然感染球虫病的易感性。