Effect of oral levamisole treatment of cockerels on their responses to experimental intraocular infection with velogenic newcastle disease virus
This study was conducted to evaluate the effect of oral levamisole treatment of cockerels on their responses to experimental intraocular infection with velogenic Newcastle disease virus (NDV) and to assess whether the treatment would affect the course of the disease process by altering the immune response. There were 3 infected groups of 20 cockerels each (4 weeks of age) with 10 as non-infected controls. The infected groups were orally treated with levamisole at 5 mg/kg daily for 3 consecutive days either before infection (TBI) or from days 4 after infection (TAI), or were not treated (NTI). Morbidity, antibody responses, mortality and pathological changes were monitored in the infected groups during the period post-infection (pi). Clinical morbidity was not affected by treatment, but mortality period was significantly (P<0.05) shorter in TBI and TAI than in NTI groups. Aggregate score of clinical signs was significantly (p<0.05) lower (56.3%) in TBI than in TAI (87.5%) and NTI (100%) groups. All infected birds showed weight loss and stunting. Hyperthermia was more severe in TBI than TAI and NTI on day 2 postinfection (pi). Antibody response was lower (P<0.05) in TBI and TAI than NTI on days 7-14 pi, but was higher (P<0.05) in TBI than TAI. Thereafter, TBI exhibited higher (P<0.05) antibody response than TAI and NTI on day 21 pi. Neuronal damage by the virus in all infected groups was evident histopathologically but only TAI and NTI showed torticollis. Levamisole treatment of infected birds did not reduce the morbidity and mortality, but suppressed antibody response at the early phase followed by a delayed strong antibody response in TBI probably due to earlier activated T-helper cell function. Therefore, immunological alterations attributable to levamisole treatment did not seem to have rescued the chickens from the outcome of the disease to warrant its use to manage Newcastle disease outbreaks.
Keywords: Clinical signs, cockerels, haemagglutination inhibition test, intraocular infection, levamisole treatment, velogenic Newcastle disease virus