COMPARATIVE PATHOLOGY OF EXPERIMENTALLY INDUCED LOW PATHOGENIC AVIAN INFLUENZA (H7N3) INFECTION IN CHICKEN, DUCKS AND QUAILS
Keywords:chicken, duck, influenza virus, low pathogenicity, pathology, quail
Low pathogenic Avian Influenza Viruses (LPAIVs) are a persistent threat to poultry and have zoonotic potential. Wild birds such as Ducks and Quails may serve as not only carrier but could be intermediate host for mutation of viruses into highly pathogenic forms. Present study compares pathogenesis of LPAIV H7N3 in chicken, ducks and quails. Thirty-two birds of each species were grouped according to route of infection i.e. Intravenous (IV), Oculo-nasal (OCN) and Oral (OR) and a control group with each comprising eight birds. Birds were challenged with LPAIV H7N3 through IV, OCN and OR routes at dose of 0.1ml/bird (1 x 109 EID50 particles) while control group was inoculated with sterile PBS. Birds were monitored daily for development of clinical signs, mortality and mean death time (MDT). Serum samples were collected before infection and days 7, 14 and 21 post-infection. Dead birds were necropsied and surviving birds were euthanized and dissected at the end of experiment for recording gross and histopathological studies. Pathogenicity indices of virus through different routes were calculated. Results revealed cyanosis of comb (75%) and wattles (75%) as the major clinical signs in chicken infected through intravenous route. Chickens infected through OCN route had swollen heads (87%) respiratory disturbance (75%). Mild clinical signs such as depression (2%) and torticollis (1%) were observed in quails. No clinical signs of infection were observed in ducks. Highest mortality was recorded in chicken inoculated through OCN (75%), followed by IV (50%) and OR (38%) routes. MDT was higher (13.6days) in OR route. Quails showed only 25% in IV infection whereas no mortality occurred in ducks. Intravenous pathogenicity index (IVPI) was higher (1.019) in chicken as compared to quails (0.544). Within chicken species higher pathogenicity score was found in OCN (1.419) group as compared to IV (1.019) and OR (0.45) routes. Gross pathological findings included nephritis as predominant lesion in chickens inoculated IV (78%) and OC (50%) routes, whereas OR route showed hypertrophied bursa (30%) and nephritis (35%). Congested lungs and livers were also observed in 25 % of dead birds. Oculo-nasal infection caused lesions in trachea (25%). No gross pathological lesions were observed in ducks and quails. Histological changes such as moderate infiltration of neutrophils cells, necrosis in the renal tubules, and urate deposition and non-suppurative focal interstitial nephritis were observed in IV group where as in OCN, mostly lung tissues showed edematous changes, hemorrhages, and severe congestion. The antibody titers after intravenous inoculation increased from day 7 p.i to day 14 but then declined at day 21. Trend observed was similar in chicken, quails and ducks. It is concluded from the results that chicken are more susceptible to LPAIV H7N3 while ducks and quails are resistant but do seroconvert.
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