Studies On The Epidemiology Of Riemerella Anatipestifer Infections And Its Control In Baise

Riemerella anatipestifer(RA) infection is a contagious disease of ducks,turkeys and various other poultries.It occurs as septicemia characterized by fibrinous pericarditis, perihepatitis,and airsacculitis.Ducklings of 1～7 wk of age are highly susceptible.It is a major disease confronting the duck industry throughout the world.It accounts for significant economic losses due to high morbidity and mortality.RA has many serotypes,and each serotype has not protection function with others.It is easy for RA to develop drug resistance. So far,seroepidemiological information of Riemerella anatipestifer in Guangxi is rare.In particular,there are no epidemiological studies of Riemerella anatipestifer infection in Baise. Therefore,this study was carried out in twelve counties of Baise within the last two years on the diseased ducks which had cellulose pericarditis,liver pericoronitis,and airsacculitis as the main feature,in a comprehensive investigation and research,and that is very necessary for effective control of RA infections.Two hundred and sixty one diseased or death birds with serositis collected from ninety eight flocks of ducks in twelve counties of Baise were used as the samples for the isolation and identification of RA.There were 106 isolates grown on chocolate agar in candle jar from the samples and the colonies were 0.5-2 mm in diameter,entire,convex,transparent,but no colonies grown on MacConkey agar.The bacteria were gram-negative,rod occurring singly, in pairs,and occasionally in chains,many cells stained bipolar with Wright's staining.In the identification of biochemical reactions,all the 106 isolates could not ferment glucose,maltose, fructose,lactose,and mannose or produce H₂S,urease,nitrate,but part of the isolates liquidated gelatins,were peroxidase positive,and that were identical with the RA reference strain NN050021â‘ .All of isolates were also tested by a PCR technique for the amplification of membrane gene and a specific 809bp fragment was amplified from all of isolates,but no from Escherichia Coli(E.coli) and Salmonella isolated from ducks.106 RA isolates were all belong to serotype 1 when a slide agglutination test was performed with the positive sera, which were prepared with RA reference strains of serotype 1,3,and 6 respectively.40 representative isolates were tested for the antibiotics sensitivity with 12 different kinds of commonly used antibiotics and the results showed that most of the isolates were highly sensitive to Cephalexin,Cefradine and Amoxicillin;secondary susceptible to Co-trimoxazole, ampicillin,norfloxacin;while some of the isolates were resistant to chloramphenicol, erythromycin,McGrady-Adriamycin,and demonstrated that the resistance to the common antibiotics was prevalent among the isolates.A total of 203 pathogenic stains were isolated from samples of diseased or death birds with serositis:106 were RA,79 were E.coli,and 18 were Salmonella.Within the positive cases of RA infection,31.13%(33/106) were single infection,51.89%(55/106) were coinfected with E.coli and 16.98%(18/106) were coinfected with Salmonella.9.20%(24/261) of the cases were single infection of E.coli.Ducklings of 2～5 week-old and the fast-growing lines were the most susceptive to RA infection.Challenge experiment showed that RA was virulent and even more virulent while coinfected with E.coli, and ducks survived from the challenge showed that the diseased ducks were less than the healthy duck in weight gain by 43.8 percent.Cephalexin and norfloxacin were used in the treatments on three diagnosed cases with mixed infections of RA with E.coli,the cure rate were 92.86%(715/770),93.26%(443/475) and 94.58%(908/960) respectively,with an average of 93.57%.While the use of Chinese herbal medicine on another three cases with mixed infections of RA with E.coli,the cure rates were 91.55%(531/580),89.25%(772/865),88.76%(679/765) respectively,with an average of 89.85%.An application of commercial vaccine contained the main popular RA serotypes and different vaccine-scale was carded out on five different farms in Baise,and the results showed that the protection rates were 91.67%(1375/1500),90.37%(2711/3000), 89.50%(1790/2000),87.13%(697/800) and 91.20%(912/1000) respectively,with an average of 89.97%.The results of the study demonstrated that RA infection has been one of the most common causes for the losses in duck industry within the 12 counties in Baise and the major epidemic serotype was type 1.RA mainly coinfected with E.coli(51.89%),and some were singly infection(31.13%),and some coinfected with Salmonella(16.98%),while single infection of E.coli were also happened(9.20 percent).Prevention and treatment with medicines and vaccination with the current vaccine are still the two effective technical measures for the control of the disease.Application of high sensitive antibiotics or Chinese herbal medicine for the treatment of six confirmed mixed infections cases of Riemerella anatipestifer with E.coli, as well as the applications of commercial vaccine on five farms in Baise achieved effective treatment and prevention results,and Chinese herbal medicine has great potential in the prevention and treatment of RA infection.Effective control of the disease incidence and prevalence of RA infection has practical significance in the duck industry on both improvement of economic efficiency and reduction of economic losses.