Efficacy of vaccination with La Sota strain vaccine to control Newcastle disease in village chickens in Nepal

The efficacy of vaccination with Newcastle disease (ND) La Sota and R₂B (Mukteswar) modified live strain vaccines was determined by experimental challenge and with ND La Sota vaccine under field conditions in Nepal. Booster vaccination with ND La Sota vaccine after a primary vaccination with ND La Sota vaccine, induced a geometric mean titre (GMT) of 5.0 log₂ haemagglutination inhibition (HI) units, compared to a GMT of 6.0 log₂ HI units following booster vaccination with R₂B vaccine 1 month after primary vaccination with ND La Sota vaccine. Both vaccines provided 100% protection against challenge with a local field ND strain. Furthermore, booster vaccination with ND La Sota vaccine induced protective levels of antibody after field use in villages in Jhapa, and no outbreaks of ND occurred during the study period. The ND La Sota modified live vaccine is immunogenic and efficacious and is a suitable vaccine for use in vaccination programmes in village chickens in the rural areas of Nepal.

     

Erratum to: Efficacy of vaccination with La Sota strain vaccine to control Newcastle disease in village chickens in Nepal

Tropical Animal Health and Production -     

NDV La Sota株三个病毒克隆株间生物学特性的比较研究

为比较新城疫病毒(NDV)La Sota株不同克隆株之间的生物学特性,本研究通过挑取细胞病变区对LaSota株病毒进行纯化,并获得了3个病毒克隆株。通过血凝素热稳定性试验、病毒复制动力学试验和免疫原性试验,对3个病毒克隆株进行分析比较。结果显示,不同的病毒克隆株间在这些生物学特性上存在着不同程度的差异,表明为了获得性质均一、稳定的病毒,有必要进行病毒的纯化,并根据实验目的进行比较取舍。     

Pathological changes of tracheal mucosa in chickens infected with lentogenic Newcastle disease virus

Forty-day-old specific-pathogen-free chickens were exposed by aerosol to lentogenic Newcastle disease virus (NDV) and observed for 24 days for pathological changes in the tracheal mucociliary system. Specific fluorescence of NDV antigen was observed through day 5 postexposure (PE) in the cytoplasm of the tracheal epithelium and desquamated epithelium in the lumen. On day 1 PE, scanning electron microscopy revealed hypertrophy of goblet cells and small patches of the deciliated epithelium scattered mainly around the openings of mucous glands. The deciliated area of tracheal surface increased through day 4 PE. Light microscopy showed small vacuoles containing lymphocytes and heterophils in the epithelial layer. Immature epithelium proliferated in some areas. On days 5 and 6 PE, ciliated areas of the trachea tended to increase as a result of regeneration of the epithelium, still leaving many nonciliated patches of various sizes. On and after day 8 PE, there remained plaques with nonciliated flat epithelium, but most areas were covered with well-ciliated epithelium. Non-ciliated plaques were observed until day 24 PE, but they gradually decreased in size. These plaques were covered by a single layer of flat epithelium and were formed upon lymph follicles in subepithelial tissue.     

Identification of field isolates of infectious bronchitis virus by interference with the La Sota of strain of Newcastle disease virus

The interference phenomenon of infectious bronchitis virus (IBV) with growth of Newcastle disease virus (NDV) in embryonating chicken eggs (ECE) was used as a diagnostic method. Fifteen field isolates obtained from presumptively infectious-bronchitis-affected chickens were analyzed by the IBV-NDV interference test. Eight isolates were capable of interfering with the growth of the La Sota strain of NDV, as measured by hemagglutination (HA) activity when IBV was inoculated 10 hr before NDV into ECE. The interference was considered specific for IBV, because it could be eliminated by adding homologous anti-IBV serum. The sensibility of this method could be demonstrated, because in some cases low-passage levels of IBV isolates showing HA interference ability were not capable of producing lesions in ECE. Furthermore, serologically negative IBV samples did not interfere with NDV growth. From these results, the IBV-NDV interference test appears to be a potential diagnostic alternative for identifying IBV field isolates.     

Scanning electron microscopy of tracheal epithelium of chickens infected with velogenic viscerotropic Newcastle disease virus

Ultrastructural changes in the tracheal epithelium of chickens infected intranasally with velogenic viscerotropic Newcastle disease virus were examined by scanning electron microscopy. Hypertrophy of the mucus-secreting, or goblet, cells was the first sign of change, followed by disoriented and deformed cilia, hemorrhage, and hyperplasia of goblet cells accompanied by an increase in mucus. By day 7 postinfection, there was a marked decrease in the number of ciliated cells. Submucosal glands and some collagen fibers were exposed to the surface, an indication of loss of the epithelial cells. Macrophages and cell debris were abundant, and hyperplasia of the basal cells was evident in the later stages of infection, probably in an attempt to regenerate the lost epithelium. However, all chickens died 10 days postinfection, before any further work could be done.     

Comparison of the immunogenicity of Newcastle disease virus strains V4, Hitchner Bl and La Sota in chickens

The immunogenicity of three Newcastle disease virus (NDV) strains--V4, Hitchner B1 and La Sota, was assessed in chickens that had varying levels of maternal antibody to the virus. Chickens were immunised at different ages by the eye drop and aerosol methods. The immune response of chickens to similar doses of the strains was affected by the presence of maternal antibody. Both the level of maternal antibody and the strain of virus used affected the result. Strain La Sota was least affected as it took higher levels of maternal antibody to depress response to it than were required to have a similar effect on Hitchner B1 and V4. Strain V4 was the strain most affected by circulating maternal antibody. The results demonstrated that strain V4 was less immunogenic than Hitchner B1 and La Sota when used in chickens with maternal antibody to NDV.     

Immunization of day-old chickens against Newcastle disease.

The avirulent Newcastle disease virus strain designated NDV-6/10, selected by B. Lomniczi at the Veterinary Medical Research Institute, Hungarian Academy of Sciences, is completely safe for day-old chickens by aerosol vaccination. Aerosol immunization using the Hungarian-made MASTERDROP generator (particle size: maximum 7 microns) caused no vaccination reactions among 206,000 chickens with different maternal antibody levels. Other vaccines given simultaneously did not significantly affect the protection elicited against Newcastle disease (ND). Almost 100% and 90% of the aerosolized chickens survived subcutaneous challenge with 10(6) LD50 NDV at 30 and 50 days old, respectively. A single immunization is sufficient for broilers; however, parent flocks should be revaccinated at 7 so 8 weeks old.     

Comparison of the immunogenicity of Newcastle disease virus strains V4, B1 and La Sota in chickens

The immunogenicity of the Australian Newcastle disease virus (NDV) strain V4 was compared with that of the International reference preparation of Hitchner B1 and a commercial La Sota strain. Immunity was assessed serologically using the log mean HI titres 21 days after immunisation, the percentage of birds in each group which developed titres greater than 2(3) and their resistance to graded challenge doses of the virulent Herts 33/56 strain of NDV. These tests showed that the V4 strain was significantly less immunogenic (P less than 0.01) than the B1 or La Sota strains when administered intraocularly (eye drop) or by aerosol methods. When given in the drinking water V4 induced a better immunity (P less than 0.01) than the B1 strain in one of 2 experiments.     

La Sota vaccination may not protect against virus shedding and the lesions of velogenic Newcastle disease in commercial turkeys

The aim of this project is to study the clinical signs and lesion of velogenic Newcastle disease (vND) in commercial turkeys, and also to find out if La Sota vaccination offered protection against these signs and lesions. The cockerels were included as positive controls. One hundred and twenty turkey poults and cockerels were divided into eight groups as follows: unvaccinated unchallenged turkeys (UUT), unvaccinated challenged turkeys (UCT), vaccinated unchallenged turkeys (VUT), vaccinated challenged turkeys (VCT), and along the same lines, the cockerel groups were UUC, UCC, VUC and vaccinated challenged cockerels (VCC). Vaccination was at 3 weeks of age while challenge was at 6 weeks of age. The unvaccinated turkeys and cockerels (UCT and UCC) showed different degrees of depression, diarrhoea and later paralysis at challenge. Total mortality was 100% in cockerels within 6 days, but 60% in turkeys. Similar but milder clinical signs were found in the VCC with a total mortality of 13.3%. The VCT showed mild drop in feed and water consumption, and no mortality. All the challenged groups had significant (p < 0.05) loss of weight when compared with their controls. Necropsy showed that while the UCC had severe proventricular haemorrhages, intestinal and caecal tonsil ulcers, the UCT had no digestive tract lesion. There was severe atrophy of the lymphoid organs in all the challenged groups. Histopathological sections of the bursa, spleen and thymus in all the challenged groups with special emphasis on the vaccinated and unvaccinated turkeys with mortalities of 0 and 60%, respectively, had very severe necrosis and depletion of the lymphoid tissue. Virus was isolated from the cloacal swabs. The haemagglutination inhibition antibodies were significantly higher (p < 0.05) in the challenged groups than the unchallenged. The above observations in the intestinal tracts of UCT are of diagnostic significance while the gross and microscopic lesions in the UCT and VCT show that La Sota vaccination may not protect turkeys against the destruction of the lymphoid organs by vND as earlier reported in chickens. This may lead to immunosuppression and production problems in areas where vND is enzootic.     

Serological response of chickens to oral vaccination with Newcastle disease virus

Conventional Newcastle disease vaccines are not suitable for application to village chickens in tropical countries of Asia. Trials with food-based vaccines are being initiated and the following experiments were performed to evaluate oral vaccination with Newcastle disease virus. Experimental chickens were vaccinated orally with the avirulent V4 strain of Newcastle disease virus and haemagglutination-inhibition antibody responses were measured. V4 virus was introduced into the crop by tube and total faecal output was collected daily and assayed for Newcastle disease virus. Virus was recovered on Days 5 and 6 after vaccination from most chickens that had received 10(7.4) and 10(6.4) 50% egg-infectious doses (EID50) of virus. There was no recovery of virus from birds receiving a lower dose of vaccine. Groups of chickens kept in cages with wire floors were given various doses of vaccine into the crop. Higher antibody titres were achieved with higher doses of virus. This dose responsiveness was not observed when various doses of vaccine were presented on food pellets and the groups of chickens were kept on concrete floors. Similar antibody responses were then seen with nominal doses of 10(5.2) and 10(8.2) EID50 per bird, possibly as a result of excretion and re-ingestion of the vaccine virus. Spread of the vaccine virus was demonstrated when control chickens and chickens receiving 10(7.7) EID50 of V4 virus on food pellets were housed together on a concrete floor. Similar antibody titres were achieved in both vaccinated and in-contact chickens.     

H5亚型高致病性禽流感病毒HA基因重组新城疫病毒活载体疫苗接种后气管黏膜损伤的研究

为了研究H5亚型高致病性禽流感病毒HA基因重组新城疫病毒活载体疫苗[rLa Sota-HA(GD)]的免疫机理,用rLa Sota-HA(GD)免疫2日龄SPF雏鸡,分别在接种后的1,3,5,10,15,18天取气管进行电镜、光镜观察,利用免疫组化染色(IHC)方法检测病毒在气管内的分布。结果表明:接种rLa Sota-HA(GD)后第1天纤毛细胞有脱纤毛现象,杯状细胞破碎,黏液成分增多,黏膜下层的纤维裸露在表面上,并可看到纤毛细胞的纤毛上有球形粒子,杯状细胞、基细胞大量增生;接种后第18天纤毛细胞脱纤毛区域进一步增大。接种后第3天黏膜下层水肿,淋巴细胞、粒细胞、浆细胞浸润,黏膜上皮形成空泡状,表层由数层不成熟的细胞组成;接种后第10天腺体腔闭塞。免疫组化染色可见气管固有层细胞呈阳性反应,棕色颗粒出现在胞浆中。结果说明气管黏膜的损伤是机体重要的防御机制和免疫机制的表现。     

Tracheal mucus transport rate and bacterial clearance in turkeys exposed by aerosol to La Sota strain of Newcastle disease virus

Tracheal mucus transport rate (TMTR) and quantitative clearance of aerosolized Escherichia coli from the trachea, lung, and air sac were measured in healthy unanesthetized turkeys and in turkeys exposed by aerosol to a La Sota vaccine strain of Newcastle disease virus (NDV). The TMTR of uninfected turkeys was 42.4 +/- 14.7 cm/min. The TMTR of NDV-infected turkeys was depressed on days 3 through 7 postexposure (PE); depression was significant (P less than or equal to 0.05) on day 7 PE. Tracheal E. coli clearance in NDV-infected turkeys was reduced on days 4 through 9 PE, significantly so on day 5 PE (P less than or equal to 0.01). Depression of TMTR and tracheal E. coli clearance were associated histologically with replacement of normal pseudostratified columnar epithelium by 3 to 8 layers of immature nonciliated cells. E. coli clearance by the lung and air sac of NDV-infected turkeys was depressed on days 5 through 9 PE.