腐蹄病节瘤拟杆菌的分子致病机制的研究进展

腐蹄病是反刍动物绵羊、山羊、鹿和奶牛等常见的一种高度接触性传染病。节瘤拟杆菌是致病作用的主要病菌之一,它是通过IV型纤毛和细胞外蛋白酶而产生作用。但从腐蹄病发病症状看,节瘤拟杆菌所致疾病的严重程度不是相同的,据此节瘤拟杆菌被分为毒性、弱毒性和良性菌,这种分类通过对该菌基因组毒性关联蛋白Vap(Virulence-associated protein)区域和毒性相关位点vrl(Virulence Related Locus)区域的研究,发现其致病特点与基因的顺序有很大联系。     

Effect of the density on the growth and survival of the Caribbean scallops Argopecten nucleus and Nodipecten nodosus in suspended culture

Juveniles of the Caribbean scallops Argopecten nucleus and Nodipecten nodosus were suspended in pearl nets at densities of 25%, 30% and 50% coverage of the bottom of the net (BC) during days. Additionally, adults of A. nucleus (>35 mm) were placed in lantern nets at densities of 40%, 50% and 65% BC during days. Stocking density affected the growth of animals, with higher growth rates obtained at the lower densities. Although the survival of the two scallops was not influenced at the densities studied, the 15-day net changes, and culture in water of <28 °C produced better survival of A. nucleus and N. nodosus respectively. Predators of the families Cymatiidae, Grapsidae, Portunidae, Majidae and Xanthidae were found in the culture nets of juvenile A. nucleus , but during the adult phase they were absent. Predators exhibited a dense-independent behaviour in relation to scallops. There was not any association between predator frequency and survival of A. nucleus .     

Severity and persistence of footrot in Merino sheep experimentally infected with a protease thermostable strain of Dichelobacter nodosus at five sites

Objective To test the hypothesis that ovine footrot associated with a thermostable protease strain of Dichelobacter nodosus undergoes self cure or is sustained as an annually recurring disease, depending on the environment.
Design and procedure Forty Merino sheep from a single blood line were infected with a protease thermostable strain of D nodosus a t each of five sites in Western Australia. Footrot lesions and microscopic evidence of D nodosus were recorded every fortnight for 2.5 years, supplemented by laboratory culture. Rainfall, soil and air temperature, pasture quantity and composition and soil types were also recorded. Flocks that apparently self cured were relocated to a more favourable site for footrot in the final spring season.
Results The maximum prevalence of feet with clinical footrot lesions was 80.6, 1.3, 14.4, 3.8 and 88.1% at the five sites. Severe footrot occurred for three consecutive spring seasons at one site that had clay loam soil and at least 3500 kg/ha total pasture dry matter annually. However, the infection was asymptomatic for up to 10 weeks between outbreaks. D nodosus was isolated from flocks for 2.5 years at only two sites, although there was microscopic evidence of the organism at other sites in the final year. A thermolabile variant (strain U6) of D nodosus was isolated from the two sites where footrot persisted.
Conclusion Depending on time and location, ovine footrot induced by a protease thermostable strain of D nodosus either self cured or persisted as annual outbreaks interspersed with periods of asymptomatic infection.     

Survival and growth of hatchery-produced postlarvae and spat of the Caribbean scallops Argopecten nucleus and Nodipecten nodosus

A study was made of the growth and survival of postlarvae and spat of Argopecten nucleus and Nodipecten nodosus produced in the laboratory and exposed to different conditions of settlement and culture. An evaluation was made of the different types of collection substrates (onion-bags, artificial-grass, fibreglass-plates), two types of settlement inducers (epinephrine, low temperature), and two culture environments (sea, laboratory). The results showed that larger numbers of postlarvae were obtained in artificial-grass collectors than on fibreglass-plates or in the onion-bags. The growth of the A. nucleus postlarvae was not affected by the collector type, while that of N. nodosus was higher on fibreglass-plates, and lesser in the onion-bags. Both thermal and chemical stimulation of the competent larvae resulted in recovery of a greater percentage of postlarvae. The growth of postlarvae of A. nucleus was better in groups exposed to the two methods of settlement induction, while those of N. nodosus remained unaffected by this treatment. The survival of the postlarvae and spat was greater in the laboratory than at sea except in the case of A. nucleus postlarvae attached to collectors, whose survival was similar in both environments. The growth of postlarvae and spat was greater in the sea than in the laboratory.     

Influence of the type of collector and collector preparation periods on the settling rate of the scallop Nodipecten nodosus L. in the laboratory

We analysed the settling rate of Nodipecten nodosus L. scallop spats during winter and spring, testing different types of collectors and collector preparation periods. Larval rearing was conducted with water exchange every 48 h, density at 2 larvae mL⁻¹ and feeding between 0.5 and 2 × 10⁴ microalgae cellsmL⁻¹. The recovery larvae based on D-larvae produced were 31.6% (Winter Trial) and 47.2% (Spring Trial), without any antibacterial additives. The mean settling rates obtained in Winter Trial were from 0.04% to 0.79% withstand in Spring Trial were 24.99–48.65%. In the Winter Trial, there was no statistical difference between the settling rate of collectors prepared for 6 or 12 days. The settling rates of the netlon collectors with pine leaves were up to 19 times higher than those of the other types of collectors. In the Spring Trial, there was no statistical difference between the settling rates of the netlon and plastic net fruit collectors. Collectors with pine leaves produced a yield of spats up to 48.65%, more than those without pine leaves ( P <0.01). The efficiency of larval rearing and settling obtained in spring, pine leaves and low-cost local material indicate the feasibility to improve and facilitate regular production of N. nodosus spats for promotion of the growth of scallop culture in Brazil.     

Experimental larval culture of the Caribbean scallops Argopecten nucleus and Nodipecten nodosus

Several experiments were performed examining the effect of different culture variables on the growth and survival of Argopecten nucleus and Nodipecten nodosus larvae. Higher growth and survival values were obtained at a low density (1 larvae mL^?1) than at a high density (5 larvae mL^?1), except for N. nodosus's survival, which was not affected by density. Higher growth was obtained when feeding the larvae a diet of Isochrysis galbana, similar results occurred with the diet of Isochrysis galbana+Chaetoceros calcitrans in A. nucleus and with I. galbana combined with the lipid emulsion EmDHA in N. nodosus. Higher survival was obtained when the diet included a mixture of microalgae than when EmDHA was supplemented. Growth and survival of the larvae of A. nucleus were greater when fed continuously, while N. nodosus grew and survived better when food was given discontinuously. Higher growth and survival values were recorded at lower food concentrations ranging from 20 to 40 cells μL^?1 of I. galbana. Higher growth was observed with increasing temperature between 22 and 28 °C, although there was a simultaneous decrease in survival. No significant effects on larval production parameters were found when the culture water was changed totally or partially, but higher larval growth of N. nodosus was verified when a partial renewal of water was performed.     

节瘤拟杆菌PCR检测方法的建立

根据节瘤拟杆菌特有保守序列设计引物，利用聚合酶链式反应（PCR）建立了一种鉴别检测该茵的方法。对可能影响PCR检测结果的一系列因素进行了较详细的研究，选择了适宜PCR检测的快捷处理病样获得反应模板的方法，对PCR反应条件进行了优化，使对已知菌株培养物检测灵敏性最高可到30个菌／30μL反应体系；用广泛的相关菌株和茵群验证引物的特异性，证明设计的引物特异性强。将PCR方法用于临床病样的初步检测，部分病样PCR检测阳性。为用PCR方法检测节瘤拟杆菌引发的牛、羊、鹿腐蹄病奠定了基础。     

The virulence of Dichelobacter nodosus,measured by the elastase test,is an important predictor for virulent footrot diagnosis in New South Wales sheep flocks

Ovine footrot is a contagious bacterial disease that causes foot lesions, and depending on the virulence of the causative strains, may lead to severe underrunning of the hoof and lameness. Virulent footrot can be identified, treated and controlled more effectively than less virulent benign forms. The in vitro elastase test for virulence of the causative bacteria, Dichelobacter nodosus, has been used to support clinical diagnosis. However, not all laboratory-designated virulent D. nodosus strains cause clinical signs of virulent footrot. This study evaluated retrospectively how well the elastase test supported clinical footrot diagnosis in 150 sheep flocks examined for suspect footrot in New South Wales between August 2020 and December 2021. Flocks were included if measures of clinical disease, environmental conditions and the virulence of D. nodosus isolates were available. Variation in the elastase activity result between D. nodosus isolated from the same flock made bacterial virulence hard to interpret, but calculating the mean elastase rate for all isolates from the same flock made correlations between bacterial virulence and flock footrot diagnosis possible. Simplifying bacterial virulence into whether there were any elastase-positive D. nodosus isolates before 12 days increased the predictive value of elastase results for virulent diagnosis, compared with using the first day that any isolate was elastase positive or the percentage of elastase-positive isolates by 12 days, but not all clinically virulent flocks had isolates with elastase activity before 12 days. Logistic regression models were fitted to identify the minimum number of predictors for virulent footrot diagnosis, with models suggesting that virulent footrot diagnosis was best predicted by adding the elastase test result and environmental conditions to the prevalence of severe foot lesions (score 4 and 5). However, performing the same analysis with different breeds, ages of sheep and seasons might highlight other factors important in the diagnosis of virulent footrot.