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PRRSV感染和管理的研究诊断进展

Monte B. McCaw 2021-11-26

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PRRS似乎在最初的繁殖系统疾病爆发后主要在保育生长群中持续存在。许多生产者,特别是那些不采用全进全出管理的生产者,会受到猪链球菌、副猪嗜血杆菌、多杀性巴氏杆菌、 胸膜肺炎放线杆菌和霍乱沙门氏菌导致的肺炎或猝死问题的困扰。

PRRSV感染和管理的研究诊断进展

 

PRRS virus (porcine reproductive and respiratory syndrome virus), the cause of the Mystery Swine Disease Syndrome, is finally yielding some answers as well as posing yet new questions as researchers, veterinarians, and pork producers work together to fight this problem. The following discussion will cover how it spreads, affects the immune system, causes disease, and maintains itself within infected herds.

 

PRRSV(猪繁殖与呼吸综合征病毒)是神秘猪病综合征的病因,随着研究人员、兽医和猪肉生产商共同努力解决这一问题,它终于有了一些答案同时也引出了新的问题。以下讨论将涵盖它如何在受感染的猪群中传播、对免疫系统影响、引起疾病和在猪群中持续传播。

 

01、Reproductive Disease 

 

繁殖系统疾病

 

Most of us know first hand or through lay magazines that PRRS outbreaks often cause abortions, stillbirths, mummies, and weakborn or thumping piglets. It is less certain whether PRRS causes irregular returns to estrus or reduced litter size by infecting and killing fetuses before 35 days of gestation. Many herds become infected (seroconvert - become positive to antibody tests) without seeing any clinical signs. However, a critical question remains: Will previously infected herds have another outbreak months or years later? Pregnant sows were infected with PRRS at 93 days gestation and farrowed severely affected litters. During the next pregnancy (7 - 8 months later) the same sows were challenged while some PRRS free pregnant sows were first infected. The previously infected sows' litters were normal while the control uninfected sows aborted or had many stillbirths or mummies. Field testimonials from the Midwest veterinarians and producers (PRRS spread rapidly there starting in 1989 whereas North Carolina apparently did not until 1992) indicate most sow herds do not experience second outbreaks. There is at least one report of a 1200 sow herd which receives gilts from an outside source that has had periodic flareups of PRRS reproductive losses during the second year after the initial outbreak. It was discovered that the gilt source was shipping predominantly negative gilts.

 

我们大多数人都直接或通过报道知道PRRS的爆发通常会导致流产、死胎、木乃伊和病弱仔猪。不太确定PRRSV是否会通过在妊娠 35 天前感染和杀死胎儿而导致不规则返情或产仔数减少。许多猪群在没有看到任何临床症状的情况下被感染(血清转化 - 抗体检测呈阳性)。然而,一个关键问题仍然存在:先前感染的猪群会在数月或数年后再次爆发吗?怀孕母猪在妊娠 93 天感染PRRSV,会严重影响分娩窝数。在下一次怀孕期间(7-8 个月后),一些阴性的怀孕母猪先被感染后,这此母猪也会再次受到攻击。先前感染过的母猪的产仔正常,而未感染的对照组母猪流产或产死胎、木乃伊。来自中西部兽医和生产者的田间数据(PRRS从1989年开始在那里迅速传播,而北卡罗来纳州直到1992年才传播)表明大多数母猪群没有经历第二次爆发。但至少有一份报告称,一个1200头母猪的猪群在最初爆发后的第二年从外部引入后备母猪,会导致PRRS周期性的繁殖损失,同时发现这些后备母猪来源为阴性群体。

 

02、Nursery-grower Pig Disease 

 

保育-生长猪疾病

 

PRRS seems to persist in herds after the initial reproductive disease outbreak mainly in the nursery grower areas. Many producers, particularly those who do not use all in - all out management, see long term pneumonia or sudden death problems with Strep suis, Haemophilus parasuis, Pasteurella multocida, Actinobacillus pleuropneumoniae, and Salmonella cholerasuis. Atrophic rhinitis also becomes worse if the herd is infected with PRRS. Antibiotics do not work as well as before (if at all) and mortality rates (15%) and feed efficiencies are elevated due to the reoccurring disease problems. PRRS has been isolated from nursery pigs in these herds up to 2.5 years later. In herds that do not see endemic disease problems in the nursery and that keep their own replacement breeding stock, gilts tested as they are added to the herd are seropositive to PRRS even years after the outbreak. This indicates that the virus continues to circulate in onsite nurseries or finishers on most farms. Therefore feces and soiled feed from the nursery and young finishing pigs can be used as feedback to purchased gilts in isolation to try to "immunize" them against PRRS. Older sows on these farms are often seronegative.

 

PRRS似乎在最初的繁殖系统疾病爆发后主要在保育生长群中持续存在。许多生产者,特别是那些不采用全进全出管理的生产者,会受到猪链球菌、副猪嗜血杆菌、多杀性巴氏杆菌、 胸膜肺炎放线杆菌和霍乱沙门氏菌导致的肺炎或猝死问题的困扰。如果猪群感染了PRRS,萎缩性鼻炎也会变得更糟。由于疾病问题的反复发生,抗生素的效果大不如前(如果之前有的话),死亡率(15%)和料肉比都提高了。直到2.5年后还能从这些猪群的保育猪中分离出PRRSV。在PRRS爆发几年后,即使在保育舍中已看不到地方性疾病流行问题,且后备猪自留,在对入群后的后备母猪进行检测时仍呈血清阳性。这表明该病毒继续在大多数猪场的保育或育肥舍中循环传播。因此,可用保育舍和育肥前期猪的粪便和污染饲料对购买的隔离期后备母猪进行返饲,以使它们对PRRS产生“免疫”。这些猪场的老母猪通常呈血清阴性。

 

03、Effects on the Immune System

 

对免疫系统的影响

 

PRRS grows almost exclusively in macrophages, the first line of defense cell in the body's immune system. A large proportion of the cells in the lungs are alveolar macrophages which PRRS easily infects. PRRS may initially stimulate these cells, but after two or three days the virus kills them and leaves the lung open to bacterial infections. This is because the immune system needs the macrophage to process the bacteria before other defense mechanisms can be activated. While the antibody response to PRRS may be slower and temporary, PRRS infection seems to actually increase the antibody titers to OTHER unrelated viruses and bacteria. This may fool people trying to make a diagnosis of what is causing a disease problem based simply upon an increase in antibody titers.

 

PRRSV几乎只在巨噬细胞中生长,它是机体免疫系统的第一道防御细胞。肺中的大部分细胞是PRRS易感的肺泡巨噬细胞。病毒最初可能会刺激这些细胞,但在两三天后会杀死它们并使肺部受到细菌感染。这是因为在免疫系统其它防御机制激活之前,需要巨噬细胞来处理细菌。虽然对PRRS的抗体反应可能缓慢且短暂,但PRRS感染实际上似乎会提高其他无关病毒和细菌的抗体滴度。这可能会蒙蔽那些试图仅根据抗体滴度的升高来诊断疾病原因的人。

 

04、Virus Spread or Transmission 

 

病毒扩散或传播

 

PRRS is very infectious, requiring only 10 to 100 viruses to infect pigs. PRRS has been isolated from boar semen for 35 days after infection by piglet inoculation. Semen from PRRS infected boars was able to infect and cause fevers and antibody production in uninfected gilts after insemination. The gilts failed to conceive and returned to estrus 21 days later. PRRS infection has been reported to decrease semen volume for 14 days after infection with variable reports on whether motility and sperm morphology are adversely affected. While the pig seems to be the only mammal that PRRS virus infects, the virus has replicated in Mallard ducks for 2 to 3 weeks. The significance of this finding and whether other birds can also replicate and possibly transmit the virus must be determined.

 

PRRS传染性强,只需要10到100个病毒颗粒即可感染猪。通过接种后的仔猪感染,可在感染后35天的公猪精液中分离出PRRSV。来自PRRS感染的公猪精液能够在授精后感染未被感染的后备猪并引起发烧和产生抗体。后备猪不能受孕并在21天后返情。据报道,PRRS会在感染后的14天内减少精液量,关于活力和精子形态是否受到不利影响的报告各不相同。虽然猪似乎是PRRSV感染的唯一哺乳动物,但该病毒可在野鸭体内复制2至3周。必须确定这一发现的重要性以及其他鸟类是否也可以复制并可能传播病毒。

 

05、Diagnostic Tests: Availability and Limitations 

 

诊断检测:实用性和局限性

 

All antibody tests developed and reported to date can detect PRRS antibody for only a year after initial infection. This is a strange characteristic of PRRS and does not necessarily mean that the test negative animals are not still carrying virus. Therefore, if an animal tests positive, it probably is infected. However, if an animal tests negative, it may not be virus free. Before purchasing gilts from new herds, have them test not only their sows but nursery and finishing pigs to establish whether their herd is infected with PRRS and whether the virus is still being spread between animals within the herd. Nursery and finishing pigs are much more likely to be antibody positive since they can only be infected within the last 6 months. Another complication of PRRS testing is the presence of different strains of the virus, namely the Lelystadt (European strain) virus which does not react on many of the current American diagnostic laboratory antibody tests. This type of virus mutates quickly, therefore there may be new antigenic forms needing new tests in the future, much like AIDS. An ELISA is being developed that may detect most or all strains of PRRS antibody responses.

 

迄今为止所有开发和报告的抗体检测,都只能在初次感染后一年内检测到PRRS抗体。这是PRRS的一个奇怪特征,并不一定意味着检测阴性的动物不再携带病毒。因此,如果动物检测呈阳性,则很可能已被感染。但是,如果动物检测结果呈阴性,则它可能不是无病毒的。在从新猪群购买后备猪之前,让他们不仅对母猪进行测试,还要对保育猪和育肥猪进行测试,以确定他们的猪群是否感染了PRRS,以及病毒是否仍在猪群内传播。保育猪和育肥猪最多在最近6个月内被感染,抗体阳性的可能性要大得多。PRRS检测的另一个难题是病毒存在不同的毒株,即Lelystadt(欧洲毒株)病毒对当前美国许多诊断实验室的抗体检测不产生反应。这种类型的病毒变异很快,因此就像艾滋病一样,未来可能会有新的抗原形式需要新的检测。正在开发的一种ELISA方法,可以检测大部分或所有PRRS毒株的抗体。

 

06、Take-Home Message 

 

实用信息

 

Determine your herd's PRRS infection status and buy only boars and gilts of equal status.

 

To determine breeding stock source's PRRS status require information on testing of nursery and finisher pigs. Do not rely only upon individual boar or gilt test results.

 

Allow long acclamation times (30 to 40 days) for purchased boars and gilts. Feed back feces and soiled feed from nursery and grow-finish.

 

Depopulate nursery for 14 days and disinfect to eliminate endemic PRRS infection and associated bacterial pneumonia and elevated death losses.

 

确定您猪群的PRRS感染状态,并只购买同等状态的公猪和后备母猪。

 

想要确定种猪来源场的PRRS状态,需要保育猪和育肥猪的检测信息。不要只依赖单个公猪或后备母猪的检测结果。

 

购买的公猪和小母猪要有很长的适应驯化时间(30 到 40 天)。可用保育猪和生长猪的粪便和被污染的饲料进行返饲。

 

保育舍清空14天并进行消毒,以清除地方性PRRS感染和相关的细菌性肺炎,降低死亡损失。

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标签 : PRRS 免疫 病毒
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