Experimental persistent infection with bovine viral diarrhea virus in white-tailed deer

Bovine viral diarrhea virus (BVDV) infections cause substantial economic losses to the cattle industries. Persistently infected (PI) cattle are the most important reservoir for BVDV. White-tailed deer (Odocoileus virginianus) are the most abundant species of wild ruminants in the United States and contact between cattle and deer is common. If the outcome of fetal infection of white-tailed deer is similar to cattle, PI white-tailed deer may pose a threat to BVDV control programs. The objective of this study was to determine if experimental infection of pregnant white-tailed deer with BVDV would result in the birth of PI offspring. Nine female and one male white-tailed deer were captured and housed at a captive deer isolation facility. After natural mating had occurred, all does were inoculated intranasally at approximately 50 days of pregnancy with 10(6) CCID(50) each of a BVDV 1 (BJ) and BVDV 2 (PA131) strain. Although no clinical signs of BVDV infection were observed or abortions detected, only one pregnancy advanced to term. On day 167 post-inoculation, one doe delivered a live fawn and a mummified fetus. The fawn was translocated to an isolation facility to be hand-raised. The fawn was determined to be PI with BVDV 2 by serial virus isolation from serum and white blood cells, immunohistochemistry on skin biopsy, and RT-PCR. This is the first report of persistent infection of white-tailed deer with BVDV. Further research is needed to assess the impact of PI white-tailed deer on BVDV control programs in cattle.     

Persistent infections after natural transmission of bovine viral diarrhoea virus from cattle to goats and among goats

Bovine viral diarrhoea virus (BVDV) is an economically important pathogen of cattle worldwide. Infection of a pregnant animal may lead to persistent infection of the foetus and birth of a persistently infected (PI) calf that sheds the virus throughout its life. However, BVD viruses are not strictly species specific. BVDV has been isolated from many domesticated and wild ruminants. This is of practical importance as virus reservoirs in non-bovine hosts may hamper BVDV control in cattle. A goat given as a social companion to a BVDV PI calf gave birth to a PI goat kid. In order to test if goat to goat infections were possible, seronegative pregnant goats were exposed to the PI goat. In parallel, seronegative pregnant goats were kept together with the PI calf. Only the goat to goat transmission resulted in the birth of a next generation of BVDV PI kids whereas all goats kept together with the PI calf aborted. To our knowledge, this is the first report which shows that a PI goat cannot only transmit BVD virus to other goats but that such transmission may indeed lead to the birth of a second generation of PI goats. Genetic analyses indicated that establishment in the new host species may be associated with step-wise adaptations in the viral genome. Thus, goats have the potential to be a reservoir for BVDV. However, the PI goats showed growth retardation and anaemia and their survival under natural conditions remains questionable.     

Cohabitation of pregnant white-tailed deer and cattle persistently infected with Bovine viral diarrhea virus results in persistently infected fawns

Economic losses due to infection with Bovine viral diarrhea virus (BVDV) have prompted introduction of organized control programs. These programs primarily focus on the removal of persistently infected (PI) animals, the main source of BVDV transmission. Recently, persistent BVDV infection was demonstrated experimentally in white-tailed deer, the most abundant wild ruminant in North America. Contact of cattle and white-tailed deer may result in interspecific BVDV transmission and birth of persistently infected offspring that could be a threat to control programs. The objective of this study was to assess the potential for interspecific BVDV transmission from persistently infected cattle cohabitated with pregnant white-tailed deer. Seven female and one male white-tailed deer were captured and bred in captivity. At approximately 50 days of gestation, two cattle persistently infected with BVDV 1 were cohabitated with the deer. In a pen of approximately 0.8 ha, both species shared food and water sources for a period of 60 days. Transmission of BVDV as indicated by seroconversion was demonstrated in all exposed adult deer. Of the seven pregnancies, four resulted in offspring that were infected with BVDV. Persistent infection was demonstrated in three singlet fawns by immunohistochemistry and ELISA on skin samples, PCR, and virus isolation procedures. Furthermore, two stillborn fetuses were apparently persistently infected. This is the first report of BVDV transmission from cattle to white-tailed deer using a model of natural challenge. Under appropriate circumstances, BVDV may efficiently cross the species barrier to cause transplacental infection and persistently infected offspring in a wildlife species.     

Transmission of bovine viral diarrhea virus to adult goats from persistently infected cattle.

The transmission of bovine viral diarrhea virus (BVDV) from persistently infected (PI) heifers to adult seronegative goats was examined in this study. Ten seronegative adult goats were exposed to 4 PI heifers. None of the goats developed any clinical signs but all goats seroconverted by 42 days after exposure to the PI cattle. Results indicate that goats are susceptible to BVDV infection when housed with PI cattle.     

Foetal Protection against Bovine Virus Diarrhoea Virus after Two‐step Vaccination

In order to assess the efficacy of a two‐step vaccination protocol with respect to foetal protection against transplacental infections with bovine virus diarrhoea virus (BVDV) with special attention to BVDV‐2 seronegative heifers were vaccinated with an inactivated BVDV‐1 vaccine and boostered with a modified live BVDV‐1 vaccine after 4 weeks. A second group was left unvaccinated as control. Between days 30 and 120 of pregnancy the heifers of both groups were intranasally challenged with a mixture of BVDV‐1 and ‐2. All heifers of the vaccinated group gave birth to nine clinically healthy, seronegative (precolostral) and BVDV‐free calves. In contrast in the control group four BVDV viraemic underdeveloped calves were born. Additionally, one calf was stillborn and another viraemic calf was not viable and died 2 days after birth. All six calves of the control group were viraemic with BVDV‐2. This study demonstrated for the first time that two‐step vaccination of breeding cattle with a modified live BVDV vaccine 4 weeks after application of an inactivated BVDV vaccine was capable of providing a foetal protection against transplacental infection with BVDV‐2.     

Foetal protection against bovine virus diarrhoea virus after two-step vaccination

In order to assess the efficacy of a two-step vaccination protocol with respect to foetal protection against transplacental infections with bovine virus diarrhoea virus (BVDV) with special attention to BVDV-2 seronegative heifers were vaccinated with an inactivated BVDV-1 vaccine and boostered with a modified live BVDV-1 vaccine after 4 weeks. A second group was left unvaccinated as control. Between days 30 and 120 of pregnancy the heifers of both groups were intranasally challenged with a mixture of BVDV-1 and -2. All heifers of the vaccinated group gave birth to nine clinically healthy, seronegative (precolostral) and BVDV-free calves. In contrast in the control group four BVDV viraemic underdeveloped calves were born. Additionally, one calf was stillborn and another viraemic calf was not viable and died 2 days after birth. All six calves of the control group were viraemic with BVDV-2. This study demonstrated for the first time that two-step vaccination of breeding cattle with a modified live BVDV vaccine 4 weeks after application of an inactivated BVDV vaccine was capable of providing a foetal protection against transplacental infection with BVDV-2.     

Histopathologic and immunohistochemical findings in two white-tailed deer fawns persistently infected with Bovine viral diarrhea virus.

Bovine viral diarrhea virus (BVDV) is an important pathogen of domestic cattle. Serologic, experimental, and individual case studies explored the presence and pathogenesis of the virus in wild ungulates; however, there remain large gaps in knowledge regarding BVDV infection in nonbovine species. Live twins were born from a white-tailed deer (Odocoileus virginianus) doe infected with noncytopathic BVDV during its first trimester of pregnancy. The twins died at 1 day of age from trauma unrelated to the infection, and tissues were collected for histologic and immunohistochemical examination. The most significant histologic abnormality was diffuse depletion of B-lymphocytes in both fawns. The BVDV antigen was distributed widely throughout many tissues and cell types, most notably epithelium and vascular endothelium, consistent with that reported in cattle. In contrast to cattle, lymphocytes exhibited only very rare positive staining.     

Evaluation of hunter-harvested white-tailed deer for evidence of bovine viral diarrhea virus infection in Alabama.

Bovine viral diarrhea virus (BVDV) is one of the most relevant pathogens affecting today's cattle industries. Although great strides have been made in understanding this virus in cattle, little is known about the role of wildlife in the epidemiology of BVDV. While persistently infected cattle are the most important reservoir, free-ranging ungulates may become infected with BVDV as demonstrated by serosurveys and experimental infections. Therefore, free-ranging wildlife may maintain BVDV as the result of an independent cycle and may serve as a reservoir for the virus. Systematic studies on prevalence of BVDV-specific antibodies or frequency of persistent BVDV infection in North American wildlife are sparse, and no information is available from the southeastern United States. The objective of this study was to evaluate blood and skin samples from hunter-harvested white-tailed deer (Odocoileus virginianus) for evidence of BVDV infection. Virus-neutralizing antibodies were detected in 2 of 165 serum samples. Skin biopsy immunohistochemistry (IHC) was performed on samples from 406 deer using a BVDV-specific monoclonal antibody (MAb) (15c5), and BVDV antigen was detected in one sample. A similar IHC staining pattern was obtained using a second BVDV MAb (3.12F1). Viral antigen distribution in the skin sample of this deer resembled that found in persistently infected cattle and in a previously described persistently infected white-tailed deer; thus, the deer was presumed to be persistently infected. Evidence of BVDV infection in free-ranging white-tailed deer should encourage further systematic investigation of the prevalence of BVDV in wildlife.     

Reproductive consequences of infection with bovine viral diarrhea virus.

Reproductive efficiency is imperative for the maintenance of profitability in both dairy and cow-calf enterprises. Bovine viral diarrhea virus is an important infectious disease agent of cattle that can potentially have a negative effect on all phases of reproduction. Reduced conception rates,early embryonic deaths, abortions, congenital defects, and weak calves have all been associated BVDV infection of susceptible females. In addition, the birth of calves PI with BVDV as a result of in utero fetal exposure is extremely important in the perpetuation of the virus in an infected herd or spread to other susceptible herds. Bulls acutely or PI with BVDV may bea source of viral spread through either natural service or semen used in artificial insemination. Management practices including elimination of PI cattle, biosecurity measures and strategic use of vaccination can be implemented to reduce the risk of BVDV related reproductive losses.Development of vaccines and vaccine strategies capable of providing better protection against fetal infection would be of benefit.     

Toxoplasma gondii-induced abortion in dairy goats

Three of 8 goats on a Maryland farm aborted or had dystocia associated with toxoplasmosis during the winter of 1984. Doe 1 aborted a decomposed fetus 30 days before term. Modified agglutination test (MAT) antibody titers against Toxoplasma gondii were found in pleural fluid of the fetus (1:1,024) and in serum of doe (1:4,096 at 31 days after abortion). Doe 2 aborted a fetus 5 days before term; MAT antibody was found in the pleural fluid of the fetus (1:16,384) and in the doe's serum (1:4,096 on the day of abortion). Placenta from both does had foci of necrosis characteristic of toxoplasmosis, and T gondii was identified in lesions. Doe 3 had dystocia 7 days before term and a partially decomposed fetus was delivered by cesarian section; MAT was found in pleural fluid of the fetus (1:1,024) and in serum from the doe (1:4,096 on the day of abortion). Focal gliosis and calcification were seen in brain specimens from 2 of the 3 fetuses. None of the does produced milk after abortion. Two other does (No. 4 and 5) delivered apparently healthy kids transplacentally infected with T gondii; MAT in serum of both does was 1:4,096. Doe 4 delivered 3 kids; MAT titer in a serum from each kid 38 days after birth was 1:16,384. Doe 5 delivered 1 kid with a serum MAT titer of 1:1,024 at 38 days after birth. The 3 remaining does had MAT titers of 1:256, 1:16, and 1:16, and all delivered healthy kids. Epizootiologic evidence suggested that the does acquired T gondii infection from oocysts passed in feces of domestic cats on the farm. The MAT titers of 4 cats on the farm were 1:65,356; 1:1,024; 1:16; and 1:1,024.     

Diagnosis of persistent bovine viral diarrhea virus infection by immunohistochemical staining of formalin-fixed skin biopsy specimens.

The objective of this study was to evaluate the efficacy of immunohistochemical (IHC) staining for diagnosis of persistent bovine viral diarrhea virus (BVDV) infection using formalin-fixed, paraffin-embedded skin biopsy specimens. Skin from 41 of 42 calves shown to be persistently infected (PI) with BVDV by repeated virus isolation more than 3 weeks apart were immunohistochemically positive for BVDV antigen. Positive IHC staining was most pronounced in the keratinocytes and in hair follicle epithelium, hair matrix cells of the hair bulb, and the dermal papilla. All of the skin sections from 10 calves experimentally infected postnatally with BVDV (10(5) median tissue culture infective doses [TCID50]) and biopsied on days 0, 5, 7, and 9 postinfection were negative for viral antigen. Ten calves from a second group experimentally infected with a higher dose of BVDV (10(8) TCID50) were biopsied when viremic between 10 and 14 days postinfection and 4 calves exhibited positive IHC staining for BVDV; however, staining in these skin biopsies was confined to small foci in the nonfollicular epidermis and follicular ostia. This staining was distinct from that observed in skin obtained from PI cattle. Skin biopsy represents an effective method for identifying animals PI with BVDV.     

BVDV对后备牛生长发育状况及繁殖性能的影响

牛病毒性腹泻/黏膜病(BVD/MD)是一种严重危害奶牛健康的病毒性传染病,其病原为牛病毒性腹泻病毒(BVDV)。BVDV感染牛后主要表现两种状态,即一过性感染(TI)和持续性感染(PI)。BVD在牛场的流行,可严重影响奶牛的生产性能、繁殖性能及牛群健康状况,对奶牛的影响可表现为流产、胎儿畸形、腹泻和免疫抑制等。怀孕母牛在特定妊娠阶段感染BVDV后,可娩出PI犊牛,部分PI犊牛能像正常犊牛一样生长发育至成年,但其生长发育状况和繁殖性能较同龄健康牛差异十分明显。为评价BVDV对后备牛生长发育及繁殖状况的影响,笔者采用ELISA方法检出北京地区28个规模化奶牛场141头BVDV-PI牛,并与同龄健康牛生长发育及繁殖数据相比较,结果表明,BVDV-PI后备牛各月龄段的体高、体重均低于健康后备牛,其首次输精日龄、配准日龄、耗精量明显高于健康后备牛,而一次情期受胎率显著低于健康后备牛。数据显示,BVDV严重影响后备牛的生长发育及繁殖状况。     

The live attenuated bovine viral diarrhea virus components of a multi-valent vaccine confer protection against fetal infection

Fetal infection with bovine virus diarrhea virus (BVDV) causes severe economic loss and virus spread in cattle. This study investigated the ability of modified live BVDV I and II components of a commercially available modified live virus (MLV) vaccine (Breed-Back FP 10, Boehringer Ingelheim Vetmedica Inc.) to prevent fetal infection and abortion, and therefore the birth of persistently infected animals. Heifers immunized with vaccine 4-8 weeks before insemination showed no adverse effects. All vaccinated animals had seroconverted to BVDV 4 weeks after immunization. Pregnant heifers were divided into two vaccination and two control groups and challenged with type I or II BVDV on days 60-90 of gestation. Seroconversion, clinical signs, immunosuppression, viremia, mortality, abortion rate, and fetal infection were studied. Post-challenge, 6/11 (type I challenged) and 8/11 (type II challenged) vaccinated heifers were free from clinical signs of BVD. Post-challenge clinical signs noted in the vaccinated groups were mild to moderate, while all unvaccinated controls had clinical signs ranging from moderate to severe. Viremia was not detected post-challenge in any of the vaccinated heifers. However, 100% of the controls were BVDV viremic on at least 1 day post-challenge. One of 22 vaccinated heifers had transient leukopenia, whereas 2/8 and 6/7 unvaccinated heifers in control groups I and II, respectively, had transient leukopenia. Type II BVDV infection led to abortion or death in 86% of unvaccinated heifers. The corresponding vaccinated group showed no deaths or abortions. All control group fetuses were infected with BVDV. The test vaccine gave 91% (type I BVDV challenged) and 100% (type II BVDV challenged) protection from fetal infection. This vaccine is safe and effective against fetal infection, abortion (type II BVDV) and the birth of persistently infected animals.     

Evolution of bovine viral diarrhea virus vaccines.

Control of bovine viral diarrhea virus (BVDV) infection is economically important to the cattle industry because the virus causes a variety of clinical diseases that adversely affect essentially all stages of the production cycle. Production losses primarily stem from reproductive failure and from immunosuppression during acute BVDV infection, which predisposes calves to respiratory or enteric diseases. Control is achieved by implementing herd health pro-grams focused on limiting exposure by avoiding persistently infected (PI) carrier cattle and by optimizing protective immunity through immunization. Vaccination cannot be relied upon solely to protect against fetal infection and losses due to BVD. This is because no single BVDV vaccine has been shown to give complete fetal protection. In addition to strategic use of vaccines, herd management practices should also be implemented to identify and eliminate PI carrier cattle and to avoid exposure to BVDV infection.     

Multiple diagnostic tests to identify cattle with Bovine viral diarrhea virus and duration of positive test results in persistently infected cattle

Several tests for Bovine viral diarrhea virus (BVDV) were applied to samples collected monthly from December 20, 2005, through November 27, 2006 (day 0 to day 342) from 12 persistently infected (PI) cattle with BVDV subtypes found in US cattle: BVDV-1a, BVDV-1b, and BVDV-2a. The samples included clotted blood for serum, nasal swabs, and fresh and formalin-fixed ear notches. The tests were as follows: titration of infectious virus in serum and nasal swabs; antigen-capture (AC) enzyme-linked immunosorbent assay (ELISA), or ACE, on serum, nasal swabs, and fresh ear notches; gel-based polymerase chain reaction (PCR) testing of serum, nasal swabs, and fresh ear notches; immunohistochemical (IHC) testing of formalin-fixed ear notches; and serologic testing for BVDV antibodies in serum. Of the 12 animals starting the study, 3 died with mucosal disease. The ACE and IHC tests on ear notches had positive results throughout the study, as did the ACE and PCR tests on serum. There was detectable virus in nasal swabs from all the cattle throughout the study except for a few samples that were toxic to cell cultures. The serum had a virus titer ≥ log₁₀ 1.60 in all samples from all the cattle except for 3 collections from 1 animal. Although there were several equivocal results, the PCR test most often had positive results. The BVDV antibodies were due to vaccination or exposure to heterologous strains and did not appear to interfere with any BVDV test. These findings illustrate that PI cattle may be identified by several tests, but differentiation of PI cattle from cattle with acute BVDV infection requires additional testing, especially of blood samples and nasal swabs positive on initial testing. Also, calves PI with BVDV are continual shedders of infectious virus, as shown by the infectivity of nasal swabs over the 11-mo study.     

Birth to weaning kid traits from a complete diallel of Boer, Kiko, and Spanish meat goat breeds semi-intensively managed on humid subtropical pasture

Boer, Kiko, and Spanish meat goats were semi-intensively managed in a complete 3-breed diallel mating scheme to evaluate genetic effects on preweaning kid performance. Over a 6-yr period, 1,547 kids were born in March and May with 1,173 kids raised by their dams to weaning at 3 mo of age. March-born kids were lighter (P < 0.01) at birth, but had greater (P < 0.01) preweaning ADG and survival rates and heavier (P < 0.01) weaning weights than May-born kids. For birth weight, the direct Boer effect was positive (P < 0.01) and direct effects were negative (P < 0.01) for Kiko and Spanish. The direct Kiko effect for preweaning ADG was positive (P < 0.05), whereas other direct breed effects for ADG and all direct effects for weaning weight did not differ from 0 (P > 0.10). Maternal Boer effects were negative (P < 0.01) for birth weight and weaning weight, whereas maternal Kiko effects were significantly (P < 0.05) positive for preweaning ADG and weaning weight. Maternal Spanish effect was positive (P < 0.05) for birth weight, but did not differ from 0 (P > 0.5) for preweaning ADG or weaning weight. Heterosis for birth weight was exhibited (P < 0.01) for each pair of breed crosses, but only between Boer and Kiko for ADG and weaning weight. Kiko and Spanish dams had greater (P < 0.01) preweaning kid survival rates than Boer dams, but the former 2 did not differ (P = 0.72). Significant genetic variation was observed between meat goat breeds for kid performance to weaning. Maternal breed effects were more influential than direct breed effects. Boer goats were not superior to Kiko or Spanish for preweaning kid performance when semi-intensively managed on humid, subtropical pasture. Kiko should be a preferred breed and to a lesser extent Spanish for enhancing birth to weaning kid performance. Findings of this study emphasize the importance of proper doe breed selection in achieving desired kid performance to weaning in meat goats.     

影响哺乳期羔羊生长的母羊因素分析

为探索母羊因素对哺乳期云上黑山羊羔羊生长发育的影响,根据母羊体重、胎次分别选取云上黑山羊初生羔羊90只和120只,公、母各半,从出生开始直至90日龄断奶,每10天进行1次体重测定,进行生长发育分析。结果表明:(1)母羊产后体重对羔羊初生重、哺乳期体重具有显著影响(P<0.05)。母羔中,38~45 kg母羊组和48~62 kg母羊组的羔羊初生重、平均日增重均显著高于28~35 kg母羊组(P<0.05)。公羔中,38~45 kg母羊组的羔羊初生重显著高于其他两组羔羊(P<0.05),48~62 kg母羊组其羔羊平均日增重显著高于其他两组羔羊(P<0.05)。(2)母羊胎次对母羔初生重没有显著影响,但对母羔哺乳期体重均有显著影响(P<0.05),母羔中,3胎、4胎母羊组的羔羊平均日增重均显著高于1胎和2胎母羊组;母羊胎次对公羔的影响不显著。说明母羊产后体重显著影响羔羊胎儿期和哺乳期的生长发育,合适的母羊体重可以为羔羊提供充足的营养;母羊胎次仅对哺乳期母羔具有显著影响,母羊的母性行为随胎次的增加而完善。     

Laboratory diagnostic investigations for bovine viral diarrhoea virus infections in cattle

There are no pathognomonic clinical signs of infection with bovine viral diarrhoea virus (BVDV) in cattle. Diagnostic investigations therefore rely on laboratory-based detection of the virus, or of virus-induced antigens or antibodies in submitted samples. In unvaccinated dairy herds, serological testing of bulk milk is a convenient method for BVDV prevalence screening. Alternatively, serological testing of young stock may indicate if BVDV is present in a herd. In BVDV positive herds, animals persistently infected (PI) with BVDV can be identified by combined use of serological and virological tests for examination of blood samples. ELISAs have been used for rapid detection of both BVDV antibodies and antigens in blood, but should preferably be backed up by other methods such as virus neutralization, virus isolation in cell cultures or amplification of viral nucleic acid. Detailed knowledge of the performance of the diagnostic tests in use, as well as of the epidemiology of bovine virus diarrhoea is essential for identification of viremic animals in affected herds.