Bovine maternal,fetal and neonatal responses to bovine viral diarrhea virus infections

Due to the affinity of BVDV for the fetus and for cells of lymphatic organs of infected cattle, reproductive failure or immunosuppression, respectively, are likely consequences of BVDV infections of susceptible cattle. Infection of susceptible pregnant cattle with noncytopathic (ncp) BVDV results in transplacental infection with induction of maternal and fetal innate and adaptive immune responses. Differences in maternal innate and adaptive immune responses are evident in late gestation between cows carrying fetuses persistently-infected (PI) with BVDV and cows with fetuses transiently-infected with BVDV. Fetal innate and adaptive immune responses to ncp BVDV infection are defined by fetal age and developmental stage of the fetal immune system. Since a functional fetal adaptive immune response does not occur in the early fetus, immunotolerance to ncp BVDV is established, virus replicates unrestricted in fetal tissues and calves are born immunotolerant and PI with the virus. In the last trimester of gestation, the fetal immune system is adequately developed to respond in an efficacious manner, most commonly resulting in the birth of a clinically normal calf with pre-colostral antibodies. Immunosuppression due to postnatal acute ncp BVDV infections of susceptible calves may contribute to the occurrence and severity of multi-factorial respiratory tract and enteric diseases.     

An outbreak of fetal and neonatal losses associated with the diagnosis of bovine viral diarrhea virus

A severe outbreak of dairy herd pregnancy wastage was investigated. At the beginning of the outbreak, a total of 121 lactating cattle were pregnant and considered to be at risk. Overall, 33.1% of the population at risk aborted, while 25.6% gave birth to calves that either died during the early neonatal period or demonstrated signs compatible with congenital defects (abnormal births). A laboratory diagnosis of bovine viral diarrhea virus (BVDV) infection was made in two surviving neonatal calves with symptoms of cerebellar hypoplasia and blindness. An on-farm investigation was conducted to determine if the abortions and abnormal births were associated with BVDV infection. The rate of abortions versus abnormal births was biphasic when graphed by the date of occurrence. The cases of abortion occurred early in the outbreak and were followed by the neonatal losses. Within the population at risk, the mean values for gestational age at the beginning of the outbreak were different between the subpopulations described by gestational outcome. The outcome of each pregnancy that existed at the beginning of the outbreak was determined. Classifications included normal birth (birth of a normal calf), abnormal birth (a neonatal loss of the type described above), abortion, and continued gestation (normal, uncompleted pregnancy). The average gestational age at the time of the index case (the first cases of pregnancy wastage) for these four pregnancy outcome classfications was 142.0, 106.2, 86.7 and 31.3 days, respectively. Reasons for assuming that this outbreak was related to BVDV are discussed.     

Viral Dose and Immunosuppression Modulate the Progression of Acute BVDV-1 Infection in Calves: Evidence of Long Term Persistence after Intra-Nasal Infection

Bovine viral diarrhoea virus (BVDV) infection of cattle causes a diverse range of clinical outcomes from being asymptomatic, or a transient mild disease, to producing severe cases of acute disease leading to death. Four groups of calves were challenged with a type 1 BVDV strain, originating from a severe outbreak of BVDV in England, to study the effect of viral dose and immunosuppression on the viral replication and transmission of BVDV. Three groups received increasing amounts of virus: Group A received 10^2.55TCID₅₀/ml, group B 10^5.25TCID₅₀/ml and group C 10^6.7TCID ₅₀/ml. A fourth group (D) was inoculated with a medium dose (10^5.25TCID₅₀/ml) and concomitantly treated with dexamethasone (DMS) to assess the effects of chemically induced immunosuppression. Naïve calves were added as sentinel animals to assess virus transmission. The outcome of infection was dose dependent with animals given a higher dose developing severe disease and more pronounced viral replication. Despite virus being shed by the low-dose infection group, BVD was not transmitted to sentinel calves. Administration of dexamethasone (DMS) resulted in more severe clinical signs, prolonged viraemia and virus shedding. Using PCR techniques, viral RNA was detected in blood, several weeks after the limit of infectious virus recovery. Finally, a recently developed strand-specific RT-PCR detected negative strand viral RNA, indicative of actively replicating virus, in blood samples from convalescent animals, as late as 85 days post inoculation. This detection of long term replicating virus may indicate the way in which the virus persists and/or is reintroduced within herds.     

Bovine viral diarrhea infections in new world camelids—A review

Bovine virus diarrhea virus (BVDV) has recently been identified as an important infectious disease of new world camelids (NWC) particularly alpacas. Both sub-genotypes 1a, 1b and genotype 2 have been isolated. However, non-cytopathic BVDV 1b is reported to be primarily implicated in cases of BVDV in NWC's. Although suspected a BVDV strain unique to camelids have not been isolated. The most important source of BVDV is the immuno-tolerant persistently infected cria. Natural transient infection of BVDV in NWCs is reported to go almost undetected except for vague signs of illness, including lethargy and anorexia. Diarrhea does not appear to be a constant finding. Embryonal/fetal disease in NWC's includes early pregnancy loss, abortion and premature birth or the birth of persistently infected crias. Persistently infected disease can occur in both acute and chronic forms. In NWCs the chronic form of the condition is most commonly reported. Signs include chronic ill-thrift, poor weight gain or being underweight, intermittent illness, chronic diarrhea, joint swelling and episodes of nasal discharge and pneumonia despite antibiotic treatment. The mortality rate in NWCs appears to be close to 100%. Seroprevalence of BVDV in NWCs ranged from 2.05% to 11.11% however the possibility that the correct (homologous) BVDV strain is not being used in serological assays need to be considered. The importance of cattle as a source of BVDV for camelids is unclear although there is consensus of a spill-over from cattle to NWC's. Assays available for BVDV in cattle appear to work for camelids. An antigen ELISA which is the usual method for detecting BVD in cattle has not been validated in NWC's.     

BVDV and innate immunity.

Infection with bovine viral diarrhea virus (BVDV) is prevalent in the cattle population worldwide. The virus exists in two biotypes, cytopathic and non-cytopathic, depending on the effect of the viruses on cultured cells. BVDV may cause transient and persistent infections which differ fundamentally in the host's antiviral immune response. Transient infection may be due to both cytopathic and non-cytopathic biotypes of BVDV and leads to a specific immune response. In contrast, only non-cytopathic BVD viruses can establish persistent infection as a result of infection of the embryo early in its development. Persistent infection is characterized by immunotolerance specific for the infecting viral strain. In this paper we discuss the role of innate immune responses in the two types of infection. In general, both transient and persistent infections are associated with an increased frequency of secondary infections. Associated with the increased risk of such infections are, among others, impaired bacteria killing and decreased chemotaxis. Interestingly, non-cytopathic BVDV fails to induce interferon type I in cultured bovine macrophages whereas cytopathic biotypes readily trigger this response. Cells infected with non-cytopathic BVDV are also resistant to induction of interferon by double stranded RNA, a potent interferon inducer signalling the presence of viral replication in the cell. Thus, non-cytopathic BVDV may dispose of a mechanism suppressing a key element of the antiviral defence of the innate immune system. Since interferon is also important in the activation of the adaptive immune response, suppression of this signal may be essential for the establishment of persistent infection and immunotolerance.     

Evaluation of a commercial E<Superscript>rns</Superscript>-capture ELISA for detection of BVDV in routine diagnostic cattle serum samples

Background  

Bovine viral diarrhoea virus (BVDV) is an important pathogen in cattle. The ability of the virus to cross the placenta during early pregnancy can result in the birth of persistently infected (PI) calves. These calves shed the virus during their entire lifespan and are the key transmitters of infection. Consequently, identification (and subsequent removal) of PI animals is necessary to rapidly clear infected herds from the virus. The objective of this study was to evaluate the suitability of a commercial E^rns-capture ELISA, in comparison to the indirect immunoperoxidase test (IPX), for routine diagnostic detection of BVDV within a control programme. In addition, the effect of passive immunity and heat-inactivation of the samples on the performance of the ELISA was studied.     

Maternal antibody blocks humoral but not T cell responses to BVDV.

Bovine viral diarrhoea virus (BVDV) contributes significantly to health-related economic losses in the beef and dairy industry. Antibodies of maternal origin can be protective against BVDV infection, however, calves with low titres of maternal antibody or that do not receive colostrum may be at risk for acute BVDV infection. Interference by high titres of maternal antibodies prevents the development of an antibody response following vaccination with either a killed or attenuated BVDV vaccine. However, the T cell mediated immune response to BVDV may be generated in the absence of a detectable serum neutralizing antibody response. Two trials were conducted to evaluate the potential to elicit T cell mediated immune responses to BVDV in calves with circulating maternal antibody to BVDV. In the first trial, calves with high levels of circulating maternal antibody to BVDV 1 and BVDV 2 were experimentally infected with BVDV 2 (strain 1373) at two to five weeks of age. The T-cell mediated immune responses of the experimentally infected calves and non-infected calves were monitored monthly until circulating maternal antibody was no longer detectable in either treatment group. Calves experimentally infected with BVDV developed BVDV specific CD4(+), CD8(+), and delta T cell responses while high levels of maternal antibody were circulating. A second challenge with BVDV 2 (strain 1373) was performed in the experimentally infected and control calves once maternal antibody could no longer be detected. Previous exposure to BVDV in the presence of maternal antibody protected calves from clinical signs of acute BVDV infection compared to the control calves. In the second trial, three groups of calves with circulating maternal antibody to BVDV were given either a modified live vaccine (MLV) containing BVDV 1 and BVDV 2, a killed vaccine containing BVDV 1 and BVDV 2, or no vaccine, at seven weeks of age. Serum neutralizing antibody levels and antigen specific T cell responses were monitored for 14 weeks following vaccination. Calves vaccinated with MLV BVDV developed BVDV 1 and BVDV 2 specific CD4(+)T cell responses, and BVDV 2 specific gammadelta T cell responses, in the presence of maternal antibody. Vaccination with killed BVDV did not result in the generation of measurable antigen specific T cell immune responses. In this trial, a second vaccination was performed at 14 weeks to determine whether an anamnestic antibody response could be generated when calves were vaccinated in the presence of maternal antibody. Calves vaccinated with either a MLV or killed BVDV vaccine while they had maternal antibody developed an anamnestic antibody response to BVDV 2 upon subsequent vaccination. The results of these trials indicate that vaccinating young calves against BVD while maternal antibody is present may generate BVDV specific memory T and B cells. The data also demonstrated that seronegative calves with memory T and B cells specific for BVDV may be immune to challenge with virulent BVDV.     

我国牛病毒性腹泻流行现状与防控策略

我国牛病毒性腹泻病(Bovine viral diarrhea,BVD)的流行比较复杂,其病原BVDV (BVDV-1和BVDV-2)不仅仅局限于已知易感动物牛群感染,其他动物种群中感染BVDV-1和BVDV-2的现象也值得注意,如猪群中BVDV感染很大程度上混淆了猪瘟等病原的监测,从而加剧病程发展。牛病毒性腹泻病毒(Bovine viral diarrhea virus,BVDV)可致持续感染(Persistent infection,PI),这一特性导致该病的净化面临巨大困难,对整个养殖场的健康发展形成了严峻威胁。BVDV抗原变异速率非常快,目前BVDV-1已有22个亚型,BVDV-2有4个亚型,鉴于病原在自然界的适应和演进特性,对该病的防控措施迟后其病原的变异速度。因此,定期摸清BVDV-1和BVDV-2在我国的流行现状是实施疫病净化的第一步和关键步骤,进一步借鉴国外BVD净化成功经验,综合考虑我国国情,采取适宜的防控策略,逐步净化该病原感染,有助于促进国内养殖业的健康发展。     

A field investigation of the effects of bovine viral diarrhea virus infection around the time of insemination on the reproductive performance of cattle

During a study of methods of synchronizing estrus in Bos indicus cattle, blood was collected from 169 heifers and 38 cows 2 to 3 days prior to artificial insemination (AI), and then again at Day 51 and Day 210 after AI to determine the incidence of infection with bovine viral diarrhea (BVD) virus. Prior to insemination 53 and 68% of the cows and heifers, respectively, were seronegative to the BVD virus. At Day 51 after AI, 70 and 32% of the seronegative cows and heifers, respectively, had seroconverted; but between Day 51 and Day 210, only 17 and 3% of the seronegative cows and heifers, respectively, had seroconverted. The Day- 51 pregnancy rate of cows which were immune (seropositive) to BVD virus infection at the time of AI was similar to the rate of the cows which became infected around the time of AI. However, the pregnancy rate of the immune heifers (44%, n=54) was significantly (P=0.04) greater than the rate of the heifers which became infected around the time of AI (24%, n=37). It was concluded that infection of susceptible females with BVD virus around the time of AI may significantly lower the pregnancy rate.     

Bovine viral diarrhea virus: its effects on estradiol, progesterone and prostaglandin secretion in the cow

Bovine viral diarrhea virus (BVDV) is a major cattle pathogen responsible for a spectrum of symptoms, including reproductive failure. This study was designed to establish the effects of BVDV infection on estradiol, progesterone and PGF2alpha secretion in the cow. Seven BVDV-free cows were challenged with non-cytopathogenic BVDV (strain Pe 515: 5x10(6) tissue culture infected dose50) so that peak viremia occurred during the initial phase of luteal development in a synchronized estrous cycle. Ovulation was also synchronized in 7 sham-infected animals. Within 2 wk of inoculation, viremia, leukopenia and serum neutralizing antibodies were recorded in all of the BVDV-infected cows but not the sham-infected animals. Between Day 4 and Day 9 post estrus the BVDV-infected cows had significantly (P<0.01) lower plasma estradiol levels than the sham-infected animals. However, the BVDV infection did not alter rectal temperatures, plasma progesterone concentrations or PGF2alpha secretion 17, 18 and 19 d post estrus. These data highlight a potential causal link between BVDV viremia, endocrine dysfunction and poor fertility in the cow.     

Studies on the Decline of Bovine Virus Diarrhoea Virus (BVD V) Maternal Antibodies and Detectability of BVDV in Persistently Infected Calves

Persistently infected (PI) animals play a significant role in spread and transmission of bovine virus diarrhoea virus (B VD V) (Duffell & Harkness 1985). The identification and removal of PI cattle from the herd is of great importance in the control of BVDV. Although PI animals often show various degrees of growth retardation and unthrifty appearance, a significant proportion is clinically normal. PI animals are often seronegative (Duffell & Harkness 1985), but calves may be tested seropositive because of the presence of maternal immunity (Meyling & Jensen 1988). The passively derived BVDV antibodies may interfere with the ability to detect virus. Considering the importance of early recognition of PI calves, it is essential to determine the earliest time when PI animals can safely be diagnosed in the herd.     

Impact of BVDV infection of white-tailed deer during second and third trimesters of pregnancy

While it has been demonstrated that persistent bovine viral diarrhea virus (BVDV) infections can be established in white-tailed deer (Odocoileus virginianus) following in utero exposure in the first trimester of gestation, there is little to no information regarding the outcome of infection in later stages of pregnancy in deer. Our goal was to observe the impact of infection of white-tailed deer in the second and third trimesters of pregnancy. Five white-tailed deer in the second trimester of pregnancy and four in the third trimester were infected with a BVDV type 2 virus previously isolated from a BVDV-infected deer harvested from the wild. Infection of deer in the second trimester of pregnancy resulted in loss of the pregnancy in three of five deer. Fawns born to the two remaining deer appeared normal and were born BVDV antigen-negative with neutralizing serum antibodies against BVDV. Infection of does in the third trimester of pregnancy did not result in fetal death or persistent infection and all does gave birth to live, healthy fawns that were BVDV antigen-negative and born with antibodies against BVDV. These results, combined with those previously reported regarding BVDV infection in the first trimester of pregnancy, suggest that the impact of BVDV infection of pregnant white-tailed deer is very similar to that observed in pregnant cattle.     

Greater numbers of nucleotide substitutions are introduced into the genomic RNA of bovine viral diarrhea virus during acute infections of pregnant cattle than of non-pregnant cattle

ABSTRACT: BACKGROUND: Bovine viral diarrhea virus (BVDV) strains circulating in livestock herds show significant sequence variation. Conventional wisdom states that most sequence variation arises during acute infections in response to immune or other environmental pressures. A recent study showed that more nucleotide changes were introduced into the BVDV genomic RNA during the establishment of a single fetal persistent infection than following a series of acute infections of naive cattle. However, it was not known if nucleotide changes were introduce when the virus crossed the placenta and infected the fetus or during the acute infection of the dam. METHODS: The sequence of the open reading frame (ORF) from viruses isolated from four acutely infected pregnant heifers following exposure to persistently infected (PI) calves was compared to the sequences of the virus from the progenitor PI calf and the virus from the resulting progeny PI calf to determine when genetic change was introduced. This was compared to genetic change found in viruses isolated from a pregnant PI cow and its PI calf, and in three viruses isolated from acutely infected, non-pregnant cattle exposed to PI calves. RESULTS: Most genetic changes previously identified between the progenitor and progeny PI viruses were in place in the acute phase viruses isolated from the dams six days post-exposure to the progenitor PI calf. Additionally, each progeny PI virus had two to three unique nucleotide substitutions that were introduced in crossing the placenta and infection of the fetus. The nucleotide sequence of two acute phase viruses isolated from steers exposed to PI calves revealed that six and seven nucleotide changes were introduced during the acute infection. The sequence of the BVDV-2 virus isolated from an acute infection of a PI calf (BVDV-1a) co-housed with a BVDV-2 PI calf had ten nucleotides that were different from the progenitor PI virus. Finally, twenty nucleotide changes were identified in the PI virus of a calf born to a PI dam. CONCLUSIONS: These results demonstrate that nucleotide changes are introduced into the BVDV infecting pregnant cattle at rates of 2.3 to 8 fold higher then during the acute infection of non-pregnant animals.     

Seroepidemiology of bovine viral diarrhoea virus (BVDV) in the Adamawa Region of Cameroon and use of the SPOT test to identify herds with PI calves

Bovine viral diarrhoea, caused by the bovine viral diarrhoea virus (BVDV) in the Pestivirus genus of the Flaviviridae, is one of the most important diseases of cattle world wide causing poor reproductive performance in adult cattle and mucosal disease in calves. In addition it causes immunosuppression and increased susceptibility to other infections, the impact of which is uncertain, particularly in sub-Saharan Africa where animals are exposed to a much wider range and higher intensity of infections compared to Europe. There are no previous estimates of the seroprevalence of BVDV in cattle in Cameroon. This paper describes the serological screening for antibodies to BVDV and antigen of BVDV in a cattle population in the Adamawa Region of Cameroon in 2000. The estimates of herd-level and within herd seroprevalences adjusted for test imperfections were 92% and 30% respectively and 16.5% of herds were classed as having a persistently infected calf (PI) in the herd within the last year based on the "spot" test approach. There was evidence of clustering of herds with PI calves across the north and west of the Region which corresponds with the higher cattle density areas and of self-clearance of infection from herds. A multivariable model was developed for the risk of having a PI calf in the herd; proximity to antelope, owning a goat, mixing with > 10 other herds at grazing and the catchment area of the veterinary centre the herd was registered at were all significant risk factors. Very little is known about BVDV in sub-Saharan Africa and these high seroprevalences suggest that there is a large problem which may be having both direct impacts on fertility and neonate mortality and morbidity and also indirect effects through immunosuppression and susceptibility to other infections. Understanding and accounting for BVDV should be an important component of epidemiological studies of other diseases in sub-Saharan Africa.     

"Self" and "nonself" manipulation of interferon defense during persistent infection: bovine viral diarrhea virus resists alpha/beta interferon without blocking antiviral activity against unrelated viruses replicating in its host cells

Bovine viral diarrhea virus (BVDV), together with Classical swine fever virus (CSFV) and Border disease virus (BDV) of sheep, belongs to the genus Pestivirus of the Flaviviridae. BVDV is either cytopathic (cp) or noncytopathic (ncp), as defined by its effect on cultured cells. Infection of pregnant animals with the ncp biotype may lead to the birth of persistently infected calves that are immunotolerant to the infecting viral strain. In addition to evading the adaptive immune system, BVDV evades key mechanisms of innate immunity. Previously, we showed that ncp BVDV inhibits the induction of apoptosis and alpha/beta interferon (IFN-alpha/beta) synthesis by double-stranded RNA (dsRNA). Here, we report that (i) both ncp and cp BVDV block the induction by dsRNA of the Mx protein (which can also be induced in the absence of IFN signaling); (ii) neither biotype blocks the activity of IFN; and (iii) once infection is established, BVDV is largely resistant to the activity of IFN-alpha/beta but (iv) does not interfere with the establishment of an antiviral state induced by IFN-alpha/beta against unrelated viruses. The results of our study suggest that, in persistent infection, BVDV is able to evade a central element of innate immunity directed against itself without generally compromising its activity against unrelated viruses ("nonself") that may replicate in cells infected with ncp BVDV. This highly selective "self" and "nonself" model of evasion of the interferon defense system may be a key element in the success of persistent infection in addition to immunotolerance initiated by the early time point of fetal infection.     

Lack of Virus Transmission from Bovine Viral Diarrhoea Virus Infected Calves to Susceptible Peers

None of 14 calves not previously exposed to BVDV became infected after being forced to have nose-to-nose contact with a group of 5 calves primarily infected with BVDV These were 5 male calves primarily infected with a type I BVDV strain, after nose-to-nose contact with a persistently viraemic calf. All 5 became infected and were clinically affected. They were slightly depressed and pyretic at 8–9 days postinfection, with a body temperature of up to 41.6°C, but no medical treatment was required. Seroconversions to BVDV were detected in these calves at 14 to 21 days postinfection. The 14 healthy calves, proved to be free from BVD virus – as well as antibodies, were introduced 2 by 2 into the group of 5 primarily infected calves on days 4, 7, 14, 21, 28, 35 and 42 after the 5 calves had been in contact with the persistently BVDV-infected calf. Each pair of calves stayed within the primarily infected group for 2 days. None of these 14 calves seroconverted to BVDV.     

Bovine virus diarrhea virus in free-living deer from Denmark

Free-living deer are suggested as a possible source of infection of cattle with bovine virus diarrhea (BVD) virus. To examine this hypothesis blood samples from 476 free-living deer were collected during two different periods and tested for BVD virus and antibody in Denmark. In 1995-96, 207 animals were tested. These included 149 roe deer (Capreolus capreolus), 29 fallow deer (Dama dama), 20 red deer (Cervus elaphus) and one sika deer (Cervus sika). For the remaining eight animals no species information was available. In 1998-99, 269 animals were tested including 212 roe deer and 57 red deer. The animals were selected from areas with a relatively high prevalence of cattle herds with a BVD persistent infection status in 1997 and 1998. All 207 samples from 1995-96 were found antibody-negative except two samples from red deer. Only 158 of the 207 samples were tested for virus and were all found negative. Of the 269 samples from 1998-99 all but one were antibody negative. The positive sample was from a red deer. All samples were virus-negative. It appears that BVD infection does not occur in roe deer in Denmark. The presence of antibody in a few red deer from various districts in Jutland probably results from cattle to deer transmission, rather than spread among deer. Hence, the possibility of free-living deer as a source of infection for cattle in Denmark seems to be remote.     

Reproductive and economic impact following controlled introduction of cattle persistently infected with bovine viral diarrhea virus into a naive group of heifers

The reproductive impact following controlled introduction of animals persistently infected (PI) with bovine viral diarrhea virus (BVDV) was evaluated in BVDV-naive heifers. Heifers were randomly allocated into two groups: an unexposed control herd (n = 34) and a herd exposed to five persistently infected (PI) animals for 7 mo, beginning 50 days before the breeding season (n = 34). Initiation of the BVDV-challenge was timed to mimic either direct contact with PI calves born in the previous calving season or accidental introduction of PI herd additions prior to the breeding season. The PI animals represented BVDV Types 1a (n = 3), 1b (n = 1) and 2 (n = 1). Two BVDV-free, seropositive bulls were used in each group for 78 days breeding seasons. In both groups, 33 of 34 heifers became pregnant, with similar distribution of fetal ages. Two heifers in each group aborted (etiology undetermined). In addition, one calf was born dead and one calf died 3 days post-partum in the BVDV-exposed group. One calf in the unexposed group died 4 mo post-partum. No calves, including the stillborn calf and the two calves that died prior to weaning, were persistently infected with BVDV. In summary, introduction of PI cattle to a group of BVDV-naive heifers 50 days prior to the breeding season did not negatively impact reproductive performance. To the contrary, the active immunity that developed following field exposure to BVDV provided effective reproductive and fetal protection during the breeding season and subsequent gestations, despite continuous exposure to PI animals until approximately midgestation. Although BVDV can have potentially devastating reproductive effects, timing of infection is a critical determinant in the outcome of a BVDV infection. A controlled breeding season with introduction of herd additions at less critical reproductive time points can mitigate the negative reproductive health consequences of BVDV.     

Changes in ovarian follicles following acute infection with bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) has been associated with several reproductive problems in cattle, including poor fertility, early embryonic deaths, abortion and congenital anomalies. Little is known about the cause of poor fertility in cows acutely infected with BVDV. The purpose of this study was to identify changes in ovarian function following acute infection with noncytopathic BVDV. The ovaries of 5 BVDV sero-negative and virus-negative pubertal heifers were monitored daily for 4 consecutive estrous cycles. The position and diameter of all follicles (> 5 mm) and luteal structures were recorded. Daily plasma samples were collected to measure peripheral progesterone and estradiol levels. Each heifer was infected intranasally with noncytopathic BVDV following ovulation of the second estrous cycle. The maximum diameter and growth rate of dominant anovulatory and ovulatory follicles were significantly reduced following acute BVDV infection. Similarly, the number of subordinate follicles associated with both the anovulatory and ovulatory follicle was reduced following infection. There were no significant differences in other follicle or luteal dynamic parameters or in peripheral progesterone or estradiol levels. Ovarian follicular growth was different during the first 2 estrous cycles following acute infection with BVDV when compared with the 2 estrous cycles preceding infection. These differences may be important in explaining reduced fertility in herds with acute BVDV infection.