Abstract
Naïve pregnant cattle exposed to pestiviruses between 40-125 days of gestation can give birth to persistently infected (PI) calves. Clinical presentation and survivability, in PI cattle, is highly variable even with the same pestivirus strain whereas the clinical presentation in acute infections is more uniform with severity of symptoms being primarily a function of virulence of the infecting virus. The aim of this study was to compare thymic depletion, as measured by comparing the area of the thymic cortex to the medulla (corticomedullary ratio), in acute and persistent infections of the same pestivirus isolate. The same general trends were observed with each pestivirus isolate. Thymic depletion was observed in both acutely and persistently infected calves. The average thymic depletion observed in acutely infected calves was greater than that in age matched PI calves. PI calves, regardless of infecting virus, revealed a greater variability in amount of depletion compared to acutely infected calves. A trend was observed between survivability and depletion of the thymus, with PI calves surviving less than 5 weeks having lower corticomedullary ratios and greater depletion. This is the first study to compare PI and acutely infected calves with the same isolates as well as to evaluate PI calves based on survivability. Further, this study identified a quantifiable phenotype associated with potential survivability.
Highlights
Bovine viral diarrhea virus 1 (BVDV-1) and BVDV-2, along with classical swine fever virus (CSFV) and border disease virus (BDV) are taxonomically classifiable within the Pestivirus genus of the family Flaviviridae [28]
Acute infection with noncytopathic BVDV is characterized in the periphery by a transient lymphopenia following exposure that can be observed by day 3, with the greatest lymphopenia occurring between 6-9 days postinfection and recovery to baseline by 12-14 dpi [15]
This is one of the first studies to compare the effects of BVDV and HoBi-like pestivirus acute and persistent infections on thymic morphology
Summary
Bovine viral diarrhea virus 1 (BVDV-1) and BVDV-2, along with classical swine fever virus (CSFV) and border disease virus (BDV) are taxonomically classifiable within the Pestivirus genus of the family Flaviviridae [28]. Clinical signs resulting from HoBi-like pestivirus infection of cattle are indistinguishable from those that result from infection with either BVDV-1 or BVDV-2 [9,10,11,12,13]. The severity of the clinical disease in naïve immune competent animals can range from mild/subclinical to severe, depending on the virulence of the strain involved in the infection [16]. Acute infection with noncytopathic (ncp) BVDV is characterized in the periphery by a transient lymphopenia following exposure that can be observed by day 3, with the greatest lymphopenia occurring between 6-9 days postinfection (dpi) and recovery to baseline by 12-14 dpi [15]. Following transplacental infection between 40-125 days of gestation, ncp BVDV and HoBi-like pestivirus strains can induce a state of viral immunotolerance that leads to lifelong viral
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