Production of Bovine Herpesvirus Type 1-Seronegative Latent Carriers by Administration of a Live-Attenuated Vaccine in Passively Immunized Calves

Abstract

The consequences of the vaccination of neonatal calves with the widely used live-attenuated temperature-sensitive (ts) bovine herpesvirus type 1 (BHV-1) were investigated. The tsstrain established acute and latent infections in all vaccinated calves either with or without passive immunity. Four of seven calves vaccinated under passive immunity became clearly BHV-1 seronegative by different serological tests, as did uninfected control calves after the disappearance of maternal antibodies, and they remained so for long periods. A cell-mediated immune response was detected by a BHV-1 gamma interferon assay, but this test failed to detect the seronegative latent carriers (SNLCs). While they are not detected, SNLCs represent a threat for BHV-1-free herds or countries. This study demonstrates that SNLCs can be easily obtained by inoculation with a live-attenuated BHV-1 under passive immunity and that latent carrier animals without any antibody do exist. Consequently, this situation could represent a good model to experimentally produce SNLCs.

Calf health from birth to weaning. III. housing and management of calf pneumonia

“…Intranasal vaccination of seronegative newborn calves decreases clinical signs in a challenge trial [107]. However, the situation is complicated by the potential for establishment of seronegative latent carriers in calves with specific maternal antibodies through field virus infection as well as through vaccination with modified-live vaccines [112,113]. In Europe, the use of conventional vaccines is prohibited in some countries.…”

Cattle immunology: The immune response to viruses

“…It is also possible that 'false' seronegative latent carriers can exist, i.e. that the diagnostic tests used have insufficient sensitivity to detect the level of antibody present (Lemaire, Meyer and others 2000).…”

Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a request from the Commission on a Definition of a BoHV-1-free animal and a BoHV-1-free holding, and the procedures to verify and maintain this status

“…However, there is evidence that field virus infection, or vaccination temperature-sensitive mutant vaccine in calves with high levels of maternal antibody may produce a delay or even abrogation of active seroconversion, the latter leading to the production of a seronegative latent carrier animal (SNLC) following the decay of maternal antibody. (Lemaire et al, 2000a;. Following the experimental challenges in each of the above studies, latent virus was reactivated from the seronegative calves.…”