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Glycoprotein H (gH) of pseudorabies virus (PrV)is a structural component of the virion and forms a complex with another glycoprotein, gL. For a detailed analysis of the function of PrV gH, we isolated a gH-deficient mutant on transcomplementing gH-expressing cells after insertion of a p-galactosidase expression cassette into a partially deleted gH gene. The absence of gH did not affect primary or secondary attachment of PrV but the mutant was not infectious. The defect in infectivity could partially be overcome by experimentally induced membrane fusion using PEG, which suggests that gH was necessary for fusion between virion and cellular membranes. After intranasal inoculation into mice, the LDso of complemented gH PrV was more than four orders of magnitude higher than that of wild-type PrV. Infection of the respiratory epithelium was much less efficient with complemented gH PrV as compared with rescued PrV, reflecting the lack of direct cell-to-cell spread. Complemented gH PrV was able to penetrate into a few trigeminal and sympathetic first order neurons accessible from the nasal cavity, whereas transneuronal transfer in the second order neurons was not observed. In summary, gH is essential for entry and cell-to-cell spread in cell culture, and for propagation in the nervous system of mice. This substantiates the hypothesis that transneuronal spread in vivo and direct cell-to-cell spread in cell culture are governed by similar mechanisms.

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that affects domesticated ruminants and occasionally humans. Classical RVF vaccines are based on formalin-inactivated virus or the live-attenuated Smithburn strain. The inactivated vaccine is highly safe but requires multiple administrations and yearly re-vaccinations. Although the Smithburn vaccine provides solid protection after a single vaccination, this vaccine is not safe for pregnant animals. An alternative live-attenuated vaccine, named Clone 13, carries a large natural deletion in the NSs gene which encodes the major virulence factor of the virus. The Clone 13 vaccine was previously shown to be safe for young lambs and calves. Moreover, a study in pregnant ewes suggested that the vaccine could also be applied safely during gestation. To anticipate on a possible future incursion of RVFV in Europe, we have evaluated the safety of Clone 13 for young lambs and pregnant ewes. In line with the guidelines from the World Organisation for Animal health (Office International des Epizooties, OIE) and regulations of the European Pharmacopeia (EP), these studies were performed with an overdose. Our studies with lambs showed that Clone 13 dissemination within vaccinated animals is very limited. Moreover, the Clone 13 vaccine virus was not shed nor spread to in-contact sentinels and did not revert to virulence upon animal-to-animal passage. Importantly, a large experiment with pregnant ewes demonstrated that the Clone 13 virus is able to spread to the fetus, resulting in malformations and stillbirths. Altogether, our results suggest that Clone 13 can be applied safely in lambs, but that caution should be taken when Clone 13 is used in pregnant animals, particularly during the first trimester of gestation.

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The incidence of clinical respiratory disease in 698 young beef bulls kept in 68 pens, and their exposure to respiratory pathogens after their arrival at 51 fattening operations in western France were assessed. Antibodies against bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1), Mannheimia haemolytica and Mycoplasma bovis were measured by ELISA. The incidence risk of respiratory disease was 18.5 per cent during the first six weeks. Cases occurred in 37 of the 68 pens, and in these pens 30.9 per cent of the bulls were affected. Their exposure to BHV-1 was very limited. When they arrived a high proportion of the bulls were seropositive to M haemolytica and a high proportion seroconverted to BRSV, M haemolytica and M bovis within the first six weeks. The risk of incidence of respiratory disease was lower in the pens in which the bulls had been vaccinated against M haemolytica. Higher proportions of the bulls were affected in pens in which small proportions of the bulls were seropositive to M haemolytica or BRSV on arrival, and in pens in which high proportions of the bulls were exposed to M haemolytica or BRSV during the first six weeks.

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BackgroundThe efficacy of a single dose of an inactivated bovine respiratory syncytial virus (BRSV) - Parainfluenaza type 3 (PI3) - Mannheimia haemolytica (Mh) combination vaccine, in calves positive for maternal antibodies, was established in a BRSV infection study.ResultsAs expected the single vaccination did not have any effect on the decline of BRSV-specific neutralising or ELISA antibody. The cellular immune system was however primed by the vaccination. In the vaccinated group virus excretion with nasal discharge was reduced, less virus could be re-isolated from lung tissues and the lungs were less affected.ConclusionsThese results indicate that a single vaccination with an inactivated BRSV vaccine was able to break through the maternal immunity and induce partial protection in very young calves. It can be speculated that the level and duration of protection will improve after the second dose of vaccine is administered. A two-dose basic vaccination schedule is recommended under field conditions.