Abstract
Two types of gammaherpesviruses (γEHV) are known to infect horses, EHV-2 and EHV-5. Foals become infected early in life, probably via the upper respiratory tract, despite maternal antibodies. In this study, we analyzed samples from a herd of mares and their foals. The foals were followed from birth to 22 months of age and the dams during the first 6 months postpartum. Blood and nasal swab samples were taken regularly for evaluation of antibody responses, virus isolation and viral load by qPCR. EHV-2 was isolated on day 5, and EHV-5 on day 12, earlier than previously reported. γEHV specific antibodies were not detectable in serum of foals before colostrum intake but peaked a few days after colostrum. Overall, EHV-2 viral load peaked in nasal swab at three to four months of age, paralleled with decline in maternal antibodies, but EHV-5 viral load did not peak until month 12. Maternal antibodies had a notable effect on the viral load and induction of endogenous antibody production. Foals were grouped in two groups depending on the mare’s γEHV specific total IgG levels in serum at birth, group-high and group-low. Group-high had higher levels of maternal γEHV specific total IgG and IgG4/7 for the first 3 months, but when the endogenous production had superseded maternal antibodies, group-low was higher. The maternal antibodies had an effect on the γEHV viral load. Group-low peaked in EHV-2 viral load one month earlier than group-high. These effects were more evident for EHV-5, as there were seven months between the viral load peaks for the groups. The study provides information on how maternal antibody transfer affects γEHV shedding and antibody production in offspring. It also extends our knowledge on the occurrence of EHV-2 and EHV-5 infection in foals during the first two years of life.
Highlights
Two gammaherpesviruses are known in horses, equid herpesvirus (EHV) 2 and 5
Pre-suckling sera from all 15 foals were negative for all γEHV antibodies tested
From month 1 the IgG4/7 levels decreased, nadir was at month 3, the levels peaked at month 9 and from the levels were fairly stable throughout the study with minor fluctuations between time points (Fig 1A)
Summary
Two gammaherpesviruses are known in horses, equid herpesvirus (EHV) 2 and 5 These viruses are closely related and result in strong serological cross reactivity [1, 2]. The viral load of EHV-2 and EHV-5 in nasal shedding varies both within and between individuals [20]. Both viruses can be detected at various sites from diseased and healthy horses at all ages. EHV-2 and EHV5 are typically present in peripheral blood leukocytes and respiratory secretions [3, 21, 22] Both viruses are ubiquitous and have been associated with a wide range of clinical signs. EHV2 has been implicated with keratoconjunctivitis [23,24,25], mild respiratory disease [13, 22, 26], pneumonia [27, 28], pharyngitis [29] and poor performance [30], and EHV-5 with equine multinodular pulmonary fibrosis [31,32,33] and dermatitis [34]
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