Cervid herpesvirus 2 and not Moraxella bovoculi caused keratoconjunctivitis in experimentally inoculated semi-domesticated Eurasian tundra reindeer

Abstract

BackgroundInfectious keratoconjunctivitis (IKC) is a transmissible disease in semi-domesticated Eurasian reindeer (Rangifer tarandus tarandus). It is regarded as multifactorial and a single causative pathogen has not yet been identified. From clinical outbreaks we have previously identified Cervid herpesvirus 2 (CvHV2) and Moraxella bovoculi as candidates for experimental investigations. Eighteen reindeer were inoculated in the right eye with CvHV2 (n = 5), M. bovoculi (n = 5), CvHV2 and M. bovoculi (n = 5) or sterile saline water (n = 3; controls).ResultsAll animals inoculated with CvHv2, alone or in combination with M. bovoculi, showed raised body temperature, increased lacrimation, conjunctivitis, excretion of pus and periorbital oedema; clinical signs that increased in severity from day 2 post inoculation (p.i.) and throughout the experiment, until euthanasia 5–7 days p.i. Examination after euthanasia revealed corneal oedema, and three animals displayed a corneal ulcer. CvHV2 could be identified in swab samples from both the inoculated eye and the control eye from most animals and time points, indicating a viral spread from the inoculation site.ConclusionsThis study showed that CvHV2 alone and in combination with M. bovoculi was able to cause the characteristic clinical signs of IKC in reindeer, whereas inoculation of M. bovoculi alone, originally isolated from a reindeer with IKC, did not produce clinical signs. Previous studies have suggested that herding procedures, animal stress and subsequent reactivation of latent CvHV2 infection in older animals is a plausible mechanism for IKC outbreaks among reindeer calves and young animals in reindeer herds. However, further studies are needed to fully understand the infection biology and epidemiology associated with IKC in reindeer.

Infectious keratoconjunctivitis in semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus): microbiological study of clinically affected and unaffected animals with special reference to cervid herpesvirus 2

“…In a natural outbreak of IKC in reindeer, the virus was most often detected and isolated at higher titers, from animals with mild or early stage signs of IKC and only from a few animals with severe signs. It was hypothesized that the peak of viral replication and shedding occurred at earlier stages, whereas secondary bacterial infections were dominant in later stages of the disease [ 15 , 21 ]. It is also possible that the virus, during the late stages of IKC, is entering the latency stage, shutting down the active replication cycle and the shedding of progeny virus.…”

“…[ 18 – 20 ], which all may play a role in the development of the disease. However, from an outbreak of IKC in reindeer it was concluded that Cervid herpesvirus 2 (CvHV2) was the causative and transmissible agent, accompanied by secondary opportunistic bacterial infections [ 15 ] and it has recently been shown experimentally that CvHV2, alone and in combination with Moraxella bovoculi, was able to cause clinical sympotms characteristic for IKC in reindeer [ 21 ].…”

Ocular Histopathological Findings in Semi-Domesticated Eurasian Tundra Reindeer (Rangifer tarandus tarandus) with Infectious Keratoconjunctivitis after Experimental Inoculation with Cervid Herpesvirus 2

“…In a recent controlled challenge experiment, we found that CvHV2 causes IKC in previously unexposed and seronegative semi-domesticated reindeer [20]. Animals inoculated with CvHV2, alone or in combination with the gram-negative bacterium M. bovoculi, developed clinical signs of IKC within two days after inoculation of the virus, and displayed conjunctival edema, hyperemia, and purulent exudate.…”

“…Moraxella bovoculi did not produce clinical signs in this controlled challenge experiment, except for a transient grey or whitish ocular discharge on the day of inoculation. In the present paper, we present the detailed histopathology of eye tissues collected from the previous challenge experiment [20].…”

“…The aim of the present study was to investigate the pathogenesis of IKC in reindeer caused by CvHV2, by characterizing early histopathological changes in various eye tissues of reindeer that were experimentally inoculated with CvHV2 and that developed IKC [20]. We also adapted a quantitative PCR assay to be able to quantify virus in the conjunctiva of the CvHV2-inoculated eyes and the non-inoculated eyes during the experimental period.…”