Serology unveils decades-long contact of the Iberian hare, Lepus
granatensis, with myxoma or antigenically-related virus.
Abstract
The 2018 outbreak of myxomatosis in the Iberian hare (Lepus
granatensis), has been hypothesized to originate from a species jump of
the rabbit-associated myxoma virus (MYXV), after natural recombination
with an unknown poxvirus. Iberian hares were long considered resistant
to myxomatosis as no prior outbreaks were reported. To provide insights
into the emergence of this recombinant virus (ha-MYXV), we investigated
serum samples from 451 Iberian hares (88 live captured, 313 hunted and
50 found dead) collected over two time periods, 1994-1999 and 2017-2019,
using a rabbit commercial indirect ELISA after validation, and tested
different tissues or sera by a qPCR targeting M0005L/R gene conserved in
MYXV and ha-MYXV. The cut-off of ELISA Relative Index 10 = 6.1 yielded
an estimated positive predictive value of 96.4% (CI95% 82.6-98.0%),
by comparison with qPCR positive and negative reference hares. Overall,
antibodies were detected in 12.6% (57/451) of the hares tested, of
which 40.3% (23/57) were also qPCR positive. Antibodies were found in
apparently healthy hares sampled in 1994-1999 (n=10, none MYXV-DNA
positive), and in 2017-2019 (n=28, of which 14% were MYXV-DNA
positive). For the Iberian hares hunted or live trapped, seroprevalence
was significantly higher in 2017-2019 (13.0%, CI95% 9.2-18.2%) than
in 1994-1999 (5.4%, CI95% 3.0-9.6%) (p=0.005), and significantly
higher in 2019 (p=0.007), being lower during the winter
(p<0.001). While our molecular and serological results show
that Iberian hares have been in contact with MYXV or an antigenically
similar virus at least since 1994, they also show an increase in
seroprevalence in 2018-2019. The more remote contact of hares with MYXV
may have occurred with strains that circulated in wild rabbit, or
unnoticed strains circulating in Iberian hare populations. This work
clearly confirms the circulation of MYXV in the Iberian hare ate least
20 years before the severe virus outbreaks observed in 2018.