BLUETONGUE VIRUS VACCINES: AN
HISTORICAL PERSPECTIVE
N. JAMES MACLACHLAN
SCHOOL OF VETERINARY MEDICINE, UNIVERSITY OF
CALIFORNIA
Bluetongue: An Historic Disease of
Africa (18th Century to Present)
Bluetongue in Africa and America: A Disease of
Certain Breeds of Sheep and Very Rarely Cattle
The Cycle of Bluetongue Virus Infection:
a Non-contagious Infection
• Culicoides insects =
biological vectors
– Only 20 or 30 of > 1000
Culicoides sp. worldwide are
vectors of BTV
• Infection of ruminants plus:
– Dogs – contaminated vaccines
– African carnivores
• Genus Orbivirus, family
Reoviridae
– Segmented genome ds RNA
– 24 (likely 25) distinct serotypes
BTV Vaccine Development in South Africa
•
Bluetongue (Bloutong) since
introduction of European sheep
OVI
– Recovered sheep resistant
•
Spreull (1902 - 1905)
– Inoculation of virulent blood and
immune sera together
•
Theiler (1906)
– Attenuated, sheep-passaged vaccine
– > 50 million doses 1907 – 1943;
Monovalent and issues of virulence!
•
Alexander - embryonated egg
polyvalent vaccines (circa 1940)
•
Howell & Erasmus - cell culture
propagated vaccines (circa 1960)
– Used today, 3 bottles of pentavalent
live-attenuated vaccine
• Introduced to Europe after 1998
M. Theiler
A. Theiler
Bluetongue: An Emerging Problem
in the United States circa 1950
Bluetongue in California
• Initial descriptions of the disease
and first virus isolation in the US
at UC Davis Veterinary School
– D. McKerchar, B. McGowan, J.
Moulton, J. Howarth, P. Kennedy etc
• Vaccine development
– Modified live vaccine grown in
embryonated chicken eggs
(McKerchar et al., 1953)
– Vaccine incorporated a California
virus (serotype 10, but unfortunately
designated strain CA-8) and
techniques pioneered at
Onderstepoort Veterinary Institute
by Alexander et al.
D. McKerchar
B. McGowan
Teratogenesis: an Adverse Product of the
First (Chicken Embryo) Bluetongue Vaccines
•
Reproductive losses in ewes and
cavitating brain lesions in fetuses
exposed at critical stages of
gestation
– Retinal dysplasia too
– Worst at 5 – 6 weeks of gestation,
milder lesions around mid-gestation
– age dependence!
– Approx. 20% incidence of
transplacental transmission
– Withdrawn in 1970
•
Replaced (approx 1978) by cell
culture derived vaccines
– These sheep vaccine strains likely
now circulate “naturally”
• low spontaneous incidence of similar
brain defects in cattle
• Detection of “field” viruses with
same genes as vaccine viruses
Bluetongue Virus Induced Teratogenic Ocular
and Cerebral Lesions: A Useful Animal Model
Sheep
Young & Cordy, J
Neuropathol Exp
Neurology, 1964
Richards & Cordy,
Science, 1967
Osburn et al., Lab
Invest, 1971; Am J
Pathol, 1972
Cattle
Maclachlan & Osburn,
Vet Pathol, 1983, 1985
Barnard & Pienaar,
Onderstepoort J Vet
Res, 1976
B.I. Osburn
D.R. Cordy
W.P. Richards
Development of the Cerebral Cortex: Role of
the Radial Glia
Bluetongue; Global Perspective in the
mid-20th Century
• Considered an
emerging
disease in the
1960 - 80s and
policies
developed to
prevent
perceived
global spread
California Paradox of Enzootic BTV Infection
but Little Disease; Trade Restrictions on
Cattle and Germplasm!
Reviewed: MacLachlan and Osburn,
J Am Vet Med Assoc, 2006
US cattle industry > 100 million
animals, value approx $80 billion
Bluetongue Global Ecosystems: Evolving
Understanding in the Late 20th Century
C. imicola plus C. pulicaris,
C. obsoletus, C. scoticus, C.
chiopterus and C. dewulffi*
C. sonorensis
10, 11, 13, 17
Unknown
C. imicola and
others
1,2,4,8,9,16
1-4, 5, 6, 8, 10, 12,
14, 17, 19, 22
Unknown
C. brevitarsis, C. actoni, C. fulvus,
C.schultzei and many other
Culicoides spp.
1-4, 8, 9, 11, 12, 15-18, 21, 23
1-3, 7, 9, 12, 15, 16, 20, 21, 23
1-16, 18-20, 22, 24
C. insignis and
possibly C. pusillus,
C. furens, C. filarifer and C.
trilineatus
C. imicola plus
C. bolitinos and
possibly others
C. brevitarsis plus C. wadai, C.
actoni, C. fulvus and possibly others
Different species of Culicoides vector disseminate different
serotypes of BTV in relatively distinct global ecosystems
•Bold indicates known or presumed principal vector
•C. dewulffi and C. chiopterus are putative vectors of BTV
serotype 8 in Europe*
Adapted from Gibbs
and Greiner, 1994
Bluetongue in Europe 1998 • Mediterranean Basin
– Serotypes 1, 2, 4, 9 and 16
• Variable virulence
– Live attenuated vaccines from
South Africa used in the region
• Circulation and infrequent
isolation from fetuses (Savini, G.
pers comm)
• Northern Europe
– Serotypes 6, 8 and 11
• Origins – laboratory and/or
vaccine strains?
• Serotype 8 virulent and high rate
of transplacental infection
– Only inactivated vaccines used
Bluetongue Serotype 8 in Northern Europe
2006 - present: Something very different!
Severe disease in all ruminant species - cattle, sheep,
goats, camelids, wild ruminants (deer to yaks) and even
zoo carnivores
Severe reproductive effects in cattle!
High Incidence of Vertical Transmission
of Serotype 8 in Northern Europe
• Teratogenic
defects in fetuses
and birth of
congenitally
infected calves
• Identical to those
described earlier
in California and
South Africa after
direct inoculation
of fetal cattle
Wouda et al. (2008). Hydranencephaly in calves
following the bluetongue virus serotype 8 epidemic in
the Netherlands. Veterinary Record 162: 422-423.
Fetal BTV Infections: a Review
• First described after use of an egg adapted vaccine in
pregnant ewes in California in the 1950s
– Confirmed in Australia that unadapted virus does not cross the
placenta whereas cell culture passaged strains do
• Age dependence of lesions in sheep and cattle
– Embryonic/fetal death, hydranencephaly, cerebral cysts prior to
midgestation and minimal lesions thereafter
– Immune competence arises by midgestation
• Fetuses infected in early gestation have developmental anomalies and
are antibody positive, virus negative at birth
• Fetuses infected later in gestation may have no abnormalities and be
virus positive at birth (antibody + or -)
– Rare spontaneous cases in cattle in areas where live attenuated
vaccines are used in sheep - California and South Africa
• Natural circulation of LAV viruses or reassortants thereof?
– A feature of BTV serotype 8 in northern Europe
• What might that imply about the origins of this virus?
Immunity to BTV: the Basis of
Vaccination
• Antibodies confer resistance to re-infection
with the homologous serotype
• Some heterotypic immunity
– Infection with 2 or more BTV serotypes generate
antibodies to serotypes of BTV to which the
animal never was exposed
– Shared neutralization epitopes among BTV
serotypes; are polyvalent vaccines possible?
Inactivated (Killed) BTV Vaccines
• PROS
– Safe and efficacious in preventing disease
• CONS
– Can be expensive and challenging to produce
• Potential for under-inactivation with residual virus
– Transient immunity typically
– Monovalent
• 24 serotypes of BTV
Live Attenuated (Modified-live) BTV
Vaccines
• PROS
– Cheap and relatively easy to manufacture
– Effective in reducing disease
– Already used in Africa, US, and Mediterranean Basin
• CONS
– Often contain “foreign” strains of BTV
– Potential for transmission and reassortment of genes
• Vaccine strains of BTV now circulate in the Mediterranean
– Some are teratogenic – chicken embryo adapted
especially – and cause embryo or fetal mortality
– Potential reversion to virulence
• genetic determinants of attenuation of BTV are unknown
– Interference between serotypes (polyvalent vaccines)
Genetic Diversity of Global Strains of
BTV
• BTV gene segments vary
amongst virus strains even
of the same serotype
– Genetic SHIFT by reassortment
of gene segments during
infection of insects or animals
with more than 1 strain or
serotype of BTV
• 89% of virus progeny =
reassortants after infection of a
calf with 2 BTV serotypes (J
Virol 61: 2670-2674, 1987)
– Genetic DRIFT by combined
quasispecies evolution and
founder effect (J Virol 75: 82988305, 2001)
Global strains of BTV Segregate as “Topotype” Clusters from
Prolonged Purifying (Negative) Selection: S10 (NS3) Gene
*
Mediterranean Basin, Asia & Australia
89
Mediterranean Basin & Africa
100
US & Caribbean Basin
US & Central America
Mediterranean Basin, Africa,
Caribbean Basin & Central America
92
Balasuriya et al., Vet Microbiol, 2008; MacLachlan et al., Virus Res, 2007
Quasispecies Evolution/Genetic Drift
and Founder Effect during Transmission
of BTV
Bonneau et al., J Virol, 2001
The Evolution of Bluetongue Virus
• Genetic drift and founder effect are central
to the diversification and evolution of
individual genes
– Leads to virus strains with distinct properties
• Each virus incursion is a founder event
followed by prolonged negative (purifying)
selection that creates BTV topotypes
• Potentially applies to genes of live
attenuated vaccine viruses if they circulate!
Improved Vaccines Increasingly Needed to Control
Incursions of BTV into Previously Unaffected Areas and to
Reassure Trading Partners
Subunit Vaccine Strategy for BTV: VLPs or
Recombinant Vaccines
The neutralization determinants
of BTV reside on VP2 but VP5
contributes through
conformational interaction
Reviewed: DeMaula et al., Virus Res, 2002
Recombinant Canarypox Virus Vectored BTV Vaccine
• Safe vector used in vaccines for horses,
dogs, cats, endangered species etc
– Co-expression of VP2 and VP5
• Sterilizing immunity in sheep
– Boone et al., Vaccine, 2007
0
Mean Body Temperature (F )
106.5
106
105.5
105
0
Temperature (F )
104.5
104
Control
Vaccinate
103.5
103
102.5
102
101.5
101
0
2
4
6
8
10
12
14
16
“Those who cannot remember the past are
condemned to repeat it” – George Santayana
Bluetongue continues to
vex scientists studying
the infection in a rapidly
changing world – but
human effort to control
the disease through
vaccination has itself
created problems on
occasion!
The 4 horsemen of the Apocalypse,
Albert Durer, Circa 1498