OS18 - Open Session 2018 Borgo Egnazia (Puglia), Italy 29 - 31 /10/2018 EuFMD Sessions\Open Session\Archive-2018\Open 2018 - Italy\6. Online & Streaming\PPTs

1. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
EVOLUTION AND COMPETITION OF SAT STRAINS DURING BUFFALO
TRANSMISSION IN A CONTROLLED CHALLENGE EXPERIMENT
Katherine Scott, L. Maake, E. Perez-Martin, L. de Klerk-Lorist,
L. van Schalkwyk, B. Beechler, E. Gorsich, B. Dugovich, J.Medlock,
A. Jolles, B. Charleston, F. Maree.

2. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
• Buffalo ecology, behaviour and physiology strongly mediated by seasonal cycles: body condition
drops (nutritional restriction, dry season (KNP: June-Sept), re-gained with rains & new grass
growth.
• Immunity in African buffalo varies seasonally in KNP (Beechler et al. 2009).
• Innate immune responses stronger in dry season (adaptive responses down-regulated)
• Trade-offs between immunity to intra- vs extra-cellular pathogens are detectable in dry season,
but not in wet season.
• Buffalo primary maintenance host of FMD but clinical FMD is mild, no obvious signs of FMD.
• Consequently, we expect strong seasonal variation, driven by resource availability, in co-
infection patterns and immunity in free-ranging buffalo; which may mediate FMDV transmission
dynamics.

3. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
• Buffalo virus recovery (field studies)
- from individuals for 5yrs
-experimental study over 1 year (Maree et al.)
- buffalo population (30-100) for 24 years
Can FMDV can perpetuate long-term without re-introduction from neighbouring populations?
• However, the frequency & titre of virus recovered decreases over time and can clear virus
over 15 months.
• significant number of animals fail to maintain persistent infection for prolonged periods as
proportion of persistently infected animals falls after reaching a peak in 1-3 year age-group.
• Serological surveys - 98% exposed to SAT 1, 2 and 3 serotypes by 2 years old.
• FMDV must maintain a high force of infection in buffalo population continually.

4. OS18
SAT-1 (MOI=0.5) & SAT-2 (MOI=2)
outcompeted SAT-3 (MOI=2).
SAT-1 (MOI=0.5) outcompeted
SAT-2 & SAT-3 (MOI=2)
Proportion of positive samples decreased
over time at a rate that differed significantly
between serotypes (P<0.001).
Buffalo infectionsCell culture co-infections
Maree et al., 2016.
Journal of Virology
Buffalo to cattle
transmission not
observed

5. OS18
Endemic
cycle
Escape
Epidemic
cycle
Buffalo calves
African Buffalo herd
Other cloven-hooved animals
Livestock
Persistently
infected with
SAT viruses
Infection of
calves 6-18
months of age
The epidemiology of FMD in Africa is influenced by
two different patterns

6. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
•Given prolonged annual birth pulse, the virus might be maintained as typical
“childhood” infection (circulating through new susceptible calves following loss of
protective maternal immunity after 3-8 months of age) with the latest born calves of
one year sparking the new epidemic.
•preliminary models of FMDV dynamics in free-ranging African buffalo suggest that calf-
to-calf transmission alone is unlikely to result in long-term persistence of FMDV.
•Or annual epidemics among susceptible calves may be initiated by persistent carriers,
or novel antigenic variants

7. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
FMD
Longitudinal
Transmission
study:
Sample every
2-3 months
for 3 years
FMD:
Probangs
Tonsil swabs
Serum
(Monitor FMD
in herd via
serology &
molecular)
Satara
64 buffalo
900 ha fenced camp
June 2015
20 new animals
2 Break-ins
Babies born

8. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
Aims:
1. What is the seroprevalence of FMDV in herd (ages, sex) over time? What are the
antibody dynamics for SATs in buffalo?
2. How variable are maternal FMDV antibodies and their drop-off over time?
3. What predicts antibody levels in mother - condition, antibody levels ?

9. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
Seroprevalence in buffalo herd
Liquid Phase blocking ELISA performed on 3 SATs, accredited diagnostic test
ARC-OVR lab

10. OS18
The average titer for each animal, across all time points when the animal had a positive (>=1.7) antibody
titer, for each SAT
Nonparametric ANOVA: Dunns multiple comparisons
Sat 1 vs. Sat 2 – p=0.0001; Sat 2 vs. Sat 3 – p=0.026; Sat 1 vs. Sat 3 – p=0.0001
Sex makes no difference ; but age does: older animals tend to have higher titers than younger animals.
2.23
1.942.06

11. OS18
*SAT1 N=75, 6.77+-0.67; median 4 captures
*SAT2 N=123, 4.28 +- 0.44; median 2 captures
+SAT3 N= 133, 2.88 +- 0.28; median 1 capture
older animals in all cases show longer antibody responses
4 2 1

12. OS18
Loss of serostatus was not affected by sex or reproductive status of the buffalo.
For SAT2, younger animals and those in worse body condition were more likely to drop their
antibody titers.
For SAT1 and SAT3, animals with low total immunoglobulins were also more likely to drop
their FMDV antibody titers.

13. OS18

14. OS18
2.3 Primary Infection events <2 yrs of age
Gain of positive serostatus was not affected by sex or reproductive status of the buffalo.
For SAT2 and SAT3, older animals were more likely to gain positive serostatus.
For SAT1, animals with higher total immunoglobulins were also more likely to raise their FMDV
antibody titers.
All SATs, animals in poor body condition were more likely to gain positive FMDV serostatus.
Given low to moderate force of
infection of FMDVs in our study herd,
rises in antibody titer from negative to
positive serostatus are often not
attributable to disease transmission.
Other biological processes, such as
changes in nutritional status or
immune status, are likely to play a role.

15. OS18
38 cases of loss of maternal protection against FMDVs, 9 for SAT1, 18 for SAT2 & 11 for SAT3.
These numbers likely reflect the observed differences in transmission rates among the
serotypes: High force of infection would make it less likely for us to observe loss of maternal
antibodies, because calves were likely to be exposed to FMDV within the 2-3 month
inter-capture interval (so that we would observe high titers both times).
Buffalo calves typically lost
their maternal immunity
between June and August
each year.

16. OS18
3.3. Susceptibility
At the herd level, susceptibility to FMDVs is distributed across all age groups of buffalo and
occurs throughout the year. Patterns in time and among age groups vary among serotypes.
These patterns are likely to affect the dynamics of endemic FMDV in their natural host
populations.
age vs susceptibility
0
2
4
6
8
10
12
14
16
18
0
2
4
6
8
10
12
14
16
18
0
2
4
6
8
10
12
14
16
18
0.0
0.2
0.4
0.6
0.8
1.0
SAT1
SAT2
SAT3
Age (years)
Susceptibilty

17. OS18
Susceptibility vs capture1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0.0
0.2
0.4
0.6
0.8
1.0
SAT1
SAT2
SAT3
Capture
Susceptibilty

18. OS18
* Cross-reaction among the SATs is widely documented in the LPBE.
Cross-reactions did not affect patterns of gain of serostatus for any SAT
4. Cross-reaction
* Cross-reactivity among SATs contributed to patterns of loss

19. OS18
Open Session of the EuFMD - Cascais –Portugal 26-28 October 2016
Conclusions
• Seroprevalence shows SAT1 has highest seroprevalence (2 main peaks) and
thereafter well maintained; SAT2 has one small peak and generally seroprevalence
decreases over time; SAT3 remains low and decreases but shows 2 main peaks.
• The SAT serotypes antibody dynamics differ significantly, with buffalo mounting a
very robust antibody titer for SAT1; intermediate titers for SAT2 and comparatively
weak titers and short-lived for SAT3. SAT1 titers are stable compared to SAT2 and
SAT3 which dip below protective levels more often.
• Buffalo frequently change serostatus but only a fractions of theses rises are
explained by (re-)exposure to the viruses.
• Incidence of primary infection was higher for SAT1 than SAT2 and SAT3.
• Susceptibility distributed across age groups and times of year, patterns are likely to
affect the dynamics of endemic FMDV in their natural host populations.
• We propose that SATs have evolved different strategies to co-exist in buffalo, with
SAT1 being highly transmissible and adapted to buffalo. How SAT2 (antigenic
changes? Cattle outbreaks) and SAT3 differ still needs to be further investigated.
• Loss of serostatus (not affected by sex or reproductive status). For SAT2, younger
animals and those in worse body condition were more likely to drop their
antibody titers, whereas for SAT1 and SAT3, animals with low total
immunoglobulins were affected, suggesting that the dynamics we observed may
be of broader significance than just FMD.

20. OS18
Thank you!
Questions