Download Role of buffalo in the maintenance of fmdv,

Role of buffalo in the maintenance of
foot-and-mouth disease virus
Bryan Charleston
Study design
3 KNP buffalo isolates
6 month old Nguni cattle (n = 4)
SAT1/KNP/196/91
SAT2/KNP/19/89
SAT3/KNP/1/08/3
PK cells
SAT-3
OVI cattle titration
≈ 1 × 104 TCID50
SAT-1
SAT-2
Skukuza buffalo challenge study
≈ 5 × 105 TCID50
Necropsy
N = 4 buffalo
Necropsy
Necropsy
N = 4 buffalo N = 4 buffalo
35DPC
95DPC
156DPC 163DPC 185DPC
1.25IU/kg
N = 4♀
Institute for Animal Health
400DPC
1.25IU/kg
ACTH stimulation (Synacthen®)
N = 4 buffalo
N = 16 FMD free buffalo (7♂9♀)
10 – 30 months old
Imfolozi Game Reserve, KZN
299DPC
Necropsy
N = 4 buffalo
Day 302
Progesterone IUD
Estrumate
Acute FMD: naïve buffalo
1DPC
2DPC
Acute FMD: naïve buffalo
Conclusion
• SAT co-infection in cattle – severe clinical FMD
• 10 × dose in naïve buffalo:
• mild clinical FMD
• integrin αvβ6 expression in tissues typically associated with FMD lesions
• viraemic for at least 5 to 7 days
• No leucopenia
• High levels type 1 IFN
• seroconverted to all three serotypes by day 14
3D primer and probe
SAT1 primer and probe
SAT2 primer and probe
SAT3 primer and probe
Chronic FMD: buffalo
Casteleyn et al.,
Budras, Bovine Anatomy
Follicles with
central crypt
M Hofmeyr
Institute for Animal Health
Chronic FMD: buffalo
Virus isolation (IBRS cells)
Number of buffalo
8
Right tonsil swab
Probang
7
6
5
4
3
2
1
0
50 DPC *109 DPC
35
35
*One round VI only
() = passage number on IBRS cells
Institute for Animal Health
126 DPC 136 DPC 155 DPC 162 DPC 168 DPC 172 DPC 185 DPC
Day post challenge
Chronic FMD: buffalo
3D primer and probe
SAT1 primer and probe
SAT2 primer and probe
SAT3 primer and probe
Institute for Animal Health
Chronic FMD: buffalo
95DPC
10µm
100µm
100µm
Anti-3B (D5)
IB11
Merge
10µm
Institute for Animal Health
FMD: buffalo
Discussion points
• Despite close contact, +ve virus isolation and ACTH stim – no transmission/ seroconversion in
cattle!
• Consistent with previous reports:
• no transmission/ transmission only after months of contact
• Rx buffalo dexamethasone (Gainaru et al., 1986)
• Rx cattle dexamethasone for 3 weeks (Ilott et al., 1997) – inhibited shedding of FMDV
• Co-infection cattle rinderpest/ bovine herpes 1 viruses (McVicar et al., 1977) – no increase virus
recovery/ transmission
• Pattern of transmission from captive buffalo during acute infection is also variable
• same pen: buffalo to buffalo/ buffalo to cattle× (Gainaru et al., 1986)/ buffalo to cattle× (Dawe et
al., 1994)
•
adjoining pen: buffalo to impala× (Gainaru et al., 1986)
Knowledge gaps and questions
• Improved methods to isolate virus/ viral sequences from carrier buffalo
• Indentify sites of virus localisation and replication in buffalo
• Propose hypothesise for mechanisms of persistence
• Test potential “triggers” for transmission: short term stress? Long term stress? “childhood
epizootic”?
• How infectious are buffalo during acute infection? Virus excretion compared cattle/sheep/pigs.
Transmission despite no/ limited FMD lesions?
Institute for Animal Health
Future work
•
FMDV maintains high force of infection in buffalo herds
 > 98% buffalo in KNP exposed to all three SAT serotypes by age 2 (Thomson, 1992)
 High rate of infection suggests common mechanism for inter-annual perpetuation
 Avoids auto-extinction small isolated herds
•
Crucial that we understand how FMDV persists in isolated buffalo herds
 Primary objective to identify triggers to affect transmission from carriers.
 If we can’t even understand this - how understand in livestock, large populations, global, multiple
serotypes?
•
3 year longitudinal study of isolated breeding herd in KNP
–
–
–
–
–
•
Account for environmental factors absent from experimental studies
Identify factors affecting FMDV status (age, sex, seasonal, co-infections etc.)
Phylogenetic and antigenic phenotype analysis of FMDV isolates
Establish infection parameters in buffalo calves (naïve population)
Test triggers under experimental conditions
We hypothesise:
– Previous demonstration of FMDV particles in lymph tissue on germinal centre FDCs provides a means of
delayed viral clearance (extracellular reservoir)
•
To affect transmission:
– Immune stimulation (enhance immune-complexed FMDV replication in Fc receptor expressing cells)
– Or suppress antibody response – for example protein-calorie restricted diet (Watson, 1985)
Acknowledgments
Nick Juleff
Lin-Mari de Klerk Lorist
Roy Bengis
Louis van Schalkwyk
At Dekker
Scalk van Dyk
Dave Cooper
Francois Maree
Ivan Morrison
Berry Mutowembwa Dan Haydon
Brenda Botha
Livio Heath
Katherine Scott
Pamela Opperman
Belinda Blignaut
Ferran JORI, Cirad
Mammal Research
Institute University of
Pretoria
Markus Hofmeyr
Peter Buss
Jenny Joubert