Transcript Document 7612242

Oral susceptibility: South Africa
Gert Venter, Ina Hermanides, Daphney Majatladi, Solomon
Boikanyo, Isabel Wright
Oral susceptibility: South Africa
Oral susceptibility
• AHSV serotype/isolates & geographic populations
• BTV-8 (Belgium isolate & SA isolate)
• Co-infection AHSV & EEV
• Co-infection AHSV & BTV
Oral susceptibility
determination and
comparison
(Materials and Methods)
10 day extrinsic incubation at 23.5°C
Midges assayed individually on BHK-21 cells
Micro titration of all positive samples
All isolates are typed by Virus neutralization (VN) on Vero cells
ARC-Onderstepoort Veterinary Institute
• Oral susceptibility (AHSV)
The number of midges that become infected after
feeding on a virus infected blood meal
Viruses:
11 recent AHSV isolates
historical reference strains (1960’s)
live attenuated vaccine strain (AHSV-7)
a midge isolate (AHSV-7)
Midge Populations:
Onderstepoort, Gauteng
Clarens, eastern Free State
Stellenbosch, western Cape
ARC-Onderstepoort Veterinary Institute
RESULTS (Oral susceptibility)
•
AHSV replicated/persisted in 11 of 22 Culicoides sp. ► multi-vector
potential
– (BTV replicated/persisted in 12 Culicoides sp.)
•
Most of these are widely distributed and abundant in South Africa and
their host preferences include horses (and ovine)
•
Significant differences between:
– Culicoides species and different populations of the same species
– Serotypes and different isolates of the same serotype
– Seasons
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Oral susceptibly of C. imicola was relatively low and C. imicola even
appears to be refractory to some of the isolates
C. leucostictus (38.0%) is a bird feeder the epidemiological
significance is not clear
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C. imicola from Clarens > susceptible than C. imicola from
Onderstepoort or Stellenbosch
C. imicola from Stellenbosch > susceptible than C. imicola from
Onderstepoort
C. bolitinos is > susceptible to infection with BTV than C. imicola but
not for AHSV
RESULTS (Oral susceptibility)
• AHSV recovery ranged from <1 to 50%; relative high virus titres
in individual midges suggests a systemic infection and that
transmission may be possible
• Recovery rates of the attenuated vaccine strain and midge
isolate were > than that of the field isolates and reference
strains.
– Attenuation of AHSV (and BTV) does not reduce its ability to infect
Culicoides species and may lead to enhanced replication that will
increase the possibility of reasortment
• Differences in the oral susceptibility of Culicoides species for
different isolates of the same serotypes suggests co-adaptation
between viruses and vectors present in a given locality
• The significant variation in oral susceptibility confirms the
intricate relationship that exists between vector and pathogen
and highlights numerous factors that may influence oral
susceptibility and vector competence
Oral susceptibility (BTV-8)
BTV-8 (SA)
BTV 8 (Belgium)
5.8 log10/TCID50
7.8 log10/TCID50
6.8 log10/TCID50
C. imicola
OP
Clarens
0/420
0/61
2/403 (0.5%) a
1/114 (0.9%) a
1/409 (0.2%) a
2/289 (0.7%) a
C. bolitinos
Clarens
0/114
20/294 (6.8%) b
4/229 (1.7%) a
C. leucostictus
Clarens
0/53
2/36 (5.5%)
BTV-8 (SA)
C. bolitinos significantly > susceptible than C. imicola from Onderstepoort (P<0.001)
or from Clarens (P=0.020)
C. imicola from Onderstepoort = C. imicola from Clarens (P=0.513)
BTV-8 (Belgium)
C. bolitinos = C. imicola from Onderstepoort (P=0.058)
C. imicola from Clarens (P=0.413)
C. imicola from Onderstepoort = C. imicola from Clarens (P=0.572)
Co-infection (AHS & EEV)
Virus
Titre
(Log10TCID50/ml)
EEV + AHS
(6.1) + (5.8)
EEV
(6.1)
AHS
(5.8)
C. imicola
Clarens
OP
AHS 4/49 (8.2%)
EEV 8/49 (163%)
AHS 1/64 (1.6%)
EEV 1/64 (1.6%)
3/69 (4.3%) NS
3/48 (6.3%) NS
1/168 (1.5%)NS
14/237 (5.9%) NS
C. bolitinos
Clarens
AHS 23/532 (4.3%)
EEV 7/532 (1.3%)
26/370 (7.0%) NS
8/416 (1.9%) NS
EEV: C. imicola Clarens = C. imicola OP
C. bolitinos = C. imicola Clarens
C. bolitinos < C. imicola OP
AHS: C. Imicola Clarens = C. imicola OP
C. bolitinos = C. imicola Clarens
C. bolitinos = C. imicola Clarens
C. Imicola OP: EEV > AHSV
C. bolitinos: EEV < AHSV
Co-infection (AHS & EEV)
Virus
Titre
(Log10TCID50/ml)
BT8>2-3 days>AHS9
5.8>>>>>>>>5.8
BT + AHS
5.8 + 5.8
BT
5.8
AHS
5.8
Clarens
0/2
0/17
0/61
3/69 (4.3%)
OP
AHS 2/410 (0.5%) NS
AHS 12/615 (2%) NS
0/420
1/168 (0.6%) NS
AHS 2/19 (10.5%) NS
0/41
0/114
26/370 (7.0%) NS
BT8>2-3days>AHS9
7.8 >>>>>>>> 5.8
BT + AHS
7.8+5.8
BT
7.8
AHS
5.8
AHS 4/70 (5.7%)
AHS 1/20 (5.0%)
1/114 (0.9%)
3/69 (4.3%)
AHS 3/68 (4.4%)
2/403 (0.5%)
4/168 (2.4%) NS
BT 4/99 (4.0%)
AHS 4/99 (4.0%)
20/294 (6.8%) NS
C. imicola
C. bolitinos
Clarens
Virus
Titre
(Log10TCID50/ml)
C. imicola
Clarens
OP
C. bolitinos
Clarens
AHS 1/14 (7.1%)
26/370 (7.0%) NS
Potential Vectors (South Africa)
BT
EHD
lab
EEV
lab
field
lab
+
+
+
+
+
+
C. bolitinos
++
+
+
+
+
+
C. gulbenkiani
+
Avaritia C. imicola
field
AHS
field
lab
C. milnei
Culicoides C. magnus
+
+
+
+
+
+
+
+
+
+
+
+
C. brucei
Remmia C. enderleni
+
+
C. nevilli
+
C. schultzei
+
Meijerehelea
C. leucostictus
+
+
C. tuttifrutti
Hoffmania C. zuluensis
field
+
+
+
+
Potential Vectors (South Africa) continue
BT
lab
EHD
field
field
lab
field
EEV
Lab
+
Beltranmyia
C. nivosus
C. pycnostictus
Lab
AHS
+
+
+
Pontoculicoides
+
C. engubandei
Synhelea
+
C. dutoiti
Monoculicoides
+
C. cornutus
C. bedfordi
+
C. huambensis
+
C. expectator
+
C. onderstepoortensis
+
+
+
+
+
field
Outbreaks: AHSV
South Africa
Gert Venter, Karien Labuschagne, Ina Hermanides, Daphney
Majatladi, Solomon Boikanyo, Isabel Wright
AHS Outbreaks
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African horse sickness
Since 2001, AHSV-2 occurred annually in the Eastern Cape (4 serotypes at
present)
Outbreaks during the past 7 years in and around the surveillance zone of the
free area in the Western Cape has each time led to the closure of the
quarantine station in Cape Town and a ban on the export of horses
In 2006, AHSV-9, uncommon in SA, occurred in the Knysna area in the Western
Cape and outbreaks and continue into the colder months
In 2008 AHSV was isolated from horses in the Port Elizabeth area
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Equine encephalosis
Isolations from dead or sick horses increased the past 2 years
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AHS Outbreaks
Port Elizabeth (2 – 9 April 2008)
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2 horses died in April from AHSV at the coast
10 collections at 9 farms, 3 641 Culicoides midges collected (avg:
364)
At the coast 5 collections:
1 414 Culicoides (avg: 282.8)
–
C. imicola (3.3%)
–
C. bolitinos (93.4%)
Inland 5 collections:
2 539 Culicoides (avg: 507.8)
C. imicola (81.2%)
C. bolitinos (11.7%)
A survey conducted from 1995-1999 at one
farm in Port Elizabeth deliver only
5 C. imicola in 170 collections
From 2006 an additional 53 collection
were made and 446 C. imicola collected
Outbreaks
Robertson (29 February – 6 March 2008)
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9 collections at 4 sites, 331 725 Culicoides (avg: 36 858)
C. imicola (99.4%)
53 pools of 200 parous C. imicola assayed for virus
EEV Kaalplaas:
–
was from 13 and BTV from 2 pools
Field infection prevalence:
–
EEV (0.14%)
–
BTV ( 0.02%)
Outbreaks
• Kimberley, Northern Cape (27-29 February 2008)
• 14 collections at 5 sites, 91 647 Culicoides midges
• C. imicola 85 645 (93.5%)
• No virus could be isolated from C. imicola (7 pools of 145-200
midges), C. pycnostictus (1 pool of 129 midges) and C.
bolitinos (1 pool of 22 midges)
• EEV Kaalplaas was isolated from 1 pool of 24 C. tuttifrutti
• Like C. imicola and C. bolitinos,
C. tuttifrutti is also in the
subgenus Avaritia.
• Relative widespread in southern
Africa but mostly uncommon
• >10 000 is not impossible
• Vector competence status
and host preference remains
unknown