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Wilna VoslooCSIRO-Australian Animal Health Laboratory
ASF has probably been around in Africa for millennia
It most probably caused outbreaks in pigs introduced to sub-Saharan Africa by Portuguese missionaries and colonists about 500 years ago
The first outbreaks in domestic pigs were reported in East Africa in the early 1900s
In South Africa, where contact between domestic pigs and warthogs occurred, similar outbreaks were recorded from 1926
Thereafter the disease was also reported in Angola, northern Mozambique (1954), most countries in central and southern Africa and then spread to West Africa {Senegal (1978 OIE) and Guinea Bissau – 1959?}
Since 1978 at least 26 African countries have reported outbreaks of ASF and since 1996 devastating outbreaks have occurred in West Africa
This increase in number of outbreaks is most probably due to increased numbers of pigs
ASF appears to persist in at least 3 different cycles:◦ Sylvatic cycle involving soft ticks and wild suids
(savannah zones mostly in central, east and southern Africa)◦ Domestic pigs and soft ticks◦ Domestic cycle involving only pigs Direct contact between pigs Indirect transmission (iatrogenic, hands, clothing etc) Virus in pig tissues / meat products fed to pigs
Outbreaks in pigs where the sylvatic cycle is not evident could be due to low level infection which then occasionally causes high mortalities
Pigs with innate resistance probably play a key role in maintaining and propagating ASFV
Village pigs seem to be more resistant and survive infection as shown by serological surveys where up to 40% of pigs can be sero-positive after an outbreak
Experimental infection indicated that this apparent resistance is not inherited
Epidemiology of ASF in Mozambique: an endemic area
Main Objectives:◦ To determine the prevalence of soft ticks in the area
◦ To verify the contact between wild and domestic pigs with soft ticks
◦ To establish whether wild and domestic pigs and soft ticks are infected with ASFV
◦ To determine the molecular epidemiology of the ASFV isolates found in the area
ASFV-endemic region
High density of warthogs in the park
Communities surrounding the park are heavily dependent on pig rearing as a source of income
N1
N2 N3 N4
N5
EggsAdult
Trans-Stadial transmission
Sylvatic Cycle Domestic Cycle
Persistent infection
Blood and sera from warthogs
Blood and sera from domestic pigs
Ticks from warthog burrows and pig pens
ASF sero-prevalence in warthogs
Blood and sera from warthogs
Samples collected from 12 warthogs
75% (9/12) of the warthog sera tested positive for ASFV antibodies
This suggest a high prevalence of ASF in the warthog population
Prevalence of soft ticks
Ticks from warthog burrows and pig pens
2556 ticks (O. porcinus porcinus) collected from 29 out of 32 warthog burrows searched in GNP (90% prevalence)
203 ticks (O. p. domesticus) collected from 2 out of 63 pig pens searched in buffer zone outside GNP (3% prevalence)
Assays Burrows positives (%)
Nested PCRs (screening assays) 72.4 %(21/29)
Virus isolation 48.3 %(14/29)
Soft ticks in sylvatic cycle
Soft ticks in domestic cycle
Assays Pig pens positives (%)
Nested PCRs (screening assays) 100 %(2/2)
Virus isolation 50 %(1/2)
Prevalence of ASFV in soft ticks
♂ ♀ 1 2 3 4 5 6 7 - + M
PCR result obtained for the different internodal stages of ticks collected from a single warthog burrow
• There was no correlation between the likelihood of a positive result and any of the internodal stages
Internodal stages
Moz 14/2006
Moz 15/2006
Moz 17/2006
AF270708 Mozambique/1960
AF301541 Tengani/60
AY494553 MAL/1/02
AF270709 Mozambique/1979
AF270711 MOZ/1/94
AF270712 MOZ/8/94
AF270710 SPEC265
Genotype V
RSA/1/96
MOz 11/2006
Moz 10/2006
Moz 18/2006
Moz 16/2006
Moz 19/2006
New genotype
AF302818 RSA/1/98
SPEC/245
RSA/1/99/Thab
SPEC/257
RSA/3/96
Lillie
Moz 8/2006
Moz 13/2006
Moz 1/2006
Moz 12/2006
Moz 9/2006
Moz 6/2006
Moz 7/2006
AY351518 MOZ/2/02
MAU/2007/1
Moz 4/2006
AF270706 MAD/1/98
Moz 3/2006
Moz 2/2006
Moz 5/2006
Genotype II
ZIM/1/92
SPEC/205
AF301542 ANG/70
AF302816 BEN/1/97
AF301539 Lisbon/60
NAM/1/95
I
AY351555 NYA/12
AY494552 TAN/1/01
AY494551 TAN/2/03
AY351542 SUM/1411
AY351543 MZI/1/92
AY351522 KAB/62
AF270705 MOZ/1/98
II
AF449463 BUR/1/84
AF449475 UGA/1/95
UGA/1B/03
III97
100
45
43
52
61
70
4853
62
93
6046
53
4259
90
60
50
75
30
54
81
4
28
3
62
69
13
50
33
6
40
0.0000.0020.0040.0060.0080.0100.0120.0140.0160.0180.0200.0220.0240.0260.0280.030Neighbour-Joining tree
Phylogenetic relationships of isolates obtained in this study base din p72 gene sequences
Genotype II was most prevalent in tick isolates obtained from the GNP
Newly identified genotype (XXIII) comprised isolates from ticks both in the park and in domestic sties
Sporadic episodes of high mortality in pigs have been reported throughout the sample period
10.32% (66/639) of the serum samples tested positive for ASFV antibodies
Low prevalence may be due to high mortality rates of infected pigs and most of samples came from young survivors and re-stocked animals
Prevalence of anti-ticks antibodies in domestic pigs
• 500 serum samples collected from domestic pigs were tested for the presence of anti-tick antibodies
• 44% of the sample contained detectable levels of antibodies
• There is a statistically significant association between anti-tick antibodies and ASFV antibodies. Mid-p < 0.03 (x2 test, 95% CI)
Moz Tick 1
Moz Tick 5
Moz Tick 3
Moz Tick 4
GNP and GNPBZ
L34328.1|O. moubata
DQ159456.1|O. Porcinus/p Mkuzi81B
DQ159455.1|O. Porcinus/p Mkuzi50A
DQ159451.1|O. Porcinus/p KNPSku7
DQ159450.1|O. Porcinus/p KNPBoy1
South Africa
Tanzania DQ159449.1|O. Porcinus/p TAN-195
DQ159453.1|O. Porcinus/p HW713
DQ159452.1|O. Porcinus/p HW714Zimbabwe
Namibia DQ159448.1| O. savignyi OS-01
EU009925.1|O. parkeri
L34327.1|O. turicata
DQ234709.1|O. sonrai NG2
DQ234707.1|O. sonrai INA1
DQ234708.1|O. sonrai NG1
DQ234706.1|O. sonrai BAN2
West Africa
AY669024.1|O. coriaceus HR3
AY669023.1|O. coriaceus CR2
AY669017.1|O. coriaceus isolate SB8
AY669016.1|O. coriaceus isolate SB7
100
100
99
77
99
53
64
85
69
47
56
92
97
98
99
99
93
0.000.020.040.060.080.100.120.140.160.18
SA is zoned with a northern region where the sylvatic cycle has been studied in some detail
All outbreaks since 1939 were in the ASF control zone where this known sylvatic cycle is present and where free-ranging pigs are kept
Expansion of wildlife farming and a focus on eco-tourism has resulted in an increased number of wild animals and warthogs are more abundant
The Transfrontier Conservation Areas planned for Africa could positively impact on warthog numbers
Warthogs cannot be fenced in and their range may increase
This could impact on the sylvatic cycle which seems to give rise to more genetically variant viruses
This in turn could impact on the development of vaccines to control ASF
In Africa, ASF affects mostly the people who can least afford it andthreatens food security
The epidemiology of ASF on the African continent is complex
The epidemiology may be changing due to climatic conditions andfarming practices and should be monitored regularly
More studies are needed to fully understand the factors that wouldimpact on disease control strategies
Regional control policies are needed
Training pig keepers and rapid diagnosis could assist in alleviatingthe negative impact of ASF virus outbreaks
Molecular epidemiology can be applied in ASFV risk analysis andoutbreak tracing, but should be based on multiple genes
The apparent segregation of genotypes based of their geographicaldistribution may be due to under-sampling
Continued monitoring of both captive and wild suid populations aswell as soft tick distribution is essential to effectively addressing theASFV problem in sub-Saharan Africa
L.E. Heath , B.A. Lubisi, R.M. Dwarka, N. Msthali, C. Quembo, A. Bastos, C. Boshoff
Staff of the Transboundary Animal Diseases Programme, ARC-OVI
Dr. Ferran Jori from CIRAD for assistance with sampling strategies and sampling in Mozambique
Wellcome Trust for funding (Mozambique studies)
Esther Blanco - CISA-INIA, Valdeolmos, Spain