Presented by Wilna Vosloo at the African Swine Fever Diagnostics, Surveillance, Epidemiology and Control Workshop, Nairobi, Kenya, 20-21 July 2011

1. Wilna Vosloo
CSIRO-Australian Animal Health Laboratory

2.  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

3.  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

4.  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

5.  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

6. 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

7.  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

8. N2 N3 N4
N1 Trans-Stadial N5
transmission
Eggs
Adult
Persistent infection Ticks from warthog
burrows and pig pens
Sylvatic Cycle
Domestic Cycle
Blood and sera Blood and sera from
from warthogs domestic pigs

9. 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

10. 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)

11. Soft ticks in sylvatic cycle
Assays Burrows positives
(%)
Nested PCRs (screening assays) 72.4 %
(21/29)
Virus isolation 48.3 %
(14/29)
Soft ticks in domestic cycle
Assays Pig pens positives (%)
Nested PCRs (screening assays) 100 %
(2/2)
Virus isolation 50 %
(1/2)

12. Prevalence of ASFV in soft ticks
Internodal stages
♂ ♀ 1 2 3 4 5 6 7 - + M
• There was no correlation
between the likelihood of a
positive result and any of the
internodal stages
PCR result obtained for the different internodal stages
of ticks collected from a single warthog burrow

13. 48 Moz 14/2006
53 Moz 15/2006
62 Moz 17/2006
53 AF270708 Mozambique/1960
AF301541 Tengani/60
Genotype V
Phylogenetic relationships of isolates 90 46
60
AY494553 MAL/1/02
AF270709 Mozambique/1979
obtained in this study base din p72 93
AF270711 MOZ/1/94
AF270712 MOZ/8/94
AF270710 SPEC265
gene sequences RSA/1/96
MOz 11/2006
28
Moz 10/2006
75
Moz 18/2006 New genotype
50
59 Moz 16/2006
42 Moz 19/2006
60 AF302818 RSA/1/98
SPEC/245
3 RSA/1/99/Thab
SPEC/257
4
RSA/3/96
30 I
13 Lillie
Moz 8/2006
Moz 13/2006
Moz 1/2006
33
Moz 12/2006
50
Moz 9/2006
Moz 6/2006
Moz 7/2006
Genotype II
6 AY351518 MOZ/2/02
MAU/2007/1
69 Moz 4/2006
AF270706 MAD/1/98
40
Moz 3/2006
Moz 2/2006
Moz 5/2006
ZIM/1/92
SPEC/205
62
AF301542 ANG/70
81
AF302816 BEN/1/97
54
AF301539 Lisbon/60
NAM/1/95
AY351555 NYA/12
43 AY494552 TAN/1/01
70 AY494551 TAN/2/03
61 AY351542 SUM/1411 II
AY351543 MZI/1/92
52
AY351522 KAB/62
45
AF270705 MOZ/1/98
AF449463 BUR/1/84
100 AF449475 UGA/1/95 III
97 UGA/1B/03
Neighbour-Joining tree 0.030
0.028
0.026
0.024
0.022
0.020
0.018
0.016
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000

14.  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

15.  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

16. 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)

17. Moz Tick 1
53
Moz Tick 5
64 GNP and GNPBZ
Moz Tick 3
85
Moz Tick 4
L34328.1|O. moubata
92
69 DQ159456.1|O. Porcinus/p Mkuzi81B
DQ159455.1|O. Porcinus/p Mkuzi50A
97 South Africa
56 DQ159451.1|O. Porcinus/p KNPSku7
47 DQ159450.1|O. Porcinus/p KNPBoy1
98
DQ159449.1|O. Porcinus/p TAN-195 Tanzania
99 DQ159453.1|O. Porcinus/p HW713
Zimbabwe
100 DQ159452.1|O. Porcinus/p HW714
99
DQ159448.1| O. savignyi OS-01 Namibia
EU009925.1|O. parkeri
93 L34327.1|O. turicata
DQ234709.1|O. sonrai NG2
100 DQ234707.1|O. sonrai INA1
West Africa
DQ234708.1|O. sonrai NG1
DQ234706.1|O. sonrai BAN2
99 AY669024.1|O. coriaceus HR3
AY669023.1|O. coriaceus CR2
99 AY669017.1|O. coriaceus isolate SB8
77 AY669016.1|O. coriaceus isolate SB7
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00

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

20.  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

21.  In Africa, ASF affects mostly the people who can least afford it and
threatens food security
 The epidemiology of ASF on the African continent is complex
 The epidemiology may be changing due to climatic conditions and
farming practices and should be monitored regularly
 More studies are needed to fully understand the factors that would
impact on disease control strategies
 Regional control policies are needed
 Training pig keepers and rapid diagnosis could assist in alleviating
the negative impact of ASF virus outbreaks

22.  Molecular epidemiology can be applied in ASFV risk analysis and
outbreak tracing, but should be based on multiple genes
 The apparent segregation of genotypes based of their geographical
distribution may be due to under-sampling
 Continued monitoring of both captive and wild suid populations as
well as soft tick distribution is essential to effectively addressing the
ASFV problem in sub-Saharan Africa

23.  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