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Epidemiology of African swine fever virus in southern Africa
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Epidemiology of African swine fever virus in southern Africa


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

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

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  • 1. Wilna VoslooCSIRO-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 AdultPersistent 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 warthogsBlood 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 ticksTicks from warthog burrowsand 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 stagesPCR result obtained for the different internodal stagesof 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/03Neighbour-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 SB70.18 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
  • 19.  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
  • 20.  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
  • 21.  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
  • 22.  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