epidemiology of african swine fever virus in southern africa

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Wilna Vosloo CSIRO-Australian Animal Health Laboratory

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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

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Page 1: Epidemiology of African swine fever virus in southern Africa

Wilna VoslooCSIRO-Australian Animal Health Laboratory

Page 2: Epidemiology of African swine fever virus in southern Africa

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

Page 3: Epidemiology of African swine fever virus in southern Africa

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

Page 4: Epidemiology of African swine fever virus in southern Africa

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

Page 5: Epidemiology of African swine fever virus in southern Africa

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

Page 6: Epidemiology of African swine fever virus in southern Africa

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

Page 7: Epidemiology of African swine fever virus in southern Africa

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

Page 8: Epidemiology of African swine fever virus in southern Africa

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

Page 9: Epidemiology of African swine fever virus in southern Africa

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

Page 10: Epidemiology of African swine fever virus in southern Africa

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)

Page 11: Epidemiology of African swine fever virus in southern Africa

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)

Page 12: Epidemiology of African swine fever virus in southern Africa

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

Page 13: Epidemiology of African swine fever virus in southern Africa

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

Page 14: Epidemiology of African swine fever virus in southern Africa

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

Page 15: Epidemiology of African swine fever virus in southern Africa

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

Page 16: Epidemiology of African swine fever virus in southern Africa

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)

Page 17: Epidemiology of African swine fever virus in southern Africa

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

Page 18: Epidemiology of African swine fever virus in southern Africa

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

Page 19: Epidemiology of African swine fever virus in southern Africa
Page 20: Epidemiology of African swine fever virus in southern Africa

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

Page 21: Epidemiology of African swine fever virus in southern Africa

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

Page 22: Epidemiology of African swine fever virus in southern Africa

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

Page 23: Epidemiology of African swine fever virus in southern 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