Unique features of foot and mouth disease in Southern Africa

Transcription

1 Unique features of foot and mouth disease in Southern Africa Gavin Thomson Commodity-based trade and enhanced market access: The vital role of the Department of Veterinary Services Gaborone; 6-7 February 2018 Approximate distribution of endemic FMD in the world today 1

2 FMD virus family tree based on molecular phylogeny Type A Type O Type C Asia Gambia 51/98 A22/USSR A24/Cruzeiro A5/Allier Ghana 9/93 South Africa 11/00 O1/BFS Angola 10/74 C3/Resende C3/Argentina C3/Indayal Pakistan 1/54 Eurasian types (O, A, C & Asia 1) evolved over last 500 years in domestic livestock. These viruses are infections of livestock So FMDV genus has two distinct lineages that separated about 500 years ago SAT X SAT India 92/99 India 281/94 China Kenya 3/57 Zimbabwe 7/83 Angola 4/74 Eritrea 12/98 88 SAT-1 SAT South Africa 14/* Tanzania 1/99 Botswana 1/68 Uganda 1/97* Zambia 10/96* Botswana 1/65 South Africa 10/90* SAT X Progenitor of all FMD viruses; SAT types have co-evolved with African buffalo in sub- Saharan Africa buffalo for about 0 years. SAT viruses are natural infections of buffalo Namibia 1/94 Acknowledgement: N J Knowles, Pirbright, UK 50 % 40 % 30 % 20 % 10 % 0 SAT 2 family tree SAT viruses more heterogeneous (variable) than Eurasian serotypes SAT2 especially (14 different genotypes) Clades IV V II I III D 97 E F G H I J K RHO/1/48 ZAM/9/93 ZAM/10/ ZAM/7/96 C ZAM/10/96 BOT/29/98 BOT/31/98 BUN/1/91 89 MAL/3/75 B 97 KEN/9/99 KEN/5/99 88 KEN/7/99 ZIMGn10/91 58 KNP/32/92 MOZ/1/79 A MOZ/4/83 65 PAL/5/83 KNP/183/91 KNP/1/92 KNP/7/88 53 KNP/19/ KNP/19/88 KNP/20/88 KNP/18/88 90 KNP/17/88 KNP/16/88 KNP/2/89 91 KNP/18/ KNP/31/ NAM/304/98 77 ZIM/7/83 55 ZIM/1/88 NAM/286/98 90 NAM/292/98 80 BOT/1/98 BOT/18/98 ZIM/267/98 ZIM/1/00 99 NIG/2/75 SEN/5/75 GHA/2/90 GHA/8/91 SEN/3/83 SEN/7/83 SEN/7/79 51 GAM/8/79 88 GAM/9/79 ERI/12/98 SAU/6/00 RWA/1/00 KEN/3/57 ZAI/1/82 ANG/4/74 Genotypes 2

3 The topotype issue Angola Zambia Malawi Mozambique Zimbabwe A genotype with a distinct geographical distribution Namibia Botswana SAT3 topotypes South Africa Topotype I Topotype II Topotype III Topotype IV The fundamental conundrum Management of all diseases, whether plant or animal, only possible with good understanding of their epidemiologies and features of the infectious agent concerned The epidemiologies of SAT- & Eurasian type FMD differ significantly (Vosloo & Thomson, 2017) Unlike Eurasian serotype FMD in livestock, SAT viruses in locations where African buffalo occur, is not eradicable (Thomson, Fosgate & Penrith, 2017) Current international standards & recommendations for the control of FMD are based on Eurasian-type FMD Consequently, sub-saharan Africa where SAT-type FMD is endemic is saddled with trying to fit square pegs into round holes! Nowhere else in the world has this problem, so we will have to come up with the solution! Management of SAT-type FMD has been a major problem in southern Africa, particularly over the last years Clearly, things need to change 3

4 Major differences between the two lineages of FMD virus Factor SAT-type FMD viruses Eurasian-type FMD viruses Relationship with wildlife Pathogenicity Evolved in and maintained naturally by African buffalo populations Generally a mild or unapparent disease in both livestock & wildlife Evolved in livestock; not maintained by any wildlife population Generally a serious disease in cattle, pigs & wildlife Natural rate of transmission Commonly slow and inefficient in endemic areas of southern Africa Commonly rapid and efficient Antigenic variation Vaccine efficacy compromised by exceptional antigenic diversity Lack of clear subtypes difficulty in matching vaccine and field viruses Less antigenic diversity Favoured by existence of clear subtypes enables effective matching of field and vaccine viruses Apparent deterioration of FMD control in Southern Africa 30 Botswana Namibia South Africa Introduction of vaccination Introduction of local vaccines 28 so far this decade 23 At face value, vaccination against FMD was excellent for 20 years but less so since However, this is a multifactorial issue; simple conclusions potentially dangerous Incidence of FMD events in cattle over 8 decades in three southern African countries 4

5 Conclusion SAT- & Eurasian-type FMD are two very different forms of the disease; they differ in their evolution, the way they behave in the field and also amenability to control by vaccination Despite the struggle against SAT-type FMD in southern Africa for >80 years, local realities still not widely understood (including by vets) This situation is complicated by international standards & recommendations being founded almost exclusively on Eurasian-type FMD We need to change this state of affairs, but the question is how? 5