Estimating the Basic Reproductive Number (R0) for African Swine Fever Virus (ASFV) Transmission between Pig Herds in Uganda

Abstract

African swine fever (ASF) is a highly contagious, lethal and economically devastating haemorrhagic disease of domestic pigs. Insights into the dynamics and scale of virus transmission can be obtained from estimates of the basic reproduction number (R 0). We estimate R 0 for ASF virus in small holder, free-range pig production system in Gulu, Uganda. The estimation was based on data collected from outbreaks that affected 43 villages (out of the 289 villages with an overall pig population of 26,570) between April 2010 and November 2011. A total of 211 outbreaks met the criteria for inclusion in the study. Three methods were used, specifically; (i) GIS- based identification of the nearest infectious neighbour based on the Euclidean distance between outbreaks, (ii) epidemic doubling time, and (iii) a compartmental susceptible-infectious (SI) model. For implementation of the SI model, three approaches were used namely; curve fitting (CF), a linear regression model (LRM) and the SI/N proportion. The R 0 estimates from the nearest infectious neighbour and epidemic doubling time methods were 3.24 and 1.63 respectively. Estimates from the SI-based method were 1.58 for the CF approach, 1.90 for the LRM, and 1.77 for the SI/N proportion. Since all these values were above one, they predict the observed persistence of the virus in the population. We hypothesize that the observed variation in the estimates is a consequence of the data used. Higher resolution and temporally better defined data would likely reduce this variation. This is the first estimate of R0 for ASFV in a free range smallholder pig keeping system in sub-Saharan Africa and highlights the requirement for more efficient application of available disease control measures.

R0 Estimation for the African Swine Fever Epidemics in Wild Boar of Czech Republic and Belgium

“…Computation of R0 was derived from the growth rate of cases [17], an approach already applied to ASF for both wild boar (e.g., in Russia [18]) and domestic pigs (e.g., in Uganda [19] and in Ukraine [20]). The assumption of this approach is that at the beginning of the epidemic, the cumulative distribution of the cases grows at an exponential rate, during which each case produces R0 new cases during the infectious period.…”

Estimating the Basic Reproductive Number for African Swine Fever Using the Ukrainian Historical Epidemic of 1977

“…Even though, in many cases, a holding was quarantined before the ASF confirmation, it has been reported that the transmission of the virus could have happened even after quarantine being imposed (Anonymous, ). To reflect the uncertainty on this parameter, two other values of a farm's infectious period were taken from the literature: 15 days (Gulenkin et al., ) and 30 days (Barongo et al., ). The entire period from 10th February to 2nd July 1977 was divided into equal periods of duration ; the number of newly infected holdings N t was calculated for each period, which resulted in the construction of the epidemic curve. An exponential model was fitted to the observed incidence during the initial stage of the epidemic, that is from the onset of the epidemic to its peak (Fig. ).…”

“…We accepted these values as boundary scenarios, while 7 days was taken as a median scenario being a mean typical infectious period of ASF in pigs ( D wf ) used in the literature (Table ).

Summary of modelling studies estimating the transmission parameters of ASFV in domestic pigs (see also Guinat et al., ) Study Genotype Virus isolate Duration of infectious period, days Between‐farm R 0 Within‐farm R 0 Belyanin et al., IIVarious6.8 (5.0–8.6)––De Carvalho Ferreira et al., ; IMalta'786.8 ± 1.8–18.0 (6.90–46.9)Netherlands'864.6 ± 1.44.92 (1.45–16.6)Pietschmann et al., IIArmenia'082–9–6.1 (0.6–14.5)5.0 (1.4–10.7)Guinat et al., IIGeorgia 2007/13–14–2.8 (1.3–4.8) within pen1.4 (0.6–2.4) between penGulenkin et al., IIStavropol 01/085 within farm2–38–1115 between farmBarongo et al., IXUganda30 between farm3.24 (3.21–3.27)–1.63 (1.6–1.72)1.90 (1.87–1.94)1.581.77 (1.74–1.81)Current studyIO–777 within farm1.65 (1.42–1.88)7.46 (5.68–9.21)19 between farm

Three epidemic waves were observed in the course of epidemics in th...…”

African swine fever: Update on Eastern, Central and Southern Africa

“…Kenya, Malawi, Mozambique, Tanzania, Uganda and Zambia have experienced multiple to frequent outbreaks (Table ). The endemic occurrence of ASF in domestic pigs has subsequently been documented in several Eastern African countries: Kenya (Gallardo, Ademun, et al, ; Gallardo, Okoth, et al, ; Lichoti et al, ; Okoth et al, ), Madagascar (Randrianantoandro, Kono, & Kubota, ; Ravaomanana et al, , ; Roger, Ratovonjato, Vola, & Uilenberg, ), Malawi (Haresnape, Lungu, & Mamu, , ); Mozambique (Penrith et al, , ; Quembo et al, ), Tanzania (Misinzo et al, ; Wambura, Masambu, & Msami, ), Uganda (Atuhaire, Afayoa, Ochwo, Mwesigwa, Okuni, et al, ; Barongo et al, ; Gallardo, Ademun, et al, ; Muhangi et al, ; Muwonge et al., ) and the Eastern Province of Zambia (Samui, Mwanaumo, & Chizyuka, ; Samui et al, ; Simulundu et al, , ; Wilkinson et al, ).…”