Ecological drivers of African swine fever virus persistence in wild boar populations: insight for control

Pepin, Kim M.; Golnar, Andrew J.; Abdo, Zaid; Podgórski, Tomasz

doi:10.1101/2019.12.13.875682

Cited by 4 publications

(4 citation statements)

References 68 publications

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“…This quantification is substantially different from what reported by Pepin et al. (2020), who estimated that 53–66% of all virus transmission would be due to a contact between a susceptible wild boar and an infectious carcass. It should be noted, though, that those quantifications were based on an initial wild boar density ranging 0.5–2.0 individuals/km 2 , as opposed to the 3.0/km 2 used in our model.…”

Section: Discussioncontrasting

confidence: 91%

“…Using a similar modelling approach and surveillance data for Eastern Poland, Pepin et al. (2020) obtained results which are more in agreement with our findings: they estimated 50–60% ASF persistence rates running an individual‐based model which comprised only direct and carcass‐mediated infection, but estimated such persistence on a time horizon of only 2 years, which makes the comparison with our study not optimal. Finally, O'Neill et al.…”

Section: Discussionsupporting

confidence: 89%

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African swine fever endemic persistence in wild boar populations: Key mechanisms explored through modelling

Gervasi

Gubertì

2021

Transbound. Emerg. Dis.

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African swine fever (ASF) is a serious global concern from an ecological and economic point of view. While it is well established that its main transmission routes comprise contact between infected and susceptible animals and transmission through contaminated carcasses, the specific mechanism leading to its long‐term persistence is still not clear. Among others, a proposed mechanism involves the potential role of convalescent individuals, which would be able to shed the virus after the end of the acute infection. Using a spatially explicit, stochastic, individual‐based model, we tested: (1) if ASF can persist when transmission occurs only through infected wild boars and infected carcasses; (2) if the animals that survive ASF can play a relevant role in increasing ASF persistence chances; (3) how hunting pressure can affect the ASF probability to persist. The scenario in which only direct and carcass‐mediated transmission were contemplated had 52% probability of virus persistence 10 years after the initial outbreak. The inclusion of survivor‐mediated transmission corresponded to slightly higher persistence probabilities (57%). ASF prevalence during the endemic phase was generally low, ranging 0.1–0.2%. The proportion of seropositive individuals gradually decreased with time and ranged 4.5–6.6%. Our results indicate that direct and carcass‐mediated infection routes are sufficient to explain and justify the long‐term persistence of ASF at low wild boar density and the ongoing geographic expansion of the disease front in the European continent. During the initial years of an ASF outbreak, hunting should be carefully evaluated as a management tool, in terms of potential benefits and negative side‐effects, and combined with an intensive effort for the detection and removal of wild boar carcasses. During the endemic phase, further increasing hunting effort should not be considered as an effective strategy. Additional effort should be dedicated to finding and removing as many wild boar carcasses as possible.

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Section: Discussioncontrasting

confidence: 91%

Section: Discussionsupporting

confidence: 89%

African swine fever endemic persistence in wild boar populations: Key mechanisms explored through modelling

Gervasi

Gubertì

2021

Transbound. Emerg. Dis.

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“…Compared with direct transmission alone, indirect transmission through infected carcasses was found to prolong the duration of viral persistence by two orders of magnitude (Lange et al, 2018). Using a different spatially explicit model to estimate the proportion of transmission events that should be attributed to contact between a live host and contaminated carcass, Pepin et al (2020) proposed that 53-66% of transmission events in wild boar populations were carcass based. Similar results were obtained across four simulated landscapes with different levels of wild boar density [a landscape of high (2 boar/km 2 ) and low (0.5 boar/km 2 ) density patches, homogenous landscapes with densities of 1, 1.5 and 2 boar/km 2 ].…”

Section: Sensitivity Of Ongoing Surveillance Activities In Estoniamentioning

confidence: 99%

“…However, it has been demonstrated previously that there is no need for long‐term infectious animals in order to replicate the observed spatio‐temporal spread of ASF in wild boar using different spatially explicit simulation models (e.g. Figure 14, Pepin et al., 2020; Lange, 2015).…”

Section: Assessmentmentioning

confidence: 99%

ASF Exit Strategy: Providing cumulative evidence of the absence of African swine fever virus circulation in wild boar populations using standard surveillance measures

Nielsen¹,

Álvarez²,

Bicout³

et al. 2021

EFS2

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EFSA assessed the role of seropositive wild boar in African swine fever (ASF) persistence. Surveillance data from Estonia and Latvia investigated with a generalised equation method demonstrated a significantly slower decline in seroprevalence in adult animals compared with subadults. The seroprevalence in adults, taking more than 24 months to approach zero after the last detection of ASFV circulation, would be a poor indicator to demonstrate the absence of virus circulation. A narrative literature review updated the knowledge on the mortality rate, the duration of protective immunity and maternal antibodies and transmission parameters. In addition, parameters potentially leading to prolonged virus circulation (persistence) in wild boar populations were reviewed. A stochastic explicit model was used to evaluate the dynamics of virus prevalence, seroprevalence and the number of carcasses attributed to ASF. Secondly, the impact of four scenarios on the duration of ASF virus (ASFV) persistence was evaluated with the model, namely a: (1) prolonged, lifelong infectious period, (2) reduction in the case-fatality rate and prolonged transient infectiousness; (3) change in duration of protective immunity and (4) change in the duration of protection from maternal antibodies. Only the lifelong infectious period scenario had an important prolonging effect on the persistence of ASF. Finally, the model tested the performance of different proposed surveillance strategies to provide evidence of the absence of virus circulation (Exit Strategy). A two-phase approach (Screening Phase, Confirmation Phase) was suggested for the Exit Strategy. The accuracy of the Exit Strategy increases with increasing numbers of carcasses collected and tested. The inclusion of active surveillance based on hunting has limited impact on the performance of the Exit Strategy compared with lengthening of the monitoring period. This performance improvement should be reasonably balanced against an unnecessary prolonged 'time free' with only a marginal gain in performance. Recommendations are provided for minimum monitoring periods leading to minimal failure rates of the Exit Strategy. The proposed Exit Strategy would fail with the presence of lifelong infectious wild boar. That said, it should be emphasised that the existence of such animals is speculative, based on current knowledge.

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Modelling the deathbed of ASF-infected wild boars in South Korea using 2019-2020 national surveillance data

Lim¹,

Vergne

Pak³

et al. 2021

Preprint

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In September 2019, African swine fever (ASF) was reported in South Korea for the first time. Since then, more than 651 ASF cases in wild boars and 14 farm outbreaks have been notified in the country. The purpose of this study was to characterize the spatial distribution of ASF-positive wild boar carcasses to identify the risk factors associated with the presence of ASF and number of ASF-positive wild boar carcasses in the affected areas. To achieve this objective, we divided the study into two periods (October 2, 2019, to January 19, 2020, and January 19 to April 28, 2020) and aggregated the number of reported ASF-positive carcasses into a regular grid of hexagons. To account for imperfect detection, we adjusted spatial zero-inflated Poisson regression models to the number of ASF-positive wild boar carcasses per hexagons. During the first study period, only proximity to North Korea was identified as a risk factor for the presence of African swine fever virus (ASFV). In addition, there were more reports in the affected hexagons with a high habitat suitability for wild boar, low heat load index (HLI), and high human density. During the second study period, proximity to an ASF-positive carcass reported during the first period was the only significant risk factor for the presence of ASF-positive carcasses. Additionally, high HLI and low elevation were associated with an increased number of ASF-positive carcasses reported in the affected hexagons. Although the proportion of ASF-affected hexagons increased from 0.06 (95% credible interval [CrI]: 0.05-0.07) to 0.09 (95% CrI: 0.08-0.10), the probability of reporting ASF-affected hexagons increased substantially from 0.49 (95% CrI: 0.41-0.57) to 0.73 (95% CrI: 0.66-0.81) between the two study periods. These results can be used to further advance risk-based surveillance.

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Ecological drivers of African swine fever virus persistence in wild boar populations: insight for control

Cited by 4 publications

References 68 publications

African swine fever endemic persistence in wild boar populations: Key mechanisms explored through modelling

African swine fever endemic persistence in wild boar populations: Key mechanisms explored through modelling

ASF Exit Strategy: Providing cumulative evidence of the absence of African swine fever virus circulation in wild boar populations using standard surveillance measures

Modelling the deathbed of ASF-infected wild boars in South Korea using 2019-2020 national surveillance data

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