Natural inactivation of African swine fever virus in tissues: Influence of temperature and environmental conditions on virus survival
Introduction
In recent years African swine fever virus (ASFV) has become the most significant threat to worldwide pig production. ASFV genotype II is present in European wild boar and domestic pig populations since 2007, but in 2018 it unexpectedly affected also the East Asian pork industry, causing severe economic loss and global concern about its further spread (Zhou et al., 2018). Despite numerous studies reporting development of an effective experimental vaccine candidate, lack of sufficient knowledge about its stability and safety hinders its commercialization and makes it still remote from being introduced to the market (O’Donnell et al., 2015b, 2015a; Barasona et al., 2019; Sánchez et al., 2019). Hence the current approach to ASF control is based on stringent biosecurity measures, mainly the implementation of sanitary procedures and immediate disease detection. In Europe, wild boar population plays a crucial role in ASF epizootics as the main virus reservoir, thus prevention of direct or indirect contact between domestic and wild animals, is the key factor determining disease emergence within commercial farms. As regards the primary disease introduction into free areas, an illegal movement of live pigs, pork products and swill feeding increase the probability of ASF appearance within new territories. The knowledge about pathogen susceptibility to environmental conditions, the time needed for its inactivation, and minimum infectious dose needed to develop clinical signs in exposed animals is crucial to determine whether pigs become infected after ingestion of contaminated feed or contact with the contaminated fomite. Up to date, only few studies were committed to address this problem since ASFV for many years has been known as an exceptionally resistant pathogen (Alvarez et al., 2019). Moreover, taking into account the presently worsening worldwide epidemiological situation, identification of potential virus sources is extremely important.
Recently it has been demonstrated that conditions mimicking 30-days long transatlantic shipping provide ASFV viability (Dee et al., 2018). Half-life of the virus survival ranged from 9.6 to 14.2 days, thus demonstrating that contaminated fomites may provide sufficient virus stability and therefore may act as mechanical vector for indirect ASFV transmission (Dee et al., 2018; Stoian et al., 2019). In-vivo studies have shown that natural consumption of contaminated feed or liquid leads to disease development. Moreover, as little as 100 TCID50 dose of virus contained in liquid is sufficient to infect susceptible animal, compared with 104 in feed (Niederwerder et al., 2019). These results are reflected in the outcomes of epidemiological investigations, which indicates contaminated feed or fomites as an ASFV source at pig farms in China and Latvia (Oļševskis et al., 2016; Wen et al., 2019; Zhai et al., 2019).
Within the affected areas, ASFV was detected in numerous state-of-the-art pig holdings, which meet the most stringent biosecurity measures (Boklund et al., 2018; Alvarez et al., 2019). Moreover, it has been observed, that outbreaks in pigs occur in seasonal pattern (May-September), thus it was suggested that insect vectors (biological or mechanical) other than Ornithodoros ticks might be much more involved in ASFV spreading than previously assessed (Olesen et al., 2018b; Alvarez et al., 2019). In relation to indirect transmission, the question of virus survival in carcasses, contaminated environment, feed, bedding, forage materials and fomites has been recently specified by EFSA as subject that needs further investigation (Alvarez et al., 2019).
In order to fill this knowledge gap and improve ASFV preventive measures, we developed a model determining the time required to inactivation of naturally contaminated tissues under selected environmental conditions.
Section snippets
Cells and viruses
Porcine pulmonary alveolar macrophages (PPAMs) were obtained from Technical University of Denmark (DTU), and subcultured in RPMI 1640, 10 % FBS, 1 % Antibiotic-Antimycotic, 1 mM sodium pyruvate and 1x non-essential amino acids. Cell cultures were grown at 37 °C in humidified atmosphere of air containing 5 % CO2.
The ASFV Pol16/20540/Out10 (GenBank accession number: MG939585.1) isolate was derived from the spleen of pig which died during the Outbreak 10, which occurred in Wysokie Mazowieckie
Artificial contamination study
Infectious virus was isolated from artificially contaminated water at all sampling points, namely: 0, 3, 7, 14 days post contamination. ASFV isolation was possible for contaminated soil and leaf litter immediately after adding the virus to matrix, nevertheless even short, 3-day period of incubation caused complete loss of virus infectivity, independent of temperature conditions.
Study of ASFV stability in various tissues dependent on temperature
Organs used in this study showed following mean
Discussion
Virus survival in the environment is the main prerequisite for its indirect transmission. Numerous studies were focused on ASFV stability and proved its extremely high resistance to environmental conditions, nevertheless most of them were based on ASFV contained in sterile medium, or blood. Up to date only limited information on virus survival in natural environment conditions was available. In this study we filled this knowledge gap by providing quantitative data regarding virus survival
Acknowledgements
This study was supported by ‘KNOW’ (Leading National Research Centre) Scientific Consortium, ‘Healthy Animal - Safe Food’, a decision of the Ministry of Science and Higher Education, no. 05-1/KNOW2/2015.
References (25)
- et al.
Factors affecting the infectivity of tissues from pigs with classical swine fever: thermal inactivation rates and oral infectious dose
Vet. Microbiol.
(2015) - et al.
Salt inactivation of classical swine fever virus and African swine fever virus in porcine intestines confirms the existing in vitro casings model
Vet. Microbiol.
(2019) - et al.
African swine fever virus introduction into the EU in 2014: experience of Latvia
Res. Vet. Sci.
(2016) - et al.
Survival of African swine fever virus (ASFV) in various traditional Italian dry-cured meat products
Prev. Vet. Med.
(2019) - et al.
Development of vaccines against African swine fever virus
Virus Res.
(2019) - et al.(2019)
- et al.
First oral vaccination of eurasian wild boar against African swine fever virus genotype II
Front. Vet. Sci.
(2019) - et al.(2018)
- et al.
The use of half-lives and associated confidence intervals in biological research
Vet. Res. Commun.
(1990) - et al.
Survival of viral pathogens in animal feed ingredients under transboundary shipping models
PLoS One
(2018)
Infectivity of African swine fever virus after drying and heat inactivaton on crops
13th EPIZONE Annual Meeting “Breaking Walls”
Stability of porcine reproductive and respiratory syndrome virus at ambient temperatures
J. Vet. Diagn. Invest.
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