PhD in Veterinary Sciences for Animal Health and Food Safety

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Phd thesis

Title: Risk assessment of Swine influenza in pig farms

Scientific background

Swine influenza (SwIA) is a respiratory disease of pigs caused by a type A Influenza virus belonging to the Orthomyxoviridae family¹. SwIA virus (SwIAV) is alarming especially because of its zoonotic potential which represents a threat to both animals and public health². Pigs are well known as mixing vessels as they can be infected with strains of different origins, both human and avian, which favour the antigenic drift and the reassortment, increasing the chance of creating new influenza strains with pandemic potential³ as shown with the most recent human H1N1 2009 pandemic, which was at least partially derived from swine virus⁴. The human-animal interface is critical in intensive farming systems. Given the number, density and movement of animals, these systems are of high relevance for the zoonotic transmission of influenza viruses⁵.

There are still gaps in the knowledge of influenza dynamics and experts highlight the need to implement research on prevention and control measures and risk assessment to improve surveillance⁶.

Aims

The project aims at evaluating the risk associated with swine influenza virus at farm level, investigating the viral introduction and circulation dynamics within pig farms, the dynamic of transmission between farms and the transmission at the animal/human interface. The following risk question has been identified: ‘What is the risk of swine influenza at farm level?’. The question has been divided in sub-questions that will be addressed with different metodologies:

1. What are the risk factors and pathways for swine influenza?
2. What is the risk of introduction and circulation of the virus within pig farms?
3. What is the risk of exposure of humans to the virus?
4. What is the risk of transmission of swine influenza within and between farms?

Materials and methods

In the first phase, a semi-quantitative risk assessment will be carried out to classify pig farms and husbandry practices, the former in terms of the likelihood of introduction and circulation of swine influenza virus by evaluating the biosecurity system of the farms, and the latter in terms of risk of exposure of workers to the virus. A sample of 30 intensive farms located in northern Italy was selected through a convenience sampling, based on farmers’ availability. This study area accounts high numbers of animals and animal density, which are recognised risk factors for SwIAV. Biosecurity data and data on husbandry practices will be collected on farms through a checklist, which was developed based on the evidence retrieved from literature. After data collection, the modified semi-quantitative Failure Mode and Effect Analysis (FMEA) method will be applied to perform the assessment. FMEA will be used to quantify potential failure of the biosecurity and management system of the farm, by assigning a risk priority code indicating increasing level of risk.

To investigate the risk of transmission of swine influenza, the second phase of the project will focus on modelling using the software R. Compartmental models will be used to understand the dynamics of transmission within the farm, while a network model will be developed to investigate the risk of SwIAV transmission between farms.

Expected results

The semi-quantitative risk assessment will allow to classify farms from those with a higher risk of SwIAV introduction to those with a lower risk and to identify the practices with the highest risk of transmission to humans, providing a method for prioritising monitoring efforts and resources towards farms with a higher risk.

Modelling will provide a better understanding of the viral spread between farms and the persistence in farms. Moreover, it will allow to evaluate the effectiveness of prevention and control measures, simulating different scenarios and providing recommendations on the best strategies to reduce the risk. Overall, the results of the study should increase the knowledge of SwIAV in Italy and provide useful tools for the surveillance of this disease.

References

1. Li Y, Robertson I. The epidemiology of swine influenza. Animal Diseases. 2021;1(1). doi:10.1186/s44149-021-00024-6
2. Lopez-Moreno G, Davies P, Yang M, et al. Evidence of influenza A infection and risk of transmission between pigs and farmworkers. Zoonoses Public Health. 2022;69(5). doi:10.1111/zph.12948
3. Ma W, Kahn RE, Richt JA. The pig as a mixing vessel for influenza viruses: Human and veterinary implications. Journal of Molecular and Genetic Medicine. 2009;03(01). doi:10.4172/1747-0862.1000028
4. Hennig C, Graaf A, Petric PP, et al. Are pigs overestimated as a source of zoonotic influenza viruses? Porcine Health Manag. 2022;8(1). doi:10.1186/s40813-022-00274-x

5. Kessler S, Harder TC, Schwemmle M, Ciminski K. Influenza a viruses and zoonotic events—are we creating our own reservoirs? Viruses. 2021;13(11). doi:10.3390/v13112250

6. EFSA. Workshop on Research Gap Analysis in Animal Influenza. EFSA Supporting Publications. 2015;12(3):787E. doi:https://doi.org/10.2903/sp.efsa.2015.EN-787