TRANSMISSION OF EBOLA VIRUS ON ANIMAL AND HUMANS
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Chapter One: Introduction
Background Information
Transboundary animal diseases (TADs) refer to highly contagious or transmissible diseases that can spread rapidly across borders, causing significant socio-economic and public health impacts (FAO, 2004). Though only a small proportion of livestock diseases, TADs are particularly concerning due to their sudden onset, severity, and the widespread losses they can cause (Chris et al., 1999).
TADs are broadly classified into two main categories: emerging diseases and zoonoses (OIE, 2012). As described by Morens and Fauci (2013), emerging diseases are divided into newly emerging and reemerging diseases. Reemerging diseases are those that expand their geographical range or infect new species, often due to genetic changes in existing pathogens. Newly emerging diseases, on the other hand, involve previously unknown pathogens that are detected for the first time. Such infectious agents do not arise spontaneously but typically originate from animal infections, as seen in outbreaks of HIV, Ebola, influenza, and Severe Acute Respiratory Syndrome (SARS) (Morens & Fauci, 2013). Zoonoses are diseases or infections that can naturally be transmitted from animals to humans. According to the National Center for Emerging and Zoonotic Infectious Diseases (NCEZID, 2013), approximately 75% of emerging infectious diseases in humans are of animal origin, and about 60% of human pathogens are zoonotic.
The rise in transboundary animal disease outbreaks is linked to the effects of globalization, which has led to increased movement of people, animals, and goods through advanced transportation networks by sea, air, and land. Other contributing factors include nomadism, transhumance, and the displacement of refugees who bring their livestock along with them, often in areas affected by conflict. Additionally, changes in livestock production systems, such as intensification and commercialization of farming, have introduced livestock into new ecosystems, like tropical rainforests, where they come into contact with previously unknown infectious diseases that may have been circulating in wildlife populations. Climate change, as well as the decline of veterinary services and infrastructure, further exacerbate the frequency and severity of these outbreaks (Chris et al., 1999).
The World Health Organization (WHO, 2014) reported that the Ebola virus was first identified in Zaire (now the Democratic Republic of the Congo) in 1976. Except for the Reston strain, Ebola outbreaks have been predominantly confined to Africa. The most recent outbreak, which is the largest recorded in nearly four decades, has caused a significant number of cases and deaths. The virus is highly infectious and lethal, with rapid spread through populations. However, swift containment efforts, such as quarantine measures, have been shown to help mitigate the impact of these outbreaks (WHO, 2014).
Table 1: Overview of Selected Emerging and Reemerging Zoonotic Transboundary Animal Diseases (NCEZID, 2014)
| Diseases | Description |
|---|---|
| Middle East Respiratory Syndrome (MERS-CoV) | Caused by a novel coronavirus, MERS-CoV was first identified in April 2012. It has since been reported in nine countries: France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Tunisia, United Arab Emirates, and the United Kingdom. All known cases have links to the Middle East, either directly or indirectly. The natural host, transmission routes, and mechanisms are still not fully understood. Approximately 50% of the reported human cases have resulted in death. |
| Nipah Virus Encephalitis | The Nipah virus emerged from bats and led to outbreaks in intensively farmed pig populations, which then served as a reservoir for transmission to humans. |
| Severe Acute Respiratory Syndrome (SARS) | Caused by a coronavirus, SARS originated in bats and spread to humans through person-to-person transmission, exacerbated by human mobility. |
| Influenza Viruses | a) H5N1 Virus: This virus was first reported in poultry in China in 2013. Human infections occurred through direct contact with infected poultry or contaminated environments, resulting in 137 cases and 45 deaths, all within China. b) H7N9 Virus: Initially confined to birds, this strain was isolated from a symptomatic 20-year-old woman in May 2013, marking the first reported human case. c) H6N1 Virus: This virus was commonly found in both wild and domestic avian species, with no human cases until the first documented infection in 2013. |
Study Objectives
This study seeks to:
- Investigate the etiology and nature of these diseases, examining how they manifest in both humans and susceptible animal populations.
- Review the broader implications of emerging and reemerging diseases like Ebola on livestock and human health.
- Evaluate potential methods for controlling transboundary animal diseases, focusing on the Ebola virus.