Emerging Communicable Diseases: Ebola

INTRODUCTION

Infectious diseases are a constant threat to human life. Various scientific research findings since the 19th century have, however, paved the way for an improved comprehension of infectious diseases with regards to their natural history and the preventive measures to control them. These measures include vector control, immunisation, and water treatment. The implementation of these measures over the last century brought about huge victories for mankind in the battle to control infectious diseases. A good example of such victories is the eradication of smallpox in the year 1979. In recent decades nonetheless, the incidence of infectious diseases which were thought to be well controlled has increased in several locations across the world. Antimicrobial resistance is also on the rise globally and diseases which were previously unknown to man have also emerged. These issues have become global problems which require urgent assessment and resolution. This essay is an in-depth critical review of the literature on Ebola, one of the emerging communicable diseases. The essay will discuss the concept of disease emergence, provide a brief history about the Ebola virus, review the factors that have contributed to the emergence of Ebola infection, discuss some of the current policies to control this disease and make recommendations on strategies to improve on the current Ebola control policies.

THE CONCEPT OF EMERGENCE

The concept of emerging infections covers two main categories of infectious diseases (Morens & Fauci, 2013). They are the newly emerging and re-emerging infectious diseases (Morens & Fauci, 2013). Emerging infectious diseases are those that have newly appeared within the human population, while re-emerging infectious diseases refer to diseases that have previously infected humans but are rapidly increasing in incidence around the world despite apparent elimination or control (Morens & Fauci, 2013). Disease emergence usually requires two equally important steps (Baylor College of Medicine, 2018). Firstly, the infectious agent must be introduced to a vulnerable host population and secondly, the agent needs to have the ability to establish itself within the host population and disseminate further (Baylor College of Medicine, 2018). According to the World Health Organization (WHO), over 40 diseases have emerged since the 1970’s (Baylor College of Medicine, 2018). These diseases include Avian flu, Swine flu, Middle Eastern Respiratory Syndrome (MERS), Zika virus infection and the focus of this essay, Ebola (Baylor College of Medicine, 2018).

HISTORICAL FACTS ABOUT EBOLA

The Ebola virus is one of the most fatal viral diseases in the world (Centre for Disease Control and Prevention (CDC), 2018 ). It was discovered in 1976 following two outbreaks of haemorrhagic fever in different locations within Central Africa (CDC, 2018). The first outbreak occurred in a village called Yambuku, in the Democratic Republic of Congo (WHO, 2018). The village is located near the Ebola river, from which the virus takes its name (WHO, 2018). The second outbreak occurred in Nzara, South Sudan (WHO, 2018). The Ebola virus belongs to the Filoviridae virus family and so far, five species of the Ebola virus have been identified (WHO, 2018). They are; Zaire, Bundibugyo, Sudan, Reston, and Tai Forest (WHO, 2018). The first three have been linked to large disease outbreaks in Africa (WHO, 2018). In fact, a majority of the Ebola outbreaks occur in Africa (CDC, 2018). The Zaire species specifically, was linked to the Ebola virus outbreak in West Africa between 2014 and 2016 (WHO, 2018).

The Ebola virus has an incubation period of about 2 to 21 days and humans are usually not infectious until the disease symptoms manifest (WHO, 2018). These symptoms include fatigue, fever, headaches, muscle pain, rash, sore throat, vomiting and diarrhoea (WHO, 2018). Internal and external bleeding can also occur in some cases (WHO, 2018). Human to human transmission occurs through direct contact with infected body fluids (WHO, 2018). Clinical diagnosis is often difficult as it is hard to differentiate the Ebola virus infection from other infectious febrile illnesses such as malaria, meningitis and typhoid fever (WHO, 2018). Confirmatory diagnostic tests such as the semi-automated nucleic acid tests (NAT) are currently available (WHO, 2018). These tests are however not feasible for use in remote settings (WHO, 2018). The treatment of the Ebola virus infection is mainly supportive as there is no proven cure available yet (WHO, 2018). A vaccine to protect individuals against the Ebola virus infection is currently being trialled (WHO, 2018).

CONTRIBUTORY FACTORS TO THE EMERGENCE OF EBOLA

The agent

As mentioned earlier, the Ebola virus belongs to the Filoviridae virus family. Like most of the emerging infectious diseases known today, the Ebola virus infection originated from animal reservoirs (Morens & Fauci, 2013). It is believed that fruit bats belonging to the Pteropodidae family, are the natural hosts for the Ebola virus (WHO, 2018). The introduction of the Ebola virus into the human population was due to the close contact of humans with secretions, blood products and bodily fluids of infected animals such as monkeys, gorillas, and chimpanzees (WHO, 2018). The successful transmission of viruses within a new host species requires the acquisition of host-adaptive mutations (Urbanowicz et al., 2016). With regards to the Ebola virus, it was hypothesized, following the recent outbreak in West Africa, that glycoprotein substitutions within the genetic sequence of the virus may have prolonged the virus shedding time from the human body (Urbanowicz et al., 2016). Subsequently, this led to an increased potential for human to human transmission (Urbanowicz et al., 2016). Current research evidence suggests that these glycoprotein mutations also increase the Ebola virus tropism for human cells (Urbanowicz et al., 2016). Recent research studies have suggested that the Ebola virus is evolving into various lineages with varying lethal abilities (Berezow, 2017). The possibility that Ebola may evolve to become more lethal through the process of natural selection is quite troubling (Berezow, 2017). However, the studies upon which these findings are based were carried out during outbreaks. Under these conditions, random sampling is often impossible, and researchers are often limited to whatever data they can aggregate (Berezow, 2017). As such, the study sample may not be a true representation of all Ebola strains (Berezow, 2017). Nonetheless, it quite evident that the genetic attributes of the Ebola virus, and its ability to evolve over the past years, has been a key factor in the emergence of this disease.

The human host

Infectious agents require entry into a susceptible host to cause infections. Susceptibility, within the context of communicable diseases, refers to the inability of a host (human or otherwise) to resist a pathogen. Human susceptibility to any infection can be attributed to factors such as age, nutrition, and genetics (Casadevall & Pirofski, 2018). Since the discovery of the Ebola virus and its recent outbreaks, extensive studies have been carried out to uncover the factors that contribute to human susceptibility to the virus. Genomic mapping has now revealed that bats and humans share similarities in the positioning of an endosomal cell receptor called the Niemann-Pick C1 receptor (Lawrence, Danet, Reynard, Volchkova, & Volchkov, 2017). The interaction between the Ebola virus glycoprotein and these endosomal cell receptors is crucial to the entry process of the Ebola virus into a host cell (Lawrence et al., 2017). The discovery of these similarities suggests that the Ebola virus would not require special adaptation to successfully enter human cells from a bat reservoir (Lawrence et al., 2017). Molecular studies have also provided evidence to support this theory (Lawrence et al., 2017).

Human demographics and behaviour have also influenced the emergence of the Ebola virus infection (Morens & Fauci, 2013). This is due to the key role that interpopulation interaction plays in the spread of pathogens (van Doorn, 2017). A booming global population has led to the invasion of human activities into many geographical locations of the world (van Doorn, 2017). This intensive urbanization has reshaped the relationship between microbes and humans (van Doorn, 2017). In some of the African regions affected by the Ebola virus spread, the movement of humans towards forest areas can be attributed to wars and conflict within those regions (van Doorn, 2017). Humans are now more in contact with animal reservoirs than in the past thus increasing the potential for the infection and spread of the Ebola virus (van Doorn, 2017). Additionally, international travel and trade are a lot easier and convenient than in the past (Morens & Fauci, 2013). This has increased the potential for the spread of the Ebola virus in ways which were previously unattainable (Morens & Fauci, 2013). The current ease of international travel and trade was a key factor in the Ebola outbreak in West Africa between 2014 and 2016.

Cultural behaviours such as bushmeat butchering and hunting have also contributed to the emergence of Ebola (Kumpel et al., 2015). The significant nature of this contribution is, however, still debatable. The Ebola virus can survive in untreated animal carcasses for up to 3 or 4 days (Kumpel et al., 2015). There is, therefore, a potential risk of transporting this virus to local bushmeat markets. Evidence to support this theory is however quite limited (Kumpel et al., 2015). More importantly, the potential for spreading overseas via bushmeat is quite minimal considering the travel time and the fact that these animal carcasses are usually smoked, thus inactivating the virus (Kumpel et al., 2015).

The human environment

The emergence of Ebola is a manifestation of many failures within the human environment. Failures in human and social development have crippled various countries thus exposing them to several hardships. The Ebola epidemic is just one example of the problems these countries must contend with. Poverty is still an important problem within the African society and has played a significant role in the emergence and spread of Ebola. The extensive poverty within many African regions is sustained by corruption, exploitation, escalating social conflict, anarchy, a distorted application of values such as human rights, and the wasteful consumption patterns exhibited by the privileged individuals within these societies (Benatar, 2015). There is also a persistent lack of vital caring social institutions such as schools and public hospitals due to a lack of political will by government leaders and officials (Benatar, 2015). The combination of these deficiencies within the socioeconomic structures of these regions has created an environment where suffering and social inequality thrives (Benatar, 2015). Such an environment provides a perfect platform for epidemics such as that of Ebola to emerge and spread unabated.

Climate change has a significant impact on the transmission of infectious diseases in general (Kassie, Roger, & Bourgarel, 2015). This is attributed to the effect of climate factors on pathogens, hosts, and epidemiological dynamics (Kassie et al., 2015). With regards to Ebola, climate change has altered the natural habitats of Ebola animal reservoirs thus forcing them to encroach on human settlements through the process of redistribution (Kassie et al., 2015). This increases human contact with the Ebola reservoirs leading to the emergence and spread of the disease (Kassie et al., 2015). Conversely, climate change has also forced humans to encroach towards the Ebola animal reservoirs (Kassie et al., 2015). Food insecurity, for example, can be worsened by climate factors (Kassie et al., 2015). As a result, people may be prompted to consider alternative sources of food such as the bushmeat (Kassie et al., 2015). The contribution of bushmeat hunting and consumption to the emergence of Ebola has been discussed in previous paragraphs. The increased interspecies contact which results from such behaviour promotes the emergence and spread of Ebola.

Additional factors within the human environment which have contributed to the spread of Ebola include; industrialization and economic development (Morens & Fauci, 2013). They arise from an interplay between human behaviour (as discussed previously), and human interaction with the environment. The human desire to develop both economically and industrially has caused the movement of human activities towards geographical areas which potentially harbour the Ebola animal reservoirs, thus increasing the potential for the transmission and spread of Ebola.

CURRENT CONTROL MEASURES FOR EBOLA

Prevention, control, and response

The successful prevention and control of the Ebola virus infection, as recommended by the WHO, requires adequate case management, safe burials of deceased patients, good laboratory services, surveillance and contact tracing, and social mobilization. Affected communities need to be engaged and aware of the risk factors for Ebola infection. Risk reduction measures include; encouraging the use of gloves and appropriate clothing when handling animal products, regular hand washing after contact with patients, prompt and safe burial of the dead, and adequate quarantine of people who have been in contact with infected patients to prevent further spread. The maintenance of good hygiene and clean environments is also important. Within health facilities, health workers are urged to use adequate personal protective equipment (PPE) and maintain proper hand and respiratory hygiene.

In the event of an outbreak, the WHO usually responds by providing logistical support, training, and assistance with safe burial practices (WHO, 2018). The WHO also aids with laboratory services, case management, and community engagement (WHO, 2018).

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