Epidemiology Of Avian Influenza Human Health Implications Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

During the past decade, outbreaks of infectious disease have been a major cause for concern Kahn, 2009, particularly in the developing countries where control is restricted by inadequate infrastructural and financial resources. It was noted that many of these emerging diseases are zoonoses (Frederick, 2008). That is, infectious diseases which are transmitted between humans and animals. Over 30 new human pathogens have been detected in the last three decades, 75% of which have originated from animals and have zoonotic potential (World Health Organisation, 2010a). Although, diseases of humans caused by bacteria, virus, parasites and other unconventional agents of animal origin have been in existance for centuries now, it appears that nearly all the recent disease episodes that have caught public attention in the past decade have involved zoonotic infectious agents (Council for Agricultural Science and Technology, 2005; Womack, 2005). Humans have long relied upon animals, both as a major source of protein and as companions or pets but this come with a price. That is, an increase in the risk of zoonotic disease transmission to humans, and an increase in zoonotic disease infections in humans, both of which are of public health concern. The situation has been worsened by travel, which allows disease to spread rapidly from country to country within the incubation period of most infectious agents (Frederick 1998). Hence, if given the opportunity, highly pathogenic infectious disease agent originating from a particular place can cause problems in a new environment in such a short period of time than would normally be expected.

1.1.1 Statement of the Problem

Until recently, infection caused by avian influenza virus was considered a disease of avian species only with zoonotic implications of limited importance. However, the emergence and unprecedented spread of the Asian lineage of highly pathogenic avian influenza (HPAI) H5N1 virus among the poultry population, and its success in eventually crossing the species barrier to cause many human fatalities changed this perspective, following the confirmation of several human cases of infection with the virus in 1997(World Health Organisation, 2005). This outbreak, which is still ongoing, is one of the greatest causes of public health concern in recent times. There are four instances in the 20th century where antigenically different strains of influenza viruses transmissible in humans have occurred; 1918 (H1N1), 1957 (H2N2), 1968 (H3N2) and 1977 (H1N1), each resulting in a pandemic with the new virus completely replacing the previous virus in the human population during the 1957 and 1968 pandemic (Capua and Alexander, 2002).

At present, there are quite a number of influenza viruses currently circulating the avian population; however H5N1 virus is presenting the greatest concern for public health (World Health Organisation, 2010b). This virus, which was first isolated during a highly pathogenic poultry disease outbreak in Hong Kong in 1997, reappeared in February 2003 when it was suspected and later confirmed to have caused infections in three family members of whom one died (Wong and Yuen, 2006). Since then the H5N1 virus has continued to spread across different countries, particular south Asian countries, causing disease in both human and poultry populations. This particular virus has now succeeded in crossing the species barrier because as at 5th July, 2010, there was 500 laboratory confirmed cases including 296 deaths (World Health Organisation, 2010c), with many more suspected, unreported and unidentified cases/death yet to be discovered. An implication for public health which is of utmost concern is the assumption that if given enough opportunities, the H5N1 virus will develop the characteristics it needs to start a new influenza pandemic.

According to the World Health Organisation (2006) this virus has met all prerequisites for the start of a new pandemic except one, that is, the ability to spread efficiently and sustainably from person to person. The reason provided is that for an influenza pandemic to occur, three conditions must be met: a new influenza virus subtype must emerge, the virus must be able to infect humans, causing serious disease, and finally it must spread easily among humans. They report that the first two conditions have already been met, and that there are new suggestions of human-to-human transmission in Thailand and Indonesia, which is the key for a pandemic.

As a veterinary doctor working in one of the largest suburb of Lagos state, Nigeria; which has the largest number of poultry farms and backyard poultry owners in the state, I could not help been concerned about the risk pose by the currently highly pathogenic avian influenza (HPAI) virus to the health of poultry handlers. Personal experiences from my area and location of practice have always demonstrated that poultry related activities of poultry workers and backyard poultry keepers should be a cause for public health concern. Following the outbreak of avian influenza in Nigeria in 2006, my interest in this area grew and I was involved in advising farmers / backyard poultry owner about how to avoid becoming infected. But after several farms in the locality where I practiced experienced avian influenza outbreak and a suspected case of human infection with avian influenza infection was confirmed, I was completely drawn to this area and wanted to research the problem of avian influenza as it relates to human health, with particular emphasis on those who handle poultry either for commercial or domestic use.

1.2 Preliminary Literature Review

The purpose of this preliminary literature review is to explore the identified problem in order to gain some insight by reviewing the literature on avian influenza as presented by theoretical and empirical research. The pool of research which exists on avian influenza is an evidence of its economic importance for the poultry industry and most importantly, its public health significance. Hence, an analysis of the issues relating to the occurrence of avian influenza infection in humans is necessary and must precede the design of strategies for tackling this public health problem, particular among poultry handlers.

1.2.1 Epidemiology of Avian influenza / Human Health Implications

The natural reservoir of avian influenza A virus subtypes are waterfowls because these viruses exist in an evolutionary equilibrium with birds so that they are able to remain asymptomatic despite been infected by this viruses with large amount of virions in their faeces (Wong and Yuen, 2006). Although, the viruses have been shown to infect both birds and mammals, birds are more readily infected than mammals while domestic fowls or poultry are most susceptible, and exposure to the virus subtypes amongst poultry population mostly resulted to outbreaks (Capua and Alexander, 2007). Human infections with avian influenza viruses are believed to mainly result following direct transmission of the virus from infected birds (Wong and Yuen, 2006; Tweed et al., 2004).

There is a general agreement over the existence of a significant species barrier to human influenza viruses infecting birds, and avian influenza viruses infecting humans and this led to the suggestions that since pigs are readily infected by human and avian viruses, then it acts as a ''mixing vessels'' for the reassortment of both viruses, with the emergence of a new virus (es) having the necessary gene(s) that is needed to allow replication and spread in the human population (originating from human), but with an entirely different hemagglutinin surface glycoprotein, that is not recognised by the human population (Capua and Alexander, 2007).

However, recent events have significantly altered this understanding. A list of the major events relating to H5N1 avian influenza outbreaks in poultry populations and human cases/death between 1996 and 2010 in various parts of the world can the accessed from the World Health Organisation's web site (World Health Organisation 2010b). Cases of human infections were only rarely reported prior to 1997, with infected individuals often presenting with conjunctivitis caused by H7N7 (Campbell et al., 1970; Taylor and Turner, 1977; Webster et al., 1981; Kurtz et al., 1999). In May 1997, the first avian influenza infection in human to cause clinical respiratory illness in recent times was reported in a child who died in Hong Kong as a result of fatal viral pneumonia with severe complications (de Jong et al., 1997; Claas et al., 1998; Subarrao et al., 1998). But it was only about 6-7 months later that the first major outbreak of the infection in humans occurred, when 18 cases of whom 6 eventually died were confirmed to have been infected with the same virus type (Shortridge et al., 1998). It was later demonstrated that the viruses isolated from the human cases in 1997 were identical with the viruses isolated following an outbreak of highly pathogenic infection that affected chickens in Hong Kong during the same year and that all the viral isolate from both the human cases and poultry outbreaks had multiple basic amino acids at their HA0 cleavage site (Capua and Alexander, 2002). This was the first sign that avian influenza viruses can effectively infect human, directly from avian species, on a large scale.

Following the 1997 event, it is assumed that sporadic cases of human H5N1 infection continued to occur but it was not until 2003 that the current epidemic of the H5N1 virus emerged again causing disease in 3 family members; with 2 confirmed H5N1 virus infections and 1 death (Wong and Yuen, 2006). Subsequent cases of human H5N1 infections were associated with outbreaks of H5N1 virus among poultry populations in several Asian countries (Katz et al., 2009). Avian influenza infection is now considered to pose significant threat for public health, due to concerns about the development of a new human pandemic virus originating from the H5N1 virus.

A notable feature of the H5N1 virus is the geographic extent of its occurrence. Although, china is regarded as the epicentre for both human and avian influenza viruses, the virus has been stretching its borders into Northern and Western Asian countries, the Middle East, Europe, and African (Katz, 2009). This expanding geographical distribution of the virus puts an increasingly larger population of people at risk of becoming infected (Chen et al., 2005). Since 2003, the H5N1 influenza virus subtype has continued to cross species barrier to cause human infections to date. As at 5th July 2010, there were 500 laboratory-confirmed human cases including 296 deaths (World Health Organisation, 2010c).

Just like H5, highly pathogenic avian influenza (HPAI) viruses of the H7 subtype have also cause human infection in North America and Europe, but their morbidity and mortality profile differ substantially from human infection with H5N1. During the 2003 outbreak of HPAI H7N7 viruses on poultry farms in Netherlands, Belgium and Germany, over 80 cases of H7N7 infections were identified in individuals involved with handling the infected birds (Fouchier et al., 2004). Although a few individuals reported respiratory illness which included one fatality, most of the affected cases presented as conjunctivitis. Tweed et al., (2004) also reported an outbreak of HPAI H7N3 virus in 2004, which was contained by depopulation of 19 million birds in British Columbia and which resulted in 57 cases of suspected H7N3 virus infection among workers who presented with either influenza-like illness or conjunctivitis.

1.2.2 Transmission

Transmission of avian influenza viruses to human occur by inhalation of infectious droplets, by direct contact, by indirect contact (with fomite), or by self-inoculation of the virus onto the upper respiratory tract or conjunctival mucosa (Bridges et al, 2003). Although, relative efficiency of the modes of transmission has not been established, most available evidences are consistent with bird-to-human, possibly environment-to-human, and limited non-sustained human-to-human transmission.

Most evidence available to date and investigations of all the most recently confirmed cases of human influenza infections, in Turkey, Indonesia, and China, have identified direct contact with infected birds as the principal sources of infection with H5N1 virus are sick or dead birds, especially occurring when people practice risky behaviors such as slaughtering, defeathering, butchering, and preparation of infected birds for consumption (Bridges et al., 2002; Mount et al., 1999; World Health Organisation, 2006).

Not all human cases have arisen from exposure to dead or visibly ill domestic birds. According to the World Health Organisation (2006), in some few cases, exposure to chicken faeces by children in areas where free-ranging poultry are allowed to roam, swimming in water where dead infected birds have been discarded or which may have been contaminated by the faeces of infected water birds, is thought to have been the source of infection with influenza viruses whereas in other cases investigations were unable to identify a definite source of exposure, suggesting that unknown environmental factor (that are yet to be known), involving contamination with the virus, may be implicated in a small number of cases. They also reported that researches published in 2005 showed that domestic ducks are able to excrete large quantities of highly pathogenic virus without showing any of the established signs of illness.

Human-human transmission of avian influenza viruses was reported by Bridges et al. (2000) who carried out a study involving health care workers, in which he found that 3.7% of health-care workers who managed avian influenza H5N1 patients subsequently became seropositive for avian influenza virus. It was also reported that during the 2003 outbreak of H7N7 infection in the Netherlands, there was evidence to show that person-to-person transmission occurred, because H7N7 infections developed in three household contacts of the initial outbreak cases (Capua and Yuen, 2006). Few other cases of infection in close contacts (within household) of avian influenza patients have also been reported, but despite suggestion of human-to-human transmission of the virus, the efficiency of such transmission is very low since sustained human-to-human transmissions have not yet been reported (Bridges et al., 2000; SKeiK and Jabr, 2008; Liem and Lim, 2004). Nevertheless, it is important to bear in mind that the possibility of genetic reassortment between avian viruses and human within the human host or other permissive animals (e.g. swine and ducks) remains a constant threat for the generation of a highly pathogenic virus that is readily transmissible from person-to-person (Yuen, 2005).

At present, avian influenza caused by H5N1 is still largely regarded as a disease of birds because the species barrier is still significant, that is, the virus does not easily cross from birds to infect humans. No efficient human-to-human transmission of the virus is known to be occurring anywhere. But the question of how long this barrier will stand before a long forgotten history of a major influenza pandemic repeats itself, as a result of the nature of poultry handling practices, still remains open. The demonstration of direct natural infections of humans with avian influenza viruses (avian-to-human infection) is of serious public health concern because it suggests that pandemic viruses could emerge through reassortment or progressive adaptation, without the need for an intermediate host or a mixing vessel such as the pig, which has been demonstrated to be susceptible to infection by a minimum of one viral strain of each of the subtypes H1-13 of influenza A viruses (Kida et al., 1994).

1.2.3 Therapeutic Intervention

The prevention of avian influenza in humans is largely dependent on the elimination of the disease in birds, but it is impossible to determine if this can be achieved especially in developing countries that have been affected. Control of avian influenza in birds is a huge task that is been addressed by the Food and Drug Organisation of the United Nations, Government of affected countries and other relevant organisations. In an attempt to halt outbreaks of avian influenza in poultry population, which is the key to preventing human infections, vaccination has always been an important option for reducing the viral load in poultry population. However, where this is attempted in the absence of other measures such as extension services to ensure that vaccination is carried out correctly and also that surveillance of vaccinated birds as a means for identifying infected birds and stamping out where infections are detected, it is unlikely that vaccination alone will have the desired effect for controlling the infection and may even make the situation worse if thing go wrong. Given these facts vaccination was never able to gain the acceptance needed for a vaccination campaign to reduce viral load within the poultry population or its presumed reduction of the risk / amount of human infections.

In the case of human vaccination against avian influenza virus infection, the seasonal human influenza vaccine does not confer protection against H5N1 influenza virus. Thus, research to come up with an effective vaccine that confers full protection against avian influenza virus is ongoing. Trials with potential vaccine candidates such as the inactivated H5N3 vaccine and MF59-adjuvanted vaccine have been carried out and more are still been tested (Wong and Yuen, 2006). Despite efforts put into vaccine research for the currently circulating avian influenza strains (particularly H5N1) a pandemic strain could be antigenically different from the vaccine in development. This means that a pandemic may result from reassortment of the currently circulating H5N1 virus strain and so vaccine development will also have to change course to be specific to the pandemic strain. Wong and Yuen (2006) reports that a significant time lag of 6 months is the minimum time needed before an effective vaccine can be commercially available for mass vaccination.

Even though, there are no vaccine capable of efficiently protecting humans against infection with avian influenza, the U.S. Food and Drug Administration approved a human vaccine against avian influenza virus, they noted that the vaccine which had been tested on volunteers, was generally tolerated by the study participants but produced the desired immune response in less than half of the study participants (U.S. Food and Drug Administration, 2009). It is hoped that the vaccine will provide an early, though limited protection to people before a vaccine specific to the pandemic strain of the virus is developed. If an efficient vaccine is successfully produced, it would most likely be the principal health tools for decreasing morbidity, mortality, and the economic effects of pandemic influenza, especially if resistance to oseltamivir begins to develop (Skeik and Jabr, 2008).

Interestingly, the projections amount of pandemic influenza vaccine courses that can be made available (in the early event of an outbreak) has been increased by the advancement in science and vaccine manufacturing capacity and vaccine manufacturers are working with the World Health Organisation (WHO) on a plan to develop a global stockpile of medication for H5N1 that can be made available at the start of a pandemic (WHO, 2007). Other measures included in the preparedness plan of WHO for a potential influenza pandemic include: rapid containment plans to stop a pandemic using public health measures (isolation, quarantine of contacts, personal hygiene and social distancing) and anti-viral as well as providing assistance to countries to increase vaccine production capacity, including research and promoting the transfer of technology to developing countries. For safety and technical reasons, current vaccines against H5N1 virus are not commercially available and also because it is impossible to predict whether the currently circulating H5N1 strain will be responsible for the next pandemic (Skeik and Jabr, 2008).

1.2.4 Health Promotion Intervention

The ongoing avian influenza (AI) epidemic, which has claimed many human lives, is undoubtedly a serious problem for most affected countries. It has been observed that most human cases of AI have occurred in rural and periurban households where small flocks of poultry are kept, with very few cases (detected) in individuals assumed to be at higher risk, such as poultry workers, workers at live poultry markets, poultry cullers, veterinary staffs, and health staff caring for infected patients without putting on adequate personal protective equipment (World Health Organisation, 2005). Because no valid reason could be found for these observations, The World Health Organisation (2006a) urged researchers to study the exposure circumstances, behaviours, and possible genetic or immunological factors that might enhance the likelihood of human infection. This was deemed very important if a pandemic is to be prevented.

While research is ongoing to going to develop effective avian influenza vaccines for human use, there is a concern that the efficacy of any effective vaccine produced may be limited by the rapid antigenic changes which is a common feature of all influenza viruses. Therefore, it is only logical that other measures are sort to reduce human exposure and possible increase in the risk of infection with avian influenza virus. Professor Gostin, a member of the World Health Organisation's consultation on influenza preparedness, mention in his paper "Pandemic Influenza: Public Health Preparedness for the Next Global Health Emergency" that, one of the most valuable means of infection control which is also the least intrusive is health education, to promote safer behaviors (Gostin, 2004).

In a study of the implication of avian influenza on animal and human health, Capua and Alexander (2007) concluded that the education of poultry handlers is very important for the control of avian influenza in animal and therefore prevention of the disease in humans. He also added that there is a speculation that the nature of bird-human interaction in particularly rural settings, is largely dependent, among other factors, on behavioural practices, and is complicated by a lack of respect for basic hygienic standards; given that most human cases that have occurred so far, have involved contacts between villagers and rural chickens or fighting cocks.

While there is an urgent need for Information, Education and Communication (IEC) programmes to provide knowledge about the basic concepts of biosecurity, farming hygiene, prevention and notification procedures, as well as an ability to self-notify outbreaks rather than attempting to escape restrictions, it must also be appreciated that human behavioural is complex and cannot undergo sudden change (World Health Organisation, 2008). To some people and in some cultures, poultry is regarded as family's assets because they are a source of income and food for families. In such setting it would require more than just providing facts and figures or verbal persuasion to convince families to change their usual interaction with poultry and worse of all give up rearing chickens in their backyards.

To illustrate the importance of selecting appropriate communication approaches, of targeting education and of integrating IEC with health and social services, it is important to be able to learn from other related or similar experience. Experience from the past have shown that messages developed to achieve behavioural change such as the fear campaign initiated in many countries during the AIV epidemic, with the reasoning that people would be shocked into behavioural change, did not produce the desired results (World Health Organisation, 2006b). Thus, effective IEC campaigns need to give consideration to cultural acceptability, literacy levels, preferred sources of information, and available infrastructures.

It can therefore be concluded that the development of messages for specific target group should take place after rapid assessment of the current knowledge, attitudes, and practices (KAP) in relation to poultry keeping and avian influenza. In this respect a number of research studies have been carried out in this respect particularly survey studies to assess the (current) KAP of different populations that work with or keep poultry either as an occupation or a normal way of life (culture). However, during the preliminary literature review process, the author did not find any literature review that brought together the findings of the different studies on knowledge, attitude and / or practice of poultry handlers in relation to avian influenza as an evidence-base for developing and implementing messages that can be tailored to the specific group perceived to be at risk and those group of individuals that have been mostly affected by the ongoing avian influenza epidemic.

From this preliminary literature review, we have learnt that avian influenza viruses, particularly H5N1 virus strain can adapt to the human host to cause disease or infection, that transmission is enhanced by direct contact of humans with infected birds and that so far (as at July 2010) about 500 cases with up to 296 human deaths have been confirmed. We have also learnt that there is no effective human vaccine to infer protect against avian influenza vaccine and that the available vaccines are yet to be produced in the quantity that will be required at the start of a pandemic. The review then demonstrated the need for tailored Information, Education, and Communication (IEC) campaigns to achieve behavioural change amongst poultry handlers, with the belief that this is the most effective non-therapeutic intervention for the prevention of the speculated human influenza pandemic. Against this backdrop, my research question is:

What are the knowledge, attitude and practices of poultry handlers regarding avian influenza infection?

1.3 Research Aim

The aim of this study is to determine the knowledge, attitude and practices of poultry handlers (poultry workers and backyard poultry keepers) regarding avian influenza, in order to inform decision making process as well as the planning and implementation of health promotion intervention programmes to reduce the risk of spread of avian influenza viruses within and between different populations of people.