Avian influenza: An overview of the current situation, and public health and economic implications in Ethiopia

Tibebe-selassie Seyoum¹, Nigatu Kebede¹, Abebe Animut¹, Tesfu Kassa¹

¹Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P. O. Box: 1176, Addis Ababa, Ethiopia

Abstract 

Avian influenza is an infectious disease of birds caused by type A strain of influenza virus of the family orthomixoviridae. Recently, out breaks of the highly pathogenic forms of avian influenza caused by H5N1 strain has been reported in different parts of the world, more frequently in Asian countries. Theses outbreaks have resulted in significant economic losses in poultry industry and a significant number of deaths in humans. Furthermore, the epidemic is expanding its territory to new areas including Africa. The spread of the infection has been observed to be fast and migratory waterfowl are playing great role in the transmission of the infection to domestic birds. The objective of this manuscript is to review, discuss and present the current situation of avian influenza. In addition, the economic and public health implications of the disease to Ethiopia have been discussed.  Furthermore, the political and social consequences of the disease to the country were tried to be contemplated. Finally, recommendations were forwarded by taking into account the current situation of the epidemic in the world and its potential risk to Ethiopia.

Key words: highly pathogenic avian influenza, poultry, waterfowl, human infection, Ethiopia, national economy

Introduction

Avian influenza is an infectious disease of birds caused by type A strain of influenza virus of the family orthomixoviridae (Buxton Bridges, et al., 2000; Katz et al., 1999). So far, all out breaks of the highly pathogenic forms have been caused by influenza A viruses of subtypes H5 and H7 (Buxton Bridges, et al., 2000; Katz, et al., 1999, FAO, 2004). The low pathogenic strains of H5 and H7 subtypes can, after circulation for short periods in a poultry population, mutate into highly pathogenic viruses (WHO/CDS, 2005). Not all virus strains of the H5 and H7 subtypes are highly pathogenic, but most are thought to have the potential. Highly pathogenic strains of H5 and H7 viruses have several amino acid residues at the cleavage site (FAO, 2005).  Cooler temperature enhances the persistence of avian influenza viruses. They can persist and retain their infectivity in faeces for at least 35 days at 4⁰C but for only about 4 days at 25⁰C. In water they can persist and retain infectivity for more than 30 days at 0⁰c and for up to 4 days at 22⁰C (FAO, 2004).

 In poultry, avian influenza causes two distinctly different forms of diseases, one common and mild, the other rare and highly lethal. Most often, out breaks are seen in poultry after having contact with feral birds sharing the same water sources. Out breaks can be so mild that they escape detection unless regular testing for the virus is in place. In the mild form of avian influenza, signs of illness range from ruffled feathers and reduced egg production to typical respiratory symptoms. The less common highly pathogenic form is characterized by sudden onset of severe disease, rapid contagion and mortality that can approach 100% within 48 hours. In this form, the virus not only affects the respiratory tract, as in the mild form of disease, but also invades multiple organs and tissues, causing massive internal hemorrhaging that has earned it the lay name of " Chicken Ebola" (WHO/CDS, 2005). H5N1 highly pathogenic avian influenza virus is excreted via the faeces and respiratory excretion of infected poultry. Most commonly, transmission is via direct contact between birds or through contact with the virus on the fomites (clothing, shoes, equipments, etc) or more rarely through air borne particles (FAO, 2004). Avian influenza (H5N1) might be less adapted to droplet transmission and its incubation period is longer (Chotpitayasunondh, et al., 2005).

 Avian influenza virus can be recovered from the yolk and albumen of eggs laid by hens at the height of the disease. The possibility of vertical transmission is unresolved; however, it is unlikely that infected embryos could survive and hatch (FAO, 2005). Wild waterfowl, gulls, and shore birds are the natural reservoir of all influenza A viruses and have historically carried low pathogenic viruses, in evolutionary equilibrium with out showing symptoms or succumbing to disease. This role may, however, have changed very recently: at least some species of migratory waterfowl are now thought to be carrying the H5N1 virus in its highly pathogenic form and introducing it to new geographical areas located along their flight routes (WHO/CDS, 2005). A virulent strain may emerge either by genetic mutation or by reassortment of less virulent strains (FAO, 2005).

Different species of waterfowls, carrying viruses, migrate from the affected areas of Europe and Asia to east Africa and excrete large quantities in their faeces. These birds are believed to reach lakes, rivers and seas found in the rift valley of Ethiopia. Most households, in rural areas of Ethiopia, practice backyard poultry production and commonly live with their poultry in the same house with no barrier. The country was estimated to have over 56 million chickens, of which more than 98% were kept under rural household conditions by the year 1996 (Tadelle and Ogle 1996). This number is expected to be higher due to the increasing demand for diet and family income. This increases the potential of becoming in contact with infected poultry droppings and corpses, which are major sources of infection (Yemane and Admas, 2005). No infected cases were reported until the middle of 2005 (Tadele et al., 2005). Despite the announcement by the ministries of health and agriculture, the disease has not been confirmed in Ethiopia and the consumption of chicken and egg is still safe. Provided certain care procedures are observed, still large percentage of population appears suspicious.  Hence both the health, economic implication of the disease can be far reaching if new cases are reported. Therefore, the objective of this paper is to present an overview of the current situation of avian influenza, its public health importance and economic implication in Ethiopia.

Clinical features of avian influenza in birds

Highly pathogenic avian influenza (bird flu) is caused by virulent strains of H5 and H7 type A avian influenza virus. In chicken, the major clinical signs of the disease include excessive lacrimation, respiratory distress, sinusitis, oedema of the head and face, cyanosis of unfeathered skin, and diarrhoea (Bankowski, 1982). These signs are variable and influenced by factors such as the virulence of the infecting virus, species affected, age, sex, concurrent diseases and environment (Alexander, 200b; Geering, et al., 1995).  The disease appears suddenly in flock and causes death of many birds with out having appeared sick or with minimal signs of depression, little food intake, ruffled feathers and fever. Other birds show weakness and staggering gate. Sick birds often sit or stand in a semi comatose state (“sleepy”) with their heads touching the ground. Some younger birds may show neurological signs (Bankowski, 1982, MoARD, 2005).

Hens may at first lay soft-shelled eggs but soon stop laying. Profuse watery diarrhoea and excessive thirsty are common. Respiration may be fast and labored. Haemorrhages may occur on unfeathered areas of the skin, especially at the shanks of the legs. Mortality varies from 50% to 100%. In turkeys, eyelids and sinuses become swollen (tnt desgnvn @ yahoo. com). Domestic ducks excrete H5N1, in its highly lethal form, with out showing signs of illness. The role of domestic ducks may help to explain why several recent human cases could not be traced to contact with diseased poultry (WHO/CDS, 2005).

The role of migratory birds

Some migratory waterfowls carry the H5N1 virus, in its highly pathogenic form, over long distances. They introduce the virus to poultry flocks in the areas that lie along their migratory routes (WHO/CDS, 2005). The death of more than 6000 migratory birds, infected with the highly pathogenic H5N1 virus that began at the Qinghai Lake in central China in the late April 2005 was highly unusual and probably unprecedented. Prior to that event, wild bird deaths from highly pathogenic avian influenza viruses were, usually occurring as isolated cases within the flight distance of poultry out breaks. Scientific studies from different out breaks have shown that viruses from the most recently affected countries, along migratory routes, are almost identical to those from dead migratory birds at Qinghai Lake. Fatal viruses from Turkey’s first two human cases were reported to be identical with viruses from Qinghai Lake (WHO/CDS, 2005, Beard, 1989).

The threat of avian influenza to humans

In the first instance of human infection the virus caused 18 cases, of which six were fatal in china, hong kong especial administrative region in 1997. The cases concided with outbreaks of highly pathogenic H5N1 in poultry farms and in live market. Of all viruses in the vast avian influenza pool, H5N1 is of particular concern for human health for two reseans. First the virus though strictly an avian pathogen, has a documented ability to pass directly from birds to humans. Second, once in humansm, the virus causes severe disease with very high mortality. These two features combine to make H5N1 of concern for a third and greater reason its potential to ignite an especially severe pandemic (WHO, 2005).

A pandemic avian influenza virus can emerge via two principal mechanisms: reassortement and adaptive mutation. For both events experts have long assumed that pigs have both human and avian receptors for the virus on the cells lining their respiratory tract served as the mixing vessel for swamping of gene segments (WHO, 2005). Pigs can be infected by both avian and human influenza A viruses. Polymorphisms of sialic acid species and linkage to galactose of both birds and humans are co-expressed in the tissue. The co-infection with avian and human influenza, therefore, allows genetic reassortment of antigenic properties of both species in the co-infected cells. Recently, it has been shown that certain avian influenza viruses in human and birds are able to bind to different target cells (Matrosovich, 2004). This could explain the observation of several cases since the end of the 1990s with transmission of avian influenza directly from poultry to humans. H5N1 and some other subtypes of influenza A virus are able to bind to receptors in the human eye (Olofson, et al., 2005).

Human beings can be infected during slaughtering, defeathering, butchering and preparation for consumption of infected birds. In a few cases, exposure to chicken faeces is thought to have been the source of infection for children. Swimming in water bodies, where the carcasses of dead infected birds have been discarded or which may have been contaminated by faeces from infected ducks or other birds might be another source of exposure (WHO/CDS, 2005).

 The disease in humans

Close contact with dead or sick birds and exposure to chicken faeces are sources of human infection with the H5N1 virus. The most common initial symptoms are fever, pneumonia, pharyngitis, intestinal symptoms, conjunctivitis, and acute encephalitis (Yuen, et al., 1998; Tran, et al., 2000; Yuen and Wong, 2005). Adult patients with initial signs of pneumonia often progress to an Acute Respiratory Disease Syndrom-like disease. In fatal cases of H5N1 influenza, reactive haemophagocytic syndrome has been described as a prominent feature. Beyond pulmonary disease with organizing diffuse alveolar damage and interstitial fibrosis, extra pulmonary involvement has been described as extensive hepatic central lobular necrosis, acute renal tubular necrosis and lymphoid depletion (To, et al., 2001). Human-to-human transmission is not reported. H5N1 also infects cats and tigers (WHO/CDS, 2005).

Chicken and eggs: is there a risk from poultry products?

Avian influenza is mainly caused by exposure to the virus during the slaughter of infected birds and their preparation for cooking. So far, no human cases are linked to the consumption of poultry products. In several such instances, the person who slaughtered or prepared an ill bird for consumption developed fatal illness while family who participated in the meal did not. The large out break in the captive tigers that occurred in October 2005 in Thailand is thought to be linked to the feeding of contaminated whole chicken carcasses. This indicates that contact with raw poultry carcasses can be a significant source of exposure to the virus. In countries affected by H5N1 out breaks, eggs should also be thoroughly cooked, as some studies have detected virus in raw eggs. WHO recommends that all meats, including that from poultry, be thoroughly cooked, so that all parts of the meat reach an internal temperature of 70⁰C. This temperature kills H5N1 virus and makes contaminated poultry meat safe for consumption (WHO/CDS, 2005).

Impact of avian influenza on national economy

The impact of highly pathogenic avian influenza has been distributed within the entire poultry market of China, affecting producers, consumers and employees in the retail industry (FAO, 2004). More than 120 million birds died or destroyed in the Asian out breaks within three months (WHO/CDS, 2005). World bank estimated earlier this year that the cost of the current out breaks in Vietnam might amount to between 0.3% and 1.8% of GDP depending on the length of the out break, the severity of culling of poultry and the spill over effect on tourism. Estimates for Thailand suggest that the rate of growth of agricultural GDP may have halved during the out break year. The total cost of the 1997 out break in Hong Kong is said to have been hundreds of millions of dollars when the costs to international trade and tourism are included. In USA, two previous out breaks of avian influenza resulted in the lose of  $65 and $140 million dollars in disease control and poultry loss (FAO, 2004) respectively. A similar economic loss may result if the virus is introduced in Ethiopia.

Political and social consequences

Out breaks of highly pathogenic avian influenza have significant political and social consequences. Public confidence can be seriously compromised particularly when cases of infection occur in people and have serious or fatal consequences. Fear of contracting disease is very hard to value, especially for those who work in poultry industry or consume poultry meat. Large exporting industries may put pressure on governments to limit smallholder production with the goal of improving general biosecurity and facilitating disease eradication. However, governments must also take into account the significant contribution of village and backyard poultry production to the supply of dietary protein and food security (FAO, 2004, Beard, 1989).

 Highly pathogenic avian influenza, in Asia, has had a major impact on small holders and villagers, whose capacity to raise poultry for food or exchange has been seriously compromised. The destruction of millions of disposal healthy birds may raise public health concern about the adverse environmental effects of carcass disposal and animal welfare. In some parts of the world, mass destruction of animals or birds is unacceptable from a societal or religious point of view, particularly if safe and effective vaccines can be used to control the disease. Destruction of birds with out using their products may lead to public doubt regarding safety of these products. Highly pathogenic avian influenza can also have a negative impact on social and cultural activities, such as raising and exhibiting songbirds, racing pigeons and fighting cocks. Governments, wishing to limit the risk of spread and to avoid human exposure, may take steps to ban social gatherings and trade in these birds, limiting social value, cultural or religious activities. The disease will also have an adverse impact on biodiversity due to its effect and control strategies, on scarce genetic resources (FAO, 2004).

Poultry Production in Ethiopia

Rising income and urbanization, in many parts of the developing world, caused a growing demand for animal products. The per capita consumption of meat doubled in the developing world from 1967 to 1997, with even more spectacular increase in the consumption of poultry. Poultry meat and egg production accounted for more than 28% of the total animal protein produced world wide in 1997. The proportional contribution of poultry by the year 2020 is believed to increase to 40%, the major increase being in the developing world. Trends in poultry production and demand are highest in Asian countries and lowest in Sub-Saharan Africa, due to the low overall economic development in the region (Delgado et al., 1999).

Poultry occupies a unique position in terms of its contribution to the provision of high quality protein food to rural smallholder farming families in Africa particularly in Ethiopia (Tadelle and Ogle, 2001). There are only few alternative animal protein sources available. Both poultry meat and eggs enrich and contribute to a well balanced diet to satisfy human needs. Village poultry could be particularly important in improving the diet of young children in Sub-Saharan Africa (Tadelle et al., 2003).

In most parts of Ethiopia, consumers have high preferences for poultry products. Poultry production serves as a simple means of generating family income and employment opportunities. Compared to other domestic animals, poultry can be raised with relatively low capital investment and readily available household labor. Thus it plays an important role in the diet and economy of the Ethiopian people (Solomon, 2004). It is estimated that Ethiopia has over 56 million chickens, of which more than 98% is kept under rural household conditions. According to the 1984 statistic of ELFORA Agro- Industries PLC, 99.2 % of all poultry is produced and consumed within a private rural setting (Tadelle and Ogle, 1996).

The typical Ethiopian rural household owns six birds from a non-crossbred strictly Ethiopian background. Chicken mortality rate in Ethiopia reaches about 61%. Of the birds, 26.6% are produced for sale, while 25% are used for sacrifice or healing, 20.3% for replacement, and only 19.5% for home consumption (Tadelle and Ogle, 1996). There is no purposeful poultry feeding in rural Ethiopia and scavenging is the most important component of the poultry diet. Full day scavenging poultry are usually capable of finding feeds for their maintenance requirement plus the production of few eggs and are vulnerable to predators and spread of infection (Solomon, 2004).

Conclusion

The highly pathogenic avian influenza virus (H5N1) is spreading worldwide. Though it is not confirmed yet, Ethiopia is also considered as the potential site of the disease due to the migration of the Waterfowls, natural reservoirs of the virus, to the rift valley lakes. This virus is known to infect poultry, humans, and other mammals. Most of the poultry production system in the country is back yard with no barrier between humans and poultries. This back yard farming system together with the prevailing poor hygienic condition of the rural dwellers will maximize the spread of the disease once introduced.  Today, there is a great suspicion of the disease in urban dwellers. As a result, consumers demand for poultry and its egg is sharply declining. However, the risk of infection can be minimized by proper poultry handling and cooking of its products (meat and egg) thoroughly. Considering the current outbreaks of the disease in different parts of the world, and its potential of occurrence in Ethiopia, the following recommendations were forwarded:

1. The government in collaboration with international community should strengthen the capacity and capability of the regional and national laboratories for early detection of the disease,
2. Regular surveillance and epidemiological studies should be conducted in wild and domesticated birds, for early identification of avian influenza virus,
3. Rapid culling of all infected or exposed birds, proper disposal of the carcasses, quarantine and rigorous disinfection of farms, and the implementation of strict sanitary, or “biosecurity” measures,
4. Public education on the transmission and zoonosis nature of the disease,

       5.  Restricting the movement of live poultry, both within and between countries.

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