Molecular characterization and serological epidemiology of viral diseases of humans and animals in Zambia [an abstract of entire text]

概要

Infectious diseases threaten global public and animal health (1). Over the last decade, a number of viral and bacterial pathogens have emerged, causing deadly disease outbreaks globally(2). Zoonotic diseases, which are transmitted from animals to humans, account for 75% of emerging pathogens (3). Furthermore, zoonotic diseases infect more than one in seven livestock in developing countries and are responsible for 2.7 million deaths annually (4). Besides being a going public health concern, zoonoses have economic implications. To exemplify this, the economic impact of rift valley fever (RVF), a viral zoonoses, has been estimated at 5 and 470 million dollars (5), however, this figure is potentially grossly underestimated due to weak surveillance systems in resource-limited countries. In contrast to zoonoses, animal epizootics pose major socio-economic consequences. For instance, diseases such as African swine fever (ASF) and Bluetongue (BT) have had a serious impact on the growth of the livestock industry globally. Economic losses due to the ASF outbreak in China were estimated at over 89.5 billion dollars (6) while those attributed to BT in Germany are estimated at 180 million dollars (7). However, the impact of zoonoses and epizootics in endemic regions in Africa is largely unknown, possibly due to weak surveillance systems and/or lack of epidemiological information.

In Africa, viral pestilences have been responsible for a large number of disease outbreaks in humans and animals. Major epizootics/epidemics in Africa are compounded by rapid population growth, lack of proper infrastructure and skilled manpower, and high burden of co-morbidities such as human immunodeficiency virus (HIV) and Tuberculosis (2). The public health and socio- economic burden of these diseases are mainly felt by the majority of poor households. Like most countries in Africa, the epidemiology of most viral diseases of public and animal health importance are poorly understood in Zambia. Yet, the socio-economic and public health risks posed by these diseases remain high. Over the last three decades, Zambia has seen a rapid population growth of about 2.9% per annum. However, the high poverty levels (60%), mostly among rural households (78%) (8), implies that that the public health and socio-economic effects of infectious diseases are largely felt by the majority of marginalized communities. Moreover, the high incidence of HIV, Malaria, and Tuberculosis along with limited resourced has led to disease prioritization. This has resulted in a number of endemic diseases being neglected. Thus, the specter of major disease epizootics/epidemics necessitates understanding the epidemiology of neglected and/or re-emerging infectious diseases. This is necessary for evidence-based disease prevention and control strategies.

In order to mitigate emerging and re-emerging infectious diseases in high burden, resource limited countries like Zambia, public and animal health systems encompassing a multidisciplinary approach are needed. The “One Health” concept is a holistic and transdisciplinary approach that embraces human, animal and environmental health sciences (9). Emerging and re-emerging infectious diseases are influenced by the biology and ecology of infectious agents, their hosts and vectors (10). Thus, understanding the ecosystem dynamics that influence the occurrence or recurrence of infectious agents, and their dissemination and extinction in natural habitats, is essential in assessing the risk of infection (11).

In chapter I of this dissertation, the epidemiology of RVF in Zambia was examined using a multidisciplinary approach. RVF emergence is a result of the complex interaction that largely depends on the host (animals or humans), vector (Mosquitoes) and environment (precipitation). Understanding this complex interaction is important for disease prediction and risk mapping. Chapter II describes first serological evidence and molecular characterization of zoonotic genotype 3 hepatitis E virus (HEV) in domestic pigs in Zambia. Swine hepatitis E possess a significant public health risk. The risk is more pronounced in pregnant woman and immunocompromised patients. Furthermore, the risk of hepatitis E is high among poor communities who mostly depend on cheap pork processed in poor sanitary conditions.

Chapter III explores the epidemiology of ASF in endemic and non-endemic regions in Zambia. ASF is the single biggest constraint to the growth of the pig industry in Zambia. In endemic regions, the disease has led to increased poverty levels and reduced food security. Understanding the complex epidemiology of ASF in endemic and non-endemic regions is vital for devising effective disease mitigating strategies. Chapter IV reports on the first serological detection and molecular characterisation of Bluetongue virus (BTV) in Zambia. While no bluetongue (BT) outbreaks have been reported in Zambia, the increased demand for European breeds of sheep by farmers in Zambia has raised the risk for BT outbreak in susceptible breeds. In order to implement pre-emptive measures such as vaccination, it is imperative that the serologic and molecular epidemiology of bluetongue is fully appreciated.