«The Economic and Social Aspects of Biodiversity Benefits and Costs of Biodiversity in Ireland REPORT PREPARED BY: CRAIG BULLOCK, OPTIMIZE CONSULTANTS ...»
Disease-causing microbes (pathogens) and parasites play an equally important role in ecosystem functioning and productivity. They are not all pleasant, but nevertheless play an essential part in natural selection, maintaining the health of ecosystems and populations of wild flora and fauna.
Cycles of infection, disease, morbidity and mortality have played a significant role in the evolution of life and have also driven the evolution of human societies and cultures (McMichael 2001, 2004, Fowler 2005).
The Problem with Microbes
We really know nothing about microbes.With 1.8 million animal or insect species identified, biologists get understandably excited whenever a new species is discovered. In fact, they need look little further than their own back garden. The average teaspoon of soil or water contains millions of micro-organisms, many of which have never been identified. The problem is that these microbes are so small and so similar.
Metagenomics is a new technique that pools all species in a sample and which sequences each by piecing together short fragments of DNA rather like a jigsaw. From such techniques, we are learning that as much as 90% of all microbial biodiversity may arise from species that are actually rather rare. We know almost nothing about these species’ functions, although we have learnt that one relatively rare bacterium could be responsible for all the fixing of nitrogen from the atmosphere. Indeed, such techniques are allowing us to find microbes in even the most unlikely of places including oxygen-less environments, deep ocean trenches and even mine-water with the acidity of battery acid.
Source: New Scientist (Nicolls, H.) 17/3/2007
Biologically rich ecosystems consist of numerous organisms that interact with each other in complex ways. An outcome of these interactions is an equilibrium between and within species, which helps to regulate the prevalence of diseases. Infectious diseases are a product of the pathogen, vector, host and environment. Intact ecosystems control the populations of pests and diseases, minimising the risk of destructive outbreaks. Many micro-organisms circulate naturally within a wild “host” population without causing any illness or symptoms of disease. An example is the multitude of bacteria and viruses found within the human digestive tract, and the other flora which occur on our skin. Other examples include certain avian influenza viruses which have no effect on the host bird species, wild immuno-deficiency viruses which are benign in their hosts, and lyme disease parasites which can circulate innocuously in rodent, deer and lizard populations.
While often having positive role on the regulation of wild species, the risk of disease arises when these micro-organisms come into contact with a species outside of the natural ecology of that organism. Ecosystem disturbance, for example, through pollution, habitat loss or fragmentation, species extinction, or the introduction of invasive species, can lead to changes in disease ecology with potentially disastrous effects for wildlife, domestic animals, crops, or man. This has been most clearly demonstrated in diseases that are caused by organisms that spend part of their life-cycle outside of their definitive host (see for example Patz et al 2000, Cifuentes and Rodriguez 2005, Plummer 2005, Kahn et al 2006, Gould et al 2006, Estrada-Pena and Venzal 2006, Cumming and Guégan 2006). Important examples of parasitic diseases in Ireland that are affected by environmental conditions include leptospirosis, varroasis, fascioliasis and cryptosporidiosis.
Zoonotic diseases (zoonoses) – those spread from animals to humans - are of particular social and economic importance. Recent epidemics of zoonotic diseases such as HIV/AIDS (originating in wild primates in Africa), SARS (from civets in Asia) and highly pathogenic avian influenza (HPAI strain H5N1 spread by migratory birds) illustrate the importance of animal reservoirs as sources of emerging infectious diseases. By virtue of their genetic, physiological, and behavioural similarities with humans, primates are thought to be likely sources of pathogens that can pose a significant threat to human populations. The HIV pandemic is a forceful example of this threat. The Millennium Ecosystem Assessment (MA) Health Synthesis notes that bushmeat is believed to have led to the first transmission of HIV to humans. SARS may have entered the human population via wild species before crossing to animals raised domestically and consumed as food in China (Bell et al 2004).
This is not to deny the role of animal populations as potential reservoirs of emerging infectious diseases, but to demonstrate the implications that disruption to ecosystems can have through unprecedented animal-human contact. Modification of landscapes and other impacts on ecosystems can lead to shifts in species interactions, population movements and demographics, in turn facilitating an increase in pests or the spread of disease organisms. There is growing evidence from around the world that disturbance of habitats and ecosystem services can lead to outbreaks of new types of communicable diseases in wildlife, livestock, crops and people. Modern intensive methods of meat and poultry production facilitate the rapid spread and amplification of disease as these systems are intensive and rear animals with low disease resistance. The Millennium Ecosystem Assessment has emphasised that alteration of ecosystems can lead to changes in the relationship between populations of vectors and potential hosts, and thus to new patterns of disease spread which are often unforeseen. The individual and societal costs are potentially catastrophic. (See also Graczyk et al 2000, McMichael 2001, Patz et al. 2004, Marcogliese 2004, Norris 2004, Baumgartner 2004, Brownstein 2005, Hampton 2005, COHAB 2005, Steele, Oviedo & McCauley 2006).
In Europe and the US, other diseases which have long been recognized in wild animals are of increasing importance as diseases of humans and of agriculture. Examples include several viral, bacterial and parasitic diseases spread from wild birds and mammals which are coming into increasing contact with people due to habitat disturbance and urbanisation. Genetic diversity is increasingly recognised as an important factor in the ability of wild populations to withstand stresses such as diseases. Indeed, this is true for man too. Recent research is indicating that a large proportion of the European population possesses genetic characteristics derived from the Great Plague which may yet have evolutionary benefits against future pandemics (Galvani & Slatkin, 2003).
Worldwide, the incidence of zoonotic diseases is expected to increase in coming decades since the opportunities for pathogenic organisms to jump across the species barrier have multiplied. Reasons include rapid urbanization, population growth and movement, the clearing of new agricultural land, the growing trade in meat, milk and other animal products, greater world trade, travel and tourism, and the rate of biodiversity loss and ecosystem change (Karesh & Cook 2005, Karesh et al. 2006, Swift et al. 2007, Pearl 2004, Kimball et al. 2004). Another important factor is global warming, which allows certain species, in particular insects, to colonize new regions where they could yet propagate new pathogens.
In Ireland, diseases such as tuberculosis, leptospirosis, toxoplasmosis, cryptosporidiosis, brucellosis and salmonellosis have known links with wildlife. There is also the risk that previously unknown diseases, or diseases which are recognised in wildlife but have not been identified as important threats to people, could cross the species barrier to the human population. Examples include the Sin Nombre virus in the USA (from wild mice), new crytosporidium strains (from wild deer) in Europe, Anaplasma parasites (from wild rodents), mange, toxoplasmosis and echinococcus throughout Europe (from foxes); and the worldwide emergence of new calcivirus strains (from marine mammals). (See Brown 2001, Ong et al. 2002, Deplazes et al. 2004, Rabinowitz & Zimra 2004, Schweiger et al. 2007.)
Wildlife sentinels of ecolog i c a l h e a l t h.
The past five years have seen a growing interest in the field of conservation medicine, a discipline at the crossroads of public health, environmental science and veterinary medicine.
Conservation medicine examines the complex relationships between nature, ecosystems and human health, recognising that human, plant and animal health are influenced by ecological sustainability and the interactions between people and the ecosphere (Aguirre et al. 2002).
The discipline has been mainstreamed into the global environmental and health sectors.
Indeed, the basic concepts of conservation medicine, i.e. that humans depend upon a healthy environment and that our actions impact on ecosystems with implications for our own society, are the basis of much EU environmental legislation.
One of the areas of this field that is of increasing importance and of particular relevance to developed countries is the use of wild animals as sentinels of ecological health (Aguirre and Tabor 2004). By observing the health and disease status of wildlife populations, particularly larger animals, scientists can often gain a greater appreciation of environmental conditions at ecosystem level. In this way, the target species can act as the canary in the mineshaft, providing an early warning of environmental health problems. Marine wildlife, in particular, has been of great interest in this regard. For reasons of public safety and food quality, research into the exposure of many food species to pollution has been ongoing for years. In this regard, assessments of the health of mammals and other species near the top of the food chain are of greater interest (Hatcher & Hatcher 2004, Bond et al. 2004, Burger & Gochfeld 2004). In Ireland, some analysis has been recently conducted on blood and tissue samples from dolphins in Irish coastal waters to determine exposure to PCBs and organochlorines (Smith et al, 2000, Berrow et al. 2002), while other assessments have looked at the expression of genetic abnormalities in cetaceans (for example, Berrow & O’Brien 2006). A wider programme of wildlife health monitoring, examining the state of health of selected marine species, is warranted, particularly when Ireland’s coastal waters are so important to wildlife and human populations alike.
9.5 R E L E VA N T D I S E A S E S A few case studies of globally important human and animal diseases relevant to Ireland are given below.
9.5.1 H an t a v i ru s e s An important example of zoonotic diseases is that of the Hantaviruses, a group of viral pathogens spread by rodents throughout the world. The organisms are spread to people through contact with rats and mice or their excreta, and are specific to geographic areas and rodent species. Infection with the virus in rodents is benign, with no illness or symptoms displayed by infected animals.
Infection in people can however be extremely serious, often presenting as a mild flu but potentially developing into a severe disease of the blood and circulatory system involving the heart, lungs or kidneys, known as Haemorrhagic Fever with Renal Syndrome (HFRS).
People are often at greatest risk in areas with high rodent population densities, or where rats and mice frequent areas of human habitation. In Ireland, this would include rural areas where rodent numbers are typically high around agricultural lands, and urban areas, around accumulations of litter, public parks, areas near landfills etc. Evidence of human Hantavirus infection has been found in blood samples taken from wild rodents and hospital patients in Northern Ireland since the 1990s (e.g. McKenna et al, 1994, McCaughey et al, 1996). As we become more urbanised, and as we impact on ecosystem integrity through physical development and habitat disturbance, there may be an increased risk of Hantavirus disease within the Irish population.
A common response to dealing with outbreaks of rodent-borne disease is to increase the use of rodenticides. Unfortunately, indiscriminate use of poisons can have severe impacts on non-target animals including species that naturally prey on rats and mice such as cats, badgers, martens, owls and other raptors, impacting upon a natural and important control mechanism for rodent populations (e.g. Kittlein 1997, Singleton, 1999, Duckett & Karuppiah 1990, Brakes 2005).
Furthermore, there is an increasing problem of rodenticide resistance among rats and mice in Europe (e.g. Russell 2003, Pelz & Klemann 2004).
9.5.2 HIV / AIDS The emergence of the Human Immunodeficiency Virus (HIV) and the associated Acquired Immune Deficiency Syndrome (AIDS) in the late 1970s alerted the scientific community to the risk of unknown and severe pandemic diseases arising in the human population from unexpected sources, in this case from human-wildlife interactions.
Recent research suggests that cross-species transmission of Simian Immunodeficiency Viruses (SIV) from primates to humans probably occurred as a result of butchering practices associated with the bushmeat trade. Subsequent human-to-human transmission eventually resulted in the spread of HIV in human populations facilitated by changes in population movements and by human impacts on the environment. International travel ensured its worldwide spread.