A comprehensive literature review identifies 1415 species of infectious organism known to be pathogenic to humans, including 217 viruses and prions, 538 bacteria and rickettsia, 307 fungi, 66 protozoa and 287 helminths. Out of these, 868 (61%) are zoonotic, that is, they can be transmitted between humans and animals, and 175 pathogenic species are associated with diseases considered to be 'emerging'. We test the hypothesis that zoonotic pathogens are more likely to be associated with emerging diseases than non-emerging ones. Out of the emerging pathogens, 132 (75%) are zoonotic, and overall, zoonotic pathogens are twice as likely to be associated with emerging diseases than non-zoonotic pathogens. However, the result varies among taxa, with protozoa and viruses particularly likely to emerge, and helminths particularly unlikely to do so, irrespective of their zoonotic status. No association between transmission route and emergence was found. This study represents the first quantitative analysis identifying risk factors for human disease emergence.

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Risk factors for human disease emergence.

Pathogens that can be transmitted between different host species are of fundamental interest and importance from public health, conservation and economic perspectives, yet systematic quantification of these pathogens is lacking. Here, pathogen characteristics, host range and risk factors determining disease emergence were analysed by constructing a database of disease–causing pathogens of humans and domestic mammals. The database consisted of 1415 pathogens causing disease in humans, 616 in livestock and 374 in domestic carnivores. Multihost pathogens were very prevalent among human pathogens (61.6%) and even more so among domestic mammal pathogens (livestock 77.3%, carnivores 90.0%). Pathogens able to infect human, domestic and wildlife hosts contained a similar proportion of disease–causing pathogens for all three host groups. One hundred and ninety–six pathogens were associated with emerging diseases, 175 in humans, 29 in livestock and 12 in domestic carnivores. Across all these groups, helminths and fungi were relatively unlikely to emerge whereas viruses, particularly RNA viruses, were highly likely to emerge. The ability of a pathogen to infect multiple hosts, particularly hosts in other taxonomic orders or wildlife, were also risk factors for emergence in human and livestock pathogens. There is clearly a need to understand the dynamics of infectious diseases in complex multihost communities in order to mitigate disease threats to public health, livestock economies and wildlife.

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Diseases of humans and their domestic mammals: pathogen characteristics, host range and the risk of emergence

Food animals in the United States are often exposed to antimicrobials to treat and prevent infectious disease or to promote growth. Many of these antimicrobials are identical to or closely resemble drugs used in humans. Precise figures for the quantity of antimicrobials used in animals are not publicly available in the United States, and estimates vary widely. Antimicrobial resistance has emerged in zoonotic enteropathogens (e.g., Salmonella spp., Campylobacter spp.), commensal bacteria (e.g., Escherichia coli, enterococci), and bacterial pathogens of animals (e.g., Pasteurella, Actinobacillus spp.), but the prevalence of resistance varies. Antimicrobial resistance emerges from the use of antimicrobials in animals and the subsequent transfer of resistance genes and bacteria among animals and animal products and the environment. To slow the development of resistance, some countries have restricted antimicrobial use in feed, and some groups advocate similar measures in the United States. Alternatives to growth-promoting and prophylactic uses of antimicrobials in agriculture include improved management practices, wider use of vaccines, and introduction of probiotics. Monitoring programs, prudent use guidelines, and educational campaigns provide approaches to minimize the further development of antimicrobial resistance.

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Antimicrobial Use and Resistance in Animals

The epidemiology of Mycobacterium bovis infections in animals and man: A review

Selenium ( Se 34 79 ) is a metalloid which is close to sulfur (S) in terms of properties The Se concentration in soil varies with type, texture and organic matter content of the soil and with rainfall Its assimilation by plants is influenced by the physico-chemical properties of the soil (redox status, pH and microbial activity) The presence of Se in the atmosphere is linked to natural and anthropogenic activities Selenoproteins, in which selenium is present as selenocysteine, present an important role in many body functions, such as antioxidant defense and the formation of thyroid hormones Some selenoprotein metabolites play a role in cancer prevention In the immune system, selenium stimulates antibody formation and activity of helper T cells, cytotoxic T cells and Natural Killer (NK) cells The mechanisms of intestinal absorption of selenium differ depending on the chemical form of the element Selenium is mainly absorbed in the duodenum and caecum by active transport through a sodium pump The recommended daily intake of selenium varies from 60 μg/day for women, to 70 μg/day for men In growing ruminants the requirements are estimated at 100 μg/kg dry matter and 200 μg/Kg for pregnant or lactating females A deficiency can cause reproductive disorders in humans and animals

Selenium in the Environment, Metabolism and Involvement in Body Functions

Part 1. General Medicine: Clinical Examination and Making a Diagnosis. General Systemic States. Diseases of the Newborn. Practical Antimicrobial Therapeutics. Diseases of the Alimentary Tract I. Diseases of the Alimentary Tract II. Diseases of the Liver and Pancreas. Diseases of the Cardiovascular System. Diseases of the Blood and Blood-Forming Organs. Diseases of the Respiratory System. Diseases of the Urinary System. Diseases of the Nervous System. Diseases of the Musculoskeletal System. Diseases of the Skin, Conjunctiva and External Ear. Part 2. Special Medicine: Mastitis. Diseases Caused By Bacteria V. Diseases Caused By Viruses and Chlamydia I. Diseases Caused By Viruses and Chlamydia II. Diseases Caused By Rickettsia. Diseases Caused By Algae and Fungi. Diseases Caused By Protozoa. Diseases Caused By Helminth Parasites. Diseases Caused By Arthropod Parasites. Metabolic Diseases. Diseases Caused By Nutritional Deficiencies. Diseases Caused By Physical Agents. Diseases Caused By Inorganic and Farm Chemicals. Diseases Caused By Toxins in Plants, Fungi, Cyanobacteria, Clavibacteria, Insects and Animals. Diseases Caused By Allergy. Diseases Caused By the Inheritance of Undesirable Characters. Specific Diseases of Uncertain Etiology. Conversion Tables. Reference Laboratory Values. Index.

R. J. Bildfell

Papers

Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses