MICROBIOLOGY Probable disease source Domestic animals Apes Rodents Unknown Disease type
Diphtheria, influenza A, measles, mumps, pertussis, rotavirus, smallpox, tuberculosis
Hepatitis B Plague, typhus Rubella, syphilis, tetanus, typhoid Table 1. Probable origins of the 15 human diseases (after Wolfe, N D et al.1
of these ‘new, emergent’ pathogens. For example, intensive pig farming which spread into virgin areas containing bats resulted in Nipah virus infections in pig farmers.3
The virus then crossed
international borders via international trade.
A challenge to clinical microbiology
here is the possibility of the development of new variants of the virus that may occur as a risk to the human population. Moreover, the deliberate or accidental introduction of hitherto new animals into new habitats has led to these animals being the likely origins of diseases. In addition to this, the increasing ageing population will exhibit lower immunological resistance and therefore add to the increased burden of disease.1
).
Means by which diseases spread Diseases Colonisation
Trade
War International travel Urbanisation
Malaria, smallpox, ?syphilis Plague
SARS, COVID Dengue, Zika virus, chikungunya virus Table 2. Modes of disease transmission (after Baker RE et al.2
Effects of climate change The role of climate change may present important challenges by altering the geographical range into which reservoir species may spread, and consequently will increase the geographical range of subsequent vectors that have the ability to transmit the disease. It has been postulated that alterations in climatic factors may have increased rodent populations with a subsequent increase in hantavirus infections.4
It may happen
that increases in temperature-sensitive pathogens may increase the ranges for dengue, Zika virus and malaria. The increased occurrence of the water- borne diseases will also be likely. It has been postulated that increasing sea temperatures have increased the global
).
suitability for the extension of the habitats of Vibrio parahaemolyticus.5 Increases in global temperature is also
postulated to lead to the enhancement of spore production of clinically important fungal species, and has also been associated with the increase in infections due to pathogenic Candida species via an avian intermediate host.6 Climate change and global warming will undoubtedly increase exposure of populations to various vectors and pathogens not previously encountered. Identifying the origin of zoonotic pathogens and their transmission will be crucial for early detection and prevention.7
Trade in animal hosts The trade in animals, both locally and globally, has resulted in the spread of diseases of certain animals with both health and economic consequences. These have included the transmission of Rift Valley fever from Africa to the Middle East.8
African swine fever transportation
has occurred to Europe in 1997, to China in 2018, and to India and South East Asia in 2020.9
It has been postulated that domestic poultry and wild birds may play a role in the re-assortment between human and avian influenza viruses.10
This is of concern
as avian influenza is associated with a high level of morbidity and mortality. Elsewhere, the importation of infected lambs from Argentina and Chile led to large outbreaks of foot and mouth disease in the United Kingdom.11
It is suggested that increasing sea temperatures have increased the global suitability for the extension of the habitats of Vibrio parahaemolyticus (colonies of the microorganism growing on thiosulphate-citrate-bile salts-sucrose [TCBS] agar).
Global spread The rapid global spread of infectious diseases has been exacerbated by international travel, as displayed by the rapid spread of SARS-CoV-2. The spread may be by human carriers, already symptomatic humans, or by the accidental transfer of vectors such as in the case of malaria from Africa to Brazil, or blue tongue virus from the Middle East into Europe. Other examples include Zika virus transfer from Polynesia to Brazil, and the emergence of West Nile virus into the United States of America. The spread of
June 2026
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