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Volume 1, Number 1—January 1995

Perspective

Factors in the Emergence of Infectious Diseases

Stephen S. MorseComments to Author 
Author affiliation: The Rockefeller University, New York, New York, USA

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Table 1

Recent examples of emerging infections and probable factors in their emergence

Infection or Agent Factor(s) contributing to emergence
Viral
Argentine, Bolivian hemorrhagic fever Changes in agriculture favoring rodent host
Bovine spongiform encephalopathy (cattle) Changes in rendering processes
Dengue, dengue hemorrhagic fever Transportation, travel, and migration; urbanization
Ebola, Marburg Unknown (in Europe and the United States, importation of monkeys)
Hantaviruses Ecological or environmental changes increasing contact with rodent hosts
Hepatitis B, C Transfusions, organ transplants, contaminated hypodermic apparatus, sexual transmission, vertical spread from infected mother to child
HIV Migration to cities and travel; after introduction,sexual transmission, vertical spread from infected mother to child, contaminated hypodermic apparatus(including during intravenous drug use, transfusions, organ transplants
HTLV Contaminated hypodermic apparatus, other
Influenza (pandemic) Possibly pig-duck agriculture, facilitating reassortment of avian and mammalian influenza viruses*
Lassa fever Urbanization favoring rodent host, increasingexposure (usually in homes)
Rift Valley fever Dam building, agriculture, irrigation; possibly change in virulence or pathogenicity of virus
Yellow fever (in new areas) Conditions favoring mosquito vector
Bacterial
Brazilian purpuric fever (Haemophilus influenzae, biotype aegyptius) Probably new strain
Cholera In recent epidemic in South America, probably introduced from Asia by ship, with spread facilitated by reduced water chlorination; a new strain (type O139) from Asia recently disseminated by travel (similarly to past introductions of classic cholera)
Helicobacter pylori Probably long widespread, now recognized (associated with gastric ulcers, possibly other gastrointestinal disease)
(associated with gastric ulcers, possibly other
Hemolytic uremic syndrome (Escherichia coli O157:H7) Mass food processing technology allowing contamination of meat
Legionella (Legionnaires' disease) Cooling and plumbing systems (organism grows in biofilms that form on water storage tanks and in stagnant plumbing)
Lyme borreliosis (Borrelia burgdorferi) Reforestation around homes and other conditions favoring tick vector and deer (a secondary reservoir host)
Streptococcus, group A (invasive; necrotizing) Uncertain
Toxic shock syndrome (Staphylococcus aureus) Ultra-absorbency tampons
Parasitic
Cryptosporidium, other waterborne pathogens Contaminated surface water, faulty water purification
Malaria (in "new" areas) Travel or migration
Schistosomiasis Dam building

* Reappearances of influenza are due to two distinct mechanisms: Annual or
biennial epidemics involving new variants due to antigenic drift (point
mutations, primarily in the gene for the surface protein, hemagglutinin) and pandemic strains, arising from antigenic shift (genetic reassortment, generally between avian and mammalian influenza strains.)

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