News Reading: New infectious diseases will continue to emerge

Dozens of new infectious diseases are likely to emerge over the next 25 years unless humans acquire an ecological perspective on infectious diseases rather than seeing microbes as simply an invading entity that should be blindly attacked with antibiotics or used as a tool for biological warfare, a conference was told last week.

Professor Tony McMichael, of the Australian National University, Canberra, said that the emergence and spread of 35 new or newly diagnosed infectious diseases in the past 25 years was a product of our modern way of life.

The risein international tra____, overc______cities, intensive f____ production, sex____ practices, pov____, and gl_____ warming were some of the ingredients that had come together to form a suitable culture medium for the emergence, maintenance, and spread of new infectious diseases, as well as allowing the resurgence of older diseases such as cholera, tuberculosis, and malaria, he said.

Speaking at the Royal Society conference last week, convened to explore the factors influencing emerging infectious diseases, Professor McMichael cited hepatitis C as an example of a disease born from socio-technological change. "The advent of illicit intravenous drug use and blood transfusion has allowed the wider spread, and now recognition, of this virus," he said.

Professor McMichael discussed the many diverse factors that influenced the emergence of infectious diseases. He spoke of the impact of the massive increase in international travel that had allowed the spread of new diseases such as HIV and severe acute respiratory syndrome (SARS) on an unprecedented scale.

The way in which humans had changed their environment had also influenced the spread of disease. Developments in agriculture, urbanisation, and deforestation had all changed ecosystems and allowed the emergence of infections. Lyme disease, a disease spread by ticks, was first identified in 1976, in the United States. Forest fragmentation, loss of predators, and the shift of suburbia closer to woodlands were all implicated in the appearance of this disease.

Another example was the Nipah virus. In 1999 this virus killed 100 people in peninsular Malaysia. The virus was normally carried by the forest fruit bat and had not previously seemed to pass to humans. However, because of deforestation and agricultural techniques the bat normal habitat and food source were changed. This forced the bats to encroach into fruit plantations, which were in close proximity to pig farms. The bats infected the pigs which in turn infected the farmers.

Professor McMichael concluded by emphasising the need to acquire an ecological perspective on infectious diseases. "In the 1970s, eminent people were saying it was the end of the infectious disease era. We now find after the experience of the 1980s and 1990s, we are sadder and wiser."

Factors in the Emergence ofInfectious Diseases

Factor / Examples of specific factors / Examples of diseases worldwide
Eco______changes (including
those due to economic
development and land use) / Agriculture; dams, changes in
water ecosystems;
deforestation/reforestation;
flood/drought; famine; climate
changes / Schistosomiasis (dams); Rift Valley fever(dams, irrigation); Argentine hemorrhagicfever (agriculture);
Human demog______, / Populationgrowth and migration;
war or civil conflict; / Introduction of HIV; spread of dengue;
International tra____ and
Comm_____ / Worldwide movement of goods
and people; air travel / “Airport” malaria; dissemination of mosquito
vectors; rat-borne hantaviruses;
introduction of cholera into South America;
Human beh______ / sexual behavior;
intravenous drug use; / Spreadof HIV and other sexually transmitteddiseases
Tech______and industry / Globalization of food supplies;
changes in food processing
and packaging;
organ ortissue transplantation;
drugscausing immunosuppression;
widespread use of antibiotics / E. colicontamination of hamburger meat, bovinespongiform encephalopathy;
transfusion-associated hepatitis (hepatitisB, C),
opportunistic infections inimmunosuppressed patients,
Creutzfeldt-Jakob disease fromcontaminated batches of human growthhormone (medical technology)
Microbial adap______andchange / Microbial evolution, response to
selection in environment / Antibiotic-resistant bacteria, “antigenic drift”
in influenza virus
Breakdown in pub___ hea____ measures / reduction inprevention programs;
inadequate sanitation and
vector control measures / Resurgence of tuberculosis in the United
States; cholera in refugee camps in Africa;
resurgence of diphtheria in the former
Soviet Union

The hard lesson we learnt in Hong Kong

Q. The severe acute respiratory syndrome(SARS)outbreak raised awareness of infectious diseases to ourhighest levels in the history of Hong Kong. Since the 1970s, there has been complacency both in the generalpublic and in the medical community about infectiousdiseases, and a general impression that they no longerpose a major health threat to Hong Kong. Asaresult, theinfectious disease specialty has been somewhat neglectedin comparison to other specialties.

In the last two decades,however, we have witnessed the emergence of new andold infectious diseases, including HIV/ AIDS, tuberculosis,H5N1 influenza anddengue, to name a few.Why do you think Hong Kong is particularly vulnerable to the invasionof infectious diseases?

Hong Kong is particularly vulnerable to the invasionof infectious diseases due to several geographical andhistorical factors. First, Hong Kong's close proximity toMainland China and its dependence on the latter for food,water and livestock can result in direct importation ofinfectious disease via cross border movement of thesegoods.
Secondly, cross border movement of people andinternational travel can bring infectious diseases into orout of HongKong. Thirdly, over-crowded living quartersand substandard hygienicconditions in some parts ofHong Kong encourage the spread of microorganisms.
Infectious disease prevention awareness among the publicleaves a great deal to be desired.Finally, the liberal and improper use of antibiotics both locally and neighboring regions is leading to the emergence of drugresistance, making treatment and control of infectiousdiseases more difficult.