Emerging and Reemerging Infectious Diseases and Pathogens Lecture Week 13 Medical Microbiology SBM 2044

FIGURE 1. Leading causes of death worldwide. About 15 million (>25%) of 57 million annual deaths worldwide are the direct result of infectious disease.

Emerging infectious diseases CDC: new, reemerging or drug-resistant infections whose incidence in humans has increased within the past three decades or whose incidence threatens to increase in the near future Infections that have newly appeared in a population or have existed previously but are rapidly increasing in incidence or geographic range (Morse 1995)

After great advances in medical research and antimicrobial drug discovery, technology development, improvement in sanitation.. WHY are microbes still posing such a problem?

Factors involved in the emergence of infectious diseases 1.Unprecedented worldwide population growth, urbanization 2.Increased international travel 3.Increased worldwide transport, migration, and relocation of animals and food products 4.Changes in food processing, handling, and agricultural practices 5.Changes in human behaviour, technology and industry 6.Human encroachment on wilderness habitats that are reservoirs for insects and animals that harbour infectious agents

7.Microbial evolution and the development of resistance to antibiotics and other antimicrobial drugs 8.Changes in ecology and climate 9.Modern medicine (e.g. immunosuppression) 10.Inadequacy of public infrastructure and vaccination programs 11.Social unrest and civil wars 12.Bioterrorism 13.Virulence-enhancing mechanism of pathogens (the mobile bacteriophages, plasmids, transposons) Factors involved in the emergence of infectious diseases

Emergence of infectious disease are the results from dynamic interactions between rapidly evolving infectious agents and changes in the environment and in host behaviour that provide such agents with favourable new ecological niches

FIGURE 2. Global examples of emerging and re- emerging infectious diseases.

Classification of Emerging Infectious Diseases Newly emerging –Have not previously been recognised in man Reemerging/resurging –Existed in the past but are now rapidly increasing either in incidence or in geographical or human host range Deliberately emerging –Microbes are those that have been developed by man, usually for nefarious use

Newly emerging infections Have not previously been recognised in man

AIDS model AIDS have affected > 60 million people worldwide jumping to humans species, may be a consequence of the consumption of ‘bush meat’ from non-human primates this allow HIV-1 and HIV-2 to evolve in host emergence is amplified by disruptions in the economic and social infrastructure in post- colonial sub-Saharan Africa urban poverty, a weakening of family structure all promoted promiscuous sexual practices, and increased travel.

Dead-end transmission of zoonotic and vector-borne diseases Arenavirus haemorrhagic fevers (inc Lassa fever) and hantavirus pulmonary syndrome (HPS) – viruses in these groups have co-evolved with specific rodent species – increased human-rodent contact as a result of modern environmental factors: farming, keeping domestic pets, hunting and camping, deforestation Malaysian Nipah virus epidemic – pigs crammed together in pens located in or near orchards, attracted fruit bats which are the natural hosts of the Nipah and Hendra viruses – virus aerosolisation caused infection of pigs –Overcrowding results in viral transmission to pig handlers

Other newly emerging agents Environmentally persistent organisms –Legionnaires caused by Legionella pneumophila due to the use of air-con –Campylobacter jejuni, Shiga-toxin-producing E. coli infect agricultural animals enter through food, milk, water or direct contact Microbial agents and chronic diseases –Chronic liver damage, hepatocellular carcinoma - Hep B and C –Cervical cancer – papillomaviruses –Burkitt’s lymphoma – Epstein-Barr virus –Gastric ulcers and gastric cancer –

Re-emerging and Resurging Infections Existed in the past but are now rapidly increasing either in incidence or in geographical or human host range

Geographical spread of infections Depend on the rate and degree to which they spread across geographical areas – the movement of human hosts/vectors/ reservoirs of infections 1933 – commercial air travel 1981 – pandemic spread of acute haemorrhagic conjunctivitis Epidemics of meningococcal meningitis during the Hajj Epidemic SARS (a newly emerging disease) from China to elsewhere worldwide

FIGURE 3. Probable cases of severe acute respiratory syndrome (SARS) with onset of illness from 1 November 2002 to 31 July 2003.

FIGURE 4 | The severe acute respiratory syndrome (SARS) pandemic and important findings.

FIGURE 5 | Schematic representation of the severe acute respiratory syndrome coronavirus (SARS-CoV) particle.

Infectious agents Malaria –Plasmodium falciparum was thought to be eradicated because of the effective use of DDT insecticide –But mosquito gain resistance Tuberculosis –Isoniazid was initially effective to cure TB –By 1980s, the era of HIV/AIDS, increased immune deficiencies of people, increases the risk of latent M. tuberculosis –Also the fact that TB is a disease of poverty – crowding, inadequate hygiene Staphylococcus aureus –Drug-resistant organism –Sulpha drugs 1940s  penicillin 1950s  methicillin 1980s  vancomycin 2002

Re-emerging vector-borne diseases Flavivirus which caused dengue – vector Aedes aegypti mosquitoes – epidemic in Hawaii – dengue has recently been transmitted by Aedes albopictus, which spreads into areas where A. aegypti are not found and persisting for longer seasonal periods

Influenza A Was known as endemic gastrointestinal viruses of wild waterfowl, now has jump species into domestic fowl, farm animals and humans Antigenic changes in haemagglutinin and neurominidase glycoproteins – ‘shifts’ (major antigenic changes in HA or NA) Deadly pandemics has occurred in 1888, 1918, 1957 and 1968

FIGURE 6. Documented human infections with avian influenza viruses, 1997–2004.

Infectious diseases on the rise Global spread of AIDS Resurgence of tuberculosis Appearance of new enemies (hantavirus, pulmonary syndrome, hepatitis C and E, Ebola virus, Lyme disease, cryptosporidiosis and E. coli O157:H7 Bird flu which attacks the Southeast Asia Prion disease of Creutzfeldt-Jakob disease Antibiotic resistance Staphylococcus bacteria Several major multistate foodborne outbreaks A new strain of drug resistance tuberculosis

FIGURE 7 | Generic model of the organization of a rapid research response to an emerging infectious disease.

Reference Morens DM, Folkers GK and Fauci AS (2004) The challenge of emerging and re-emerging infectious diseases. Nature 430: Prescott. Chapter Brooks Chapter 29 pages only. Emerging and Re-emerging Infectious Diseases: the Perpetual Challenge uci.html uci.html