Lecture 19 : Re-Emerging Infectious Diseases Overview

1. Lecture 19 : Re-Emerging Infectious DiseasesOverview ANTIBIOTIC RESISTANT BACTERIA Staphylococcus aureus Streptococci pyrogenes Pneumonoccus Enterococcus faecium Clostridium difficile RE-EMERGING DISEASES Malaria Tuberculosis Yellow Fever Cholera Bubonic Plague

2. Staphlyococcus aureus

3. Staphylococcus Aureus • Staphylococcus aureus is very common, but also very deadly if it gets into the blood stream. • It was formerly a major cause of death following surgery. • Penicillin proved to be very effective. • When penicillin began to fail in 1950s, methicillin proved effective. • Methicillin resistant strains were identified in 1961 but did not become common until the 1990s (MRSA). • Vancomycin was an effective drug of last resort, but VRSA was reported in the late 1990s. • About 2 billion people worldwide carry Staph A. and about 50 million carry MRSA.

4. Streptococcus pyrogenes

5. Streptococcus Pyrogenes • Streptoccus pyrogenes was cause of scarlet fever, rheumatic fever, and puerperal fever but more or less vanished by 1960. • Displaced by Strep B. • Reappeared in 1989. Causes necrotizing fasciitis – the ‘flesh eating bug’. Can only be stopped by amputation. • Still susceptible to penicillin, but resistant to macrolides (e.g. Erythromycin).

6. Streptococcus pneumoniae

7. Other Resistant Bacteria • Penicillin resistant Pneumococcus was discovered in Spain in 1980s. Became resistant to cephalosporin antibiotics in US in 1990s. Still responds to vancomycin. • Enterococcus faeciumdeveloped a Vancomycin resistant form (VRE) in 1989. It is now resistant to all antibiotics. • Severe diarrhoea in patients on antibiotics caused by Clostridium difficile. At least two fatal epidemics in the community. Developing resistance to quinolones. • Broad-spectrum antibiotics may also kill commensals (i.e. beneficial bacteria) which help keep the pathogenic bacteria in check (e.g. Candida albicans).

8. Clostridium difficile

9. Synopsis • Drug resistent bacteria in the developed world mostly evolved in hospitals: • Antibiotics; • Immune compromised patients; • Cutbacks in hospital spending. • Although still largely confined to hospitals, there have been several outbreaks in communities. • They now kill more Americans than AIDS and breast cancer combined.

10. Re-Emerging Infectious Diseases • Most of the victims of antibiotic resistent bacteria in developed countries are sick people in hospitals. • Some infectious diseases that strike down otherwise healthy people in the general population are also posing a renewed threat for similar reasons. • However, the impact is mostly (although not exclusively) felt in the Third World.

11. Malaria • US-funded global campaign 1958-63. Outcry against DDT following Rachel Carson’s Silent Spring. • Mosquitoes developed resistance to DDT used in agriculture in Third World countries. • Resistance to chloroquine was noticed in southern Asia in the 1950s. By the 1960s some strains of Plasmodium falciparum had developed resistance to the 4 main anti-malarial drugs. • A new drug, mefloquine, was adopted in the 1970s, but resistant strains of falciparum emerged by the 1980s. • Strains of falciparum in Thailand have evolved an enzyme which expels all hostile chemicals, making it resistant to drugs that have not even been invented.

13. Tuberculosis(1) • Tuberculosis caused 1 billion deaths in 19th and 20th centuries. • Declined in developed countries, but it has been on the increase since the 1980s. It is the main pathogenic cause of death worldwide. • Many people carry the bacillus but do not develop symptoms unless their immune system is compromised. • The resurgence in tuberculosis is associated with HIV infection. • Once they develop symptoms, they can infect other people.

14. Tuberculosis(2) • The problem is compounded by the emergence of drug resistant strains, due to patients not completing antibiotic courses. • In 1980 50 per cent of TB bacilli were resistant to 1 drug. • Multi-drug resistant TB (MDR-TB) began to emerge. There are now an estimated 1.5m MDR cases worldwide. • Extreme drug resistance (XDR-TB) was reported in 2006. • The first completely drug resistant (CDR-TB) case was reported in Italy in 2007.

15. Yellow Fever • Yellow fever was formerly a jungle disease, but it is now endemic in Latin American cities. • Aedes aegypti is actually more common in North America, prompting fears that yellow fever could become endemic if there was a sufficient reservoir of infection.

16. Yellow fever – endemic regions

17. Cholera • There were no new pandemics for most of the 20th century, but the 7th pandemic began in the 1960s (the O1-El Tor strain). It spread to Latin America in the 1980s. Developed countries have so far escaped. • An even more virulent strain (O139) has emerged in the Sea of Bengal. This may be the beginnings of 8th pandemic. There is no guarantee that developed countries will escape.

18. Endemic Cholera Areas ca. 2004

19. Bubonic Plague • A bubonic plague epidemic in India in 1994 infected 2,500. Fortunately it had low virulence and was amenable to tetracycline. • Bubonic plague is endemic in the US, but only in ground burrowing rodents. Introduced in 1900 in San Fransisco during the 3rd pandemic. Has been spreading east ever since.

20. Conclusion • The re-emerging old infectious diseases have made relatively little impact upon the public imagination in DCs because either they affect only a small number of people, many of whom are already sick (e.g. MRSA) or poor (e.g. TB), or else they are 'out there' in the Third World where 'life is cheap' and 'these things happen'. • However, given the rapid development of drug-resistant strains, coupled with rapid air transportation, it may be only a matter of time before one of our ghosts from the past come back to haunt us.