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CHAPTER 10

The Resurgence of Infectious Diseases

HIV/AIDS

Was first recognized in the U.S. in 1981

Is now a worldwide killer

Is caused by a retrovirus

Attacks the immune system

Screening test recognizes antibodies.

We can measure viruses in the blood.

Now many drugs are available but no cure.

HIV/AIDS Transmission

Sexual contact:

Homosexual

Most common in U.S.

Heterosexual

Most common around the world

Sharing needles:

Intravenous drug use

Medical use of unsterile needles

HIV/AIDS Transmission (cont.)

Mother to infant

Prenatal or during birth

Breastfeeding

Blood transfusions

No longer in the U.S.

Circumcision helps protect men against contracting HIV from women, but it doesn’t protect women from contracting it from men.

HIV/AIDS Treatments

Highly active antiretroviral therapy (HAART), a drug combination, led to dramatic improvements in survival rates.

Reduces viral load to undetectable levels in blood and body fluids

Encourages infected people to be tested and treated, preventing transmission

Fusion inhibitors

Integrase inhibitors

Where Did HIV Originate?

Probably originated in Africa

Transmitted cross-species from monkeys or apes

Spread in human populations due to disruption of traditional lifestyles

Spread to Western countries due to changing patterns of sexual behavior and international travel

Other Emerging Viruses

Ebola

Monkeypox

Zika

Other hemorrhagic fevers

West Nile virus

SARS

Factors That Lead to Emergence of New Infectious Diseases

Human activities that cause ecological damage and close contact with wildlife

Modern agricultural practices

International travel

International distribution of food and exotic animals

Breakdown of social restraints on sexual behavior and intravenous drug use

Influenza

Influenza is an RNA virus like HIV.

Virus is constantly mutating.

Vaccine must be changed frequently.

New lethal strains appear periodically.

Epidemic of 1918–1919 killed 20 million to 40 million worldwide.

Bird flu and H1N1 are concerns.

New Bacterial Threats

Legionnaires’ disease

Lyme disease

Group A streptococci

E. coli O157:H7 in food

Antibiotic resistance

From improper medical use

Use in agriculture

MRSA

Tuberculosis

TB is the leading cause of infectious-disease death worldwide.

One third of the world population is infected.

There was a resurgence in the U.S. in the early 1990s.

People with HIV are at much higher risk.

TB is transmitted by aerosol.

Fatality rate is 50% for untreated TB.

Tuberculosis (cont.)

Antibiotics are effective but must be taken for several months.

Improper use of antibiotics leads to resistance, including multidrug resistance.

Then, mortality rate can exceed 50%.

Directly observed therapy works.

It is the best approach for preventing antibiotic resistance.

In 2007, the CDC revised its requirements for overseas medical screening of applicants for immigration to the U.S.

Prions

Creutzfeldt–Jakob Disease (CJD)

Sporadic CJD is most common.

CJD usually appears in later life.

Bovine spongiform encephalopathy (BSE) or “mad cow disease” has a history in Britain.

New variant of CJD (vCJD) in the UK in younger people is thought to be caused by eating infected beef.

Regulations have been tightened on animal feed.

Gerstmann–Straussler–Scheinker syndrome

Fatal familial insomnia

Kuru

Public Health Response to Emerging Infections

Global surveillance

Improved public health capacity

Veterinary surveillance

Reduction of inappropriate use of antibiotics

Institute of Medicine recommendations:

New vaccines

New antimicrobial drugs

Measures against vector-borne diseases

Threat of Bioterrorism

Approach to bioterrorism is the same as that for natural disease outbreaks.

Bioterrorism will probably first be recognized by surveillance.

First signs of an attack are likely to be seen by physicians and hospital emergency room staff.

It is best defended against by the same methods as natural outbreaks.

Discussion Question 1

Consider the spread of the following emerging infectious diseases, using the chain of infection: E. coli O157:H7, Lyme disease, Ebola virus, hantavirus, influenza, tuberculosis, vCJD.

For each disease, explain how the chain of infection can be interrupted.

Discussion Question 2

What are the reasons for the rapid emergence of AIDS as a worldwide epidemic?

Discussion Question 3

What are three public health measures that could reduce the probability that bacteria will develop resistance to antibiotics?

Discussion Question 4

Visit the website of the National Institute of Allergy and Infectious Diseases, www.niaid.nih.gov.

Under “News & Events,” review the news releases over the past year.

On what diseases has the Institute released news about progress in research?

Discussion Question 5

Visit the website of the CDC’s journal, Emerging Infectious Diseases, www.cdc.gov/ncidod/eid.

What emerging diseases are discussed in the current issue?