Emerging and Re-Emerging Infectious Diseases¶
Chapter 486 | Part 17: Global Medicine
KEY CLINICAL POINTS¶
- Emerging Infectious Diseases (EIDs) are newly recognized pathogens, while Re-Emerging Infectious Diseases (REIDs) are previously known pathogens reappearing due to environmental, societal, or biological factors.
- Historical pandemics like the Justinian plague (544 AD), Black Death (1347–1349 AD), and 1918 H1N1 influenza highlight the long-standing impact of EIDs on global health.
- Mechanisms of emergence include zoonotic spillover, environmental degradation, antibiotic resistance, and viral evolution via mutation and reassortment.
- Clinicians must recognize EIDs through epidemiologic patterns, atypical presentations, and collaboration with public health systems.
- Global preparedness, surveillance, and rapid response are critical to mitigating EID outbreaks and preventing pandemics.
1. DEFINITION & OVERVIEW¶
Emerging infectious diseases (EIDs) are pathogens newly recognized in humans, while re-emerging infectious diseases (REIDs) are previously known pathogens reappearing due to environmental, societal, or biological factors. EIDs and REIDs are distinct but interconnected phenomena, often driven by ecological, demographic, and socioeconomic changes. The chapter emphasizes the historical context of pandemics and the modern challenges of controlling EIDs.
Table 486-1: Emerging and Re-Emerging Infectious Diseases¶
| Category | Definition | Examples |
|---|---|---|
| Emerging Infectious Diseases (EIDs) | Newly recognized pathogens in humans | HIV/AIDS, SARS, Nipah virus, COVID-19 |
| Re-Emerging Infectious Diseases (REIDs) | Previously known pathogens reappearing | Polio, cholera, influenza, antibiotic-resistant TB |
| Subcategories of REIDs | Accidental release | Vaccine-derived poliovirus, 1979 Sverdlovsk anthrax outbreak |
| Subcategories of REIDs | Intentional harm (bioterrorism) | 2001 anthrax attacks, Oregon salad bar poisonings |
Table 486-2: Selected Emerging Infectious Diseases of Note¶
| Year | Name | Deaths | Comments |
|---|---|---|---|
| 430 BCE | Plague of Athens | ~100,000 | First transregional pandemic |
| Year | Name | Deaths | Comments |
|---|---|---|---|
| 541 AD | Justinian plague (Yersinia pestis) | 30–50 million | Killed half of the known world population |
| 1340s | Black Death (Yersinia pestis) | ~50 million | Killed at least one-quarter of the world population |
| 1494 | Syphilis (Treponema pallidum) | >50,000 | Pandemic brought to Europe from the Americas |
| c. 1500 | Tuberculosis | High millions | Ancient disease; became pandemic in the Middle Ages |
| 1520 | Hueyzahuatl (Variola major) | 3.5 million | Pandemic brought to New World by Europeans |
| 1793–1798 | The American plague | ~25,000 | Yellow fever terrorized colonial America |
| 1832 | Second cholera pandemic (Paris) | 18,402 | Spread from India to Europe/Western Hemisphere |
| 1918 | Spanish influenza | ~50 million | Led to additional pandemics in 1957, 1968, 2009 |
| 1976–2020 | Ebola | More than 15,000 deaths | First recognized in 1976; 29 regional epidemics to 2020 |
| 1981 | HIV/AIDS | >40 million | Ongoing pandemic |
| 2002 | SARS | 774 | Near-pandemic |
| 2009 | H1N1 'swine flu' | 284,000 | Fifth influenza pandemic in less than 100 years |
| 2014 | Chikungunya | Uncommon but high morbidity | Pandemic, mosquito-borne |
| 2015 | Zika | ~1000? | Pandemic, mosquito-borne |
1.1 Classification of EIDs and REIDs¶
EIDs include pathogens like HIV, SARS-CoV-2, and Nipah virus. REIDs include pathogens like polio, cholera, and influenza, which re-emerge due to factors such as antibiotic resistance, environmental changes, or human behavior. Subcategories of REIDs include accidental release (e.g., vaccine-derived poliovirus) and intentional harm (e.g., bioterrorism).
1.2 Historical Context¶
EIDs have shaped human history, with pandemics like the Justinian plague (544 AD), Black Death (1347–1349 AD), and 1918 H1N1 influenza causing massive mortality. Modern EIDs include HIV/AIDS, SARS, MERS, and COVID-19, reflecting ongoing global health challenges.
2. EPIDEMIOLOGY¶
EIDs and REIDs have significant global impact, with historical pandemics causing millions of deaths. Modern EIDs like HIV/AIDS, SARS, and MERS reflect ongoing challenges. REIDs such as polio, cholera, and antibiotic-resistant TB re-emerge due to environmental, socioeconomic, and biological factors. The Global Burden of Disease Study highlights the persistent threat of EIDs.
2.1 Risk Factors¶
Key risk factors include poverty, environmental degradation, antibiotic misuse, climate change, and human-animal interactions. Crowding, poor sanitation, and inadequate public health infrastructure exacerbate the spread of EIDs and REIDs.
2.2 Demographics¶
EIDs disproportionately affect low-income populations, with regions like sub-Saharan Africa and South Asia experiencing higher burdens. REIDs such as cholera and tuberculosis are more prevalent in areas with poor sanitation and limited healthcare access.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
EIDs arise from zoonotic spillover, environmental changes, and viral evolution. REIDs re-emerge due to antibiotic resistance, ecological disruption, or human behavior. Pathogens like influenza and coronaviruses adapt to new hosts through mutations and reassortment, leading to pandemics.
3.1 Zoonotic Transmission¶
Many EIDs originate from animal reservoirs, such as bats (SARS-CoV, Nipah virus) and rodents (Hantavirus). Deforestation, farming practices, and wildlife trade increase human-animal contact, facilitating spillover events.
3.2 Viral Evolution¶
RNA viruses like influenza and coronaviruses evolve rapidly through mutation and reassortment. This enables them to escape immunity and adapt to new hosts, as seen in the emergence of SARS-CoV-2 and the periodic re-emergence of influenza pandemics.
4. CLINICAL FEATURES¶
EIDs and REIDs present with varied symptoms, including fever, respiratory distress, and neurological complications. Atypical presentations, such as dengue hemorrhagic fever or HIV-associated opportunistic infections, require careful differentiation from other diseases.
4.1 Common Presentations¶
Symptoms include fever, fatigue, respiratory symptoms, and gastrointestinal issues. Severe cases may involve shock (dengue shock syndrome), encephalitis (Japanese encephalitis), or multi-organ failure (HIV/AIDS).
4.2 Atypical Features¶
EIDs often present with non-specific symptoms, such as unexplained fever or rash. REIDs may exhibit recurrent or relapsing patterns, such as antibiotic-resistant TB or periodic cholera outbreaks.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnosis includes other infectious diseases with similar presentations, such as malaria, dengue, and viral hepatitis. Clinicians must consider geographic prevalence, travel history, and exposure risks to distinguish EIDs from common infections.
5.1 Key Differentiators¶
EIDs often lack established diagnostic markers, requiring epidemiologic and clinical correlation. REIDs may have known pathogens but present with atypical features, such as drug-resistant strains or unusual transmission patterns.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic approaches include molecular testing (PCR), serology, and imaging. Surveillance systems and public health reporting are critical for early detection. Laboratory confirmation and epidemiologic data guide outbreak response.
6.1 Diagnostic Criteria¶
Molecular testing (e.g., RT-PCR) is used for viral EIDs like SARS-CoV-2. Serology detects antibodies for REIDs such as dengue or HIV. Imaging (e.g., chest X-ray) aids in diagnosing complications like pneumonia.
6.2 Surveillance Systems¶
Global surveillance networks like the WHO and GBD Study track EID trends. Early detection relies on reporting systems, case clustering analysis, and real-time data sharing between clinicians and public health agencies.
7. MANAGEMENT & TREATMENT¶
Treatment involves antivirals, antibiotics, and supportive care. Public health measures like quarantine, vaccination, and vector control are essential. Research into universal vaccines and antiviral therapies remains a priority.
7.1 Pharmacologic Interventions¶
Antivirals (e.g., oseltamivir for influenza, remdesivir for COVID-19) and antibiotics (e.g., for bacterial co-infections) are used. HIV is managed with antiretroviral therapy (ART), while antibiotic-resistant TB requires prolonged multidrug regimens.
7.2 Public Health Measures¶
Isolation, contact tracing, and vaccination programs are critical. Vector control (e.g., mosquito eradication for dengue) and hygiene education reduce transmission. Global initiatives like PEPFAR and GAVI support EID control.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by disease, with severe EIDs like Ebola or dengue shock syndrome having high mortality. Complications include secondary infections, organ failure, and long-term sequelae (e.g., post-COVID-19 syndrome).
8.1 Mortality Rates¶
Historical pandemics (e.g., 1918 influenza) had mortality rates up to 30%, while modern EIDs like HIV/AIDS have lower mortality with ART. REIDs like antibiotic-resistant TB have higher mortality due to drug resistance.
8.2 Long-Term Effects¶
Chronic complications include HIV-associated opportunistic infections, post-COVID-19 lung damage, and neurocognitive deficits from dengue or Zika. Early intervention improves outcomes.
9. SPECIAL CONSIDERATIONS¶
Pregnancy, pediatrics, and the elderly are at higher risk for severe EID outcomes. Specialized care is required for vulnerable populations, with tailored prevention strategies to mitigate transmission and complications.
9.1 Pregnancy¶
Pregnant women are at increased risk for severe outcomes from EIDs like Zika (congenital malformations) and influenza (preterm birth). Vaccination and antiviral prophylaxis are recommended.
9.2 Pediatrics¶
Children are susceptible to severe REIDs like dengue and measles. Vaccination programs and early detection are critical to prevent outbreaks in pediatric populations.
10. KEY POINTS & CLINICAL PEARLS¶
- EIDs and REIDs are driven by ecological, socioeconomic, and biological factors. 2. Historical pandemics like the Black Death and 1918 influenza underscore the need for global preparedness. 3. Clinicians must integrate epidemiologic data with clinical findings to diagnose EIDs. 4. Public health collaboration and rapid response are essential to mitigate outbreaks. 5. Research into universal vaccines and antivirals is critical for future EID control.