Infectious Diseases (College Board AP® Environmental Science): Study Guide

Plague is a rare disease carried by organisms infected with the plague bacteria Yersinia pestis

It is transferred to humans via:

• the bite of an infected organism (usually fleas)

• through contact with contaminated fluids or tissues

• inhaling respiratory droplets from an infected person or animal

The bacteria can survive in a wide range of temperatures, but it dies quickly if exposed to temperatures above 40 °C

Exposureto UV light kills the bacteria quickly

The bacteria can persist in the soil or water

Bubonic

• Characterized by swollen and painful lymph nodes, or 'buboes', fever, chills, and weakness

Septicemic

• This occurs when the 'buboes' burst and the infection spread through the bloodstream, causing organ failure and death

Pneumonic

• Pneumonic is the most deadly but rarest form

• Caused when bacteria spread to the lungs from untreated bubonic or septicemic plague

• It spreads through inhaling infectious droplets from coughs and sneezes

The condition can be treated with quick diagnosis and antibiotic therapy

Recovery rates are high if detected and treated in time

• Usually within 24 hours of the onset of symptoms 

Although plague is rare, it still occurs in rural Africa, Asia, and South America

Improved cleanliness, rodent control, and disease education can prevent outbreaks

Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis

It primarily affects the lungs but can spread to other parts of the body

It spreads through:

• Inhaling respiratory droplets from an infected person’s coughs or sneezes

• Contact with contaminated surfaces is less common but possible in rare cases

TB bacteria can survive in dried sputum for weeks, particularly in cool, dark environments

Exposure to UV light and heat kills the bacteria relatively quickly

Latent TB

• The bacteria remain inactive in the body and cause no symptoms

• People with latent TB are not contagious

Active TB

• Causes cough (sometimes with blood), chest pain, fever, night sweats, and weight loss

• Highly contagious through respiratory droplets

TB can be treated with a combination of antibiotics taken over 6 to 9 months

Directly Observed Therapy (DOT) helps ensure patients complete treatment

Drug-resistant strains require longer treatment with specialized medications

TB remains a global health threat, particularly in parts of Africa, Asia, and Eastern Europe

Poor healthcare access, crowded living conditions, and weakened immune systems contribute to outbreaks

Vaccination (BCG) offers some protection, especially for children

Malaria is a parasitic disease caused by Plasmodium species, transmitted through the bite of infected female Anopheles mosquitoes

It cannot be spread directly from person to person

Transmission routes include:

• Mosquito bites

• Blood transfusions from infected donors

• Sharing contaminated hypodermic needles

The parasite thrives in warm, tropical climates where mosquitoes breed

Stagnant water and poor sanitation contribute to mosquito breeding grounds

Uncomplicated malaria

• Fever, chills, headache, muscle aches, nausea, and fatigue

• Symptoms follow a cyclic pattern based on the parasite’s lifecycle

Severe malaria

• Can cause organ failure, seizures, severe anemia, and death

• More common with Plasmodium falciparum infections

Treatment depends on the species and severity of infection

Antimalarial drugs like artemisinin-based combination therapies (ACTs) are effective

Prompt diagnosis and treatment improve survival rates

Malaria is most common in tropical and subtropical regions, including sub-Saharan Africa, Southeast Asia, and parts of South America

Prevention strategies include mosquito nets, insecticides, and antimalarial drugs for travelers

West Nile virus (WNV) is a mosquito-borne virus that can infect humans, birds, horses, and other animals

It spreads through:

• Bites from infected mosquitoes

• Blood transfusions, organ transplants, and from mother to baby (rare)

The virus can survive in infected birds and mosquitoes, particularly in warm climates

WNV is not spread through casual human contact

West Nile fever

• Mild symptoms include fever, headache, body aches, and rash

Severe West Nile disease

• Causes inflammation of the brain (encephalitis) or spinal cord (meningitis)

• Symptoms include high fever, confusion, muscle weakness, seizures, and paralysis

There is no specific antiviral treatment

Supportive care includes fluids, pain relief, and hospitalization for severe cases

The virus was first identified in the West Nile district of Uganda in 1937

WNV has since spread to parts of North America, Europe, Africa, the Middle East, and Asia

Prevention focuses on mosquito control and avoiding bites

Severe Acute Respiratory Syndrome (SARS) is a viral respiratory illness caused by SARS-CoV-1 (the first identified strain of the SARS-related coronavirus)

It spreads through:

• Respiratory droplets from coughs or sneezes

• Contact with contaminated surfaces or objects

The virus survives longer in cool, dry environments but is destroyed by heat and disinfectants

Respiratory illness

• Fever, cough, shortness of breath, body aches, and pneumonia

Some cases progress to severe respiratory failure

There is no specific antiviral treatment

Supportive care includes oxygen therapy, mechanical ventilation, and managing complications

Experimental treatments were used during outbreaks

SARS originated in China in 2002 and caused a global outbreak in 2003

No known natural cases have occurred since 2004

Prevention includes infection control, surveillance, and quarantine measures

Middle East Respiratory Syndrome (MERS) is a viral respiratory illness caused by MERS-CoV (another strain of coronavirus)

It spreads through:

• Respiratory droplets

• Contact with infected camels or contaminated surfaces

The virus is stable in cool, dry environments but killed by heat and disinfectants

Respiratory illness

Fever, cough, shortness of breath, and pneumonia

Severe cases progress to organ failure

No specific antiviral treatment exists

Supportive care includes oxygen therapy, mechanical ventilation, and managing complications

MERS was first identified in Saudi Arabia in 2012

Most cases occur in the Arabian Peninsula, with limited transmission elsewhere

Prevention focuses on avoiding contact with camels and enhancing infection control

Zika virus is a mosquito-borne virus primarily spread by Aedes mosquitoes

It can also spread through:

• Sexual contact

• Blood transfusions

• From pregnant mother to baby (congenital transmission)

The virus is stable in warm, humid environments where mosquitoes thrive

Most infections are asymptomatic

Mild illness

• Fever, rash, joint pain, and red eyes

Congenital Zika syndrome

• Causes birth defects such as microcephaly when pregnant women are infected

There is no specific antiviral treatment

Supportive care includes rest, fluids, and pain relief

Zika was first identified in Uganda in 1947, but it wasn't until 2007 that it caused its first known outbreak on the island of Yap in Micronesia

Zika outbreaks have spread to the tropical areas of the Americas, Africa, Asia, and the Pacific

Prevention focuses on mosquito control and avoiding mosquito bites

Pregnant women are advised to avoid travel to outbreak areas

Cholera is a bacterial infection caused by Vibrio cholerae

It spreads through:

• Consumption of contaminated water or food

• Direct contact with contaminated feces (fecal-oral transmission)

The bacteria thrive in brackish water and areas with poor sanitation

Mild to moderate cholera

• Watery diarrhea, nausea, and vomiting

Severe cholera

• Profuse watery diarrhea, severe dehydration, and shock

• Can be fatal without rapid treatment

Prompt rehydration therapy is critical, including oral rehydration salts or IV fluids

Antibiotics can reduce severity and duration in severe cases

Cholera outbreaks occur in areas with inadequate water treatment and sanitation, especially in parts of Africa, South Asia, and Haiti

Prevention focuses on clean water access, proper sanitation, and vaccination in high-risk areas