Naming the likely agent from fever, timing, source and who got sickest
Almost every case study on a Disease Detectives test asks you to name the likely agent, and plenty of standalone questions do too: "acquired after petting tortoises or chickens," "unpasteurized milk or soft cheeses, dangerous for pregnant people and newborns." You won't be given the organism's name. You'll be given its clues, and a list of answer choices that look alike on purpose.
Read the clues in this order. Each one cuts the list of suspects down before you get to the next:
No fever plus vomiting within a few hours points to a toxin already in the food (Staph, B. cereus), not an infection that needs time to grow.
Hours, days, weeks or months? The incubation ladder below sorts the core suspects by exactly this.
Food, water, an animal, a bite, or another person? Petting a turtle, eating undercooked chicken and skinning a rabbit point to three different agents.
Pregnant people and newborns, young children, older adults, hunters, travelers: the high-risk group is often the final tie-breaker.
Each bar runs from the shortest to the longest typical incubation period, on a stretched time scale so hours and years fit on one chart. Toxins cluster on the far left; the slowest agents (rabies, prions) sit on the far right.
These are the groups tests like to put side by side as answer choices. For each one, find the single clue that splits them apart.
Petting vs. eating vs. skinning
| SalmonellosisSalmonella (non-typhoidal) | CampylobacteriosisCampylobacter jejuni | TularemiaFrancisella tularensis | |
|---|---|---|---|
| Timing | 6 hours to 6 days (usually 12 to 72 hours) | 2 to 5 days | 3 to 5 days (1 to 14) |
| Fever | Usually | Usually | Usually |
| Source | Undercooked poultry and eggs; contact with reptiles (turtles, tortoises, lizards) and live poultry (chicks, ducklings) | Undercooked poultry, raw milk, untreated water, cross-contamination from raw chicken | Handling infected rabbits or rodents (hunting, skinning); tick and deer fly bites |
| Key symptoms | diarrhea; fever; abdominal cramps | diarrhea (often bloody); cramping; fever | skin ulcer where bacteria entered; swollen lymph nodes; fever |
| Most at risk | Young children, older adults, people who handle reptiles or backyard poultry | Anyone who eats undercooked chicken; rare link to Guillain-Barre syndrome | Hunters, landscapers (mowing over animal carcasses) |
| The tell | Fever plus a poultry, egg or reptile link. Petting a turtle or baby chick is a classic exposure. | Eating (not petting) undercooked chicken. A leading bacterial cause of diarrhea in the U.S. | Skin ulcer and swollen glands after skinning a wild rabbit. |
Soft cheese and pregnancy vs. raw goat milk and a wave-like fever vs. undercooked beef and bloody diarrhea
| ListeriosisListeria monocytogenes | BrucellosisBrucella | STEC infectionE. coli O157:H7 (STEC) | |
|---|---|---|---|
| Timing | Usually within 2 weeks (same day to 10 weeks); the stomach form within a day | 1 to 4 weeks (can be months) | 1 to 10 days (usually 3 to 4) |
| Fever | Usually | Usually | No or minimal |
| Source | Soft cheeses (queso fresco, brie), unpasteurized milk, deli meats, hot dogs, cut melon; grows in the refrigerator | Unpasteurized milk and cheese from infected goats, sheep or cows; contact with livestock | Undercooked ground beef, raw (unpasteurized) milk and juice, contaminated leafy greens, petting zoos |
| Key symptoms | fever; muscle aches; sometimes diarrhea | fever that comes and goes (undulant fever); sweats; joint pain | severe stomach cramps; watery diarrhea turning bloody; little or no fever |
| Most at risk | Pregnant people, newborns, adults over 65, people with weakened immune systems | Farmers, veterinarians, slaughterhouse workers, people who drink raw goat milk | Young children and older adults (risk of hemolytic uremic syndrome, HUS) |
| The tell | Soft cheese or deli meat plus pregnancy or a newborn. It can grow at refrigerator temperature. | Undulant (wave-like) fever after raw goat or sheep milk, or working with livestock. No special pregnancy link on tests. | Bloody diarrhea with little fever after undercooked ground beef. Kidney failure (HUS) in children. |
All within hours: pastries vs. fried rice vs. gravy
| Staphylococcal food poisoningStaphylococcus aureus (toxin) | B. cereus food poisoningBacillus cereus | C. perfringens food poisoningClostridium perfringens | |
|---|---|---|---|
| Timing | 30 minutes to 8 hours (usually 2 to 4) | 30 minutes to 6 hours (vomiting type); 6 to 15 hours (diarrheal type) | 6 to 24 hours |
| Fever | No or minimal | No or minimal | No or minimal |
| Source | Foods handled by people and left warm: cream pastries, ham, potato and egg salads | Cooked rice left at room temperature, then reheated ("fried rice syndrome") | Large batches of meat, poultry and gravy cooled too slowly (banquets, cafeterias) |
| Key symptoms | sudden, forceful vomiting; nausea; cramps | sudden vomiting; nausea; watery diarrhea | watery diarrhea; abdominal cramps; little vomiting or fever |
| Most at risk | Anyone; comes from food handlers | Anyone | People at catered events and institutions |
| The tell | Vomiting within a few hours, no fever. The heat-stable toxin survives reheating. | Reheated fried rice. Spores survive cooking and make toxin when rice sits out. Two kinds: the vomiting type comes from a toxin already made in the food (30 minutes to 6 hours); the diarrhea type happens when the bacteria make toxin after they reach the intestines (6 to 15 hours). | Big-batch meat or gravy at a banquet; diarrhea and cramps, rarely vomiting. People get sick after eating a large number of the bacteria (they multiply in food cooled too slowly), which then make toxin in the intestines. |
Breakbone pain vs. microcephaly vs. jaundice vs. cyclic fever from a protozoan
| Dengue feverDengue virus | Zika virus diseaseZika virus | Yellow feverYellow fever virus | MalariaPlasmodium | |
|---|---|---|---|---|
| Timing | 4 to 10 days (usually 4 to 7) | 3 to 14 days | 3 to 6 days | 7 to 30 days (can be longer) |
| Fever | Usually | Sometimes | Usually | Usually |
| Source | Bite of Aedes mosquitoes (daytime biters); tropics and subtropics | Bite of Aedes mosquitoes; also sexual transmission and mother to fetus | Bite of Aedes and Haemagogus mosquitoes in Africa and South America | Bite of female Anopheles mosquitoes (night biters) |
| Key symptoms | high fever; severe headache; pain behind the eyes | often no symptoms; mild fever; rash | fever; headache; muscle pain | cycles of fever, shaking chills and sweating; headache; anemia |
| Most at risk | Travelers to the tropics; a second infection can cause severe dengue | Pregnant people: a teratogen that causes microcephaly | Unvaccinated travelers; some countries require proof of vaccination | Young children and pregnant people in Africa; travelers without prophylaxis |
| The tell | "Breakbone fever" 4 to 7 days after an Aedes mosquito bite. | Mild or no illness in adults, but a teratogen: microcephaly in babies. | Mosquito-borne fever with jaundice, prevented by a travel vaccine. Named for the yellow skin. | Fever and chills that come in cycles after travel; a protozoan, not a virus. |
The 3 Cs and Koplik spots vs. a teratogen vs. blisters vs. puffy cheeks
| MeaslesMeasles virus | RubellaRubella virus | ChickenpoxVaricella-zoster virus | MumpsMumps virus | |
|---|---|---|---|---|
| Timing | 7 to 21 days (rash about 14 days after exposure) | About 14 days (12 to 23) | 10 to 21 days | 16 to 18 days (12 to 25) |
| Fever | Usually | Sometimes | Usually | Usually |
| Source | Airborne; lingers in a room for up to 2 hours; one of the most contagious diseases (R0 12 to 18) | Respiratory droplets | Airborne and direct contact with blisters; the virus can later reactivate as shingles | Respiratory droplets and saliva; outbreaks on college campuses and at sports teams |
| Key symptoms | high fever; cough, runny nose, red eyes (the 3 Cs); Koplik spots inside the cheek | mild rash starting on the face; low fever; swollen lymph nodes behind the ears | itchy blister-like rash appearing in crops; fever; tiredness | swollen, painful salivary glands (puffy cheeks and jaw); fever; headache |
| Most at risk | Unvaccinated people; prevented by the MMR vaccine | Pregnant people: infection early in pregnancy causes congenital rubella syndrome (a teratogen); prevented by MMR | Unvaccinated children; prevented by the varicella vaccine | People in close-contact settings; prevented by MMR |
| The tell | Cough, runny nose, red eyes, then Koplik spots and a head-to-toe rash. Extremely contagious. | A mild illness for most, but a teratogen during pregnancy. | Itchy blisters in different stages at once. Nothing to do with chickens. | Swollen cheeks and jaw (parotitis). |
Bullseye rash vs. skin ulcer vs. buboes
| Lyme diseaseBorrelia burgdorferi | TularemiaFrancisella tularensis | PlagueYersinia pestis | |
|---|---|---|---|
| Timing | 3 to 30 days | 3 to 5 days (1 to 14) | 2 to 8 days (bubonic) |
| Fever | Usually | Usually | Usually |
| Source | Bite of blacklegged (deer) ticks; Northeast and upper Midwest U.S. | Handling infected rabbits or rodents (hunting, skinning); tick and deer fly bites | Bites of fleas from infected rodents (prairie dogs, rats); pneumonic form spreads person to person |
| Key symptoms | expanding bullseye rash (erythema migrans); fever; fatigue | skin ulcer where bacteria entered; swollen lymph nodes; fever | sudden fever; very swollen, painful lymph nodes (buboes); chills |
| Most at risk | Hikers and people outdoors in wooded areas in late spring and summer | Hunters, landscapers (mowing over animal carcasses) | People in the rural western U.S. near prairie dogs and their fleas |
| The tell | Bullseye rash after a tick bite on a hike. | Skin ulcer and swollen glands after skinning a wild rabbit. | Buboes (huge swollen lymph nodes) after flea bites; caused the Black Death. |
The pathogens that come up most often, grouped by how they usually spread. Scroll the table sideways on a phone.
| Disease | Organism | Type | Incubation | Fever | Symptoms | Source | Most at risk | The tell |
|---|---|---|---|---|---|---|---|---|
| Foodborne | ||||||||
| Salmonellosis | Salmonella (non-typhoidal) | Bacterial | 6 hours to 6 days (usually 12 to 72 hours) | Usually | diarrhea; fever; abdominal cramps; occasional vomiting | Undercooked poultry and eggs; contact with reptiles (turtles, tortoises, lizards) and live poultry (chicks, ducklings) | Young children, older adults, people who handle reptiles or backyard poultry | Fever plus a poultry, egg or reptile link. Petting a turtle or baby chick is a classic exposure. |
| Typhoid fever | Salmonella Typhi | Bacterial | 6 to 30 days | Usually | sustained high fever; weakness; stomach pain; headache; rose-colored spots on the trunk | Food or water contaminated by a human carrier; common in travelers to South Asia | Travelers to areas with poor sanitation | Humans are the only reservoir. Chronic carriers like Typhoid Mary spread it through food they prepare. |
| STEC infection | E. coli O157:H7 (STEC) | Bacterial | 1 to 10 days (usually 3 to 4) | No or minimal | severe stomach cramps; watery diarrhea turning bloody; little or no fever | Undercooked ground beef, raw (unpasteurized) milk and juice, contaminated leafy greens, petting zoos | Young children and older adults (risk of hemolytic uremic syndrome, HUS) | Bloody diarrhea with little fever after undercooked ground beef. Kidney failure (HUS) in children. |
| Campylobacteriosis | Campylobacter jejuni | Bacterial | 2 to 5 days | Usually | diarrhea (often bloody); cramping; fever; occasional vomiting | Undercooked poultry, raw milk, untreated water, cross-contamination from raw chicken | Anyone who eats undercooked chicken; rare link to Guillain-Barre syndrome | Eating (not petting) undercooked chicken. A leading bacterial cause of diarrhea in the U.S. |
| Staphylococcal food poisoning | Staphylococcus aureus (toxin) | Toxin | 30 minutes to 8 hours (usually 2 to 4) | No or minimal | sudden, forceful vomiting; nausea; cramps; no fever | Foods handled by people and left warm: cream pastries, ham, potato and egg salads | Anyone; comes from food handlers | Vomiting within a few hours, no fever. The heat-stable toxin survives reheating. |
| B. cereus food poisoning | Bacillus cereus | Toxin | 30 minutes to 6 hours (vomiting type); 6 to 15 hours (diarrheal type) | No or minimal | sudden vomiting; nausea; watery diarrhea; abdominal cramps | Cooked rice left at room temperature, then reheated ("fried rice syndrome") | Anyone | Reheated fried rice. Spores survive cooking and make toxin when rice sits out. Two kinds: the vomiting type comes from a toxin already made in the food (30 minutes to 6 hours); the diarrhea type happens when the bacteria make toxin after they reach the intestines (6 to 15 hours). |
| C. perfringens food poisoning | Clostridium perfringens | Toxin | 6 to 24 hours | No or minimal | watery diarrhea; abdominal cramps; little vomiting or fever | Large batches of meat, poultry and gravy cooled too slowly (banquets, cafeterias) | People at catered events and institutions | Big-batch meat or gravy at a banquet; diarrhea and cramps, rarely vomiting. People get sick after eating a large number of the bacteria (they multiply in food cooled too slowly), which then make toxin in the intestines. |
| Botulism | Clostridium botulinum | Toxin | 12 to 72 hours (usually 18 to 36; rarely up to 10 days) | No or minimal | blurred or double vision; drooping eyelids; slurred speech; trouble swallowing; descending paralysis | Improperly home-canned foods; honey in infants under 1 year | Infants fed honey; people who eat home-canned vegetables | Paralysis that moves down the body, with no fever. Foodborne botulism comes from eating food that already contains the toxin, often improperly canned food. Infant botulism is different: babies swallow spores (honey can carry them), and the bacteria grow and make toxin inside the intestines, with symptoms days to weeks later. |
| Listeriosis | Listeria monocytogenes | Bacterial | Usually within 2 weeks (same day to 10 weeks); the stomach form within a day | Usually | fever; muscle aches; sometimes diarrhea; meningitis in high-risk people; miscarriage or stillbirth | Soft cheeses (queso fresco, brie), unpasteurized milk, deli meats, hot dogs, cut melon; grows in the refrigerator | Pregnant people, newborns, adults over 65, people with weakened immune systems | Soft cheese or deli meat plus pregnancy or a newborn. It can grow at refrigerator temperature. |
| Hepatitis A | Hepatitis A virus | Viral | 15 to 50 days (average 28) | Usually | jaundice (yellow skin and eyes); dark urine; fatigue; nausea; stomach pain | Food handled by an infected worker; contaminated produce or shellfish; fecal-oral | Unvaccinated people; restaurant customers of an infected food handler | Jaundice about a month after eating at a restaurant. Vaccine-preventable. |
| Waterborne & recreational water | ||||||||
| Cholera | Vibrio cholerae | Bacterial | 12 hours to 5 days | No or minimal | profuse watery "rice-water" diarrhea; severe dehydration; vomiting; little fever | Water or food contaminated with sewage; raw shellfish | Areas without clean water, especially after disasters | Rice-water diarrhea and fast dehydration from contaminated water. John Snow's disease. |
| Giardiasis | Giardia lamblia (duodenalis) | Parasitic | 1 to 3 weeks | No or minimal | greasy, foul-smelling diarrhea; gas; bloating; no blood or fever | Untreated stream or lake water ("beaver fever"); daycares | Hikers and campers who drink untreated water | Greasy, smelly diarrhea about 1 to 2 weeks after a camper drinks from a stream. |
| Cryptosporidiosis | Cryptosporidium | Parasitic | 2 to 10 days (average 7) | Sometimes | watery diarrhea; cramps; low fever; nausea | Swimming pools and water parks (resists chlorine); untreated water; calves | Swimmers, young children, people with weakened immune systems | Pool or splash pad outbreak; it survives normal chlorine levels. |
| Person-to-person | ||||||||
| Shigellosis | Shigella | Bacterial | 1 to 2 days (up to 7) | Usually | bloody, mucus-streaked diarrhea; high fever; stomach cramps | Person to person (fecal-oral), especially in daycares; very few bacteria needed | Children in daycare and their families | Spreads person to person in daycares because a tiny dose (10 to 100 bacteria) causes illness. |
| Norovirus infection | Norovirus | Viral | 12 to 48 hours | Sometimes | sudden, explosive vomiting; watery diarrhea; nausea; cramps; sometimes low fever | Person to person, contaminated food and surfaces; cruise ships, schools, nursing homes | Anyone in close quarters | Explosive vomiting in a crowded setting, over in 1 to 3 days. Hand sanitizer doesn't kill it well. |
| Respiratory / airborne | ||||||||
| Legionnaires' disease | Legionella pneumophila | Bacterial | 2 to 14 days | Usually | high fever; cough; shortness of breath; pneumonia; muscle aches | Inhaling mist from cooling towers, hot tubs, decorative fountains, building plumbing; NOT spread person to person | Adults over 50, smokers, people with chronic lung disease | Pneumonia among hotel guests or hospital patients near a cooling tower or hot tub. Not contagious. |
| Influenza | Influenza virus | Viral | 1 to 4 days (usually 2) | Usually | sudden fever; chills; cough; sore throat; body aches; fatigue | Respiratory droplets; seasonal winter epidemics; antigenic drift and shift | Adults over 65, young children, pregnant people, people with chronic conditions | Winter season, sudden fever and body aches. Antigenic shift causes pandemics. |
| Vaccine-preventable | ||||||||
| Measles | Measles virus | Viral | 7 to 21 days (rash about 14 days after exposure) | Usually | high fever; cough, runny nose, red eyes (the 3 Cs); Koplik spots inside the cheek; rash starting on the face and spreading down | Airborne; lingers in a room for up to 2 hours; one of the most contagious diseases (R0 12 to 18) | Unvaccinated people; prevented by the MMR vaccine | Cough, runny nose, red eyes, then Koplik spots and a head-to-toe rash. Extremely contagious. |
| Pertussis | Bordetella pertussis | Bacterial | 7 to 10 days (5 to 21) | Sometimes | cold-like start (runny nose, sneezing, mild fever); violent coughing fits; whooping sound when breathing in; vomiting after coughing | Respiratory droplets; vaccine immunity fades, so teens and adults spread it to babies | Infants too young to be fully vaccinated; prevented by DTaP and Tdap | Starts like a cold, then coughing fits with a 'whoop.' Most dangerous for babies. |
| Rubella | Rubella virus | Viral | About 14 days (12 to 23) | Sometimes | mild rash starting on the face; low fever; swollen lymph nodes behind the ears | Respiratory droplets | Pregnant people: infection early in pregnancy causes congenital rubella syndrome (a teratogen); prevented by MMR | A mild illness for most, but a teratogen during pregnancy. |
| Vector-borne | ||||||||
| West Nile virus disease | West Nile virus | Viral | 2 to 14 days | Usually | most infections cause no symptoms; fever, headache, body aches; rarely encephalitis or meningitis (stiff neck, confusion) | Bite of Culex mosquitoes; summer and early fall | Adults over 60 and people with weakened immune systems | Summer, dead birds, mosquitoes. About 8 in 10 infected people never feel sick. |
| Dengue fever | Dengue virus | Viral | 4 to 10 days (usually 4 to 7) | Usually | high fever; severe headache; pain behind the eyes; severe joint and muscle pain ("breakbone fever"); rash | Bite of Aedes mosquitoes (daytime biters); tropics and subtropics | Travelers to the tropics; a second infection can cause severe dengue | "Breakbone fever" 4 to 7 days after an Aedes mosquito bite. |
| Zika virus disease | Zika virus | Viral | 3 to 14 days | Sometimes | often no symptoms; mild fever; rash; joint pain; red eyes | Bite of Aedes mosquitoes; also sexual transmission and mother to fetus | Pregnant people: a teratogen that causes microcephaly | Mild or no illness in adults, but a teratogen: microcephaly in babies. |
| Malaria | Plasmodium | Parasitic | 7 to 30 days (can be longer) | Usually | cycles of fever, shaking chills and sweating; headache; anemia | Bite of female Anopheles mosquitoes (night biters) | Young children and pregnant people in Africa; travelers without prophylaxis | Fever and chills that come in cycles after travel; a protozoan, not a virus. |
| Lyme disease | Borrelia burgdorferi | Bacterial | 3 to 30 days | Usually | expanding bullseye rash (erythema migrans); fever; fatigue; joint pain later | Bite of blacklegged (deer) ticks; Northeast and upper Midwest U.S. | Hikers and people outdoors in wooded areas in late spring and summer | Bullseye rash after a tick bite on a hike. |
| Zoonotic (animal contact) | ||||||||
| Toxoplasmosis | Toxoplasma gondii | Parasitic | 5 to 23 days | Sometimes | often no symptoms; flu-like illness; swollen lymph nodes; birth defects if infected during pregnancy | Cat feces (litter boxes, garden soil); undercooked meat | Pregnant people (why they shouldn't change litter boxes); people with weakened immune systems | Cat litter box plus pregnancy. |
| Tularemia | Francisella tularensis | Bacterial | 3 to 5 days (1 to 14) | Usually | skin ulcer where bacteria entered; swollen lymph nodes; fever; chills | Handling infected rabbits or rodents (hunting, skinning); tick and deer fly bites | Hunters, landscapers (mowing over animal carcasses) | Skin ulcer and swollen glands after skinning a wild rabbit. |
| Rabies | Rabies virus | Viral | 1 to 3 months (days to more than a year) | Usually | fever and tingling at the bite site; agitation, confusion; fear of water (hydrophobia); almost always fatal once symptoms start | Bite or scratch from an infected mammal: bats (most U.S. deaths), raccoons, skunks, foxes, unvaccinated dogs | Anyone bitten; post-exposure prophylaxis given before symptoms prevents it | Animal bite, long incubation, hydrophobia, nearly 100% fatal once symptoms appear. |
Less common on tests, but they still show up in case studies and in Guess the Pathogen. Same clues, same order: fever, timing, source, who got sickest.
| Disease | Organism | Type | Incubation | Fever | Symptoms | Source | Most at risk | The tell |
|---|---|---|---|---|---|---|---|---|
| Foodborne | ||||||||
| Brucellosis | Brucella | Bacterial | 1 to 4 weeks (can be months) | Usually | fever that comes and goes (undulant fever); sweats; joint pain; fatigue | Unpasteurized milk and cheese from infected goats, sheep or cows; contact with livestock | Farmers, veterinarians, slaughterhouse workers, people who drink raw goat milk | Undulant (wave-like) fever after raw goat or sheep milk, or working with livestock. No special pregnancy link on tests. |
| Vibriosis | Vibrio parahaemolyticus | Bacterial | About 24 hours (4 to 96) | Sometimes | watery diarrhea; cramps; nausea; vomiting; sometimes fever | Raw or undercooked oysters and shellfish from warm coastal water | People who eat raw oysters, especially in summer | Raw oysters in summer. |
| Cyclosporiasis | Cyclospora cayetanensis | Parasitic | About 1 week (2 to 14 days) | No or minimal | watery, relapsing diarrhea; loss of appetite; fatigue; weight loss | Imported fresh produce: raspberries, basil, cilantro, lettuce | Anyone eating contaminated imported produce, mostly in summer | Long, relapsing diarrhea linked to imported berries or herbs. |
| Trichinellosis | Trichinella spiralis | Parasitic | Stomach symptoms in 1 to 2 days; muscle symptoms in 2 to 8 weeks | Usually | muscle pain; swelling around the eyes; fever; earlier diarrhea and nausea | Undercooked wild game (bear, wild boar) or pork | Hunters and people who eat wild game | Muscle pain and puffy eyes weeks after eating undercooked bear meat. |
| Mad cow disease / variant Creutzfeldt-Jakob disease | Prion (BSE / vCJD) | Prion | Years to decades | No or minimal | depression and anxiety; loss of coordination; rapidly worsening dementia; always fatal | Eating beef products from cattle with BSE | Rare; linked to the 1990s UK BSE outbreak | A misfolded protein, not a living organism; years-long incubation, always fatal. |
| Person-to-person | ||||||||
| Rotavirus infection | Rotavirus | Viral | About 2 days | Usually | watery diarrhea; vomiting; fever; dehydration | Fecal-oral spread among young children | Infants and young children; prevented by a routine infant vaccine | Severe watery diarrhea in babies; there's a routine infant vaccine. |
| Ebola virus disease | Ebola virus | Viral | 2 to 21 days | Usually | fever; severe weakness; vomiting and diarrhea; unexplained bleeding | Direct contact with blood or body fluids of a sick person or someone who died of it; fruit bats | Health workers and family caregivers; burial practices | Hemorrhagic fever spread by body fluids; the 21-day window sets how long contacts are monitored. |
| Ringworm / athlete's foot | Dermatophyte fungi (Trichophyton) | Fungal | 4 to 14 days | No or minimal | red, itchy, ring-shaped rash; scaly skin; cracked skin between toes | Skin contact with infected people or pets; locker room floors, shared mats (wrestlers) | Wrestlers, athletes, children with pets | Ring-shaped rash from a fungus, not a worm. Wrestling teams and locker rooms. |
| Respiratory / airborne | ||||||||
| Tuberculosis | Mycobacterium tuberculosis | Bacterial | Weeks to years (can stay latent) | Usually | cough lasting 3+ weeks; coughing up blood; night sweats; weight loss; fever | Airborne droplet nuclei from a person with active lung TB | Close contacts, people with HIV, people in crowded settings | Long cough, night sweats and weight loss. Can stay latent (no symptoms, not contagious) for years. |
| Vaccine-preventable | ||||||||
| Chickenpox | Varicella-zoster virus | Viral | 10 to 21 days | Usually | itchy blister-like rash appearing in crops; fever; tiredness | Airborne and direct contact with blisters; the virus can later reactivate as shingles | Unvaccinated children; prevented by the varicella vaccine | Itchy blisters in different stages at once. Nothing to do with chickens. |
| Mumps | Mumps virus | Viral | 16 to 18 days (12 to 25) | Usually | swollen, painful salivary glands (puffy cheeks and jaw); fever; headache; muscle aches | Respiratory droplets and saliva; outbreaks on college campuses and at sports teams | People in close-contact settings; prevented by MMR | Swollen cheeks and jaw (parotitis). |
| Vector-borne | ||||||||
| Yellow fever | Yellow fever virus | Viral | 3 to 6 days | Usually | fever; headache; muscle pain; in severe cases jaundice (yellow skin) and bleeding | Bite of Aedes and Haemagogus mosquitoes in Africa and South America | Unvaccinated travelers; some countries require proof of vaccination | Mosquito-borne fever with jaundice, prevented by a travel vaccine. Named for the yellow skin. |
| Zoonotic (animal contact) | ||||||||
| Plague | Yersinia pestis | Bacterial | 2 to 8 days (bubonic) | Usually | sudden fever; very swollen, painful lymph nodes (buboes); chills; weakness | Bites of fleas from infected rodents (prairie dogs, rats); pneumonic form spreads person to person | People in the rural western U.S. near prairie dogs and their fleas | Buboes (huge swollen lymph nodes) after flea bites; caused the Black Death. |
| Hantavirus pulmonary syndrome | Hantavirus (Sin Nombre virus) | Viral | 1 to 8 weeks | Usually | fever; muscle aches; then coughing and severe shortness of breath | Breathing in dust from deer mouse droppings and urine when cleaning cabins, sheds, barns | People cleaning closed-up cabins or sheds in rural areas | Severe breathing trouble weeks after sweeping out a mouse-infested cabin. |
| Anthrax | Bacillus anthracis | Bacterial | 1 to 7 days (skin form) | Usually | painless skin sore with a black center (eschar); fever; inhaled form: severe breathing trouble | Spores from infected livestock, hides and wool; used in the 2001 letter attacks | Farmers, wool and hide workers; a bioterrorism agent | Black skin sore after handling animal hides; mailed spores in 2001. |