Bacterial, Fungal, and Parasitic Infections: Symptoms and Causes

Acne Vulgaris

Pathogen: Propionibacterium acnes (Humans)

Signs and Symptoms: Sebum and dead cells clog pores, leading to papule and pustule formation, scarring, and distress.

Extra: More common among teenagers and young adults.

Hallmark: Cystic acne – an uncommon, severe form of acne with painful pustules.

Gas Gangrene (Clostridial Myonecrosis)

Pathogen: Clostridium perfringens (Soil)

Signs and Symptoms: Muscle and soft tissue destruction, gas pockets in tissues compress small blood vessels, leading to gangrene.

Mode of Transmission: Bacterial spores enter open wounds.

Extra: May require amputation of the affected limb.

Hallmark: Palpable crepitus (cracking during palpation due to gas pockets under the skin).

Hansen’s Disease (Leprosy)

Pathogen: Mycobacterium leprae (Armadillos)

Signs and Symptoms: Macules, nodules, ulcers, numbness, sensation loss, muscle weakness, facial hair loss, congestion, paralysis.

Mode of Transmission: Inhalation of infected respiratory secretions or contact with infected armadillos.

Extra: Long-term exposure to infection increases risk.

Anthrax

Pathogen: Bacillus anthracis (Animals – wool)

Signs and Symptoms: Varies by entry portal.

a. Cutaneous Anthrax: Black eschars due to exotoxins.

b. Inhalation Anthrax: Flu-like symptoms progressing to severe respiratory distress.

c. Gastrointestinal Anthrax: Nausea, vomiting, pain, leading to diarrhea, dysentery, or death.

d. Injection Anthrax: Infection at the injection site, leading to organ failure.

Mode of Transmission: Through skin, inhalation, or ingestion of contaminated meat.

Extra: Possible bioterrorism weapon, also known as wool-sorter’s disease.

Staphylococcal Skin Infections

Pathogen: Staphylococcus aureus (Humans)

Types: Folliculitis, hordeolum (sty), furuncle (boils), carbuncle, scalded skin syndrome (rare toxin-producing strain).

Signs and Symptoms of Scalded Skin Syndrome: Fever, malaise, redness, blisters, epidermis peeling over large areas (burn-like), treated in burn units or ICUs.

Mode of Transmission: Person-to-person or healthcare-associated infections via hands of asymptomatic nasal carriers (under 5 years old or immunocompromised).

Extra: Some strains are antibiotic-resistant (MRSA).

Streptococcal Skin Infections (Scarlet Fever)

Pathogen: Streptococcus pyogenes (Humans)

Signs and Symptoms: Fever, sore throat, bright red rash starting on the neck, axilla, and groin (macular, then papular, fading within a week).

Mode of Transmission: Inhalation or contact with secretions from infected oropharyngeal sources.

Hallmark: Bright red rash (neck, axilla, and groin).

Streptococcal Skin Infections (Necrotizing Fasciitis)

Pathogen: Streptococcus pyogenes (Humans) – “flesh-eating” strain.

Signs and Symptoms: Red, swollen, warm skin, blisters, severe pain, fever, rapid destruction of soft tissues.

Mode of Transmission: Bacteria enter through breaks in the skin.

Extra: Strain produces exoenzymes that rapidly destroy soft tissues; debridement may be needed.

Gonococcal Conjunctivitis (Gonococcal Ophthalmia Neonatorum)

Pathogen: Neisseria gonorrhoeae (Humans)

Signs and Symptoms: Conjunctival inflammation, redness, purulent discharge, potential scarring.

Mode of Transmission: Infected birth canal during delivery or finger-to-eye contact with infected genital secretions.

Note: Gonococcal ophthalmia neonatorum is a complication in newborns, usually appearing 2-5 days after birth.

Chlamydial Conjunctivitis (Chlamydial Ophthalmia Neonatorum)

Pathogen: Chlamydia trachomatis (Humans)

Signs and Symptoms: Inflammation of the conjunctiva, redness, purulent discharge, potential scarring.

Mode of Transmission: Infected birth canal during delivery or finger-to-eye contact with infected genital secretions.

Note: Chlamydial ophthalmia neonatorum is a complication that appears later (5-14 days) after birth, with blood in the eyes.

Necrotizing Ulcerative Gingivitis (Trench Mouth)

Pathogen: Mixed anaerobic bacteria (Humans – Oral microbiota)

Signs and Symptoms: Painful, bleeding gingivae, fever, swollen cervical lymph nodes, extreme halitosis.

Prevention: Maintaining good oral hygiene. Not contagious.

Extra: Inflammation of the gingivae and ulceration of interdental papillae can be severe in immunocompromised individuals.

Chronic Bacterial Gastritis

Pathogen: Helicobacter pylori (Humans)

Signs and Symptoms: Chronic gastric inflammation leading to early satiety, abdominal pain, nausea, and vomiting; ulcers leading to pyrosis and epigastric pain.

Mode of Transmission: Person-to-person via contact with saliva, vomit, or feces.

Hallmark: Sharply demarcated peptic ulcers surrounded by inflamed mucosa – perforation leads to peritonitis.

Typhoid Fever

Pathogen: Salmonella typhi, Salmonella paratyphi (Humans – patients/carriers)

Signs and Symptoms: Endotoxin release leading to fever, malaise, severe headache, dry cough, loss of appetite; death in 10% of cases.

Mode of Transmission: Fecal-oral route, ingestion of contaminated food or water (houseflies facilitate contamination).

Hallmark Symptom: Rose spots – red macular rash on the chest.

Trachoma

Pathogen: Chlamydia trachomatis (Humans)

Signs and Symptoms: Conjunctiva and cornea inflammation, leading to eyelid swelling, pain, photophobia, and potential blindness.

Mode of Transmission: Contacting infected ocular secretions, fomites (towels), or flies.

Risk Factors: Crowded living conditions, poor hygiene, and inadequate sanitation.

Extra: Leading preventable cause of blindness, no vaccine available.

Musca sorbens, a close relative of the housefly (Musca domestica) that usually breeds in human feces, is an eye-seeking/bazaar fly that causes trachoma.

Pertussis (Whooping Cough)

Pathogen: Bordetella pertussis (Humans)

Signs and Symptoms: Inflammation of the pharynx, larynx, trachea, and bronchial tubes.

1. Prodromal Stage: Mild cold-like symptoms.
2. Paroxysmal Stage: Bouts of severe coughing (paroxysm) with a “whooping” sound on inspiration.
3. Convalescent Stage: Gradual resolution of symptoms.

Mode of Transmission: Inhaling infected respiratory secretions.

Extra: High risk for unvaccinated infants; immunity may wane.

Diphtheria

Pathogen: Corynebacterium diphtheriae (Humans)

Signs and Symptoms: Inflammation of the pharynx and larynx: throat pain, dysphagia, fever, headache, enlarged tonsils, cervical lymphadenopathy.

Mode of Transmission: Inhalation of or contact with infected oropharyngeal secretions.

Prevention: DTaP (under 7 years old) and Tdap (over 7 years old) vaccines provide prevention.

Extra: Rare in the U.S. but common in Africa and South Asia.

Hallmark: Pseudomembrane formation leading to airway obstruction.

Streptococcal Pharyngitis

Pathogen: Streptococcus pyogenes (Humans)

Signs and Symptoms: Inflammation of the pharynx – pain, dysphagia, fever, headache, enlarged tonsils, cervical lymphadenopathy.

Mode of Transmission: Inhalation of or contact with infected oropharyngeal secretions.

Diagnosis: Rapid strep test (approximately 80% sensitive, approximately 95% specific).

Prevention: Handwashing, disinfecting surfaces.

Typical Pneumonia

Pathogen: Streptococcus pneumoniae (Humans)

Signs and Symptoms: Inflammation of the alveoli – rapid onset, pain, dyspnea, productive cough, fever, and severe illness; radiographic abnormalities equal physical symptoms.

Mode of Transmission: Inhalation of infected respiratory or oropharyngeal secretions; contact with contaminated articles.

Atypical Pneumonia

Pathogen: Mycoplasma pneumoniae (Humans)

Signs and Symptoms: Inflammation of the alveoli – gradual onset, dry cough, fever, no chest pain or dyspnea, and mild illness; radiographic abnormalities are greater than physical symptoms.

Mode of Transmission: Inhalation of infected respiratory or oropharyngeal secretions; contact with contaminated articles.

Legionnaires’ Disease (Pontiac Fever)

Pathogen: Legionella pneumophila (Water sources)

Signs and Symptoms: Inflammation of the alveoli – similar to typical pneumonia; requires lab tests for confirmation.

Mode of Transmission: Inhalation of contaminated mist or dust particles.

Campylobacter Enteritis

Pathogen: Campylobacter jejuni (Pigs, cattle, chicken)

Signs and Symptoms: Inflammation of the small intestine leading to nausea, vomiting, abdominal pain, fever, and diarrhea.

Mode of Transmission: Ingestion of infected meat or food prepared on contaminated cutting boards.

Psittacosis (Ornithosis/Parrot Fever)

Pathogen: Chlamydophila psittaci (Birds)

Signs and Symptoms: Inflammation of the alveoli – similar to atypical pneumonia; requires lab tests for confirmation.

Mode of Transmission: Inhalation of dried droppings or respiratory secretions from infected birds.

Hallmark: Dermatological manifestation – Horder spots.

Cholera

Pathogen: Vibrio cholerae (Contaminated water, shellfish)

Signs and Symptoms: Profuse watery diarrhea with mucus flecks, vomiting, rapid dehydration, death in 50% of untreated cases.

Mode of Transmission: Fecal-oral route via ingestion of contaminated food or water.

Hallmark: Liquid stools with mucus flecks (“rice-water stools”).

Pulmonary Tuberculosis

Pathogen: Mycobacterium tuberculosis (Humans)

Signs and Symptoms: Alveolar inflammation – fever, weight loss, productive cough, dyspnea, chest pain, hemoptysis.

a. Latent Tuberculosis: Present but not active. No signs or symptoms, but positive tuberculosis test.

b. Active Tuberculosis: Multiplying, active infection.

Mode of Transmission: Inhalation of respiratory droplets.

Diagnoses:

a. Tuberculosis skin test (Mantoux test).

b. Tuberculosis blood test (Interferon-gamma release assays).

c. Confirmation – chest X-ray and sputum smear/culture.

Prevention: Preventing exposure to M. tuberculosis while traveling abroad, BCG vaccine, treating latent tuberculosis.

Hallmark:

a. Red, acid-fast bacilli in a sputum specimen (smear).

b. Brown, granular colony in Löwenstein-Jensen medium (culture).

c. Inflammation and cavity formation in chest X-ray.

Salmonellosis

Pathogen: Salmonella enterica (Pigs, chicken, cattle)

Signs and Symptoms: Abdominal pain, nausea, vomiting, diarrhea (caused by a bacterial toxin).

Mode of Transmission: Fecal-oral route, ingestion of contaminated food, ingestion of uncooked eggs.

Shigellosis

Pathogen: Shigella dysenteriae (Humans – patients/carriers)

Signs and Symptoms: Abdominal pain, nausea, vomiting, fever, dysentery (caused by Shiga toxin); complications may occur in children.

Mode of Transmission: Fecal-oral route via ingestion of contaminated food or water.

Clostridioides difficile Colitis

Pathogen: Clostridioides difficile (Humans)

Signs and Symptoms: Antibiotics disrupt resident microbiota, leading to C. difficile proliferation, colon inflammation, and diarrhea.

Mode of Transmission: Fecal-oral route via spores persisting on surfaces, transferred via healthcare workers’ hands.

Enterohemorrhagic Escherichia coli (EHEC) Enterocolitis (EHEC = STEC)

Pathogen: Enterohemorrhagic Escherichia coli (Humans, cattle)

O157:H7 strain produces Shiga toxin (identical to Shigella dysenteriae).

Signs and Symptoms: Nausea, vomiting, abdominal cramps, dysentery (Shiga toxin).

Mode of Transmission: Fecal-oral route, ingestion of infected beef, contaminated fruits, green leafy vegetables, or fluids.

Complication: Destruction of red blood cells and platelets by the Shiga toxin, leading to acute kidney failure (glomeruli clogged).

Extra: 5% develop hemolytic uremic syndrome (HUS); leading cause of diarrheal outbreaks.

Enterotoxigenic Escherichia coli (ETEC) Enterocolitis

Pathogen: Enterotoxigenic Escherichia coli (Humans, cattle)

a. LT strain – produces a heat-labile toxin.

b. ST strain – produces a heat-stable toxin.

Signs and Symptoms: Nausea, vomiting, abdominal cramps, diarrhea.

Mode of Transmission: Fecal-oral route, ingestion of infected beef, contaminated fruits, green leafy vegetables, or fluids.

Extra: Leading cause of traveler’s diarrhea (Asia, Africa, and Central and South America).

Chancroid

Pathogen: Haemophilus ducreyi (Humans)

Signs and Symptoms: Small, painful papules – buboes; enlarged inguinal lymph nodes.

Mode of Transmission: Sexual contact (genital-genital, oral-genital, oral-anal, genital-anal).

Urinary Tract Infections (UTIs)

a. Ascending: Bacteria migrate up from the urethra to the kidneys.

b. Descending: Bacteria spread to the kidneys via the bloodstream.

Upper UTIs

1. Nephritis: Inflammation of the kidneys.
2. Ureteritis: Inflammation of the ureters.

Lower UTIs

3. Cystitis: Inflammation of the urinary bladder.
4. Urethritis: Inflammation of the urethra.

Pathogens: Escherichia coli (approximately 90%), Neisseria gonorrhoeae, Chlamydia trachomatis, Pseudomonas aeruginosa (Humans)

Signs and Symptoms:

a. Upper UTIs: Fever (more common), chills, lumbar pain.

b. Lower UTIs: Fever (less common), pelvic discomfort, frequent urge to urinate, burning sensation, hematuria.

Mode of Transmission: Person-to-person via sexual contact, urinary catheterization in healthcare settings.

Prevention: Adequate fluid intake, wiping front-to-back, emptying the bladder after intercourse, avoiding holding urination.

Hallmark: E. coli in urine specimen (Gram-negative bacilli), some have been phagocytosed by neutrophils.

Gonorrhea

Pathogen: Neisseria gonorrhoeae (Humans)

Signs and Symptoms:

a. Urethral Gonorrhea: Dysuria, purulent discharge, testicular or scrotal pain.

b. Rectal Gonorrhea: Anal itching, purulent discharge, rectal bleeding.

c. Oropharyngeal Gonorrhea: Sore throat, dysphagia, swollen cervical lymph nodes.

Mode of Transmission: Sexual contact (genital-genital, oral-genital, oral-anal, genital-anal).

Epidemiology: Second most common bacterial sexually transmitted infection.

Complications:

a. Can spread via the bloodstream to one or more joints – Septic Arthritis.

b. Can spread to the uterus and fallopian tubes – Pelvic Inflammatory Disease (PID).

c. Can spread to the epididymides – Epididymitis.

Extra: Developed plasmid-mediated resistance to almost all antibiotics.

Hallmark: Neisseria gonorrhoeae in a urethral discharge specimen (Gram-negative diplococci), some have been phagocytosed by neutrophils.

Chlamydia

Pathogen: Chlamydia trachomatis (Humans)

Signs and Symptoms:

a. Urethral Chlamydia: Dysuria, purulent discharge, abdominal or pelvic pain, bleeding between periods.

b. Rectal Chlamydia: Anal itching, purulent discharge, rectal bleeding.

c. Oropharyngeal Chlamydia: Sore throat, dysphagia, swollen cervical lymph nodes.

Mode of Transmission: Sexual contact (genital-genital, oral-genital, oral-anal, genital-anal).

Epidemiology: Most common bacterial sexually transmitted infection.

Complications:

a. Can spread to the uterus and fallopian tubes – Pelvic Inflammatory Disease (PID).

b. Can spread to the epididymides – Epididymitis.

Extra: Plasmid-mediated resistance is rare in Chlamydia trachomatis.

Hallmark: Bacteria observed in McCoy cell (mouse fibroblast) culture (membrane-bound inclusion bodies stain brown with iodine).

Syphilis

Pathogen: Treponema pallidum (Humans)

Spiral-shaped bacterium observed using darkfield microscopy – reflects light.

Signs and Symptoms: Varies by stage.

a. Primary: Chancre (painless ulcer) develops after 3 weeks.

b. Secondary: Chancre turns inward, leading to rash and lymphadenopathy.

c. Tertiary: Central nervous system, cardiovascular, or other issues, possible death.

Mode of Transmission: Sexual contact; transmission via placenta.

Complications: Congenital syphilis – half die around birth, vision or hearing loss, skeletal abnormalities, growth defects.

Extra: Hutchinson Teeth: Peg-shaped teeth with notches are late manifestations of congenital syphilis, found in 50% of infants with positive mothers.

Hallmark: Soft, non-cancerous growths may occur in tertiary syphilis – Gummas.

Lymphogranuloma Venereum

Pathogen: Chlamydia trachomatis (serotypes L1, L2, L3)

Signs and Symptoms: Painless genital ulcer, leading to inflamed lymph nodes, painful pus-filled buboes; buboes may rupture.

Mode of Transmission: Sexual contact (genital-genital, oral-genital, oral-anal, genital-anal).

Bacterial Vaginosis

Pathogens: Anaerobic bacteria outnumbering lactobacilli (Humans)

Signs and Symptoms: Inflammation of the vagina – greyish-white discharge (watery, foul), itching, burning.

Mode of Transmission: Possibly sexually transmitted.

Risk Factors: Natural lack of lactobacilli (which converts sugar to lactic acid), rinsing out the vagina with water or other substances.

Epidemiology: United States = 20%-30%, recurrence within 3-12 months.

Infective Endocarditis

Pathogens: Staphylococcus aureus, Streptococcus pyogenes (Humans)

Signs and Symptoms: Flu-like symptoms, abnormal heart rhythm, myalgia, arthralgia, abscesses around heart valves.

i. Osler’s Nodes: Painful, erythematous nodules on fingers and toes.

ii. Janeway Lesions: Painless, erythematous patches on palms and soles.

Mode of Transmission: Entry of bacteria into the bloodstream after dental procedures, oral surgery, or intravenous drug use with contaminated needles/syringes.

Risk Factors: People with artificial or damaged heart valves.

Complications: Vegetations can break loose and travel to the brain, lungs, or kidneys.

Hallmark: Vegetations on the mitral valve visible in imaging or during surgical interventions.

Rocky Mountain Spotted Fever (RMSF)

Pathogen: Rickettsia rickettsii (Dogs, deer, and rodents)

Bacteria invade and multiply within endothelial cells that line the small blood vessels.

Signs and Symptoms: Fever, headache, nausea, vomiting, loss of appetite, myalgia.

i. Red, macular, non-itchy rash appears 3-5 days after onset (may involve palms and soles).

Mode of Transmission: Bite of an infected Rocky Mountain wood tick or American dog tick.

Prevention: Wear pants and long-sleeved shirts, use insect repellents.

Hallmark: Rash typically appears as macules (flat red spots).

Ehrlichiosis

Pathogens: Ehrlichia species (Ticks)

Bacteria invade and multiply within white blood cells (neutrophils, eosinophils, basophils, monocytes, and lymphocytes).

Signs and Symptoms: Similar to RMSF – fever, headache, nausea, vomiting, abdominal pain, myalgia; rash is less common and typically does not affect palms or soles.

Mode of Transmission: Bite of an infected lone star tick.

Prevention: Wear pants and long-sleeved shirts, use insect repellents.

Hallmark: Bacteria invade and multiply within neutrophils, monocytes, and lymphocytes.

Plague

Pathogen: Yersinia pestis (Rodents, fleas)

Signs and Symptoms: Initially fever, headache, weakness, chills, myalgia.

Mode of Transmission:

a. Bubonic/Septicemic: Bite of infected fleas.

b. Pneumonic: Inhalation of respiratory droplets from infected individuals.

Epidemiology: Pandemics in 541, 1347, 1894; now approximately 10 cases per year.

Plague Types:

1) Bubonic Plague: Bacteria multiply within the lymph nodes – Buboes (cervical, axillary, or inguinal).

2) Septicemic Plague: Bacteria multiply within the bloodstream, leading to blackening and death of tissues in the extremities.

3) Pneumonic Plague: Bacteria multiply within the lung alveoli, leading to dyspnea and hemoptysis.

Lyme Disease

Pathogen: Borrelia burgdorferi (Ticks)

Signs and Symptoms: Fever, headache, chills, myalgia, arthralgia, rash.

Mode of Transmission: Bite of an infected deer/black-legged tick.

Prevention: Wear pants and long-sleeved shirts, use insect repellents.

Epidemiology: Most common vector-borne disease in the US.

Hallmark: Bull’s-eye rash (erythema migrans).

Bacterial Meningitis (Purulent Meningitis)

Pathogens: Haemophilus influenzae (children), Neisseria meningitidis (adolescents), Streptococcus pneumoniae (elderly).

Signs and Symptoms: Fever, headache, nuchal rigidity, altered mental status (confusion leading to coma).

Mode of Transmission: Inhalation of infected respiratory secretions (children, elderly), oropharyngeal secretions during close contact.

Listeriosis

Pathogen: Listeria monocytogenes (Soil and water)

Signs and Symptoms:

a. Mild (healthy adults): Fever, diarrhea.

b. Meningoencephalitis (high-risk groups): Fever, headache, nuchal rigidity, altered mental status.

Mode of Transmission: Ingestion of contaminated foods (e.g., meats, dairy, vegetables, fruits).

Botulism

Pathogen: Clostridium botulinum (Soil, contaminated food)

Bacteria secrete a toxin that inhibits acetylcholine release from axon terminals at neuromuscular junctions, leading to decreased motor response.

Signs and Symptoms: Ptosis, diplopia, dysphagia, muscle weakness progressing to paralysis (can include respiratory failure).

Mode of Transmission:

a. Foodborne: Ingestion of pre-formed toxin (canned foods).

b. Wound: Infection of open wounds with bacterial spores.

c. Infant: Ingestion or inhalation of spores (e.g., honey, soil).

Extra: BOTOX® Cosmetic was approved by the FDA in 2002 for wrinkles.

Tetanus (Lockjaw)

Pathogen: Clostridium tetani (Soil)

Bacteria secrete a toxin that inhibits gamma-aminobutyric acid (GABA) release in motor neurons, leading to involuntary muscular contractions.

Signs and Symptoms: Spasms of the masseter, neck, and respiratory muscles.

Mode of Transmission: Entry of bacterial spores into open wounds.

Prevention: Vaccines (DTaP for under 7 years old and Tdap for 7 years and older); Tdap booster every 10 years.

Hallmark: Opisthotonus – abnormal posture seen in severe tetanus where the back becomes extremely arched due to muscle spasms.

Tinea (Ringworm)

Pathogens: Multiple species (>40) in the genera Microsporum, Epidermophyton, Trichophyton (Infected humans, soil)

Type of Mycosis: Cutaneous (hair, skin, and nails)

Fungi: Eukaryotic, non-photosynthetic organisms (yeasts & moulds)
– Cell walls contain a polysaccharide – chitin
– Can be unicellular (yeasts) or multicellular (moulds)
A. When grown at body temperature (98) – Yeast
B. When grown at room temperature (76) – Mould

Amebiasis Pathogen – Entamoeba histolytica (Humans)
– S/S: Fever, N/V, abdominal pain, diarrhea/ dysentery; Amebic abscesses in the liver, amebomas in the colon
– Transmission: Fecal-oral route via ingestion of contaminated food or water
– Extra: Amebae – move by means of pseudopodia
* Hallmark: dysentery, mucus stool

i. Gross liver specimen with an amebic abscess – pus
ii. Endoscopic view of the recto-sigmoid junction with amebomas – mass

Malaria Pathogen – Multiple species in genus Plasmodium (Humans and mosquitoes)
a. vivax, P. ovale, P. falciparum – Tertian malaria (fever spikes every 48 hours)
b. P. malariae – Quartan malaria (fever spikes every 72 hours)
– S/S: Fever, chills, sweating, headache, N/V; possible liver & kidney failure, pulmonary & cerebral edema, coma, & death
– Transmission: Bite of an infected female Anopheles mosquito
– Prevention: Wearing pants and long-sleeved shirts, using insect repellents
– Epidemiology: Most cases in the US occur among travelers
– Extra: Sporozoa- protozoa with no visible means of locomotion