Infectious Diseases: Bacterial, Viral, Fungal, and Parasitic Infections
Infectious Diseases
Skin Infections
- Skin-Bac-Folliculitis: Caused by Staphylococcus infection, can spread to blood and organs.
- Staphylococcal Scalded Skin Syndrome: Caused by Staphylococcus. Death is rare but can occur due to secondary infections. Common in infants; treated with antimicrobial drugs.
- Impetigo (Pyoderma): Red face and limbs, caused mostly by Staphylococcus aureus. Hyaluronic acid and pyrogenic toxins are involved. Treated with oral and topical antimicrobial drugs.
- Erysipelas: Infection of the lymph nodes, treated with penicillin.
- Necrotizing Fasciitis: Redness, pain, swelling, and mental confusion. Caused by Streptococcus pyogenes, often through breaks in the skin. High mortality rate (20%). Treated with clindamycin and penicillin.
- Acne: Associated with gram-positive, rod-shaped diphtheroids.
- Cat Scratch Disease: Caused by Bartonella, transmitted by cats and ticks. Treated with antimicrobial drugs.
- Pseudomonas Infection: Can cause shock, blue-green pus (pyocyanin). Rarely causes disease except in burn victims. Treated with a combination of antimicrobial drugs due to multidrug resistance.
- Spotted Fever (Rickettsial): Rocky Mountain Spotted Fever is the most severe form. Non-itchy rash on trunk and appendages, organ failure. Gram-negative bacteria that do not use glucose as a nutrient and do not secrete toxins.
- Cutaneous Anthrax: Caused by Bacillus anthracis.
- Gas Gangrene: Muscle tissue death (black), gas bubbles. Caused by Clostridium, a gram-positive, endospore-forming bacterium. C. perfringens is often isolated. Endospores must be introduced to dead tissue. High mortality rate (40%). Diagnosis is often apparent.
Skin Viral Infections
- Poxvirus: DNA virus, induces a strong immune response. Smallpox is acquired through inhalation of the virus; others through direct contact.
- Herpes: Affects mucous membranes. Can be fatal in newborns. Chemotherapy drugs can control but not cure.
- Warts: Spread through direct contact and fomites.
Systemic Viral Infections
- Rubella (German Measles): Childhood rash. In adults, can cause arthritis and encephalitis. Can cause birth defects or death of the fetus. Spreads from the respiratory system to the body via the blood. Transmitted via respiratory secretions.
- Measles: Characterized by Koplik’s spots. Subacute sclerosing panencephalitis is a rare complication. Symptoms are caused by the immune response. Fatal in children. Highly contagious. Treated with Vitamin A, antibodies, and ribavirin.
- Erythema Infectiosum (Fifth Disease): Respiratory infection with a rash. Can cause anemia and joint pain in adults.
Superficial Mycoses (Fungal Infections)
- Most common fungal infections.
- Pityriasis Versicolor: Colored patches of scaly skin. Produces keratinase. Infected skin appears pale green under UV light.
Cutaneous Mycoses (Fungal Infections)
- Dermatophytoses (Ringworm): Grow in the skin.
Parasitic Infections
- Leishmaniasis:
- Cutaneous: Large, painless lesions.
- Mucocutaneous: Lesions encompass mucous membranes.
- Visceral: Parasite spread by macrophages.
- Scabies: Itchy blisters caused by female mites.
Nervous System Infections
Bacterial Infections
- Either infect cells (meningitis, leprosy) or release toxins that affect neurons (botulism, tetanus).
- Bacterial Meningitis: Meningeal inflammation, increased white blood cells, encephalitis. Develops rapidly. Caused by several species, including:
- Neisseria meningitidis (meningococcus)
- Streptococcus pneumoniae (leading cause in children and the elderly)
- Haemophilus influenzae
- Listeria monocytogenes (rarely pathogenic)
- Streptococcus agalactiae (normal vaginal microbiota in some women, acquired during birth)
- Leprosy:
- Tuberculoid: Non-progressive.
- Lepromatous: Rare.
- Botulism:
- Foodborne: Progressive paralysis on both sides of the body. Slow recovery as new nerve cell endings grow.
- Infant: Ingestion of endospores.
- Wound: Contamination of a wound by endospores.
- Open airway
- Wash intestinal tract
- Administer botulism immune globulin
- Antimicrobial drugs
- Tetanus: Tight jaw, muscle spasms and contractions, irregular heartbeat and blood pressure, profuse sweating. Caused by Clostridium tetani, which produces the neurotoxin tetanospasmin. High mortality rate (50%) if untreated. Diagnosed by muscle contractions.
Viral Infections
- Viral Meningitis: 90% caused by RNA viruses in the enterovirus group (Coxsackie A, Coxsackie B, echovirus). Spread via fecal contamination. Crosses the blood-brain barrier. No specific treatment.
- Poliomyelitis: Fewer than 100 acquired cases in 2015. Endemic only in Pakistan and Nigeria. No specific treatment.
- Rabies: Zoonotic. Treatment involves injecting immunoglobulin and vaccine.
- Arboviral Encephalitis: Arthropod-borne. Rarely affects humans but can cause encephalitis if it crosses the blood-brain barrier. West Nile virus is an example. Treatment is supportive.
Fungal Infections
- Spread from the lungs to the CNS via the blood, can produce fungal meningitis.
- Cryptococcal Meningitis: Loss of vision, coma in later stages. Caused by Cryptococcus neoformans (two variants of yeast). Treated with IV antifungal drugs.
Protozoan Infections
- African Sleeping Sickness: Three stages:
- Lesion
- Parasites create fever, lymph swelling, and headache
- Protozoa invade the CNS, causing meningoencephalitis
- Primary Amebic Meningoencephalopathy: Caused by Acanthamoeba and Naegleria. Drugs have limited success.
Prion Diseases
- Prion = infectious protein. Mad cow disease can be transmitted to humans by eating infected cattle.
- Variant Creutzfeldt-Jakob Disease: Insomnia, weight loss, memory failure. Caused by an abnormal form of protein. No treatment.
Cardiovascular System Infections
Bacterial Infections
- Septicemia, Bacteremia, Toxemia: Can lead to septic shock. Osteomyelitis can occur if bacteria invade bones. Immunocompetent individuals rarely develop septicemia. Prompt diagnosis and administration of antimicrobial drugs are crucial.
- Endocarditis: Infection of the endocardium, causing difficulty breathing and tachycardia. Patients often have an obvious source of infection. Normal microbiota are often responsible. Viridans streptococci cause 50% of cases.
- Brucellosis: Fever that spikes in the afternoon. Caused by Brucella melitensis strains, often from contaminated dairy products.
- Tularemia: Lesions and swollen lymph nodes, ascending lymphangitis. Caused by Francisella tularensis, often from an infected tick bite or contact with an infected animal.
- Plague:
- Bubonic: Enlarged lymph nodes called buboes. Fatal in 50% of untreated cases.
- Pneumonic: Bacteria spread to the lungs, causing rapid difficulty breathing. Fatal in 100% of untreated cases.
- Lyme Disease: Three phases:
- Bullseye rash
- Neurological symptoms
- Severe arthritis
Viral Infections
- Yellow Fever: Three stages:
- Fever, headache, and muscle aches
- Period of remission
- Delirium, seizures, coma, and hemorrhaging
- Infectious Mononucleosis (Mono): Transmitted via saliva. Treatment is to relieve symptoms.
- Cytomegalovirus (CMV): Most infections are asymptomatic. Dangerous in fetuses, newborns, and immunocompromised individuals. Can cause birth defects when the virus infects stem cells (teratogenic). One of the most common human infections. Many treatments are ineffective.
- Dengue Fever: Two phases:
- Fever, edema, headache, and muscle ache
- Return of fever and red rash
- African Viral Hemorrhagic Fever: Fever and fatigue, minor petechiae progressing to severe internal hemorrhaging. Caused by Ebola virus or Marburg virus. Primarily in Africa.
Protozoan and Helminthic Infections
- Malaria: Symptoms associated with the parasite’s life cycle in erythrocytes. Anemia, weakness, and fatigue gradually develop. Caused by at least four Plasmodium species. Endemic throughout the tropics. Causes approximately 1 million deaths annually. Various antimicrobial drugs are used for treatment.
- Toxoplasmosis: Most individuals are asymptomatic. In immunocompromised individuals, can cause fever, malaise, and infection of the lungs, liver, and heart. Can cause spontaneous abortion or stillbirth. Cats are the definitive host. Can be consumed in undercooked meat containing the parasite. Treatment is only necessary in AIDS patients, pregnant women, and newborns.
- American Trypanosomiasis (Chagas’ Disease): Swelling at the infection site. Chronic manifestations can occur years after infection. Endemic throughout Central and South America.
- Schistosomiasis: Swimmer’s itch. Eggs deposited throughout the body can cause other symptoms. Caused by three species of Schistosoma (each species is geographically limited; not found in the US).
Upper Respiratory Tract Infections
Bacterial Infections
- Streptococcal Respiratory Diseases: Pharyngitis (sore throat, trouble swallowing). Laryngitis and bronchitis can spread to the lower respiratory tract. Complications include scarlet fever, rheumatic fever, and acute glomerulonephritis in some cases. Caused by Group A Streptococcus (S. pyogenes). Treated with oral penicillin.
- Diphtheria: Sore throat, fever, pseudomembrane that can obstruct the airway. Caused by Corynebacterium diphtheriae. Leading cause of death among unvaccinated children (suffocation).
- Rhinosinusitis and Otitis Media: Inflamed nasal passages. Otitis media causes pain in the ears. Caused by various respiratory microbiota. No known way to prevent rhinosinusitis.
- Common Cold: Enteroviruses (rhinoviruses) are a common cause. Highly contagious.
Lower Respiratory Tract Infections
Bacterial Infections
- Lower respiratory organs are usually axenic (sterile). Bacterial infections can cause life-threatening illnesses.
- Bacterial Pneumonias: Described by the affected region or the organism causing the disease.
- Lobar pneumonia (one lobe)
- Mycoplasmal pneumonia (small, typically parasitic bacteria that lack cell walls)
- Healthcare-associated pneumonia
- Legionnaires’ Disease: Pulmonary function can rapidly decrease. Treated with quinolones or macrolides.
- Tuberculosis (TB): Leading infectious disease killer in the world. Declined in the industrialized world. Symptoms are not always present. Characterized by the presence of a mycolic acid capsule (unique cell wall structure). Treated with a drug combination. Drug-resistant strains of M. tuberculosis exist. BCG vaccine is used where TB is common.
- Pertussis (Whooping Cough): Caused by Bordetella pertussis. Highly contagious. Treatment is supportive. DTaP vaccine is available.
- Inhalation Anthrax: Severe coughing, lethargy, shock, and death. Acquired by contact or inhalation of endospores. Vaccine available to select individuals.
Viral Infections
- Influenza (Flu): Pharyngitis, myalgia, sudden fever. Caused by Influenza types A and B. Concern that changes in type A could cause a major pandemic.
- Coronavirus: Recent SARS and MERS outbreaks. Causes dry cough and pneumonia.
- Respiratory Syncytial Virus (RSV): Immune response to RSV damages the lungs.
- Hantavirus Pulmonary Syndrome (HPS): Transmitted from rodents. No pharmaceutical treatments.
Fungal Infections
- AIDS patients are particularly susceptible to fungal infections.
- Coccidioidomycosis: Can become systemic in immunocompromised individuals. Caused by Coccidioides immitis (yeast). Common in the Southwestern US and northern Mexico. Treated with Amphotericin B (drills holes in the cell membrane).
- Histoplasmosis: Cough with bloody sputum, skin lesions. Common in the eastern US.
- Pneumocystis Pneumonia: Difficulty breathing, anemia, hypoxia.
Digestive System Infections
Bacterial Infections
- Dental Caries (Cavities): Caused by Streptococcus mutans. Dextran and fimbriae allow biofilm formation.
- Gingivitis: Treated with scaling and antibacterial rinses.
- Periodontal Disease: Caused by Porphyromonas gingivalis. Proteases break down gingival tissue. Sucrose increases the risk of decay.
- Peptic Ulcers: Abdominal pain. Caused by Helicobacter pylori.
- Bacterial Gastroenteritis: Caused by contaminated food and water and poor living conditions. Symptoms include nausea, vomiting, abdominal pain, and cramps. Treatment involves fluid and electrolyte replacement.
- Shigellosis: Caused by four species of Shigella. Virulence factors include type III secretion systems and enterotoxins. Diagnosed by the presence of Shigella in stool. Treated with antimicrobial drugs.
- Traveler’s Diarrhea: Caused by E. coli. Treatment involves fluid and electrolyte replacement. Antidiarrheal drugs may prolong symptoms.
- Campylobacter Diarrhea: Often caused by contaminated chicken or raw poultry.
- Clostridium difficile Diarrhea (Antimicrobial-Associated): Caused by overuse of antibiotics, which kills beneficial bacteria. Any antimicrobial drug can trigger this. Can lead to pseudomembranous colitis. Treated with antimicrobial drugs and fecal transplants.
- Salmonellosis: Often from raw eggs. Self-limiting.
- Typhoid Fever: Treated with antimicrobial drugs.
- Cholera: Caused by Vibrio cholerae (found in salt and fresh water). Produces cholera toxin. The toxin, not the bacteria, causes damage.
- Bacterial Food Poisoning: Often caused by Staphylococcus aureus. Treatment involves fluid and electrolyte replacement.
Viral Infections
- Viral Gastroenteritis: Dehydration. Caused by caliciviruses, astroviruses, and rotaviruses. Treatment involves fluid and electrolyte replacement.
- Viral Hepatitis: Jaundice, abdominal pain, weight loss. Symptoms can occur years after infection. Five different viruses cause hepatitis: A, B, C, Delta, and E. Vaccines are available for hepatitis A and B.
Protozoan Infections
- Giardiasis: Diarrhea lasting up to 4 weeks. Cysts are resistant to chlorine, heat, drying, and stomach acid. Treated with anti-protozoal drugs like tinidazole or metronidazole (in the US) and oral rehydration therapy.
- Cryptosporidiosis: Watery diarrhea. Treatment involves fluid and electrolyte replacement.
- Amebiasis:
- Luminal amebiasis is asymptomatic.
- Invasive amebic dysentery causes severe diarrhea, colitis, and appendicitis.
- Invasive extraintestinal amebiasis causes necrotic lesions in various organs.
Helminthic Infections
- Tapeworm (Cestode): Flat, segmented, parasitic helminth. Treated with niclosamide or praziquantel. Prevented by thoroughly cooking meats.
- Pinworm (Nematode): Long, thin, unsegmented, cylindrical helminth. Caused by Enterobius vermicularis. Common in children. Enterobius is the most common parasitic worm in the US. Prevention involves strict personal hygiene.
- Anisakiasis: Approximately 20,000 cases worldwide. Treated by removing worms from the intestine. Prevented by avoiding raw and undercooked marine fish.
Urinary System Infections
Bacterial Infections
- Bacterial Urinary Tract Infection (UTI): Cloudy urine, often caused by E. coli.
- Leptospirosis: Zoonotic, primarily in animals. Causes abrupt fever and muscle stiffness. Rarely fatal and rare in the US. Treated with antimicrobial drugs.
Reproductive System Infections (Non-Venereal)
- Staphylococcal Toxic Shock Syndrome: Primarily affects menstruating females. A medical emergency. Treatment involves removal of foreign material and antimicrobial drugs. Avoid tampon use.
- Bacterial Vaginosis: White vaginal discharge with a fishy odor. Associated with multiple sexual partners and douching. Treated with oral or vaginal metronidazole.
- Vaginal Candidiasis (Yeast Infection): Vaginal itching and burning. Caused by Candida albicans. Treated with azole or fluconazole. Prevented by avoiding persistent moisture in the genital area.
Reproductive System Infections (Sexually Transmitted Diseases – STDs)
Bacterial Infections
- Gonorrhea:
- Men: Painful urination and a purulent (milky) discharge.
- Women: Asymptomatic or pelvic inflammatory disease.
- Syphilis: Occurs worldwide. Treated with Penicillin G (except for tertiary syphilis).
- Chlamydial Infections:
- Men: Painful urination and discharge.
- Women: Asymptomatic.
Viral Infections
- Genital Herpes: Small blisters around the genitals or rectum. The virus can become latent in nerve endings. Acyclovir or other antiviral agents can lessen symptoms.
- Genital Warts: Can form in other places. Caused by HPV (human papillomaviruses). The most common STD in the US. Causes cervical cancer.
Protozoan Infections
- Trichomoniasis:
- Men: Asymptomatic.
- Women: Vaginal discharge and irritation.