Major Infectious Diseases: Causative Agents, Transmission, and Clinical Features

Whooping Cough (Pertussis)

Causative Agent and Transmission

• Causative Agent: Bordetella pertussis, a gram-negative coccobacillus.

• Transmission: Airborne droplets.

General Disease Information

• Symptoms: Primarily affects children; characterized by prolonged coughing fits with mucus, often followed by a "whooping" sound during inhalation after coughing.

• Vaccine: DTaP for young children; Tdap for older children and adults.

• Toxin: Ac toxin.

• Zoonotic: No.

• Nationally Notifiable: Yes.

• Emerging Infectious Disease: Re-emerging due to lowered vaccination rates.

Gonorrhea

Causative Agent and Transmission

• Causative Agent: Neisseria gonorrhoeae, gram-negative diplococcus.

• Transmission: Sexually transmitted (direct contact), vertical transmission possible.

General Disease Information

• Symptoms: Purulent discharge in males; females often asymptomatic. Can lead to Pelvic Inflammatory Disease (PID) and cause infertility and ectopic pregnancy in females.

• Vaccine: No.

• Zoonotic: No.

• Nationally Notifiable: Yes.

• Emerging Infectious Disease: No.

Strep Throat (Pharyngitis) and Scarlet Fever (Scarlatina)

Causative Agent and Transmission

• Causative Agent: Streptococcus pyogenes, gram-positive cocci, beta-hemolytic strains.

• Transmission: Direct and droplet communication/contact with mucus.

General Disease Information

• Symptoms: Ranges from a sore throat to a cough and high fever.

• Unique Symptoms: Severe sore throat, swollen tonsils with exudates. Scarlet fever presents with scarlatiniform rash, high fever, and "strawberry tongue."

• Vaccine: No; too many serovars to develop an effective vaccine.

• Toxin: Streptococcal Pyrogenic Exotoxin (SPE) in Scarlet Fever.

• Zoonotic: No.

• Nationally Notifiable: No.

• Emerging Infectious Disease: No.

Pneumococcal Pneumonia

Causative Agent and Transmission

• Causative Agent: Streptococcus pneumoniae, gram-positive cocci.

• Transmission: Direct contact/droplets.

General Disease Information

• Symptoms: Most severe in older adults (>65). Causes chest pain, cough, and pleuritic chest pain. Can result in severe respiratory impairment and complicate chronic pulmonary disease.

• Vaccine: Pneumococcal conjugate vaccines (PCV13 or PCV23) or Pneumococcal polysaccharide vaccine (PPSV23).

• Toxin: Cytolysin.

• Zoonotic: No.

• Nationally Notifiable: No.

• Emerging Infectious Disease: No.

Lyme Disease

Causative Agent and Transmission

• Causative Agent: Borrelia burgdorferi, gram-negative spirochete.

• Transmission: Tick-borne (Ixodes species), generally in hilly/wooded areas.

General Disease Information

• Symptoms: Early: "bullseye" rash at bite site. If left untreated, can spread to joints, heart, and nervous system.

• Vaccine: No; LYMErix was discontinued in 2002.

• Toxin: No.

• Zoonotic: Yes.

Tuberculosis (TB)

Causative Agent and Transmission

• Causative Agent: Mycobacterium tuberculosis, acid-fast bacillus.

• Transmission: Airborne/droplet.

General Disease Information

• Diagnosis: Tuberculin skin test (TST) or TB blood test. Granulomas (calcified tubercles) visible on X-rays.

• Vaccine: BCG is available outside the US.

• Unique Symptoms: Latent TB infection (LTBI) possible.

• Zoonotic: No.

• Nationally Notifiable: Yes.

• Emerging Infectious Disease: Yes.

Rocky Mountain Spotted Fever

Causative Agent and Transmission

• Causative Agent: Rickettsia rickettsii, very small gram-negative rod.

• Transmission: Tick-borne; requires tick attachment for transmission.

General Disease Information

• Symptoms: High fever and rash; can cause toxic shock syndrome with a high mortality rate.

• Vaccine: No effective vaccine yet.

• Zoonotic: Yes.

• Nationally Notifiable: Yes.

• Emerging Infectious Disease: No.

Chlamydia

Causative Agent and Transmission

• Causative Agent: Chlamydia trachomatis, small gram-negative coccoid.

• Transmission: Sexually transmitted, vertical transmission possible.

General Disease Information

• Symptoms: Inflammation of the urethra and cervix; frequently asymptomatic. Can lead to PID.

• Vaccine: No.

• Toxin: No.

• Zoonotic: No.

• Nationally Notifiable: Yes.

• Emerging Infectious Disease: No.

Antibiotic Associated Diarrhea (C. diff)

Causative Agent and Transmission

• Causative Agent: Clostridium difficile, gram-positive bacilli, forms spores, anaerobic.

• Transmission: Direct or indirect fecal-oral transmission, fecal-oral route.

General Disease Information

• Symptoms: Mild to severe diarrhea and colitis. Severe cases can lead to dehydration and bloody diarrhea.

• Vaccine: No.

• Toxins: Toxin A and Toxin B (sometimes referred to as "A" and "B" but both are important).

• Zoonotic: No.

• Nationally Notifiable: No.

• Emerging Infectious Disease: No.

Summary Table: Key Features of Major Infectious Diseases

Disease	Causative Agent	Transmission	Vaccine	Zoonotic	Nationally Notifiable	Emerging Infectious Disease
Pertussis	Bordetella pertussis	Airborne	DTaP/Tdap	No	Yes	Yes
Gonorrhea	Neisseria gonorrhoeae	Sexual/vertical	No	No	Yes	No
Strep Throat/Scarlet Fever	Streptococcus pyogenes	Droplet/contact	No	No	No	No
Pneumococcal Pneumonia	Streptococcus pneumoniae	Droplet/contact	PCV13/PCV23	No	No	No
Lyme Disease	Borrelia burgdorferi	Tick-borne	No	Yes	No	No
Tuberculosis	Mycobacterium tuberculosis	Airborne	BCG (outside US)	No	Yes	Yes
Rocky Mountain Spotted Fever	Rickettsia rickettsii	Tick-borne	No	Yes	Yes	No
Chlamydia	Chlamydia trachomatis	Sexual/vertical	No	No	Yes	No
C. diff Diarrhea	Clostridium difficile	Fecal-oral	No	No	No	No

Additional info:

• These diseases are relevant to chapters on Principles of Disease and Epidemiology, Microbial Mechanisms of Pathogenicity, and Innate/Adaptive Immunity.

• Some diseases (e.g., TB, Pertussis) are re-emerging due to changes in vaccination rates or drug resistance.

• Nationally notifiable diseases are those that must be reported to public health authorities.