Infectious Diseases and Their Pathogens

Brucellosis (Undulant Fever)

  • Also known as Undulant Fever.

  • Rare in the United States.

  • Caused by Brucella abortus, which is a Gram-negative bacterium.

  • Key Features:

    • Undulant fever is characterized by recurring daily high fever, chills, and night sweats.

    • It is not fatal.

  • Mode of Transmission:

    • Primarily from unpasteurized milk from infected animals.

    • Can also occur from direct contact with infected animals; described as a zoonotic disease.

  • Prevention Measures:

    • Vaccination of livestock and wild animal populations is essential.

    • Consumption of pasteurized milk to reduce risk.

  • Treatment:

    • Prolonged treatment with antibiotics is necessary for recovery.

  • Diagnosis:

    • Based on clinical signs and laboratory tests.

  • Predisposing Factors:

    • Higher risk for dairy workers and handlers of animal hides such as leather makers and hunters.

Hepatitis A

  • Hepatitis A is an inflammation of the liver caused by the Hepatitis A virus (HAV), which is classified as an RNA virus.

  • Key Features:

    • The virus is shed during the acute phase and can survive for several days on surfaces.

    • Resistant to chlorine treatment of drinking water.

    • The virus multiplies in the epithelial lining of the intestinal tract and spreads to the liver, kidneys, and spleen (referred to as viremia).

  • Signs and Symptoms:

    • Primarily asymptomatic in children; adults tend to show symptoms including anorexia, nausea, diarrhea, headache, fever, chills, and jaundice in later stages.

  • Incubation Period:

    • Typically lasts 2 to 6 weeks.

  • Mode of Transmission:

    • Primary: Contaminated food and water.

    • Secondary: Human-to-human contact.

  • Prevention Measures:

    • Inactivated HAV vaccine is available, emphasizing the importance of vaccination.

  • Diagnosis:

    • Identified through serology tests and the detection of antiviral antibodies (IgM).

  • Outcomes:

    • Infection does not become chronic; the mortality rate is low, and recovery entails lifelong immunity due to memory B cells.

Viral Gastroenteritis (Stomach Flu)

Rotavirus

  • Classifications: RNA virus.

  • Commonly found in children, especially in daycare centers.

  • Signs and Symptoms:

    • Characterized by low-grade fever, prolonged diarrhea, and vomiting lasting about 1 week (approximately 2-3 days duration).

  • Prevention Measures:

    • Live oral vaccine available.

  • Virus Shedding:

    • Viral antigens can be detected in feces during infections, especially in winter months.

Norovirus

  • Classifications: RNA virus.

  • Affects both adults and children.

  • Key Features:

    • Known for its low Infectious Dose (ID50), making it highly contagious.

  • Signs and Symptoms:

    • Symptoms include diarrhea and vomiting for 2-3 days with a short incubation period of 18-48 hours.

Poliomyelitis (Polio)

  • Commonly known as paralytic Polio, caused by the poliovirus, classified as an RNA virus.

  • Pathophysiology:

    • The virus multiplies in motor neurons, predominantly asymptomatic; however, less than 1% experience paralysis due to the virus affecting the nervous system.

  • Mode of Transmission:

    • Primary transmission through contaminated water.

    • Secondary mode involves human-to-human contact through fecal-oral route.

  • Prevention Measures:

    • Salk vaccine: an injected, inactivated or killed vaccine.

    • Sabin vaccine: an oral, attenuated live vaccine offering lifelong immunity.

  • Treatment:

    • No specific treatment; primarily supportive care provided during recovery.

Giardiasis

  • Causative Agent: Giardia intestinalis; classified as a flagellated protozoan parasite.

  • Lifecycle:

    • Displays a multi-stage lifecycle, including dormant cysts (ingested) and trophozoite (active).

  • Signs and Symptoms:

    • Prolonged diarrhea, hydrogen sulfide gas production (characterized as a rotten egg smell), weight loss, cramps, often described as "explosive diarrhea."

  • Diagnosis:

    • Stool samples indicate the presence of the protozoan.

  • Mode of Transmission:

    • Commonly contracted through drinking from rivers and streams.

Amoebiasis (Amoebic Dysentery)

  • Causative Agent: Entamoeba histolytica; classified as a protozoan parasite.

  • Lifecycle:

    • Also exhibits a multi-stage lifecycle with cysts transforming into trophozoites.

  • Signs and Symptoms:

    • Symptoms include nausea, fever, abdominal cramps, ulceration, and perforation of intestinal walls, potentially leading to bloody diarrhea.

  • Pathophysiology:

    • The trophozoite form may invade the liver, creating necrotic liver abscesses.

  • Mode of Transmission:

    • Primary: Contaminated water sources.

  • Prevention Measures:

    • Boiling water before consumption to eliminate cysts.

  • Treatment:

    • Involves anti-parasitic and protozoal drugs.

Tapeworm Infections (Taeniasis)

Tapeworm Lifecycle

  • Causative Agent: Taenia saginata (beef tapeworm infection)

  • Lifecycle:

    • Displays a multi-stage lifecycle that includes both adult stages in definitive hosts and larval stages in intermediate hosts.

    • Sexual reproduction occurs in definitive hosts (humans), while asexual reproduction occurs in intermediate hosts (cattle).

  • General Statistics:

    • Adult tapeworms can reach lengths of 4-8 meters and consist of 1000-2000 segments.

  • Mode of Transmission:

    • Infection occurs through consumption of contaminated or undercooked meat.

  • Prevention Measures:

    • Ensure meat is thoroughly cooked to eliminate potential larvae.

Anatomy of the Tapeworm

  • Key Structure:

    • Scolex (head) with hooks for attachment to intestinal walls and suckers for nutrient absorption.

    • Cuticle serves as an outer covering for protection and nutrient absorption.

    • Proglottids (body segments) contain reproductive systems, with each segment containing both testes and ovaries.

  • Lifecycle Summary:

    1. Human (definitive host) consumes raw/undercooked beef containing cysticerci larvae.

    2. Cysticerci larvae develop into adult tapeworms in the human intestines.

    3. Mature proglottids containing eggs are passed in feces and disintegrate, releasing eggs into the environment.

    4. Cattle (intermediate host) becomes infected by ingesting contaminated food/grass containing the eggs.

  • Prion Diseases:

    • Caused by abnormally folded, infectious protein particles, primarily affecting the nervous system.

    • Highly resistant to degradation and transmission occurs through consumption of contaminated animal tissue.

  • Incubation period for prion diseases usually spans years before symptoms manifest, typically involving progressive degeneration of brain tissue; classified under transmissible spongiform encephalopathy.

    • Includes conditions such as Mad Cow Disease (Bovine Spongiform Encephalopathy), Creutzfeldt-Jakob Disease (CJD), and Sheep Scrapie.

    • Prevention strategies involve incineration of contaminated materials; there is no known treatment, and these diseases are often chronic and fatal.