Zoonotic Diseases & Bordetella (Francisella, & Yersinia)

Pathogenic Microbiology, MICR 3343

Zoonotic Diseases

  • Definition: Diseases primarily of animals that can be transmitted to humans from contact with infected animal populations, either directly or indirectly.

Types of Zoonosis

  • Tularemia

  • Brucellosis

  • Bubonic Plague

  • (Anthrax)

Francisella tularensis

  • Isolation History: First isolated from rodents in 1919 by Dr. Francis in Tulare County, CA.

  • Virulence: Considered one of the most virulent organisms that infect humans.

  • Statistics: Approximately 100-200 cases reported annually in all 50 states, although actual numbers are likely higher due to difficulties in confirmation and diagnosis.

Morphology and Physiology

  • Structural Characteristics:

    • Gram-negative rod, pleomorphic (coccoid to filamentous).

    • Facultative anaerobe.

    • Fastidious organism requiring specific culture media (cysteine-containing medium such as chocolate agar or BCYE agar) and long incubation times.

Reservoirs

  • Natural Reservoir Hosts:

    • Wild mammals (e.g., rabbits, squirrels, muskrats, beavers, deer).

    • Blood-sucking arthropods (e.g., ticks, deer flies).

    • Domestic animals, birds, and fish.

Transmission Routes

  • Transmission occurs via:

    • Inhalation of infectious aerosols.

    • Oral ingestion (hand-to-eye/mouth contact).

    • Dermal contact through broken skin with infected material.

    • Bite of infected arthropods (ticks, deer flies).

Major Clinical Manifestations of Tularemia

  • Varieties and Symptoms:

    • Ulceroglandular (70-85%): Local ulceration, cellulitis, lymphadenopathy, bacteremia, fever, disseminated lymphadenopathy.

    • Glandular (5-10%): Similar, but without ulceration.

    • Typhoidal (5-10%): Systemic disease with fever and severe illness.

    • Pneumonic (1-5%): Inflamed lungs, can be acquired via respiratory route with severe consequences.

    • Oculoglandular (1-2%): Involves painful purulent conjunctivitis and regional lymphadenitis.

    • Oropharyngeal (rare): Symptoms include sore throat and lesions in the mouth.

Pneumonic (Pulmonary) Tularemia

  • Severity and Morality Rates:

    • High mortality rates (30% untreated, 10% treated).

    • Characterized by the presence of very few organisms needed to cause disease (LD50: 1-10 organisms).

    • Possible symptoms include peribronchial infiltrates and pleural effusion.

Diagnosis of Tularemia

  • Difficult due to intracellular nature and non-specific symptoms.

Treatment of Tularemia

  • First Line: Gentamicin is the drug of choice.

  • Alternatives: Doxycycline or Ciprofloxacin for treatment or prophylaxis.

  • Mortality: Reduced to <1% with treatment.

Prevention of Tularemia

  • Preventive Measures:

    • Wear rubber gloves when handling infected materials.

    • Avoid contact with potential reservoirs (e.g., sick rabbits, ticks).

    • Use protective clothing and insect repellent.

    • Live attenuated vaccine exists but is rarely used for humans.

Brucellosis (Malta Fever)

  • Historical Context:

    • Dr. David Bruce linked Brucellosis to goat’s milk in 1887 during an epidemic among British troops in Malta.

Epidemiology of Brucellosis

  • Primarily affects those who work with animals (slaughterhouse workers, farmers, veterinarians).

  • Four species of Brucella infect humans, with 100-200 cases per year reported.

Morphology & Physiology of Brucella

  • General Characteristics:

    • Facultative intracellular aerobe.

    • Gram-negative, non-motile cocobacilli.

  • Species Involved:

    • Brucella abortus (Cattle)

    • Brucella suis (Swine)

    • Brucella melitensis (Goats and sheep)

    • Brucella canis (Dogs)

Brucellosis Transmission and Pathogenesis

  • Transmitted through contact with infected tissues or ingestion of contaminated milk.

  • Localizes in erythritol-rich organs (e.g., breasts, uterus) causing abortions, mastitis, sterility in animals.

Symptoms of Brucellosis

  • Common Symptoms:

    • Aches, chills, fever (often undulating), drenching sweats, fatigue, myalgia, muscle weakness, and common relapses.

Diagnosis of Brucellosis

  • Based on symptom history and culture on enriched media, blood culture, serology (titer >640), and skin tests with brucellergin.

Treatment of Brucellosis

  • Prolonged use of rifampin with tetracycline or streptomycin.

Yersinia pestis (Plague)

  • Historical Impact: Mankind has suffered substantial mortality from plague, notably in the 6th century (~100 million deaths) and in the 14th century (~25 million deaths in Europe).

Yersinia pestis History

  • Identified by Dr. Yersin in 1894, mainly seen in sylvatic cases in the Southwestern U.S. with occasional urban cases.

Morphology and Physiology of Yersinia pestis

  • Characteristics:

    • Gram-negative, pleomorphic bacillus.

    • Facultative anaerobe with optimal growth at 28 °C.

Forms of Plague

  • Sylvatic Plague: Found in animal populations (rodents, rabbits).

  • Bubonic Plague: Transmitted from infected flea bites to humans.

  • Pneumonic Plague: Spreads from human to human via aerosols.

Yersinia pestis Life Cycle

  • Steps involved in the infective process via fleas:

    1. Bacteria form in flea gut.

    2. Flea regurgitates bacteria during a bite on an animal/human.

    3. Most bacteria destroyed by immune cells, some survive.

    4. Surviving bacteria re-encapsulate and grow.

    5. Progeny are resistant to intracellular killing.

Symptoms of Bubonic Plague

  • Clinical Presentation:

    • Initially cutaneous lesions at puncture sites; later development of purpuric lesions.

    • Symptoms include: Sudden onset headache, malaise, myalgia, fever, and painful swollen lymph nodes (buboes).

Symptoms of Pneumonic Plague

  • Characteristics:

    • Acquired through inhalation of infectious aerosols with flu-like symptoms.

    • Rapid progression to severe respiratory issues, often leading to death within 1-3 days.

Pathogenicity of Yersinia pestis

  • Virulence Factors:

    • Calcium-dependent morphology changes.

    • Plasmid-encoded proteins (e.g., proteins V & W for rapid proliferation, F-1 antigen as an antiphagocytic factor).

Diagnosis of Plague

  • Methods:

    • Examine aspirate from buboes, blood, or sputum.

    • Use of bipolar staining and fluorescent antibody tests for identification.

Treatment and Prevention for Plague

  • Treatment: Requires strict isolation and hospitalization. Medications include tetracycline, ciprofloxacin, or doxycycline.

  • Prevention: Manage rodent and flea populations to reduce outbreaks.

Bordetella pertussis

  • Reported Cases: Historical numbers from 1922-2013 show significant incidence of pertussis (whooping cough).

Morphology of Bordetella pertussis

  • Characteristics:

    • Very small, gram-negative coccobacilli.

    • Strict aerobe that does not ferment but can oxidize amino acids.

Disease Progression in Pertussis

  • Stages:

    • Initial catarrhal stage: Mild symptoms.

    • Paroxysmal stage: Characterized by whooping cough episodes.

    • Convalescent stage: Gradual recovery.

Complications from Pertussis in Infants

  • Severe complications are prevalent in infants under 1 year, with hospitalization rates around 50%.

    • Risk of pneumonia (23%).

    • Convulsions (1.6%).

    • Apnea (67%).

    • Risk of encephalopathy (0.4%) and mortality (1.6%).

Complications for Teens and Adults

  • Generally less severe but may lead to significant issues from severe coughing:

    • Passing out, fractured ribs, pneumonia (2%).

Virulence Factors of Bordetella pertussis

  • Mechanisms:

    • Symptoms caused by pertussis toxin and other virulence factors [e.g., filamentous hemagglutinin, pertactin]. These promote adherence and local tissue destruction in the respiratory tract.

Epidemiology of Pertussis

  • Human Reservoir: Pertussis is spread among humans, commonly affecting children under 1 year and older children/youth, particularly those unvaccinated.

Vaccine Recommendations

  • Current Vaccination Strategy:

    • DTaP for infants protects against diphtheria, tetanus, and pertussis.

    • Tdap booster recommended as immunity wanes.

    • New recommendations suggest earlier boosters for adults than previously every 10 years.