Soilborne & Insect Transmitted Pathogens

Anthrax

• Association with history

  • 5th & 6th plaques of exodus

  • Black Bane in 17th century Europe

  • Epidemics in Europe during 18th & 19th centuries

• Bacillus anthracis

  • Sporulating

  • Disease due to toxin

  • Aerobic

• 3 forms

  • Cutaneous anthrax

  • Gastrointestinal anthrax

  • Inhaled anthrax

Zoonosis

• Transmission in animals by ingestion of spores while grazing

• Transmission to humans by contact with contaminated animal products or inhalation of spores

Anthrax — Virulence Factors

• Capsule 2-binary toxins with common B-component

Types of Anthrax

• Cutaneous anthrax

  • Eschar formation after endospores enter through abrasions

• Pulmonary anthrax

  • Spores are picked up by aveolar macrophages which may transport them to lymph nodes

  • Spores resist phagocytosis and germinate in macrophages eventually lysing them

  • Symptoms: flu-like to pneumonia-like

Vaccines

• Anthrax vaccines first produced by Louis Pasteur

  • Current vaccines are accellular

Clostridium perfringens

• Gram positive rod

• Spore form in soil

• Germinates in animal intestine or in damaged tissue (anaerobic)

• The only clostridia sp. to invade tissue

Major Toxin — α Toxin

• Other major toxins present:

  • β toxin: loss of intestinal mucosa

  • ε toxin: increase permeability of GI wall

  • ι toxin: AB toxin with ADP ribosylating activity

C. perfringens Nagler Reaction

• Lecithinase (α-toxin; phospholipase) hydrolyzes phospholipids in egg-yolk agar around streak on right

• Antibody against α-toxin inhibits activity around left streak

Minor Toxins — C. perfringens type A

• δ Hemolysin

• ν DNase

• μ Hyalurnidase

• κ Collagenase

• θ Hemolysin

• λ Protease

Organic Acids — C. perfringens type A

• H₂

• CO₂

• H2_S

• C₂H₄O₂

• C₄H₈O₂

Clostridial myonecrosis

• Treatment

  • Antibiotics

  • Surgical excision, debridement

  • Hyperbaric oxygen

Clostridium tetani

• Tetanus toxin — A-B toxin (plasmid encoded)

  • Small polypeptide of tetanus toxin blocks release of inhibitory neurotransmitter

  • Both muscles fully contract. The arm flexes because biceps brachii is larger and stronger

• Symptoms begin in head & neck region then progress through body

• Treatment & prevention

  • Passive immunization with tetanus immunoglobulin to bind any circulating toxin

  • Antibiotics to destroy any tetanus bacteria

  • Vaccination with tetanus toxoid induces antibody against the heavy chain, preventing attachment of toxin to target cells

Borrelia hermsii

• Hosts

  • Small rodents or humans

• Vectors

  • Insects

• Humans are often accidental hosts for most vector-borne diseases

  • Dead end host

    • Not a complete cycle

• Antigenic variation — type C

Borrelia burgdorferi

• Lyme disease transmitted by deer tick (Ixodes)

• Borrelia changes outer surface protein (OSP) expression depending upon host

  • Borrelia Osp C binds a tick salivary protein (Salp15) on its way from the tick’s midgut to a new animal host

  • Once inside its new animal host, the OspC-Salp15 complex protects Bb from antibody-mediated killing

  • Has also been shown to inhibit the activation and proliferation of CD4+ helper T-cells

• Borrelia binds to complement regulatory protein Factor H, a protein that prevents complement lysis of our own cells

Erythema migrans

• Early symptoms

  • Malaise, fatigue, fever, chills, head & body aches

• Long-term complications

  • Arthritis

  • Cardiac-conduction system

  • Secondary erythema migrans

  • Acrodermatitis chronica atrophicans

  • Brain damage

Human Monocytic Ehrlichiosis vs Human Granulocytic Anaplasmosis

• These two illnesses are similar in terms of symptoms but are typically found in different areas of the U.S. Why might this be?

• Which of the two may have something in common with Lyme disease? What is it that they share?

Yersinia pestis

• Endemic foci

• Flea is actually infected. The Hemin system of Yersinia causes a blockage between the esophagus and midgut

  • Transmission of Y. pestis occurs during the futile attempts of the flea to feed

  • Ingested blood dislodges bacteria lodged in the blocked area and is regurgitated back into the host circulatory system