Infectious Diseases and Anthrax Quiz

Integrated Pathology: Infectious Disease

• Infectious disease is detected when an agent causes pathological effects on tissues and cells. Infectious agents are contagious and/or transmittable, causing infection.
• Determining infectivity has implications for diagnosis, treatment, prognosis, and prevention.
• Infectious diseases are easily transmitted, especially through air or water. They have a causative agent (aetiological agent), often microscopic organisms (microorganisms or microbes).
• Infectious agents cause infection when they damage tissues or cells, leading to symptomatic disease.

Causes of Infectious Disease

• Infectious diseases are caused by bacteria (prokaryotes), viruses (non-cellular), fungi (eukaryotes), protozoa (eukaryotes), prions (proteins, non-cellular), helminths (non-microbial, eukaryotes), and arthropods (non-microbial, eukaryotes).
• Each causative agent has unique characteristics (e.g. organism type, replicative processes, structural and molecular composition, and genetics).
• These characteristics influence how they interact with the host and cause disease.
• Archaea have a possible role in periodontal disease, but no infectious agent is currently known.

When Infectious Diseases Occur

• Microorganisms can be commensal (harmless), obligate pathogens (always cause disease), or opportunistic pathogens (cause disease when conditions are favourable).
• The human microbiome includes archaea, bacteria, fungi, and viruses in various locations (mouth, skin, digestive, urogenital).

Koch's Postulates

• Koch's postulates (1890): to identify a microbe as the causative agent of a disease.
• The agent must be present in all cases of disease but not in healthy individuals.
• The agent should be isolated in pure culture.
• The isolated agent should cause the disease when inoculated in an animal model.
• The same agent should be re-isolated from the infected animal.
• Cause-and-effect is more important than just association.

Routes of Transmission

• Aerosol transmission: inhalation of airborne droplets containing microorganisms.
• Oral transmission: ingestion of contaminated food or water.
• Direct contact transmission: contact with infected individuals or bodily fluids through entry sites (e.g., eyes, mouth, nose or wound).
• Fomite transmission: via contaminated surfaces of inanimate objects (e.g., cages, door handles, medical equipment).
• Vector-borne: transmission by other living organisms (e.g., mosquitoes, ticks).
• Zoonotic: transmission from animals to humans.

Transmission of Disease-Causing Agents

• Infectious agents must be transmitted between hosts through various routes.
• The routes are specific to the microorganism and the tissue or cell it infects.
• For example, rhinoviruses (common cold) infect the respiratory tract and spread through airborne droplets of sputum and mucus— inhaled by another person.

Case Study: Bacillus anthracis

• Gram-positive bacilli, endospore-forming bacteria present in the environment (soil, water, contaminated animal products - wool, hides, hair).
• Occurs globally.
• Has a capsule and two toxins (lethal factor and edema factor).
• Different transmission routes cause various forms of anthrax: cutaneous, gastrointestinal, inhalation, injection (needle-administered drug use), and welders' anthrax.

Case Study: Pathologies and Transmission: Bacillus anthracis

• Cutaneous anthrax: Wound contamination with spores (from environment or animals), typical black eschar, 1-6 days onset, 20% fatality rate if untreated, but 100% survival with treatment.
• Gastrointestinal anthrax: Ingestion of spores from infected animal meat, diarrhea, bloody diarrhea, stomach pain, abdominal swelling, headache, fainting, flushing, 50% fatality rate if untreated, but 60% survival with treatment.
• Inhalation anthrax: Breathing in spores from contaminated animal products, 1-2 months onset, fever, chills, sweating, headache, body aches, cough, chest discomfort, shortness of breath, nausea, vomiting, extreme tiredness, 100% fatality if untreated, 55% survival with treatment.
• Injection contracted anthrax: Contaminated needles, swelling at injection site, nausea, vomiting, sweats.
• Welder's anthrax: B. cereus group, produces anthrax toxin, pneumonia-like symptoms, fever, chills, cough, shortness of breath (dyspnea), and coughing up blood.

Pathological effects in infectious diseases

• Spores germinate at low level in tissues.
• Spores are phagocytosed by macrophages.
• Bacilli containing macrophages spread through lymphatic system.
• Capsule prevents phagocytosis of vegetative cells.

Infectious disease toxins

• Edema toxin: increases intracellular cyclic AMP levels, protective antigen binds to cells.
• Lethal toxin: zinc metalloprotease triggers inflammation via MAPKK and leads to shock, ROS and proinflammatory cytokines.

Regional hemorrhagic lymphadenitis

• Bacilli spread in blood causing septicaemia (10⁷ to 10⁸ organisms per milliliter of blood), spreading to brain and meninges, pulmonary blockage.

Routes of Transmission: RTI agents

• Airborne pathogens transmit through inhalation of airborne droplets.
• Specific pathogens infect specific body regions in the respiratory tract (e.g., upper respiratory tract, lower respiratory tract.)

How can ID be characterized?

• Infectious diseases are characterized by signs (objective) and symptoms (subjective).
• Signs can be detected and measured (e.g., fever, coughing).
• Symptoms can be described(e.g., pain, nausea).
• Infection pathology results in these signs and symptoms, leading to a syndrome.

Case Study: Influenza Syndrome

• Causative agent: segmented, negative-sense ssRNA influenza virus.
• Pleomorphic nucleocapsid.
• Signs and symptoms: fever, cough, sore throat, congestion, muscle/body aches, fatigue, vomiting, and diarrhea.

Clinical signs and symptoms

• Data comparing clinical signs and symptoms of Covid-19, Flu, and Common Cold.

Characteristics of Infectious Disease: Phases

• Incubation period—time between infection and symptom onset.
• Prodromal phase—mild, non-specific symptoms.
• Clinical phase—typical signs and symptoms appear.
• Decline phase—subsidence of symptoms.
• Recovery phase—return to health and strength.

Characteristics of Infectious Diseases: Duration

• Acute—rapid development and progression.
• Chronic—slow development, less severe, long-lasting.
• Latent—no symptoms between outbreaks.

Characteristics of Infectious Diseases: Classification (By Location)

• Local—confined to a specific area.
• Systemic—spreads to multiple body sites and tissues.

Characteristics of Infectious Diseases: Classification (By Timing)

• Primary—initial infection in a previously healthy person.
• Secondary—occurs in a weakened person (after primary infection).

Case Study: Primary Infection

• Human Immunodeficiency Virus (HIV)
• +ve ssRNA genome, enveloped capsid
• Transmission—bodily fluids
• Flu-like illness 2-6 weeks (80% of cases initially)
• Symptoms: fever, sore throat, body rash
• T-cell infection and decrease in CD4+ cells (important aspect of disease). 500 and 1,200 cells per µl.

Secondary Infection

• Infection after a primary infection in a person whose immune system is weakened.
• Risk increases when CD4+ T-cell count is lower than 350 cells per µl.
• Opportunistic infections, such as pneumonia, occur.

Pathogenesis of Infectious Diseases

• How infectious agents cause disease.
• Mechanisms of pathogenicity depend on the infecting pathogen.
• Production of cell-and-tissue-damaging poisons (e.g., by bacteria).
• Direct invasion and destruction of host cells (e.g., viruses).
• Triggering host immune responses, leading to disease signs and symptoms.

Steps in Infection

• Entry and attachment to the body.
• Colonization, local or general spread through the body.
• Replication.
• Exit (shedding from the body).

Pathogenesis of Infectious Diseases

• Pathological effects of diseases can be due to multiple causative agents.
• Some shared pathogenesis (e.g., respiratory infections, bloodstream infections, encephalitis, meningitis, endocarditis, gastrointestinal disease).

Pathogenesis of Infectious Diseases: Skin and Soft Tissue

• Mucocutaneous lesions.
• Abscess formation (infection and inflammation of hair follicle).
• Spreading infections.
• Necrotizing infections.
• Skin manifestations by systemic infections.

Insight to site specific pathogenesis

• Understanding skin infections from direct contact, connecting skin structure to the site of infection and the infectious agent.

Diagnosis of Infectious Diseases

• Signs and symptoms.
• Detection of microorganisms.
• Pathology: diagnostic histopathology
• Pathology procedures: molecular immunohistochemistry, in situ hybridization on formalin fixed paraffin embedded tissues.
• Assessing tissue reactions and lesion characteristics to associate them with infection.
• Determining type of inflammatory reaction (e.g., fibrinous, purulent, lymphocytic, granulomatous).

Diagnosis Using Microscopy

• Specific stains for identifying microorganisms (e.g., Ziehl-Neelson, Gomori Grocott, Acian blue, Warthin Starry).
• Immunohistochemistry: using antibodies to identify microorganisms in tissue samples.
• Other methods: in situ hybridization (ISH), electron microscopy (EM), and molecular biology (PCR) for identifying microorganisms.

Diagnosis of Infectious Diseases

• Uses in emerging infectious diseases (e.g. Zika, HIV/AIDS).
• Observations of associated pathologies provide insights into pathogenic effects and mechanisms.
• Limitations include the availability of specific antibodies.

Emerging Infectious Diseases

• Newly appeared or rapidly increasing diseases.
• Factors that cause emergence: resistance to antimicrobial drugs, new/unknown/spread agents to new locations.
• Examples: Gonorrhea, measles, and Zika.

In Summary

• Infectious diseases can result in diverse pathological diseases.
• Determining the causative agent aids in treatment and prevention.
• Considerations are needed for infectious disease versus asymptomatic carriage.
• Microbiota studies provide insights into health/disease states.
• Diagnosis needs combination of signs, symptoms, clinical diagnosis, and epidemiological insights.
• Infectious disease management is needed.

Further Reading

• Resources, like review articles or book chapters, about Ecthyma Gangrenosum, Escherichia coli or Pseudomonas aeruginosa.
• Books, like Brock Biology of Microbiology (2019), with information about immunological and molecular tools for disease diagnosis.

References

• List of relevant scientific articles and studies.

Test your knowledge on infectious diseases, specifically focusing on anthrax and its manifestations. This quiz covers the symptoms, immune responses, and transmission routes associated with Bacillus anthracis. Ideal for students in microbiology or infectious disease courses.