Microbiology Lecture: Central Nervous System Disorders (part2)
Tetanus (Lockjaw) and Clostridium tetani
Introduction to Tetanus - Tetanus is a central nervous system infection that is frequently associated with skin trauma, particularly puncture wounds. - The common cultural association with tetanus is stepping on a rusty nail. - It often results in a condition colloquially known as "lockjaw."
Causative Agent: Clostridium tetani - Classification: It is a gram-positive, rod-shaped bacterium. - Spore Formation: It forms endospores, which serve as a protective mechanism against oxygen. - Oxygen Tolerance: It is a strict anaerobe and cannot survive in environments where oxygen is present. - Pathogenic State: The bacteria remain in a nearly dormant, non-pathogenic endospore state when oxygen is available. They only transition to a vegetative, toxin-secreting state in oxygen-deprived environments.
Signs and Symptoms - Tetanospasmin: A powerful neurotoxin released by the bacteria that binds to motor neurons. - Mechanisms of Action: The toxin causes neurons to fire uncontrollably, resulting in uncontrollable and continuous muscle contractions. - Initial Symptoms: Typically begins with the flexing of the jaw muscles, leading to the name "lockjaw," where patients have difficulty opening or closing their mouths. - Risus Sardonicus: Patients often exhibit a "sardonic grin" due to the constant contraction of facial muscles. - Severe Complications: Contractions can become so violent that they cause the patient to break their own back through extreme flexion. - Mortality: Death can occur due to the paralysis of the respiratory muscles or heart failure.
Infection Dynamics - The mere presence of endospores in a wound is insufficient for infection; the environment must be anaerobic. - Tissue Damage: Significant tissue damage is required to create a vascularly compromised, oxygen-deprived area. - Secondary Causes: Severe cold (frostbite) can create an oxygen-deprived environment suitable for $Clostridium tetani$. - The Chemistry of Rust: Rust is an oxidation reaction; the association with rusty nails is due to the fact that rust indicates an environment where oxygen is being consumed/depleted, which may favor the bacteria. - Growth Rate: The bacteria grow very slowly in humans, but even a small amount of growth allows for the release of tetanospasmin into systemic circulation.
Epidemiology and Transmission - General Transmission: Endospores enter the body through trauma, burns, crush injuries (e.g., hand or foot), or frostbite. - High-Risk Populations: - Geriatric patients: Often due to waning immunity. - Intravenous (IV) drug users: Needles exposed to the elements may harbor spores. Diagnosis in this group is difficult as symptoms may be confused with seizures. - Maternal/Neonatal: Historically high due to contaminated umbilical stumps, though mortality has significantly decreased with better care. - Regional Incidence: Incidence is fairly low in North America due to high vaccination rates.
Prevention and Treatment - Vaccination: Tetanus is one of the few bacterial diseases we vaccinate against widely. The vaccine is highly effective but does not last a long time, requiring regular boosters. - Post-Exposure Prophylaxis: Because the bacteria grow so slowly, a booster shot is often administered immediately after a suspected exposure (e.g., after stepping on a nail). - Antitoxin: Tetanospasmin can be neutralized using an antitoxin if administered early. - Antibiotics: While they can be used, they are not the primary focus because the toxin, not the bacteria itself, causes the primary damage. - Lethal Dose: Tetanospasmin requires a relatively high dose to cause death compared to other potent toxins.
Botulism and Clostridium botulinum
The Concept of Intoxication - Botulism is technically an "intoxication" rather than a traditional infection because the harm is caused by the ingestion or presence of toxins rather than the proliferation of the bacteria itself. - Analogy: Similar to alcohol intoxication, where the person is under the effects of a toxin ($alcohol$).
Causative Agent: Clostridium botulinum - Classification: Gram-positive, rod-shaped bacterium. - Oxygen Tolerance: Strict anaerobe; forms endospores in response to oxygen. - Habitat: Found in soil, water, and some animal bile. It is distributed worldwide but found more frequently in the Northern Hemisphere.
The Botulinum Toxin - This is the most potent toxin on the planet; no known compound requires a smaller amount to kill a human. - Potency Comparison: An aspirin-sized amount of botulinum toxin would be sufficient to kill the entire population of Salt Lake City. - Mechanism of Action: It is a neurotoxin that circulates through the body and binds to neurons, but it has the opposite effect of tetanospasmin. - Flaccid Paralysis: It forces muscles to relax completely and prevents contraction. Death occurs when the heart stops beating or the lungs stop breathing because the muscles used for these functions are too relaxed to move.
Signs and Symptoms - Early Symptoms: Double vision, difficulty swallowing, dizziness, and slurred speech. - Misdiagnosis: Early symptoms are often mistaken for alcohol intoxication. - Late Symptoms: Full muscle paralysis and severe respiratory distress.
Epidemiology and Relevant Risks - Food Preservation: Often associated with poorly preserved foods and improper canning. - Utah Relevance: Because many people in Utah practice home canning, there is a regional emphasis on safety. The first step of canning involves removing oxygen, which creates the perfect environment for $Clostridium botulinum$ to enter a vegetative state if aseptic techniques are not followed. - Identification in Cans: The metabolism of the bacteria can produce gas/pressure, causing cans to bulge or show irregularities. - Toxin Resistance: The botulinum toxin is surprisingly resistant for an exotoxin; simply cooking food may not be enough to neutralize or remove it.
Diagnosis and Treatment - Public Health Emergency: Any suspected case must be reported immediately to the Health Department and the CDC due to potential bioterrorism concerns and the need for immediate recalls. - CDC Antitoxin: The CDC maintains supplies of antitoxin at outreach centers across the country (e.g., Northern Colorado) to be airlifted to hospitals. - Clinical Management: Hospitalization and mechanical incubation (ventilator) are mandatory because the lungs will eventually fail. - Mortality Rate: Even with perfect medical intervention, there is a mortality rate across all demographics.
Therapeutic Uses of Botulinum Toxin - Botox: Highly diluted botulinum toxin is used cosmetically to relax facial muscles and reduce wrinkles. This requires a prescription and FDA approval to ensure safety. - Neurological Treatment: Originally used to treat neurological tics and Tourette's syndrome, as a small dose relaxes the neurons enough to reduce violent, uncontrollable movements.
Rabies
General Characteristics - Rabies is a viral, zoonotic infection (capable of jumping from animals to humans). - It is characterized by fatal encephalitis (inflammation of the brain). - It has an extremely high mortality rate (nearly ) without clinical intervention.
Transmission and Epidemiology - Primary Reservoirs: Wild animals such as raccoons, bats, skunks, foxes, and badgers. Small rodents are less likely carriers in Wyoming specifically. - Mode of Entry: Typically enters through the saliva of an infected animal via a bite. It can also enter through mucous membranes (eyes/nose) or if a large amount of blood/saliva enters an open wound. - Bats: In the US, bats are a major transmission source, often carrying the virus asymptomatically.
Pathogenesis and Life Cycle - Incubation Period: Can range from days to months (average to months). The period is shorter if the entry site is near the head. - Progression: The virus remains dormant at the trauma site while multiplying, then enters nerve endings, travels through the spinal cord, and reaches the brain. - Salivary Glands: The viral cycle completes in the salivary glands, priming the host to pass the virus on via saliva.
Signs and Symptoms - Prodromal Phase: Fever, nausea, vomiting, and headache. - Neurological Stage: Severe behavioral changes, irrationality, and aggression. - Hydrophobia: Patients develop a fear of water because the act of swallowing causes immense pain due to the viral load in the salivary glands. This prevents the virus from being diluted by liquids. - Hyper-salivation: Patients produce thick, virus-laden saliva and suffer from extreme dehydration, which eventually leads to death.
Diagnosis and Treatment - Testing: PCR (Polymerase Chain Reaction) is used to detect viral DNA in the wound or saliva. - Animal Testing: It is infinitely easier to test the animal that bit the patient than to test the patient themselves. If the animal can be captured or killed, its brain and saliva are tested. - Post-Exposure Prophylaxis (PEP): Consists of a combination of passive and active vaccination. This involves multiple doses of the vaccine and human rabies immunoglobulin ($HRIG$). - Vaccine Progression: Historically, individuals required shots in the abdomen; current protocols have reduced this significantly (approximately shots). - Populations for Preventative Vaccination: Only recommended for high-risk individuals, such as fish and game wardens in endemic areas.
Cytomegalovirus (CMV)
Viral Profile - CMV is a member of the human beta herpesvirus family. - It has a very large and complex genome. - Prevalence: It is very widespread, with to of adults being infected at some point in their lives. - Persistence: Like other herpesviruses, CMV results in a lifelong infection that can remain dormant in the body for years.
Variations of Disease - Mononucleosis (Mono): Often called the "kissing disease" because it spreads through saliva. While often caused by the Epstein-Barr virus ($EBV$), CMV is another common cause. - Symptoms: Severe fatigue, sore throat, fever, and swollen glands. - Age Factors: Most severe in infants and older adults/teens; often mild in children aged to . - Treatment: Palliative care (rest and fluids). Steroids may be used for swelling but can prolong the infection by suppressing the immune system. - Pneumonia: Can occur in immunocompromised individuals. - Congenital CMV: Vertical transmission from parent to child in utero.
Congenital CMV in Detail - Over infants are born in the US annually with CMV. - Primary Risk factor: A mother contracting an active CMV infection for the first time while she is pregnant. If she had it before pregnancy, the risk is much lower. - Symptoms in Infants: Low birth weight, microcephaly (small head), seizures, and liver damage (jaundice). - Long-term Damage: Even asymptomatic infants may develop neurological issues or developmental delays. - Deafness: CMV is the leading cause of non-genetic deafness.
Prevention and Treatment for CMV - Hygiene: Good handwashing and being cautious with saliva (e.g., not sharing food/drinks or kissing babies on the mouth). - Screening: Currently, testing for CMV is not mandatory for expectant mothers like Group B Streptococcus testing is, but many advocate for its inclusion. - Antivirals: Drugs like Ganciclovir and Valganciclovir can be used to treat active infections and reduce viral load. - Early Intervention: Detecting hearing loss early leads to much better outcomes (e.g., cochlear implants).
Questions & Discussion
Audience Participation: Tetanus Associations - Instructor: "What do we often associate tetanus with?" - Student (Mark): "Jaw." - Instructor: "And what usually spurs someone to [think] they might potentially have tetanus…?" - Student: "Rusty nails. Step on a rusty nail."
Discussion of Popular Culture - The instructor mentions the movie series 28 Days Later, noting that the "Rage Virus" is actually modeled on the behavioral symptoms of rabies (aggression and lack of swallowing