Microbiology and Infectious Diseases Quiz

Microbial Diseases of the Nervous System

• The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS).
• The CNS (brain and spinal cord) is highly protected by bone and other structures.
• The blood-brain barrier prevents most circulating pathogens from entering the CNS.
• The three membranes covering the brain and spinal cord are the meninges (dura mater, arachnoid mater, and pia mater).
• Cerebrospinal fluid (CSF) fills the subarachnoid space, with a volume of 100 to 160 ml in adults.

Damage to the Nervous System

• Damage to the CNS can cause significant health problems including deafness, blindness, learning disabilities, paralysis, and death.
• Cerebrospinal fluid is vulnerable because it lacks many of the defenses found in blood.
• Pathogens causing nervous system diseases often have unique virulence characteristics, such as the ability to replicate in peripheral nerves and spread to the CNS.

Inflammation of the Nervous System

• Bloodstream and lymphatic systems are the most common routes of CNS invasion when the blood-brain barrier permeability is altered.
• Meningitis is inflammation of the meninges (protective membranes surrounding the brain and spinal cord).
• Encephalitis is inflammation of the brain.
• Meningoencephalitis is inflammation of both the meninges and the brain.
• Different pathogens can cause meningitis, including viruses, bacteria, fungi, and protozoa.

Bacterial Meningitis

• Initial symptoms of bacterial meningitis include fever, headache, stiff neck, followed by nausea and vomiting, and potentially progressing to convulsions and coma.
• Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type B are three main causes of bacterial meningitis.
• Opportunistic pathogens like Listeria monocytogenes, group B streptococci, and some gram-negative bacteria can also cause it.
• Diagnosis involves investigating CSF with Gram stain and latex agglutination tests.

Haemophilus influenzae Meningitis

• Haemophilus refers to the need for blood factors in growth.
• It's a gram-negative aerobic bacteria commonly found in the normal throat microbiota.
• Most cases occur in children between 6 months and 4 years old.
• Infections can also lead to pneumonia, otitis media, and epiglottitis.
• It's preventable by the Hib vaccine.

Neisseria Meningitis

• Also known as meningococcal meningitis, it's caused by Gram-negative, aerobic cocci with a capsule.
• Five capsular serotypes (B, C, Y, W-135) occur with variation in distribution.
• Serotype B & C are more common in the U.S. and Serotype A is prevalent in Africa.
• Throat infection, rash, and rapid production of endotoxins can result.
• Healthy carriers are common reservoirs.
• High mortality rate (80%) without chemotherapy.
• Vaccination is recommended for college students.

Streptococcus pneumoniae Meningitis

• Also called pneumococcal meningitis, it's caused by gram-positive diplococcus.
• 70% of people are healthy nasopharyngeal carriers.
• Most common in children (1 month to 4 years).
• High mortality rate (30% in children, 80% in elderly) without treatment.
• Preventable by a conjugated vaccine.

Listeriosis

• Caused by Listeria monocytogenes.
• A gram-positive aerobic rod, appearing in two forms: infecting adults and causing fetal/newborn infections.
• Commonly found in ready-to-eat meats and dairy products.
• Capable of growing at refrigerator temperatures.
• High infant mortality rate (about 60%).
• Spreads phagocyte-to-phagocyte.
• Penicillin G is the antibiotic of choice for treatment.

Diagnosis and Treatment of Bacterial Meningitis

• CSF sample is obtained via lumbar puncture.
• Gram stain and culture are performed on the sample.
• Pathogens are sensitive to storage and temperature changes; rapid and accurate treatment is vital.
• Chemotherapy is typically initiated before pathogen identification.
• Broad-spectrum third-generation cephalosporins are often used.

Tetanus

• Caused by Clostridium tetani, a Gram-positive, endospore-forming, obligate anaerobe found in soil contaminated with animal feces.
• Grows in deep wounds.
• Tetanospasmin, released from dead cells, blocks relaxation pathways in muscles, causing opposing muscles to contract.
• Characterized by spastic paralysis.
• The bacteria do not spread extensively from the infection site.
• Treatment involves tetanus immune globulin (TIG).

Botulism

• First described in the 1800s as a sausage disease, caused by Clostridium botulinum, a Gram-positive, endospore-forming, obligate anaerobe.
• Produces an exotoxin (neurotoxin) in anaerobic environments (like sealed cans).
• Intoxication results from ingesting botulinal toxin.
• The toxin blocks the release of acetylcholine, halting neurotransmitter function.
• Multiple serological types of botulinal toxins exist (e.g., A, B, E).

Botulism Types

• Type A toxin is proteolytic, highly virulent (60-70% mortality). Common in the U.S. (California, Washington, Colorado) and found in many food products.
• Type B toxin (25% mortality) is common in Europe and eastern U.S.
• Type E toxin is found in marine or lake sediments (e.g., seafood). Common in Northern U.S. (Alaska, Great Lakes area)

Botulism Symptoms and Treatment

• Symptoms include flaccid paralysis developing in 1–10 days, often with blurred vision, difficulty swallowing, and general weakness. Death is possible due to respiratory and cardiac failure.
• Infant botulism results from C. botulinum growth in the intestines (often associated with honey).
• Wound botulism results from C. botulinum growth in wounds.
• Treatment includes supportive care, antitoxin, and in the case of infant botulism, intravenous human immune globulin.
• Prevention includes proper food handling (boiling/canning), storage, and avoidance of honey in infants.

Diagnosis of Botulism

• Diagnosed through injecting samples from patient serum, stool, vomitus, or suspected food into mice.
• Antibodies are introduced to cause a response.

Use of Botox

• Botulism toxin (Botox) has therapeutic uses for conditions like chronic headaches, muscle contractions, and cerebral palsy.
• Application for cosmetic purposes to eliminate forehead wrinkles.

Leprosy

• Also known as Hansen's disease.
• Caused by Mycobacterium leprae, an acid-fast rod.
• Grows best at 30°C.
• Characterized by preference for the outer and cooler parts of the body, growing in peripheral nerves and skin cells.
• Transmission requires prolonged contact with an infected person.
• Two main types: Tuberculoid (neural form) characterized by loss of sensation, positive lepromin test; Lepromatous (progressive form) characterized by disfiguring nodules, negative lepromin test.

Leprosy Diagnostics and Treatment

• Diagnosis is via skin biopsy for identifying acid-fast bacilli in nerves.
• Armadillos can be used to culture the bacillus.
• Treatment involves a combination of drugs: Dapsone, rifampin, and clofazimine.

Poliomyelitis (Polio)

• Caused by Poliovirus (ss RNA virus).
• Transmitted via ingestion.
• Initial symptoms include sore throat and nausea; viremia (viruses in the blood).
• Can cause paralysis in <1% of cases due to motor cell destruction.
• Prevention focuses on vaccination (e.g., Oral Polio Vaccine (OPV), Inactivated Polio Vaccine (IPV), enhanced-inactivated polio vaccine).

Rabies

• Caused by rabies virus, transmitted through animal bites.
• Two types of rabies: furious and paralytic.
• Furious rabies: restlessness, highly excitable behavior.
• Paralytic rabies: animals appearing unaware.
• Virus initially replicates in skeletal muscles, then in brain cells causing encephalitis.
• Symptoms include muscle spasms, difficulty swallowing, and hydrophobia.
• Animals commonly infected by rabies (in U.S.) include raccoons, bats, skunks, foxes.

Rabies Prevention

• Pre-exposure prophylaxis (PEP) involves injections of Human Diploid Cell Vaccine (HDCV) administered in 3 doses with spacing from 1-7-21 days..
• People at high risk (veterinarians, animal handlers) should receive this.
• Post-exposure treatment involves rabies immune globulin (RIG) and 4 doses of rabies vaccine (spaced 1-3-7-14 days) following a probable exposure.
• Wound cleaning is critical.

Arboviral Encephalitis

• Caused by arboviruses transmitted by arthropods (e.g., mosquitos, ticks).
• Viruses belong to families like Flavoviridae and Togaviridae, and specific viruses cause different types of encephalitis (e.g., Western equine encephalitis, Eastern equine encephalitis, St. Louis encephalitis, California encephalitis, West Nile encephalitis).
• Prevention involves controlling mosquito populations.
• Vaccines are available for some types.

Cryptococcus neoformans Meningitis

• Also called cryptococcosis, caused by a soil fungus found in pigeon and chicken droppings.
• Transmitted via the respiratory route, spreading through the bloodstream to the CNS, leading to meningitis.
• High mortality rate (up to 30%) without treatment.
• Treatment includes antifungals such as amphotericin B and flucytosine.

African Trypanosomiasis

• Caused by Trypanosoma brucei gambiense (chronic, 2-4 years) or Trypanosoma brucei rhodesiense (acute, few months).
• Transmitted by the tsetse fly.
• Prevention focuses on eliminating the vector.
• Treatment involves eflornithine, an enzyme blocker for the parasite.

Naegleria fowleri

• Free-living protozoan that infects nasal mucosa.
• Often transmitted from swimming water.
• Leads to a fulminant brain infection (Primary amoebic meningoencephalitis).
• Rare disease.

Transmissible Spongiform Encephalopathies (Prion Diseases)

• Caused by prions (proteins).
• Includes diseases like sheep scrapie, Creutzfeldt-Jakob disease, Kuru, and bovine spongiform encephalopathy.
• Chronic and often fatal.
• Prions are notably difficult to destroy.
• Prevention involves sterilizing surgical instruments with NaOH and extended autoclaving.

Chronic Fatigue Syndrome (CFS)

• Also called myalgic encephalomyelitis (ME).
• Characterized by unexplained fatigue lasting at least 6 months, plus four of the following: sore throat, tender lymph nodes, muscle pain, pain in multiple joints, headaches, unrefreshing sleep, malaise after exercise, memory/concentration impairment.
• Experimental treatments include promoting antiviral interferons.

Test your knowledge on leprosy, meningococcal infections, and listeriosis in this comprehensive quiz. Explore various aspects of diagnosis, treatment, and characteristics of these infectious diseases. Gain insight into important microbiological concepts and their clinical significance.