Quiz 3 Review

Quiz 3 Review

Coronavirus Overview

  • Regular Coronaviruses (HCoV): There are four main types of coronaviruses:

    • COVID-19 (SARS-CoV-2)

    • SARS-CoV

    • MERS

    • Other seasonal coronaviruses

  • Transmission: SARS-CoV-2 is spread via the respiratory route and is highly contagious. Vaccination has limitations due to the potential for the virus to mutate and re-emerge, making consistent vaccination efforts less effective in the long term.

  • Reservoirs:

    • Bats are primary reservoirs for coronaviruses.

    • Intermediate host of SARS-CoV: Palm Civet - it is not highly transmittable and has a prodrome period where it is not infectious until respiratory symptoms appear. This makes isolation methods crucial.

  • Receptor Details:

    • SARS-CoV utilizes the ACE2 receptor located in the upper respiratory tract of its hosts.

Mortality and Transmission Rates

  • MERS (Middle East Respiratory Syndrome):

    • Reservoir: Camels; mortality rate is 36%, but it is not highly transmittable. In humans, it uses the DPP4 receptor.

    • Transmission is lower due to the differing receptor sites in camels (upper) and humans (lower).

  • SARS-CoV-2:

    • Mortality is low but it is highly contagious. Uses the ACE2 receptor, with transmission occurring via short-range aerosols. Many individuals are asymptomatic, with some acting as super spreaders. The mortality rate in children is low.

    • Diagnosis: Typically done through nasal swab and PCR testing.

    • Immunity: Following infection, neutralizing antibodies develop but can decline over several months; notably, the severity of initial infection correlates with the quantity of antibodies produced.

Vaccines

  • Vaccine Types:

    • mRNA vaccines have been linked to adverse effects such as myocarditis and thrombosis.

    • Risk Factors for Severe COVID:

    • Advanced age

    • Cardiovascular diseases

    • Obesity

    • Lung diseases

Lyme Disease

  • Pathogen: Lyme disease is caused by the spirochete Borrelia burgdorferi.

  • Incubation Period: Ranges from 1 to 31 days.

  • Transmission: Spread through tick bites, with the primary reservoir being the white-footed mouse (also, chipmunks, voles, and other rodents can transmit).

    • Tick Lifecycle: It’s important to note that the tick cycle does not allow the spirochete to pass through the ovaries to the eggs, preventing congenital transmission.

Stages of Lyme Disease

  1. Early Stage: Symptoms include achy joints. Erythema migrans is observed, leading to an expanding rash over weeks.

  2. Early Disseminated: Involves multiple skin lesions, heart block, and cranial nerve palsies.

  3. Late Lyme Disease: Characterized by arthritis, peripheral neuropathy, encephalopathy, and acrodermatitis chronica atrophicans.

  • Pregnancy and Lyme: There is currently no identified congenital Lyme disease syndrome.

  • Treatment Options: Tetracycline and doxycycline are commonly used antibiotics.

  • Immunological Response: There are five bands of IgG (Immunoglobulin G) associated with testing for Lyme disease.

Prion Disease

  • Characteristics: Prion diseases are marked by the accumulation of amyloid fibrils in the brain.

  • Pathophysiology: The normal prion protein (PrP) misfolds into a disease-causing form (PrPSc), initiating a chain reaction that converts other PrP proteins into the pathogenic form.

  • Transmission:

    • Ingestion of the pathogenic protein leads to its localization in lymphoid tissues and the gastrointestinal tract, eventually reaching the brain via nerves.

Epidemiology

  • Incidence: Overview suggests approximately 1-2 million cases annually.

  • Types of Disease:

    • 1% Acquired, 14% Genetic, 85% Sporadic disease.

  • Specific Disorder: sCJD (sporadic Creutzfeldt-Jakob disease) results in severe neurological symptoms.

    • Testing is done via RT-QuIC; however, this test is less effective for vCJD (variant Creutzfeldt-Jakob disease).

    • Genetic Disease: PrP misfolding can lead to scrapie in sheep (PrPM).

Relation to Bovine Disease

  • vCJD: Associated with bovine spongiform encephalopathy (BSE), also known as mad cow disease, where human infection occurs through contaminated beef products. Younger individuals are at higher risk of infection.

Bordatella Pertussis (Whooping Cough)

  • Description: Whooping cough is characterized by a persistent cough that results in a 'whooping' sound during inspiration due to oxygen deprivation.

  • Culture Characteristics: It is a hard-to-culture, Gram-negative coccobacillus bacterium.

  • Infectious Nature: Pertussis is highly infectious.

  • Stages of Infection:

    1. Catarrhal Stage: Early presentation of cold-like symptoms.

    2. Paroxysmal Stage: Severe coughing fits.

    3. Convalescent Stage: Recovery phase.

  • Diagnosis: Conducted via PCR testing.

  • Treatment Options: Azithromycin is commonly prescribed.

Vaccination Strategy

  • Available Vaccines:

    • DTaP for children, TdaP for adults and pregnant women. DTwP vaccine has been noted to offer better immunity compared to current formulations despite potential neurotoxicity. No vaccine offers lifelong immunity.

  • Cocoon Vaccination: Pregnant mothers are encouraged to receive vaccination around 27 weeks of pregnancy to protect newborns.

Pathogenic Escherichia Coli

  • General Information: E. coli is a type of bacteria present in the intestines of all humans and is associated with diarrhea when it acquires specific genetic traits.

  • Culture Characteristics: When observing pink colonies on MacConkey agar, it indicates the presence of E. coli.

  • Treatment Protocol:

    • Antibiotics are not recommended unless the infection is systemic (i.e., in the bloodstream) due to the self-limiting nature of these infections.

E. coli Strains and their Impact

  • Shiga Toxin Production: Certain strains of E. coli produce Shiga toxin leading to disorders such as hemorrhagic colitis:

    • EHEC (Enterohemorrhagic E. coli): If the strain shows attaching and effacing lesions, particularly in the colon rather than the small intestine.

    • Shiga toxin 1 and 2 cause bloody diarrhea without a fever. Shiga toxin 2 is particularly concerning as it can lead to hemolytic uremic syndrome (HUS), characterized by renal failure.

    • Administering antibiotics to patients with Shiga toxin 2 can lead to increased toxin release, worsening the symptoms of HUS.

Specific Strains

  • O157:H7 Strain:

    • Often linked to contaminated agricultural products from cattle due to its inability to ferment sorbitol, making it identifiable in typical lab tests.

    • Other strains need molecular testing for accurate identification.

Rabies Overview

  • Causing Agent: Rabies is fueled by a Lyssavirus and is a zoonotic infection.

  • Transmission Routes: Spread occurs mainly through animal saliva, organ transplants, and rare cases involving aerosol transmission.

    • Currently, most rabies cases in the U.S. originate from bats, with many infections resulting from unnoticed contact.

  • Incidence: Approximately 2-3 cases annually in the U.S., predominantly bat-related.

  • Incubation Period: Rabies features a long incubation period which allows for effective vaccination post-exposure.

Pathogenesis of Rabies Infection

  • Neural Pathways: The virus enters via peripheral nerves, traveling retrograde to the nervous system before descending anterogradely through somatic and autonomic nerves, infecting various tissues including the skin, ocular regions, salivary glands, and kidneys.

  • Types of Rabies Manifestations: Infection may lead to either encephalitic (80%) or paralytic (20%) forms.

  • Diagnosis Method: Salivary biopsies or culture methods can confirm rabies infection.

  • Vaccine History: The rabies vaccine developed by Louis Pasteur provides effective post-exposure prophylaxis due to the virus's long incubation.

  • Treatment Outlook: Unfortunately, there is no effective treatment for rabies once symptoms develop; survivors may receive rabies vaccines post-exposure.

HIV (Human Immunodeficiency Virus)

  • General Characteristics:

    • HIV is a retrovirus belonging to the lentivirus family. It converts its RNA into DNA through reverse transcriptase, which becomes incorporated into the DNA of host cells.

  • Evolutionary Background: HIV evolved from simian immunodeficiency virus (SIV) found in primates; primarily circulates within human populations since the 1920s.

  • Transmission Methods:

    • Modes of transmission include sexual contact, intravenous drug use, from mother to fetus, and through blood transfusions.

    • Infections are less likely to spread from women to men compared to the reverse.

Disease Stages

  1. Acquisition Stage: Initial phase post-exposure with potential acute response.

  2. Acute HIV Infection: This phase can often be asymptomatic but includes the window of seroconversion.

  3. Chronic HIV Stage:

    • Individuals remain asymptomatic for an extended period (over 6 months).

    • This can progress to AIDS when CD4 counts drop below 200 cells/mm³.

Virion Structure

  • Components: HIV consists of two RNA molecules, three essential enzymes, structural proteins encased in a capsid, and a lipid membrane containing glycoproteins gp120 and gp41 derived from host membranes.

  • Mechanism of Action:

    • Reverse transcriptase (RT) generates single-stranded DNA, then converts it to double-stranded DNA, subsequently degrading the viral RNA. Incorporation into the host genome is facilitated by integrase, resulting in a provirus capable of replication. Protease activities mature viral proteins for encapsidation and budding.

Antiretroviral Therapy

  • Mechanism of HIV Entry: Gp120 binds to the CD4 receptor in host cells, requiring a co-receptor (either CCR5 or CXCR4) for successful fusion.

  • Gp41 Role: Responsible for mediating cell membrane fusion during HIV entry.

  • Genetic Instability: The reverse transcriptase enzyme lacks proofreading abilities, resulting in an average of 5 errors per genome and significant genetic diversity, which enhances immune evasion by creating new antigenic variants.

  • Antiretroviral Therapy Goals:

    • Suppress HIV RNA levels, enhance CD4 cell populations, and reduce the risk of transmission across networks.

Antibiotic Resistance Overview

  • Background: The use of antibiotics fosters an environment where resistance can evolve and spread due to selective pressure.

  • Misuse Scenarios: Inappropriate prescription of antibiotics for viral infections and the overuse in agriculture (livestock and aquaculture) intensify resistance patterns.

  • Bacterial Classification:

    • Gram-positive bacteria: Features an inner lipid cell membrane and a thick peptidoglycan cell wall. Penicillins can effectively target the peptidoglycan layer.

    • Gram-negative bacteria: Comprises an inner lipid membrane, a thin peptidoglycan layer, and a more complex outer membrane, which limits access for penicillins.

  • Types of Resistance:

    • Intrinsic resistance emerges from structural characteristics like impermeable outer membranes. Acquired resistance arises from genetic mutations or the incorporation of resistant genes via mechanisms such as conjugation, transformation, or transduction.

Connective Note on HIV and AIDS

  • Defining AIDS: AIDS is characterized by specific opportunistic infections, malignancies, or a CD4 T-cell count dropping below 200 cells/mm³. Notably, HIV-2 has been found to be less virulent when compared to HIV-1.