Infectious Diseases: Definitions and Chain of Infection

Infectious Diseases Definitions

• Infection describes the establishment of microorganisms or infectious agents in a host, leading to replication and harm, inducing a host response.
• Illness results from the interaction between a host and an invading pathogen, often a microorganism.
• Colonization refers to the presence of microorganisms at an anatomical site without causing harm.
• Latent infection occurs when a microorganism survives in a dormant state within host cells or tissues after an initial invasion.
• Communicable diseases are infectious and can be transmitted from person to person.
• Infectious diseases occur when the causative agent or the host's response to it is capable of causing illness or harm.
• The terms "infection" and "infectious disease" are used interchangeably, though not all infections are infectious or transmissible.

The Chain of Infection

• The chain of infection describes the six key elements of transmissible disease:
• An infectious agent is the organism causing the disease.
• The portal of entry refers to the site where the infectious agent first accesses the body.
• A reservoir is where the agent maintains its population.
• The portal of exit as the point where the infectious agent leaves the reservoir.
• Transmission is how the infectious agent moves from the reservoir to a human host, either directly or via a vector or fomite.
• The disease will only develop if the person who receives the infectious agent is a susceptible host.

Host-Pathogen Interactions

• Pathogenicity defines an organism's ability to cause disease.
• Virulence quantifies the degree to which a pathogen can cause disease.
• Pathogens utilize virulence factors, such as proteins, that contribute to disease development.
• Genetic diversity enhances a bacteria's pathogenicity through virulence factor genes found on plasmids or phages.
• Primary pathogens invariably cause disease in exposed individuals, regardless of the host's immunological status.
• Opportunistic pathogens only cause disease in individuals with compromised host defenses.
• Pathogens can produce toxins, which cause negative impacts on host cells.
• Endotoxin is a lipid component of Gram-negative bacteria's outer membrane, released upon damage to bacterial cells.
• Exotoxins are released proteins produced by living bacteria that target specific organs.

Infection Prevention and Control

• Infection Prevention and Control (IPC) involves implementing measures to cut the chain of infection.
• Health care-associated infections (HCAI) develop post-admission to a healthcare facility; it often refers to nosocomial infections.
• Nosocomial bacterial infections are commonly caused by antibiotic-resistant organisms, MRSA, extended spectrum β-lactamases (ESBLs), carbapenemase-producing Enterobacteriaceae (CPE), and glycopeptide-resistant enterococci (GRE).

Immunization

• Immunization can occur passively or actively.

Passive Immunization

• Passive immunization uses administered antibodies from blood to target a pathogen and give immediate protection.
• Passive immunization has a short duration.
• Passive immunization carries the risk of disease transmission and hypersensitivity reactions.
• It aims to prevent or reduce the severity of an infection both before and after exposure.

Active Immunization

• Active immunization occurs via vaccinations where whole live microorganisms/their components generate a response.
• Live microorganisms in vaccines are more immunogenic.
• Vaccination gives a vaccine, so the immune system develops protection from a disease.

Indications for Post-Exposure Prophylaxis (PEP) with Immunoglobulins

• Post-exposure prophylaxis (PEP) uses immunoglobulins.

Human Normal Immunoglobulin (Pooled Immunoglobulin)

• Human normal immunoglobulin is used for Hepatitis A (unvaccinated contacts).
• Human normal immunoglobulin is used for Measles (exposed child with heart or lung disease).

Human Specific Immunoglobulin

• Human specific immunoglobulin is used for Hepatitis B (sexual partners, inoculation injuries, infants born to infected mothers).
• Human specific immunoglobulin is used for Tetanus (high-risk wounds or incomplete or unknown immunization status).
• Human specific immunoglobulin is used for Rabies.
• Human specific immunoglobulin is used for Chickenpox (immunosuppressed children and adults, pregnant women).

Shingles (Herpes Zoster)

Cause

• Shingles result from the varicella zoster virus that has been dormant in a nerve root ganglion.
• Reactivation can occur spontaneously (usually in the middle-aged or elderly) or due to immunosuppression.

Clinical Features

• Shingles includes symptoms like burning sensations, followed by vesicles in the affected dermatome, especially if it is a thoracic dermatome.
• Shingles vesicles normally appear later, normally 3-4 days, and are associated with brief viremia.
• The ophthalmic division of the trigeminal nerve is frequently affected, leading to corneal ulceration.
• Ramsay Hunt syndrome includes geniculate ganglion involvement resulting in facial nerve palsy, and ipsilateral loss of taste sensation and buccal ulceration and vesicles in the external auditory canal.

Management and Prevention for Shingles

• Early therapy with aciclovir or related agents can reduce early- and late-onset pain, particularly in patients over 65.
• Postherpetic neuralgia, involves severe pain after rash healing, persists for months and requires aggressive analgesia along with amitriptyline 25–100 mg and gabapentin 300 mg daily.

Actinomycosis

Clinical Forms

• Cervicofacial actinomycosis, also known as lumpy jaw, is the most common type, often post dental infection/trauma/surgery related.
• Thoracic actinomycosis afflicts smokers with poor dental hygiene, including aspiration of infective material.
• Abdominal actinomycosis follows surgery for bowel perforation.
• Pelvic actinomycosis affects women (IUCD users).

Cervicofacial Actinomycosis

• Non-tender, nodular swelling occurs in perimandibular, soft tissue (angle of the jaw), becoming woody and hard in the later stages of fibrosis.
• Sinus tracts discharge purulent material containing granules with a yellow sulphur-like appearance in the cheek or submandibular area.
• Lymphadenopathy and fever are typically absent.
• The risk factors are oral surgery and/or poor dental hygiene.
• Osteomyelitis of the mandible or cranial bones or bloodstream spread is possible in untreated patients.

Thoracic Actinomycosis

• Thoracic actinomycosis accounts for 15-20% of cases.
• Aspiration of oropharyngeal secretions with actinomycetes is the usual mechanism of infection.
• It generally shows a pulmonary infiltrate or mass.
• The pleura, pericardium, and chest wall may be involved, with formation of sulphur granule emitting sinuses.

Abdominal and Pelvic Actinomycosis

• Risk factors include surgery for bowel perforations (e.g., ruptured appendicitis) and ingestion of foreign bodies such as chicken or fish bones.
• Actinomycetes can be introduced into the deep tissues by the above processes.
• The most frequent site is the ileocecal region, which presents as a slowly growing tumor.
• Pelvic actinomycosis in women shows a risk factor: IUCD if it is in place for more than 8 years.

Diagnosis of Actinomycosis

• Provisional diagnosis can be made from clinical assessment and imaging studies.
• The differential diagnosis includes abscesses and tumors.
• Definitive diagnosis requires organization identification in smears/cultures from sulphur granules/biopsy specimens.
• A tissue biopsy reveals characteristic inflammation and the organism's presence.
• Penicillin G is the drug of choice.
• Surgery is an option in selected cases.

Sarcoidosis Investigations

• Complete Blood Counts (CBC): Lymphopenia is characteristic with a decrease in CD4+ lymphocyte count.
• Serum Calcium will show Hypercalcemia, (following exposure to strong sunlight).
• Serum ACE levels: elevated (a non-specific marker of disease activity and can assist in monitoring the clinical course).
• Chest radiography/High resolution CT (HRCT): used for diagnosis /staging.
• Histopathological examination is also used.

Mycetoma

Definition

• Mycetoma is a chronic suppurative infection of the deep soft tissues, skin, and bones of the limbs abdominal or chest wall or head.

Clinical Features

• 80% of Mycetoma occur in feet (Madura foot), begins as a painless swelling at the implantation site.
• It becomes chronic and progressive and extends into the bone.
• Nodules typically develop under the epidermis and these rupture, revealing sinuses.
• The grains are discharged, sinuses heal/scar and fresh sinuses appear later.
• People who develop mycetoma likely have a weakened immune system.

Tuberculosis (TB)

Etiology and Mode of Spread

• Tuberculosis (TB) is caused by infection with Mycobacterium tuberculosis (MTB), part of a complex including M. bovis (cattle reservoir) and M. africanum (human reservoir).

Mode of Infection and Spread of TB

• M. tuberculosis infection: spread by inhalation of aerosolized droplets from infected patients.
• The pulmonary TB infection occurs in healthy individuals but is frequently subclinical.
• The tuberculin skin test gives a reactive, positive result.
• M. bovis infection: spread by drinking non-sterilized milk from infected cows; primarily affects the Gastrointestinal Tract.
• Scrofula is cervical Tuberculosis.
• It is an infection of lymph nodes near the mouth and esophagus.

Pathology and Pathogenesis

• Once inhaled, an organism lodges in the alveoli and initiates macrophage and lymphocyte recruitment.
• Macrophages undergo transformation into epithelioid and Langhans cells.
• Macrophages aggregate with the lymphocytes to form the classical tuberculous granuloma.
• Numerous granulomas aggregate to form a primary lesion called the 'Ghon focus'.
• 'Ghon focus' is normally a pale yellow, caseous nodule, usually located in the lung.
• Spread of organisms to the hilar lymph nodes is followed by a similar pathological reaction.
• The combination of the primary lesion and regional lymph nodes gives the primary complex of Ranke.
• Reparative processes encase the primary complex, limiting the spread of bacilli.
• The calcifies legion becomes visible on a chest X-ray..

Oral Manifestations of Tuberculosis

• Oral lesions are rare but may develop in only 0.5-15 of the cases with TB.
• Oral primary TB infection is extremely rare.
• Oral TB lesions are secondarily with infected sputum or due to hematogenous spread.
• The oral lesion has many forms such as ulcers, nodules, tuberculomas and granulomas.
• Oral lesions is the dorsum of the tongue, gingiva, floor of the mouth and buccal mucosa.
• The lesions involves deep painful tubercular ulcers of the tongue that involve regional lymphadenopathy

Rhinoscleroma

• Rhinoscleroma is a chronic granulomatous bacterial disease of the nose caused by Klebsiella rhinoscleromatis which can infect the upper respiratory tract.
• It primarily affects the nasal cavity along with the nasopharynx, larynx, trachea, and bronchi.
• Rhinoscleroma affects more females and patients aged 10-30.
• It is also considered a tropical disease endemic to North Africa, South Asia, and Central America but less common in the United States.
• The disease the atrophic stage characterized by atrophic Rhinitis and smells purulent nasal discharge.
• Diagnosis occurs from a MacConkey agar in 50-60% of cases.
• Streptomycin (1g/day) and tetracycline (2g/day) treatment is given together for 4-6 weeks.
• Antibiotics and Ciprofloxacin are also sometime used.

Leprosy

Clinical Features with Skin Lesions

• Macules or plaques appear in most common lesions.
• Lesions are typically hypopigmented and anesthetic in tuberculoid patients.
• Skin includes papules, nodules, or diffuse skin infiltration and occurs with numerous, confluent lesions, in lepromatous leprosy.
• Nerve pain, sudden palsy, and new skin lesions happen due to lepra reactions in Borderline cases.
• Anesthesia is due to damage along the skin's fibers in the lesions. Sweat and the distribution of nerve fiber becomes damaged.

Oral Manifestations of Primary Syphilis

• Primary syphilis involves a painless ulcer (chancre) that is shown on the coronal sulcus of the penis, as well as inguinal painless lymphadenopathy.
• Chancres may develop on the vaginal-wall.

Acquired Syphilis

Early Syphilis

• Secondary Syphilis may involve mucous patches that affect the genitalia, mouth, pharynx, or the larynx. It can the the 'Snail track ulcers'.
• The clinical manifestations may resolve without treatment or relapse within the first year of infection before the disease enters a latency phase.

Latent Syphilis (no evidence of clinical disease)

• Latent syphilis involves positive syphilis serology with diagnostic cerebrospinal fluid (CSF) abnormalities of neurosyphilis in an untreated patient.
• Early latency occurs within 2 years of infection, when syphilis sexually transmits, compared to Late Latency, when the patient is no longer sexually infectious.

Viral Hepatitis

• Viral hepatitis must be considered presenting with hepatitis liver blood tests where transaminases are high.

Clinical Features of Viral Hepatitis:

• All hepatitis viruses cause illnesses with similar clinical or pathological features that are typically asymptotic.
• The viruses are caused by the route of transmission and the tendency to cause acute and chronic infections.
• Hepatitis A virus (HAV) belongs to the picornavirus class/enterovirus group (RNA virus).
• HAV is highly infection via the fecal-oral route.

Signs and Symptoms

• Asymptomatic patients can still excrete the virus within feces for a few weeks before symptoms.
• Infections are typically common among children with jaundice.
• Infections are also more among poor sanitation.
• Water and fish cause the transmission in outbreaks.

Serology of HBV Infection:

• Hepatitis B surface antigen is an idication of active disease and chronic diseases if above 6 months.
• Antibodies persis for for many years
• The antibody is initially of IgM type

Investigations For Blood and Inflammation.

• Involve routine inspection for blood, microscopy for leukocytes, ova, cysts, and parasites, and may need sever stools.
• Sigmoidoscopy may used.
• Neutrophilia are tested along with for other issues.
• Also test ultrasonic for other issues.

Investigations.

• Stool involves an examination of parasites.
• Stool is performed and C. difficile toxin is performed.

Diagnosis for the Thyroid

• Involves regulation of cells in the nucliated cells.
• Also Structuraly with normal thyroid function.

Investigations of Thyroid Diseases.

• All involve hyperthyroidism.
• Involves an enlargement of thyriod.

Hyperparathyroidism.

• Diagnoses for for levels for plasma with scanning.
• Mostly dont result in treat, advise high fludintake.
• Also perform supplemation with D.

Diseases of Severe Hypocalcaemia

• Immediate management involves mLs, and continous for monitors

Growth Hormine

Has Acromegaly in adults involves growth and feet.

The Diagnostic Criteria For Diabetes

A confirmed fasting glucose is 7.

Serology Complications

Miro and macro.

Cushing's Syndrome

Cushings caused by prolonged activation of glucocoritord.

• There are other cases such as tumors.

Clinical For Heart Issues

• High Blood pressure
• Nausea
• Vomiting
• Cistipation.
• Low blood Sugar.

Transmission from Pneumonia.

• Inhailaing.
• Bacteria Spread.
• Respitory illness with shadowing.

Asthma Transmission

• Airways with coughs in the night with brathese.
• Can be periodic.

Management

• For the acute severe, prophylaxis can prevent.