Infections and Transmission

Infections

• An infection is a process of tissue invasion by microorganisms, where they multiply in the body of the host to cause disease.
• There are four types of infections:
  • Bacterial
  • Fungal
  • Viral
  • Parasitic

Cross-Infection

• Cross-infection is the transmission of infection between patients and patients, and healthcare professionals.

Viral Infections

• Examples of viral infections:
  • CMV (Cytomegalovirus)
  • Hepatitis virus
  • HSV1 and HSV2 (Herpes Simplex Virus)
  • HIV (Human Immunodeficiency Virus)
  • Measles
  • Mumps
  • Influenza
  • Rubella
  • Adenovirus
• HSV1 and HSV2:
  • HSV1 is spread by infected saliva
  • HSV2 is spread by sexual contact
  • Incubation period: 2-12 days
  • Clinical features:
    • Orolabialis infection (oral herpes)
    • Sore throat, fever
    • Vesicles on pharynx, buccal mucosa, gingiva, and tongue
    • Lymphadenopathy (enlargement of lymph nodes)
    • Recurrence
  • Associated infections:
    • HSV-1: eye infections (blindness can occur)
    • HSV-2: genital/anal infections
  • Complications:
    • Encephalitis (affects temporal lobes)
    • Neonatal (mortality is 60% for newborns; c-section may be needed)
    • Erythema multiforme (skin reaction)
    • Eczema herpeticum (virus affects a large part of the skin)
  • Treatment:
    • Acyclovir
    • Valacyclovir

Herpes Zoster

• Herpes zoster is caused by the reactivation of the varicella-zoster virus.
• Clinical features:
  • Radicular pain (pain that radiates from the back and hip into the legs through the spine)
  • Hyperaesthesia (increase of sensitivity) of overlying skin
  • Rash
  • Erythema caused by inflamed blood capillaries
  • Oral, palatal, or pharyngeal involvement if the trigeminal nerve is affected
• Complications:
  • Post-herpetic neuralgia
  • Meningitis (neurological)
• Treatment:
  • Acyclovir
• Complication that treatment has no effect on:
  • Post-herpetic neuralgia

Infectious Mononucleosis

• Infectious mononucleosis is caused by the Epstein-Barr virus.
• Incubation period: 4-14 days
• Clinical features:
  • Anorexia, malaise, fever
  • Sore throat
  • Cervical lymphadenopathy (swelling of lymph nodes)
  • Macular rash due to ampicillin
  • Palatal petechiae
  • Palpable spleen
  • Jaundice in 10% of cases
• Complications:
  • Hepatitis
  • Respiratory obstruction
  • Ruptured spleen
• Diagnosis:
  • Monospot test

Chicken Pox

• Chicken pox is caused by the varicella-zoster virus.
• Incubation period: 14-16 days
• Clinical features:
  • Rash that starts on the scalp/trunk and then spreads to limbs and face
  • Vesicles dry and crust
  • Pruritis (itchiness)
  • Shallow ulcers on mucous membranes
• Complications:
  • Cellulitis/impetigo
  • Pneumonia
  • Acute cerebellar ataxia, Reye's syndrome (neurological)
  • Congenital abnormalities
• Treatment:
  • Antihistamines
  • Acyclovir (for severe cases/complications)

Mumps

• Mumps is caused by the paramyxovirus (RNA).
• Incubation period: 16-21 days
• Spread:
  • Droplets from saliva and nasopharyngeal secretions
• Clinical features:
  • Asymptomatic in 40%
  • Fever, malaise
  • Enlargement of 1/both parotids
  • Earache and displacement of earlobe
  • Partoid papillae inflamed
  • Difficulty in swallowing
  • Submandibular glands may be affected
• Complications:
  • Neurological: aseptic meningitis, encephalitis
  • Orchitis (common in post-puberty, 20-25%)
  • Non-parotid mumps: ovaries, thyroid, pancreas, breasts
• Treatment:
  • Good oral hygiene
  • Bed rest

Childhood Exanthemas

• Examples of childhood exanthemas:
  • Measles
  • German measles
  • Enteroviral infection
  • Infectious mononucleosis
  • Scarlet fever
  • Erythema infectiosum
  • Roseola infantum
  • Drug eruption

Measles and German Measles

• Measles is caused by the paramyxovirus (RNA).
• Incubation period: 10 days
• Clinical features:
  • Conjunctivitis (red eyes)
  • Lymphadenopathy
  • Koplik's spots (white spots on the inside of the cheeks)
  • Florid maculopapular rash (begins behind the ears and spreads to the face and trunk, with brown discoloration remaining after)
• Complication:
  • Gingivostomatitis
• German measles (Rubella) is caused by the Rubella virus (RNA).
• Incubation period: 14-21 days
• Clinical features:
  • Fever, malaise, catarrhal
  • Lymphadenopathy
  • Rash that starts on the face and then spreads to limbs
• Complication:
  • Congenital Rubella (important for pregnant women)

COVID-19

• Disease: COVID-19
• Virus: SARS-CoV-2
• How the virus works:
  • Uses the membrane-bound angiotensin-converting enzyme 2 (ACE2) receptor of the host to penetrate the cells
• Portals of entry:
  • Mucosal membrane of the oral cavity
  • Respiratory tract
  • Eyes
• Categories of transmission:
  • Symptomatic transmission (direct from a COVID-19 patient)
  • Presymptomatic transmission (direct from a SARS-CoV-2 positive person without symptoms yet)
  • Asymptomatic transmission (direct from a SARS-CoV-2 positive person who never develops symptoms)
  • Environmental transmission (indirect transmission which is not traceable to an index patient)

Enteroviral Infections

• Enteroviral infections are caused by the coxsackie virus A and B.
• Example: Hand-foot-and-mouth disease
• Clinical features:
  • Malaise, fever, anorexia
  • Sore mouth and throat
  • Vesicular rash involving buccal mucosa with or without the tongue, palate, or gingiva
  • Hands are involved in 65% of cases
  • Feet are often affected
• Treatment:
  • Topical steroids to treat ulceration

Erythema Infectiosum

• Erythema infectiosum is caused by the parvovirus B19.
• Clinical features:
  • Rash (livid erythema of the cheeks, "slapped cheeks")
  • Maculopapular rash on feet and hands
• Diagnosis:
  • Clinically
• Treatment:
  • No specific treatment

Active and Passive Immunity

• Active immunity:
  • Components:
    • Live attenuated vaccines
    • Inactivated organisms
    • Immunizing components of organisms
    • Toxoid (inactivated toxin)
• Passive immunity:
  • Components:
    • Natural transmission from mother to fetus
    • Artificial (high levels of human/non-human immunoglobulin)

Hepatitis B and C

• Hepatitis B and C:
  • Transmission:
    • Via contact with infected blood
  • Hepatitis B:
    • Type of virus: DNA virus
    • Incubation period: 45-180 days
    • Prevention: Vaccination
• Hepatitis C:
  • Type of virus: RNA virus
  • Percentage of individuals with overt Hep C: 10% (acute phase is usually asymptomatic)
  • Clinical features:
    • Lichenoid reaction
    • Xerostomia

HIV Infection

• HIV infection:
  • Diseases strongly associated with HIV infection:
    • CHKN (Candidiasis, Hairy Leukoplakia, Kaposi's Sarcoma, Non-Hodgkin's Lymphoma)

Scarlet Fever

• Scarlet fever:
  • Caused by: Group A beta-haemolytic streptococci which produces erythrogenic toxin
  • Clinical features:
    • Rash (diffuse erythema which blanches on pressure)
    • Skin folds are dark