Comprehensive Guide to Viral Infections: Symptoms, Transmission, and Prevention

Posted on Nov 8, 2024 in Biology

Viral Infections

Chickenpox (Varicella)

Pathogen:

Varicella-zoster virus

Clinical Features:

Mild fever, malaise followed by a rash
Rash appears on the trunk first and spreads
Rash progression: macular -> papular -> vesicular -> crusting
Infection resolves within 5 to 10 days, but can be severe
Chickenpox lesions are present in different stages of development at a particular time

Modes of Transmission:

Humans

Person-to-person by direct contact (touching a vesicle or vesicular fluid)
Inhalation of aerosols from vesicular fluid

Prevention:

2 doses of the varicella vaccine – First between 12 to 15 months of age and second between 4 to 6 years of age
Fewer cases reported since the 2-dose varicella vaccination program began in 2006

Shingles (Herpes Zoster)

Pathogen:

Varicella-zoster virus

Clinical Features:

Unilateral, painful, vesicular rash on the neck or chest
Pain can persist for months or years after the rash clears

Cause for Recurrence:

Dorsal root ganglion neurons reactivate the virus
Usually in the cervical or thoracic dorsal root ganglia

Prevention:

2 doses of the herpes zoster vaccine 2 to 6 months apart for individuals aged 50 years or older

Measles (Rubeola)

Pathogen:

Rubeola virus

Clinical Features:

Fever, runny nose, cough, conjunctivitis, and photosensitivity
Koplik spots: appear in the mouth – small, irregularly shaped, red spots with a central dot
Maculopapular rash appears on the face first then spreads
Infection resolves within 5 to 10 days, but can cause respiratory and neurological complications
Koplik spots are an early sign of measles, appearing before the facial rash

Modes of Transmission:

Reservoir – Humans

Inhaling infected respiratory or oropharyngeal secretions
Contacting articles freshly soiled with infected respiratory or oropharyngeal secretions

Prevention:

2 doses of the MMR vaccine – First between 12 to 15 months of age and second between 4 to 6 years of age

German Measles (Rubella)

Pathogen:

Rubella virus

Clinical Features:

Mild fever and malaise followed by a rash
Maculopapular rash usually appears first on the face and then spreads
Milder than measles (rubeola) and resolves within 3 days – AKA: 3-day measles
Infection in pregnancy causes stillbirth or multiple congenital malformations in infants – Congenital rubella syndrome
Congenital rubella syndrome triad: hearing loss, heart defects, and eye abnormality
Other features include microcephaly, petechiae and purpura, and hepatosplenomegaly

Modes of Transmission:

Reservoir – Humans

Inhaling infected respiratory or oropharyngeal secretions
Contacting articles freshly soiled with infected respiratory or oropharyngeal secretions

Prevention:

2 doses of the MMR vaccine – First between 12 to 15 months of age and second between 4 to 6 years of age
Rare in the US with less than 10 cases per year

Smallpox (Variola)

Pathogen:

Variola virus

Clinical Features:

High fever and prostration followed by a rash
Rash usually appears all over the body
Rash progression: macular -> papular -> vesicular -> crusting
Rash leaves permanent scars
Severe infection results in bleeding into the skin and mucous membranes, followed by resolution (21 to 28 days) or death
Smallpox lesions typically present in the same stage of development at a particular time

Modes of Transmission:

Reservoir – Humans

Person-to-person by direct contact (touching a vesicle or vesicular fluid)
Inhalation of aerosols from vesicular fluid

Historical Notes:

Smallpox has been eradicated
Last known case in 1978
Two locations where the virus is stored – CDC in the US and Vector Institute in Russia

Acute Viral Rhinitis

Pathogen:

Rhinovirus (>160 types)

AKA:

Coryza, common cold

Clinical Features:

Inflammation of mucous membranes of the upper respiratory tract:
Clear nasal discharge
Itchy eyes
Sore throat, hoarseness
Malaise

Modes of Transmission:

Reservoir – Humans

Inhaling infected respiratory or oropharyngeal secretions
Contacting articles freshly soiled with infected respiratory or oropharyngeal secretions

Prevention:

Handwashing, disinfecting surfaces
No vaccine
Healthy adults can acquire 1 to 6 infections per year, which usually resolve within a week

Croup

Pathogen:

Parainfluenza virus (4 types)

AKA:

Laryngotracheitis, laryngotracheobronchitis

Clinical Features:

Inflammation of the mucous membranes of the upper and lower respiratory tract:
Typically affects children under 5 years of age
Initially resembles the common cold, but fever and airway narrowing occur in 2 to 3 days
Harsh cough compared to a seal – Barking cough
Whistling sound heard during inspiration – Stridor
*sounds are common when the child is asleep

Modes of Transmission:

Inhaling infected respiratory or oropharyngeal secretions
Contacting articles freshly soiled with infected secretions

Prevention:

Handwashing, washing toys
No vaccine
Most cases of croup are mild and resolve on their own within a week

Hantavirus Pulmonary Syndrome

Pathogen:

Hantavirus (>5 types)

Clinical Features:

Inflammation of the mucous membranes of the lower respiratory tract
High fever, chills, productive cough, fatigue, headache, myalgia
Alveoli fill with fluid resulting in dyspnea
“tight band around the chest” or a “pillow over the face”

Modes of Transmission:

Reservoirs – infected rodents

Inhaling aerosolized rodent feces, urine, and saliva

Prevention:

Minimizing contact with rodents and their habitats

Influenza (Flu)

Pathogen:

Influenza virus (A, B, and C)

Clinical Features:

Inflammation of the mucous membranes of the lower respiratory tract:
High fever, chills, dry cough, nasal congestion, fatigue, headache, myalgia
Serious in children under 5, adults over 65, and the chronically ill

Modes of Transmission:

Reservoir – Humans

Inhaling infected respiratory or oropharyngeal secretions
Contacting articles freshly soiled with infected respiratory or oropharyngeal secretions

Prevention:

Handwashing, disinfecting surfaces, seasonal flu vaccine
Each year’s flu vaccine offers protection from 3 or 4 virus subtypes that are expected to be the most common

Epidemiological Considerations:

A and B viruses cause epidemics almost every winter
C viruses cause a mild respiratory illness and not epidemics
Influenza A viruses are classified based on two surface proteins: Hemagglutinin (H1-H18) and Neuraminidase (N1-N11)
Circulating A viruses – H1N1 & H3N2

Avian Influenza (Bird Flu)

Pathogen:

Avian influenza virus (type A)

Clinical Features:

Inflammation of the mucous membranes of the lower respiratory tract:
High fever, chills, dry cough, nasal congestion, fatigue, headache, myalgia
Can progress to viral pneumonia if untreated

Modes of Transmission:

Reservoir – infected birds

Contacting infected poultry or surfaces soiled with secretions/excretions from infected birds
Person-to-person transmission is rare

Ecological Considerations:

Most virulent subtypes – H5N1 and H7N9

Prevention:

Avoiding contact with infected poultry
Using antiviral chemoprophylaxis if exposed to infected birds

Coronavirus Infections

1. SARS-CoV:

Emerged in 2002: SARS: Severe Acute Respiratory Syndrome

2. MERS-CoV:

Emerged in 2012: MERS – Middle East Respiratory Syndrome

3. SARS-CoV-2:

Emerged in 2019: COVID-19 – Coronavirus Disease 2019

Clinical Features:

Reservoirs – Bats (SARS-CoV), camels (for MERS-CoV)

Inflammation of the mucous membranes of the lower respiratory tract
High fever, chills, dry cough, fatigue, headache, myalgia

Modes of Transmission:

Person-to-person by inhaling infected respiratory and oropharyngeal secretions

Prevention:

Staying up to date with COVID-19 vaccines
Cleaning hands often
Covering the mouth and nose when coughing
Wearing a mask
Cleaning and disinfecting frequently

Herpes Labialis

Pathogen:

Herpes simplex virus (usually type 1)

AKA:

Cold sores, fever blisters

Clinical Features:

Burning pain, followed by a vesicular eruption on the lips or around the mouth
Blisters break and fuse to form painful, circular sores which crust and heal within 20 days – no scarring

Mode of Transmission:

Reservoir – Humans: Person-to-person by direct contact (vesicle or vesicular fluid)

Prevention:

Handwashing, avoiding kissing or oral sex during an active outbreak
No vaccine

Cause for Occurrence/Recurrence:

Reactivation of latent virus in the trigeminal (CN V) ganglion neurons

Viral Gastroenteritis (Stomach Flu)

Pathogens:

Rotavirus, Norovirus, Adenovirus

Clinical Features:

Nausea, vomiting, abdominal pain, dysentery, severe dehydration, fever
Self-limiting disease lasting for 24 to 48 hours, but can be fatal in infants and children

Modes of Transmission:

Reservoirs – infected humans, “shellfish”

Often = fecal-oral, sometimes = ingestion of contaminated things

Prevention:

Handwashing, disinfecting surfaces (especially in the bathroom and kitchen)
Rotavirus vaccine

Viral Hepatitis

Pathogens:

Hepatitis A, B, C, D, or E virus

AKA:

“hepatotropic” due to a high affinity for the liver

Researchers believe that some unknown viruses may also cause hepatitis (non-A-E hepatitis or hepatitis X)

A. Acute Viral Hepatitis – HAV & HEV

Pre-icterus phase: Myalgia, arthralgia, fatigue, anorexia, nausea, vomiting, abdominal pain, elevated ALT and AST
Icterus phase: Abdominal pain, increased serum bilirubin
Convalescent phase: Increased sense of well-being, return of appetite, disappearance of jaundice

B. Chronic Viral Hepatitis – HBV, HCV, & HDV

May lead to cirrhosis followed by portal hypertension, liver failure, or hepatocellular carcinoma

Hepatitis A

Pathogen:

HAV

Transmission:

Fecal-oral route

Prognosis:

Benign and self-limiting, does not cause chronic hepatitis or induce a carrier state

Prevention:

HAV vaccine

Recommended for:

Food handlers
Children around high infection rates
Individuals traveling to poorly sanitized areas
Individuals working with animals

Hepatitis B

Pathogen:

HBV

Transmission:

Condomless sex, injection drug use

Prognosis:

Serious, can cause chronic hepatitis or induce a carrier state

Prevention:

HBV vaccine

Recommended for:

Everyone under 60 years of age
Individuals who inject drugs
International travelers to HBV endemic areas
Individuals living with HIV

Hepatitis C

Pathogen:

HCV

Transmission:

Injection drug use

Prognosis:

Serious, can cause chronic hepatitis or induce a carrier state

Prevention:

HCV vaccine is not available

HCV has high genetic variability (>75 subtypes)

Prevention depends upon reducing the possibility of exposure

Hepatitis D

AKA:

“Satellite virus” or “defective virus”

Relies on HBV to supply surface proteins during replication

Pathogen:

HDV

Transmission:

Condomless sex, injection drug use

Prognosis:

Serious, can cause chronic hepatitis or induce a carrier state

Prevention:

HBV vaccine (HDV vaccine is not available)

Hepatitis E

Pathogen:

HEV

Transmission:

Fecal-oral route

Prognosis:

Benign and self-limiting, does not cause chronic hepatitis or induce a carrier state

Prevention:

HEV vaccine

Vaccine was approved in China in 2012

No FDA-approved vaccine to prevent HEV infection in the US

HIV Infection & AIDS

Pathogen:

Human immunodeficiency virus (types 1 and 2)

HIV invades and destroys the CD4+ helper T cells resulting in immunosuppression
Normal range: 500-1,500 cells per mm³ of blood

Clinical Features:

Untreated infections progress through 3 stages:

Acute HIV infection: Flu-like illness within 2 to 4 weeks after the virus enters the body – characterized by fever, headache, myalgia, swollen lymph nodes, and painful oral ulcers (most infectious stage)
Chronic HIV infection: No specific S/S (lasts ≥ 10 years)
Acquired immunodeficiency syndrome (AIDS): Fatigue, recurrent fever, diarrhea, and involuntary weight loss – if CD4+ helper T cell count drops below 200 cells per mm³ of blood or opportunistic infections occur

HIV Infection & AIDS – Examples of Opportunistic Infections:

Candida albicans infection: Fungus infects the mouth (thrush), esophagus, trachea, bronchi, lungs, and genitals
Human herpesvirus 8 infection: Virus infects the endothelial lining of blood vessels (risk of Kaposi sarcoma)
Mycobacterium tuberculosis infection: Bacterium infects the lungs (pulmonary tuberculosis) or spreads to the brain, kidneys, or bones (disseminated tuberculosis)

Modes of Transmission:

Reservoir – Humans

Person-to-person by direct sexual contact
Sharing of contaminated needles or syringes
Mother-to-child during pregnancy, labor, or breastfeeding
Pricked by a contaminated needle or another sharp object
Transfusion of contaminated blood or blood products

Prevention:

Limiting sex partners, using condoms, not sharing needles
Pre-exposure prophylaxis (PrEP) – daily oral pill
Post-exposure prophylaxis (PEP) – oral pills for 28 days
Treatment as prevention (TasP) – Taking antiretroviral therapy consistently to maintain viral suppression

Viral Hemorrhagic Fevers

Pathogens:

Ebola virus, Marburg virus, Dengue virus, Zika virus, Yellow fever virus

Clinical Features:

High fever, fatigue, dizziness, myalgia, arthralgia
Bleeding under the skin (petechiae, purpura), internally, or from the mouth, nose, or ears
Some can be life-threatening (Ebola, Marburg, Dengue), whereas others are less serious (Zika, Yellow fever)

Modes of Transmission:

Reservoir – Humans

Ebola & Marburg virus: Person-to-person by contact with infected body fluids
Dengue, Zika, & Yellow fever virus: Bite of mosquitoes in the genus Aedes: Viruses are arboviruses (spread by insect bites)

Herpes Genitalis

Pathogen:

Herpes simplex virus (usually type 2)

AKA:

Anogenital herpes

Clinical Features:

Itching, followed by a vesicular eruption on the vulva, penis, or anus
Blisters break and fuse to form painful, circular sores that crust and heal within 10 days – results in scarring

Mode of Transmission:

Reservoir – Humans

Person-to-person by direct sexual contact (genital-genital, oral-genital, oral-anal, or genital-anal)

Prevention:

Avoiding sexual contact during an active outbreak
Using condoms (reduces transmission by ~50%)
No vaccine

Cause for Occurrence/Recurrence:

Reactivation of latent virus in the dorsal root ganglia neurons – Usually in the sacral dorsal root ganglia

Infectious Parotitis (Mumps)

Pathogen:

Mumps virus

Clinical Features:

Fever, poor appetite, headache, myalgia, malaise, followed by painful swelling of one or both parotid salivary glands
Can result in complications: orchitis and oophoritis

Modes of Transmission:

Reservoir – Humans

Inhaling infected respiratory or oropharyngeal secretions, kissing, sharing items that may have saliva

Prevention:

2 doses of the MMR vaccine – First between 12 to 15 months of age and second between 4 to 6 years of age
The vaccine has drastically reduced the number of mumps cases in the US, but infections still occur in close-contact settings

Condyloma Acuminatum

Pathogen:

Human papillomavirus (> 200 types)

AKA:

Genital warts, genital papillomatosis

Clinical Features:

Rapidly growing, small, moist, pink or skin-colored growths that may develop stalks
Rough surfaces give them a cauliflower-like appearance
Multiple warts can grow on the vulva, penis, or anus
Types 16 & 18 cause cervical, penile, and anal cancers

Mode of Transmission:

Reservoir – Humans – Person-to-person by direct sexual contact

Prevention:

2 doses of the HPV vaccine at 11-12 years of age

Viral Meningitis

Pathogens:

Several types of viruses

AKA:

Aseptic, abacterial, or nonbacterial meningitis

Clinical Features:

Fever, headache, nuchal rigidity, altered mental status
Less serious than bacterial meningitis
* Reservoirs and modes of transmission vary

Viral Encephalitis

Pathogens:

Arboviruses

Eastern equine encephalitis
Western equine encephalitis
West Nile Virus

Clinical Features:

Fever, headache, nuchal rigidity, altered mental status
Can be life-threatening in vulnerable age groups

Modes of Transmission:

Eastern equine encephalitis: Horses
Western equine encephalitis: Aedes and Culex mosquitoes
West Nile Virus: Culex mosquitoes

Prevention:

Wearing pants and long-sleeved shirts, using insect repellents

Rabies

Pathogen:

Rabies virus

Clinical Features:

Fever, headache, nausea, vomiting, agitation, anxiety, confusion, excessive salivation, and progressive paralysis
Paralysis starts in the lower limbs and progresses upwards
Fear and panic when attempting to drink fluids because of intense spasms in the throat – Hydrophobia

Mode of Transmission:

Reservoirs: dogs, bats, skunks, raccoons, foxes

Direct contact with saliva from an infected animal

Prevention:

Rabies vaccine for animal handlers
Human rabies immune globulin (HRIG) given after exposure
Rare in the US with only 1 to 3 cases reported annually

Poliomyelitis (Polio)

Pathogen:

Poliovirus

Clinical Features:

~75% of people with infection are asymptomatic
~24% of people with infection develop fever, sore throat, fatigue, nausea, and stomach pain
~1% of people with infection develop paresthesia in the legs and paralysis of the arms or legs
Paralysis: motor neuron damage, leads to disability and death

Modes of Transmission:

Reservoir – Humans

Most often via the fecal-oral route, sometimes via ingesting contaminated food and water

Epidemiological Considerations:

Poliovirus vaccine became available in the 1950s
Polio was eradicated in the US in 1979 (1 case in July 2022)
Polio is still endemic in Afghanistan and Pakistan