Viral Diseases in humans

Herpes simplex virus (HSV) types

HSV-1: oral herpes

HSV-2: genital herpes

herpes simplex virus structure

double stranded DNA virus in the Herpesviridae family

icosahedral capsid surrounded by a lipid envelope

herpes simplex virus latency

after initial infection, HSV enters latent phase in neurons

remains dormant for long periods of time and can reactivate later, causing recurrent symptoms

HPS transmission

spreads through direct contact with infected bodily fluids, skin, or mucous membranes, even when symptoms aren’t present

HVS lifelong infection

causes a lifelong infection because of its ability to evade immune system and persist in a latent state

HSV symptoms

painful blisters or sores

fever

malaise 

HSV diagnosis

can be diagnosed using PCR, viral culture, or serology

HSV treatment

antiviral medication such as acyclovir, valacyclovir, or famciclovir can help reduce symptoms and frequency of outbreaks but does not cure infection

HSV prevention

safe sec practices

avoiding contact during outbreak 

smallpox causative agent

caused by the variola virus (Poxviridae family)

large, double stranded DNA virus 

smallpox eradication

officially eradicated in 1980

first and only human disease to be eradicated

smallpox transmission

spreads through respiratory droplets, direct contact with infected bodily fluids, or contaminated objects

highly contagious

smallpox symptoms

presents with fever and malaise, followed by a progressive rash that turns into pustules, mainly affecting the face, arms, and legs

smallpox incubation period

ranges from 7-17 days

person infected is asymptomatic

smallpox vaccine

originally made from a related virus (vaccinia virus)

crucial in eradication efforts

provides long term immunity 

smallpox bioterrorism concern

stocks of the virus are held in high-security laboratories

smallpox diagnosis

before eradication, diagnosis was based off clinical symptoms and confirmed through electron microscopy and viral culture 

influenza family

part of the Orthomyxoviridae family

envelope, single-stranded RNA virus

influenza subtypes

subtypes of 2 surface glycoproteins 

• hemagglutinin (H)

• neuraminidase (N)

influenza antigenic drift

small, gradual mutations in the virus’s RNA led to seasonal flu

influenza antigenic shift

major genetic charge, often from reassortment of viral genome segments can result in new influenza A subtypes, leading to pandemics

influenza host

humans

birds

pigs

influenza transmission

spreads via respiratory droplets, direct or contact with contaminated surface

influenza symptoms

fever

cough

sore throat

muscle aches

fatigues

sometimes gastrointestinal symptoms

influenza epidemics and pandemics

typically responsible for seasonal flu outbreaks

influenza vaccinations

annual flu vaccines are developed to target most likely circulating strains

influenza antiviral treatment

drugs like oseltamivir (Tamiflu) zanamivir (Relenza) and baloxavir

influenza diagnosis

rapid diagnosis test, RT-PCR, or viral culture

influenza public health impact

influenza A is a significant public health concern due to its potential for rapid spread, high mutation rates, and potential for causing severing 

Ebola Hemorrhagic fever causative agent

caused by Ebola virus

member of filoviridae family 

enveloped, single-stranded RNA virus

Ebola natural reservoir

believed to be fruit bats

other animals like non-human primates can also become infected with the Ebola virus 

Ebola transmission

transmitted through direct contact with blood, body fluids (vomit, urine, sweat) or tissues of infected individuals or animals 

Ebola symptoms

starts with flu-like symptoms

progresses to severer gastrointestinal symptoms, organ failure, and potentially death

Ebola’s high mortality rate

25-90%

Ebola pathophysiology

targets and damages the endothelial cells, immune cells, and liver, leading to

Ebola incubation period

2-21 days after exposure

Ebola diagnosis 

can be confirmed through RT-PCR, ELISA, viral isolation

Ebola treatment

no specific cure for Ebola

supportive care is critical

antiviral drugs (remdesivir) and monoclonal antibodies

Ebola vaccine

rVSV-ZBOV vaccine was approved and has been used to control outbreaks

Ebola public health concern

still a significant global health threat due to its potential for large outbreaks

SARS virus causative agent

Severe Acute Respiratory Syndrome

caused by SARS-CoV (SARS-associated coronavirus)

enveloped, single-stranded RNA virus in the Coronaviridae family

SARS origin

believed to be bats with civets as an intermediate host

first identified in 2002-2003 outbreak in Guangdong, China 

SARS transmission

respiratory droplets

SARS symptoms

presents with flu-like symptoms

can progress to dry cough, shortness of breath

in severe cases, patients develop acute respiratory distress syndrome

SARS incubation period

2-10 days, average of 4-6 days

SARS epidemiology

over 8000 cases

774 deaths

SARS receptor binding

virus attaches to ACE2 (angiotensin-converting enzyme 2) receptors on host cells on lungs and GI tract

SARS diagnosis

RT-PCR

SARS treatment

no specific antiviral treatment

oxygen therapy, fluids, and mechanical ventilation in severe cases

some antiviral agents and corticosteroids were used experimentally during the outbreak

SARS prevention and control

quarantine, travel restrictions, and isolation of individuals

rotavirus causative agent

double-stranded RNA virus from Reoviridae family

wheel-like appearance

rotavirus structure

icosahedral, triple layered capsid

rotavirus epidemiology

leading cause of severe gastroenteritis in infants and young children worldwide

responsible for hundreds of thousands of child deaths

rotavirus transmission

fecal-oral route

rotavirus symptoms

severe diarrhea, vomiting, fever, abdominal pain, which leads to dehydration

can be life threatening to young children

rotavirus incubation period

1-3 days

rotavirus diagnosis

diagnosed through ELISA, latex agglutination, or PCR

rotavirus vaccine

oral vaccine

rotavirus prevention

proper hygiene

handwashing

ensuring access to clean water and sanitation

rotavirus treatment

no antiviral treatment for rotavirus

treatment focuses on oral rehydration therapy along with intravenous fluids

rotavirus pathophysiology

infects and damages epithelial cells of small intestine, which leads to malabsorption and fluid loss

also produces viral enterotoxins, like NSP4

rotavirus global disease burden

still continues to cause around 200,000 child deaths annually where access to vaccines and healthcare is limited 

HIV causative agent 

retrovirus from the Lentivirus genus in the Retroviridae family 

single-stranded RNA that is reverse transcribed into DNA within host cells

HIV structure

enveloped virus with a conical capsid

genome encodes important structural and enzymatic proteins like reverse transcriptase, protease, integrase, and envelope proteins (gp120 and gp41) 

HIV target cells

targets CD4+ using the CD4 receptor and co-receptors and co-receptors (CCR5 or CXCR4)

HIV transmission

contact with infected blood, semen, vaginal fluids, rectal fluids, and breast mil

HIV replication cycle

reverse transcribes its RNA into DNA, which integrates into host genome

stages of HIV infection

1. acute HIV infection 

   1. occurs 2-4 weeks after exposure with flu-like symptoms

2. clinical latency (chronic HIV)

   1. virus remains active but reproduces at low levels

3. AIDS (acquired immunodeficiency syndrome) 

   1. HIV severely weakens the immune system, leading to opportunistic infections

   2. CD4+ cell count drops below 200 cells/ul

HIV diagnosis

diagnosed using serological tests or PCR

HIV treatment antiretroviral therapy

main treatment for HIV

combination of drugs that target different stages of HIV life cycle 

cannot cure HIV but can reduce viral load to undetectable levels

HIV opportunistic infections

weakened individuals can be vulnerable to other infections such as tuberculosis, pneumocystis, pneumonia, toxoplasmosis, and Kaposi’s sarcoma 

HIV global impact

approximately 38 million people living with HIV as of 2021

HIV research and vaccines

no cure or vaccine