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Hepatitis C is an infection of the liver caused by the hepatitis C virus (HCV). Hepatitis C virus is an RNA virus and a member of the genus Hepacivirus and the family Flaviviridae. The infection can be transmitted through infectious blood or body fluids and may be transmitted during childbirth or through IV drug use or sexual intercourse. Hepatitis C virus can cause both acute and chronic hepatitis, ranging from a mild to a serious, lifelong illness including liver cirrhosis and hepatocellular carcinoma (HCC). Hepatitis C infection is diagnosed by testing for the presence of HCV antibodies and HCV RNA. Management is supportive but includes direct antiviral agents (DAAs) if infection does not resolve spontaneously.

Hepatitis B Virus

Hepatitis B virus (HBV) is a partially double-stranded DNA virus, which belongs to the Orthohepadnavirus genus and the Hepadnaviridae family. Hepatitis B virus is transmitted by exposure to infectious blood or body fluids. Examples of types of exposure include sexual intercourse, IV drug use, and childbirth. The virus can cause potentially life-threatening liver disease. Most individuals with acute HBV infection are asymptomatic or have mild, self-limiting symptoms. Chronic infection can be asymptomatic or create hepatic inflammation, leading to liver cirrhosis and hepatocellular carcinoma (HCC). Management of acute hepatitis is typically supportive. Administration of antivirals or liver transplantation may be necessary in fulminant and chronic cases.

Labial and Genital Herpes

Genital herpes infections are common sexually transmitted infections caused by herpes simplex virus (HSV) type 1 or 2. Herpes simplex virus type 1 is more commonly associated with non-genital herpes, while HSV-2 is more commonly associated with genital herpes. Primary infection often presents with systemic, prodromal symptoms followed by clusters of painful, fluid-filled vesicles on an erythematous base, dysuria, and painful lymphadenopathy. Primary infection can also be asymptomatic. Herpes infections are unique in that the virus is able to remain dormant in the neuronal ganglia, which allows for recurrent infections. Recurrent outbreaks are usually less severe than the initial infection. Treatment is with antiviral therapy, primarily acyclovir.

Retroviridae: HIV

The human immunodeficiency virus (HIV) is a species of Lentivirus, a genus of the family Retroviridae, which causes HIV infections and acquired immunodeficiency syndrome (AIDS). The virus has high genetic variability and is divided into 2 major types, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). The human immunodeficiency virus is a single-stranded, positive-sense, enveloped RNA virus, which targets and destroys WBCs, leading to frequent opportunistic infections and, eventually, death.

Parvovirus B19

Primate erythroparvovirus 1 (generally referred to as parvovirus B19, B19 virus, or sometimes erythrovirus B19) ranks among the smallest DNA viruses. Parvovirus B19 is of the family Parvoviridae and genus Erythrovirus. In immunocompetent humans, parvovirus B19 classically results in erythema infectiosum (5th disease) or “slapped cheek syndrome.” Other manifestations vary with the immunologic and hematologic status of the host due to the viral tropism for erythrocyte precursors. Diagnosis is primarily clinical and management is generally supportive.

Mumps Virus/Mumps

Mumps is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae and the subfamily Rublavirinae. The mumps virus is contagious and spreads only among humans by respiratory droplets or direct contact transmission from an infected person or fomite. Mumps is typically a disease of childhood, which manifests initially with fever, muscle pain, headache, poor appetite, and a general feeling of malaise, and is classically followed by parotitis. Complications include meningitis, pancreatitis, permanent deafness, and testicular inflammation, which can result in infertility. Mumps is managed with supportive care and is preventable by vaccination.

Equine Encephalitis Viruses

Equine encephalitis viruses (EEVs), belonging to the Togaviridae family and Alphavirus genus, are mosquito-borne arboviruses that infect humans and cause minor illness or, in severe cases, encephalitis. The eastern equine encephalitis (EEE) virus complex consists of the EEE virus, found in North America and the Caribbean; and the Madariaga virus, found in South and Central America. Other viruses in this complex include western EEV and Venezuelan EEV. The virus is maintained in a cycle between mosquitoes and avian hosts, but can spread to humans via bridge vectors (other species of mosquitoes). Initial symptoms after the mosquito bite include fever, headache, and vomiting. A majority of patients recover, but the illness can progress to severe encephalitis. Diagnosis is by clinical findings and CSF analysis using serology, and also by virus antigen or genomic sequence detection. There is no specific treatment, and therapy is largely supportive. Prevention of mosquito bites is key in management.

Poliovirus/Poliomyelitis

Poliomyelitis is an infectious disease caused by the poliovirus. This virus is a member of the Picornaviridae family. It is a small, single-stranded, positive-sense RNA virus without a lipid envelope. Transmission occurs through the fecal–oral route and, occasionally, through respiratory aerosols. The majority of patients will be asymptomatic or have a mild, abortive presentation with flu-like symptoms. Those who develop nonparalytic poliomyelitis will develop signs and symptoms of aseptic meningitis. A very minor proportion of patients will progress to paralytic poliomyelitis, with neurologic progression (including asymmetric flaccid paralysis). The diagnosis is determined by the clinical presentation and can be supported by viral culture, PCR, and serology. Current antivirals are ineffective, and management is supportive. There are 2 vaccines available, which have almost eradicated this disease worldwide.

Coxsackievirus

Coxsackievirus is a member of a family of viruses called Picornaviridae and the genus Enterovirus. Coxsackieviruses are single-stranded, positive-sense RNA viruses, and are divided into coxsackie group A and B viruses. Both groups of viruses cause upper respiratory infections, rashes, aseptic meningitis, or encephalitis. Group A viruses cause herpangina; hand, foot, and mouth disease; and acute hemorrhagic conjunctivitis. Group B viruses cause myopericarditis, epidemic pleurodynia, and systemic neonatal disease. The diagnoses are usually made clinically. Viral culture and PCR can be performed for confirmation if the diagnosis is uncertain. Coxsackievirus infections are self-limiting and the management is supportive.

Picornaviridae: Echovirus

Echoviruses are single-stranded positive-sense RNA viruses belonging to the genus Enterovirus. Transmission is most commonly through the fecal-oral route. The majority of patients are asymptomatic. Patients who are symptomatic can exhibit a wide range of illnesses ranging from nonspecific upper respiratory infections and exanthems to severe and life-threatening illnesses such as aseptic meningitis, encephalitis, and myocarditis. The diagnosis is usually made clinically, but laboratory confirmation using PCR and viral culture may be necessary for patients with severe disease. Most infections are self-limiting and require no specific therapy.

Yellow Fever Virus

Yellow fever is a disease caused by the yellow fever virus, a single-stranded, positive-sense RNA virus of the genus Flavivirus. Humans and primates serve as reservoirs, and transmission occurs from the bite of an infected female mosquito. Most patients present with fever and flu-like symptoms. Severe disease can cause multiorgan dysfunction resulting in jaundice, renal dysfunction, hemorrhage, shock, and potential death. The diagnosis can be confirmed with serology and PCR. There is no antiviral treatment, so management is supportive. Prevention includes mosquito avoidance and vaccination.

Tick-borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) is a positive-sense, single-stranded RNA virus of the genus Flavivirus. Transmission occurs primarily via Ixodes ticks found in Europe, the former Soviet Union, and Asia. The virus causes tick-borne encephalitis. Most patients are asymptomatic; however, symptomatic individuals may experience a biphasic illness. After recovering from nonspecific symptoms, patients can develop neurologic manifestations, such as meningitis, encephalitis, or meningoencephalitis. Serology or PCR can confirm the diagnosis. There is no effective antiviral therapy for TBEV infections, so management is supportive.

St. Louis Encephalitis Virus

The Saint Louis encephalitis virus (SLEV) is a member of the genus Flavivirus and is the cause of St. Louis encephalitis. This small, enveloped, positive-sense, single-stranded RNA virus is transmitted by Culex mosquito species and is prevalent in the United States. Most infections are asymptomatic. Symptomatic individuals may have varied presentations, with flu-like symptoms, aseptic meningitis, encephalitis, or meningoencephalitis. The diagnosis is confirmed with serology. There is no effective antiviral treatment, so management is supportive. Prevention is aimed at local mosquito control and personal protection with insect repellent and protective clothing.

Parainfluenza Virus

Human parainfluenza viruses (HPIVs) are single-stranded, linear, negative-sense RNA viruses of the family Paramyxoviridae and the genus Paramyxovirus. Human parainfluenza viruses are the 2nd most common cause of lower respiratory disease in children, after the respiratory syncytial virus. Upper respiratory infections, including croup, are caused by HPIVs as well, but to a lesser extent. Management of HPIV infections relies on supportive care, racemic epinephrine, and steroids.

West Nile Virus

West Nile virus is an enveloped, positive-sense, single-stranded RNA virus of the genus Flavivirus. Birds are the primary hosts and the disease is most often transmitted by Culex mosquitoes. Most people infected with West Nile virus are asymptomatic. Some patients develop West Nile fever (a self-limited, febrile illness) and a very small proportion of patients develop West Nile neuroinvasive disease. West Nile neuroinvasive disease includes meningitis, encephalitis, and acute flaccid paralysis. The diagnosis is confirmed with serum serology, CSF serology, or PCR. Antiviral therapy is not available; therefore, management is supportive. Prevention is aimed at local mosquito control and donated blood and organ screening.

Rubella Virus

Rubella (also known as German measles or three-day measles) is caused by a single-stranded, positive-sense RNA virus of the Togaviridae family and the Rubivirus genus. Rubella only infects humans and spreads prenatally via vertical transmission or postnatally via droplet contact. Congenital rubella is particularly devastating and is associated with a classic triad of symptoms: cataracts, cardiac defects, and deafness. Infection in children and adults may be mild and present with constitutional symptoms along with a viral exanthem resembling the measles virus. Diagnosis is made clinically and confirmed with serum virus detection and serologic studies. Treatment is supportive and may be targeted depending on the organ system involved. Prevention is achieved through childhood vaccination with the measles, mumps, and rubella (MMR) vaccine.

Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is an enveloped, single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae and the genus Orthopneumovirus. Two subtypes (A and B) are present in outbreaks, but type A causes more severe disease. Respiratory syncytial virus causes infections of the lungs and respiratory tract and spreads via respiratory droplets. Respiratory syncytial virus is a leading cause of lower respiratory tract infections in infants and young children. Complications include bronchiolitis, pneumonia, and otitis media. Respiratory syncytial virus is managed with supportive care.

Dengue Virus

Dengue virus (DENV) is a small, positive-sense, single-stranded RNA virus of the genus Flavivirus. The infection can be transmitted to humans by the bite of female Aedes mosquitoes. The majority of infections are asymptomatic. Symptomatic individuals may progress through 3 stages of the disease, with severe manifestations occurring in those with previous infections. The febrile phase includes a high fever, headache and retro-orbital pain, severe myalgias and arthralgias (“breakbone” pain), and macular or maculopapular rash. The critical phase includes more-severe manifestations of capillary leakage, hemorrhage, and shock. A resolution of signs and symptoms occurs in the convalescent phase. The diagnosis is made based on the clinical history, examination, serology, antigen testing, or PCR. Management is supportive.

Lymphocytic Choriomeningitis Virus

Lymphocytic choriomeningitis virus (LCMV) is a single-stranded RNA virus transmitted to humans via rodents, the primary reservoir. Viral infections can occur through direct contact (such as through a break in the skin) with rodent urine, saliva, or droppings or via inhalation of aerosolized virus. Vertical transmission and, rarely, organ transplantation also lead to infections. The disease typically results in a self-limited, febrile, biphasic disease. In severe cases, patients can present with encephalitis, aseptic meningitis, or meningoencephalitis. Lymphocytic choriomeningitis virus infections of pregnant women have also been recognized as a significant teratogen resulting in fetal death or congenital defects. Diagnosis is by serology or RT-PCR. Management is supportive.

Chikungunya Virus

Chikungunya virus belongs to the Alphavirus genus and causes a viral infection characterized by fever and joint pain. The arthropod-borne (arbovirus) virus is transmitted by mosquitoes (commonly Aedes albopictus and Aedes aegypti). Symptoms usually appear within 1 week of infection. Additional manifestations of chikungunya virus may include muscle pain, headache, maculopapular rash, and lymphadenopathy. Most infected individuals recover, but chronic arthritis may develop. Treatment is aimed at relieving symptoms. The disease is prevented by mosquito avoidance, use of insect repellent, and protective clothing.

Rabies Virus

Rabies virus is a single-stranded, negative-sense RNA virus. This bullet-shaped virus belongs to the family Rhabdoviridae and the genus Lyssavirus. Rabies is a preventable disease most often transmitted to humans through the bite of an infected animal (e.g., bats, raccoons, skunks, and foxes). This life-threatening disease affects the CNS, resulting in severe neurologic manifestations. There are 5 stages of disease in humans: incubation, prodrome, acute neurologic period, coma, and death. The diagnosis is made with antibody, antigen, or viral RNA detection in tissue biopsy, serum, CSF, and saliva. There is no effective treatment for symptomatic disease, so prevention with human rabies immunoglobulin and vaccination is the mainstay of management.

Epstein-Barr Virus

Epstein-Barr virus (EBV) is a linear, double-stranded DNA virus belonging to the Herpesviridae family. This highly prevalent virus is mostly transmitted through contact with oropharyngeal secretions from an infected individual. The virus can infect epithelial cells and B lymphocytes, where it can undergo lytic replication or latency. The initial infection can present as infectious mononucleosis, and reactivation (often in patients who are HIV positive) can cause oral hairy leukoplakia. An important feature of EBV infections is the ability to transform B cells, which provides immortalization and proliferation. Thus, EBV is associated with lymphoproliferative disorders and malignancies, such as Burkitt lymphoma, Hodgkin lymphoma, hemophagocytic lymphohistiocytosis, post-transplant lymphoproliferative disease, certain gastric cancers, and nasopharyngeal carcinoma.

Adenovirus

Adenovirus (member of the family Adenoviridae) is a nonenveloped, double-stranded DNA virus. Adenovirus is transmitted in a variety of ways, and it can have various presentations based on the site of entry. Presentation can include febrile pharyngitis, conjunctivitis, acute respiratory disease, atypical pneumonia, and gastroenteritis. Severe manifestations include acute hemorrhagic cystitis, hepatitis, myocarditis, and disseminated infection. The diagnosis is confirmed with PCR and antigen testing. Most infections are self-limited, so management is generally supportive. Antiviral therapy is reserved for immunocompromised patients and severe infections.

Cytomegalovirus

CMV is a ubiquitous double-stranded DNA virus belonging to the Herpesviridae family. CMV infections can be transmitted in bodily fluids, such as blood, saliva, urine, semen, and breast milk. The initial infection is usually asymptomatic in the immunocompetent host, or it can present with symptoms of mononucleosis. After the primary infection, the virus becomes latent. Reactivation can occur in immunocompromised individuals, leading to conditions such as CMV esophagitis, colitis, hepatitis, retinitis, encephalitis, and pneumonia.

Varicella-Zoster Virus/Chickenpox

Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Varicella-zoster infections are highly contagious and transmitted through aerosolized respiratory droplets or contact with infected skin lesions. Chickenpox is the primary infection and occurs most commonly in children. The typical clinical presentation includes prodromal symptoms and a generalized, intensely pruritic vesicular rash. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. The diagnosis is primarily clinical. Management is supportive, although antiviral therapy can be used in certain patient populations. Complications can include secondary bacterial infections, encephalitis, or pneumonia. Varicella-zoster vaccine is recommended as a preventive measure in early childhood.

Norovirus

Norovirus is a nonenveloped, single-stranded, positive-sense RNA virus belonging to the Caliciviridae family. Norovirus infections are transmitted via the fecal-oral route or by aerosols from vomiting. The virus is one of the most common causes of non-bacterial gastroenteritis epidemic worldwide. Symptoms include watery and nonbloody diarrhea, nausea, vomiting, and low-grade fever. Although the infection is self-limiting, severe dehydration can occur. The diagnosis is usually presumptive, and viral detection using PCR or enzyme immunoassay may be used for patients with severe disease or immunocompromised status. Management is supportive and may include rehydration therapy.

Reoviridae: Rotavirus

Rotavirus belongs to the Reoviridae family and is a non-enveloped, double-stranded RNA virus. Transmission occurs through the fecal-oral route. Rotavirus is a common cause of severe gastroenteritis in children. Severe infections can result in dehydration and death. Diagnostic testing is not usually required, but the virus can be detected in stool samples using ELISA or PCR. Oral rehydration therapy is the mainstay of treatment. A live-attenuated vaccine is available to prevent rotavirus infections.

Orthopoxvirus

Orthopoxvirus is a genus of large, brick-shaped, double-stranded DNA viruses. Several clinically relevant species exist, including variola virus (the cause of smallpox), monkeypox virus, vaccinia virus, and cowpox virus. Transmission varies depending on the species but can be through contact with infected bodily secretions, skin lesions, or fomites. Smallpox is the most severe disease, presenting with constitutional symptoms and a diffuse, well-circumscribed maculopapular rash that progresses through an evolutionary process that results in scarring. Smallpox is associated with a high mortality rate. Monkeypox presents similarly but has lower mortality and is associated with lymphadenopathy. Vaccinia and cowpox produce milder disease with localized lesions acquired from direct skin-to-skin contact. These infections are diagnosed with the aid of PCR, serology, viral culture, and/or electron microscopy. There are no known treatments for these diseases, and management is generally supportive. Vaccination has led to the eradication of smallpox.

Papillomaviridae: HPV

Human papillomavirus (HPV) is a nonenveloped, circular, double-stranded DNA virus belonging to the Papillomaviridae family. Humans are the only reservoir, and transmission occurs through close skin-to-skin or sexual contact. Human papillomaviruses infect basal epithelial cells and can affect cell-regulatory proteins to result in cell proliferation. There are > 200 serotypes that can cause several conditions, including cutaneous warts, anogenital warts, and neoplasms.

Zika Virus Infection

Zika virus belongs to the genus Flavivirus and is primarily transmitted by Aedes aegypti mosquitoes, but can also be transmitted sexually and transplacentally. Although most infected patients are asymptomatic, some may present with low-grade fever, pruritic rash, and conjunctivitis. Congenital Zika syndrome is the most severe complication of a Zika virus infection, where transplacental fetal infection manifests with ocular defects, microcephaly, spasticity, and seizures. The diagnosis is made either by RT-PCR or serology. Since there is no definitive management for a Zika virus infection, the treatment is mostly supportive. Prevention includes controlling the mosquito population, using insect repellants, and wearing protective clothing.

Bunyavirales

Bunyaviridae is a family of RNA viruses that is classified into 5 genera: Orthobunyavirus (La Crosse virus), Hantavirus, Nairovirus (Crimean-Congo hemorrhagic fever virus), Phlebovirus (Rift Valley fever virus), and Tospovirus. The common characteristics of the virus family include an enveloped spherical structure containing a single-stranded, negative-sense RNA genome, which is triple-segmented. Infections are generally either arthropod borne or rodent borne. There are several clinical manifestations, which overall present as hemorrhagic fevers and/or encephalitis. Diagnostic measures include serology and RT-PCR. Management is largely supportive.

Herpes Simplex Virus 1 & 2

Herpes simplex virus (HSV) is a double-stranded DNA virus belonging to the family Herpesviridae. Herpes simplex virus commonly causes recurrent infections involving the skin and mucosal surfaces, including the mouth, lips, eyes, and genitals. Typical mucocutaneous infections are characterized by an acute localized appearance of clusters of small, painful vesicles on an erythematous base. Although overlap exists, HSV-1 is classically associated with oropharyngeal lesions, whereas HSV-2 is mostly responsible for genital herpes, an STI. Systemic and severe infections including encephalitis, meningitis, and neonatal herpes may also occur. The diagnosis is made based on clinical presentation and history, which can be confirmed by the microscopic examination of a stained smear of a fresh vesicle, nucleic amplification test using PCR, direct immunofluorescence, or serologic tests. The therapy for mucocutaneous lesions is usually symptomatic, but antiviral therapies involving acyclovir, valacyclovir, or famciclovir are useful if given early, and are always part of the therapy for serious systemic infections.

Ebolavirus/Marburgvirus

"Ebolavirus and Marburgvirus are members of the Filoviridae family. They are single-stranded, negative-sense RNA viruses with a characteristic filamentous, pleomorphic morphology. Transmission mainly occurs through contact with secretions from an infected individual. These viruses cause similar diseases, with flu-like symptoms, diarrhea, hemorrhage, multiorgan dysfunction, and shock. The diagnosis can be made using PCR, antigen detection, and serology. Management is mainly supportive, although monoclonal antibody therapy has been promising for treating Ebola virus disease. "

Lassa Virus

Lassa virus, part of the Arenaviridae family, is an ssRNA virus that causes Lassa fever, a type of viral hemorrhagic illness. The virus is endemic in parts of West Africa (Sierra Leone, Liberia, Guinea, and Nigeria) and neighboring countries. The reservoir is the multimammate rat (Mastomys natalensis), and transmission is via inhalation or contact with rodent excretions or consumption of rodents. Human-to-human transmission also occurs. The majority of infected patients are asymptomatic. However, symptomatic patients present with fever, malaise, headaches, vomiting, and chest pains, which can progress to hemorrhage, hypovolemia, and shock. Treatment is mainly with ribavirin and supportive care. There is no effective vaccine, but preventive measures such as avoiding rodent exposures and use of PPE can reduce transmission. Ribavirin is also given as postexposure prophylaxis.

JC Virus and BK Virus

BK virus (BKV) and JC virus (JCV) are small, nonenveloped, single-stranded DNA viruses belonging to the Polyomaviridae family, which are ubiquitous in the human population. While the primary infection is usually asymptomatic, the infection leads to lifelong latency in the kidneys and lymphoid organs. Latent infections can become active in immunosuppressed patients. Reactivation of BKV is most often seen in transplant patients and can lead to nephropathy, allograft loss, hemorrhagic cystitis, and urethral stenosis. Reactivation of JCV causes progressive multifocal leukoencephalopathy (PML), which is considered an AIDS-defining condition. Diagnosis can be confirmed with PCR or tissue biopsy. Specific therapy is not available. Management aims to reduce immunosuppression.

Human Herpesvirus 6 & 7

Human herpesvirus (HHV)-6 and HHV-7 are similar double-stranded DNA viruses belonging to the Herpesviridae family. Human herpesviruses are ubiquitous and infections are commonly contracted during childhood. Both HHV-6B and HHV-7 cause a common childhood illness known as roseola infantum (also known as roseola or 6th disease). Roseola is a self-limiting disease that presents with high fever, followed by a diffuse, rose-pink maculopapular rash. The diagnosis is clinical, and management is supportive.

Human Herpesvirus 8

Human herpesvirus 8, also known as Kaposi sarcoma–associated herpesvirus, is a double-stranded DNA virus belonging to the Herpesviridae family. This uncommon oncogenic virus causes Kaposi sarcoma (an AIDS-defining condition), primary effusion lymphomas, and multicentric Castleman disease mainly in immunocompromised patients. The process occurs through the induction of cellular growth activity and the inhibition of apoptosis in infected cells.

Hepatitis E Virus

The hepatitis E virus (HEV) is a small nonenveloped virus that contains linear, single-stranded, positive-sense RNA, making it similar to norovirus. Transmission of HEV is via the fecal–oral route and is clinically similar to that of hepatitis A. However, unlike hepatitis A, hepatitis E is quite severe, especially in pregnant women, and may cause fulminant hepatitis along with hepatic encephalopathy over a period of approximately 8 weeks. Management is mainly preventive and includes avoiding contaminated drinking water, good sanitation, and adequate personal hygiene.

Rhinovirus

Rhinovirus is an acid-labile, positive-sense RNA virus of the Picornavirus family. The virus, which causes the common cold, is most often acquired through the airway via the inhalation of aerosols containing rhinovirus and fomites. Because rhinovirus is inactivated by gastric acid, the virus can only affect the nasal mucosa and conjunctiva, causing edema of subepithelial tissues and resulting in the common cold 1–3 days after transmission. Diagnosis is clinical and the disease is typically mild and self-limiting. Management is supportive and may include increased fluid intake, NSAIDs, and nasal decongestants.

Hepatitis A Virus

The hepatitis A virus (HAV) is a nonenveloped virus of the Picornaviridae family with single-stranded RNA. The virus replicates in the liver, is excreted in the bile, and is found in high concentrations in the stool of acutely infected individuals. The 2 main routes of infection are consumption of contaminated food or water and direct contact with an infected person. HAV causes an acute, highly contagious hepatitis with unspecific prodromal symptoms such as fever and malaise followed by jaundice and elevated liver transaminases. Most individuals recover fully within a few months, and the immunity resulting from HAV infection is lifelong. Unlike hepatitis B and C, HAV infection does not result in chronic infection or chronic liver disease. Preventive vaccination is available for HAV and is recommended for individuals with increased risk of exposure and, in some countries such as the United States, for all children > 12 months of age.

Antivirals for Influenza

Antiviral agents against influenza are important in preventing and treating influenza infection. Influenza is often self-limited, but high-risk populations suffer significant morbidity and mortality from the illness. Different classes of drugs act on the influenza virus. Neuraminidase inhibitors include oseltamivir (oral), zanamivir (inhalation) and peramivir (IV); these drugs act by inhibiting neuraminidase, the enzyme that cleaves off the new virus particle. By blocking the enzymatic effect, further release of progeny virus to nearby respiratory cells is reduced. Baloxavir, a selective inhibitor of influenza cap-dependent endonuclease, inhibits viral mRNA synthesis. Both neuraminidase inhibitors and baloxavir have activity against influenzas A and B. Adamantanes, or M2 inhibitors, include amantadine and rimantadine, which are active against influenza A but are not often used owing to resistance.

Virology: Overview

Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. The replication cycle differs between viruses that infect bacteria (bacteriophages) and viruses that infect eukaryotic cells. Bacteriophages have either a lytic or lysogenic replication cycle, while eukaryotic viruses have a defined 6-step replication process.

Influenza Viruses/Influenza

Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Symptoms of gastroenteritis may also commonly occur in children. Influenza is usually a self-limiting condition, though viral or secondary bacterial pneumonia may complicate the disease. Management is generally supportive, although NA inhibitors can be helpful if initiated within 48 hours of infection. Prevention relies on the annual vaccination of the public and practicing good hygiene.

Measles Virus

Measles (also known as rubeola) is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae and the genus Morbillivirus. It is highly contagious and spreads only among humans by respiratory droplets or direct-contact transmission from an infected person. Typically a disease of childhood, measles classically starts with cough, coryza, and conjunctivitis, followed by a maculopapular rash. Complications include diarrhea, pneumonia, and encephalitis. Measles can be prevented through vaccination, and thanks to this, had largely been eradicated until recent years. Most cases are managed with supportive care, although in select patients, antivirals can be indicated.

AIDS-defining Conditions

Human immunodeficiency virus (HIV) infection is a sexually transmitted or blood-borne infection that destroys CD4 T cells. Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. These serious and life-threatening diseases are generally not seen in immunocompetent patients. Treatment of HIV is very important in managing these diseases, and the incidence of AIDS-defining conditions has declined with the use of antiretroviral therapy.

HIV Infection and AIDS

Human immunodeficiency virus (HIV), a single-stranded RNA virus belonging to the Retroviridae family, is the etiologic agent of acquired immunodeficiency syndrome (AIDS). The human immunodeficiency virus is a sexually transmitted or blood-borne infection that attacks CD4+ T lymphocyte cells, macrophages, and dendritic cells, leading to eventual immunodeficiency. The presentation is marked by constitutional symptoms such as lymphadenopathy and fever. Further progression predisposes to opportunistic infections and malignancies. Diagnosis is by enzyme immunoassay for HIV-1 and -2. Additional tests include HIV viral load, genotyping, and CD4+ T lymphocyte count to determine therapy and evaluate treatment response and disease progression. Immediate treatment with combination antiretroviral therapy is recommended.

How are Viruses Studied? 03:56 min

How are Viruses Studied? 1 quiz question

How are Viruses Studied? 1 concept page
Viral Culture and Virus Quantification 05:46 min

Viral Culture and Virus Quantification 6 quiz questions

Viral Culture and Virus Quantification 1 concept page
Double-stranded DNA (dsDNA) Genomes – DNA Viruses 03:45 min

Double-stranded DNA (dsDNA) Genomes – DNA Viruses 3 quiz questions

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Gapped Double-stranded DNA (dsDNA) Genomes – DNA Viruses 03:03 min

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Single-stranded DNA (ssDNA) Genomes – DNA Viruses 02:20 min

Single-stranded DNA (ssDNA) Genomes – DNA Viruses 3 quiz questions

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Double-stranded RNA (dsRNA) – RNA Virus Genomes 03:58 min

Double-stranded RNA (dsRNA) – RNA Virus Genomes 3 quiz questions

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Positive-sense Single-stranded RNA ((+)ssRNA) Virus – RNA Virus Genomes 06:21 min

Positive-sense Single-stranded RNA ((+)ssRNA) Virus – RNA Virus Genomes 4 quiz questions

Positive-sense Single-stranded RNA ((+)ssRNA) Virus – RNA Virus Genomes 1 concept page
Negative-sense Single-stranded RNA ((-)ssRNA) Virus – RNA Virus Genomes 04:28 min

Negative-sense Single-stranded RNA ((-)ssRNA) Virus – RNA Virus Genomes 4 quiz questions

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Ambisense RNA Virus Genomes 01:58 min

Ambisense RNA Virus Genomes 1 quiz question

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Genetic Engineering of Viruses 03:59 min

Genetic Engineering of Viruses 4 quiz questions

Genetic Engineering of Viruses 0 Concept Pages
Breakthrough in Virology 05:34 min

Breakthrough in Virology 4 quiz questions

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Viral Genomes 05:14 min

Viral Genomes 10 quiz questions

Viral Genomes 1 concept page
Adenoviruses 11:23 min

Adenoviruses 6 quiz questions

Adenoviruses 1 concept page
Herpesviruses 05:12 min

Herpesviruses 3 quiz questions

Herpesviruses 2 Concept Pages
Herpex Simplex Virus-1 and Herpes Simplex Virus-2 – Herpesviruses 11:46 min

Herpex Simplex Virus-1 and Herpes Simplex Virus-2 – Herpesviruses 5 quiz questions

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Varicella-Zoster Virus (VZV) – Herpesviruses 05:37 min

Varicella-Zoster Virus (VZV) – Herpesviruses 3 quiz questions

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Epstein-Barr Virus (EBV) – Herpesviruses 07:39 min

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Epstein-Barr Virus (EBV) – Herpesviruses 1 concept page
Cytomegalovirus (CMV) – Herpesviruses 05:46 min

Cytomegalovirus (CMV) – Herpesviruses 3 quiz questions

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Roseolovirus (HHV-6 and HHV-7) – Herpesviruses 02:38 min

Roseolovirus (HHV-6 and HHV-7) – Herpesviruses 2 quiz questions

Roseolovirus (HHV-6 and HHV-7) – Herpesviruses 1 concept page
Kaposi's Sarcoma-associated Herpesvirus (KSHV) – Herpesviruses 04:01 min

Kaposi's Sarcoma-associated Herpesvirus (KSHV) – Herpesviruses 1 quiz question

Kaposi's Sarcoma-associated Herpesvirus (KSHV) – Herpesviruses 1 concept page
Papillomaviruses 22:33 min

Papillomaviruses 4 quiz questions

Papillomaviruses 1 concept page
BK and JC Virus – Polyomaviruses 07:14 min

BK and JC Virus – Polyomaviruses 3 quiz questions

BK and JC Virus – Polyomaviruses 1 concept page
Poxviruses 04:39 min

Poxviruses 3 quiz questions

Poxviruses 1 concept page
Molluscum Contagiosum Virus (MCV) – Poxviruses 01:57 min

Molluscum Contagiosum Virus (MCV) – Poxviruses 1 quiz question

Molluscum Contagiosum Virus (MCV) – Poxviruses 1 concept page
Hepatitis B Virus – Hepadnaviruses 12:15 min

Hepatitis B Virus – Hepadnaviruses 5 quiz questions

Hepatitis B Virus – Hepadnaviruses 1 concept page
B19 Parvovirus – Parvoviruses 07:58 min

B19 Parvovirus – Parvoviruses 4 quiz questions

B19 Parvovirus – Parvoviruses 1 concept page
Rotavirus and Colorado Tick Fever Virus – Reoviruses 08:17 min

Rotavirus and Colorado Tick Fever Virus – Reoviruses 4 quiz questions

Rotavirus and Colorado Tick Fever Virus – Reoviruses 2 Concept Pages
Picornaviruses 01:47 min

Picornaviruses 1 quiz question

Picornaviruses 4 Concept Pages
Enteroviruses – Picornaviruses 13:24 min

Enteroviruses – Picornaviruses 7 quiz questions

Enteroviruses – Picornaviruses 1 concept page
Rhinoviruses – Picornaviruses 06:17 min

Rhinoviruses – Picornaviruses 2 quiz questions

Rhinoviruses – Picornaviruses 1 concept page
Hepatitis A Virus (HAV) – Picornaviruses 06:07 min

Hepatitis A Virus (HAV) – Picornaviruses 3 quiz questions

Hepatitis A Virus (HAV) – Picornaviruses 1 concept page
Norwalk Virus and Hepatitis E Virus (HEV) – Caliciviruses 05:23 min

Norwalk Virus and Hepatitis E Virus (HEV) – Caliciviruses 3 quiz questions

Norwalk Virus and Hepatitis E Virus (HEV) – Caliciviruses 2 Concept Pages
Flaviviruses 01:06 min

Flaviviruses 1 quiz question

Flaviviruses 4 Concept Pages
Hepatitis C Virus (HCV) – Flaviviruses 06:01 min

Hepatitis C Virus (HCV) – Flaviviruses 2 quiz questions

Hepatitis C Virus (HCV) – Flaviviruses 1 concept page
Arboviruses – Flaviviruses 08:16 min

Arboviruses – Flaviviruses 4 quiz questions

Arboviruses – Flaviviruses 2 Concept Pages
Rubella and Other Togaviruses 11:09 min

Rubella and Other Togaviruses 5 quiz questions

Rubella and Other Togaviruses 2 Concept Pages
Retroviruses 02:59 min

Retroviruses 2 quiz questions

Retroviruses 1 concept page
Human Immunodeficiency Virus (HIV) – Retroviruses 09:24 min

Human Immunodeficiency Virus (HIV) – Retroviruses 5 quiz questions

Human Immunodeficiency Virus (HIV) – Retroviruses 2 Concept Pages
AIDS-defining Diseases – Human Immunodeficiency Virus (HIV) 17:15 min

AIDS-defining Diseases – Human Immunodeficiency Virus (HIV) 5 quiz questions

AIDS-defining Diseases – Human Immunodeficiency Virus (HIV) 3 Concept Pages
Hepatitis E Virus (HEV) – Hepeviruses 08:08 min

Hepatitis E Virus (HEV) – Hepeviruses 4 quiz questions

Hepatitis E Virus (HEV) – Hepeviruses 1 concept page
Paramyxoviruses 03:04 min

Paramyxoviruses 2 quiz questions

Paramyxoviruses 2 Concept Pages
Measles Virus – Paramyxoviruses 06:41 min

Measles Virus – Paramyxoviruses 4 quiz questions

Measles Virus – Paramyxoviruses 1 concept page
Mumps Virus – Paramyxoviruses 03:17 min

Mumps Virus – Paramyxoviruses 2 quiz questions

Mumps Virus – Paramyxoviruses 1 concept page
Parainfluenza Viruses – Paramyxoviruses 05:44 min

Parainfluenza Viruses – Paramyxoviruses 3 quiz questions

Parainfluenza Viruses – Paramyxoviruses 2 Concept Pages
Rabies Virus – Rhabdoviruses 09:01 min

Rabies Virus – Rhabdoviruses 5 quiz questions

Rabies Virus – Rhabdoviruses 1 concept page
Ebola and Marburg Viruses – Filoviruses 06:02 min

Ebola and Marburg Viruses – Filoviruses 3 quiz questions

Ebola and Marburg Viruses – Filoviruses 1 concept page
Influenza Viruses – Orthomyxoviruses 12:45 min

Influenza Viruses – Orthomyxoviruses 6 quiz questions

Influenza Viruses – Orthomyxoviruses 2 Concept Pages
Lymphocytic Choriomeningitis Virus (LCMV) and Lassa Fever Virus – Arenaviruses 04:50 min

Lymphocytic Choriomeningitis Virus (LCMV) and Lassa Fever Virus – Arenaviruses 3 quiz questions

Lymphocytic Choriomeningitis Virus (LCMV) and Lassa Fever Virus – Arenaviruses 2 Concept Pages
Bunyaviruses 02:20 min

Bunyaviruses 1 quiz question

Bunyaviruses 1 concept page
Hantaviruses – Bunyaviruses 02:45 min

Hantaviruses – Bunyaviruses 2 quiz questions

Hantaviruses – Bunyaviruses 1 concept page
California Encephalitis Virus – Bunyaviruses 03:01 min

California Encephalitis Virus – Bunyaviruses 1 quiz question

California Encephalitis Virus – Bunyaviruses 1 concept page

5 Stars		21
4 Stars		4
3 Stars		4
2 Stars		4
1 Star		3

5 Stars		21
4 Stars		4
3 Stars		4
2 Stars		4
1 Star		3

Viruses

Course Details

Content

Your Educators of course Viruses

Vincent Racaniello, PhD

Sean Elliott, MD

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