Adenoviruses are transmitted by aerosol-droplets. They are not transmitted by fecal / oral route, direct inoculation of conjunctiva by tonometers or fingers, or tick or mosquito bite.

Rubella virus is a member of the togavirus family and not the herpes virus, neisseriae (family of bacteria), adenovirus, and picornavirus.

Hepatitis B virus (HBV) is a human carcinogen associated with hepatocellular carcinoma. The incidence of hepatocellular carcinoma is higher in a person who becomes infected with HBV earlier in life. The pattern observed is: person develops chronic hepatitis leading to cirrhosis of the liver and eventually to liver cancer 20-50 years post-infection. The genome of HBV is small and comprises a small, circular, partially double stranded DNA molecule. HBV replicates in hepatocyte and involves RNA intermediate and a virus coded reverse transcriptase. HBV can become integrated into the cellular chromosome during chronic infection and may promote genetic instability in the cell.

Herpes simplex virus type 1 (HSV-1) is a member of the Herpesviridae family and consists of a double stranded DNA genome. Primary infection with HSV-1 mostly involves the mouth and/or throat. Gingivostomatitis is a classic clinical presentation of HSV-1 infection. It is characterized by formation of vesicles on the mouth and gums, which rupture to become ulcers.

Coxsackievirus type A and coxsackievirus type B are members of the Picornaviridae family. Picornaviruses are naked viruses with an icosahedral nucleocapsid. The genome consists of single molecule of single stranded RNA.Coxsackievirus type A is associated with herpangina, which is commonly seen in children. Herpangina is a severe febrile pharyngitis characterized by vesicles or nodules primarily on the soft palate.

Coxsackievirus type B is associated with Bornholm disease seen mainly in older children and young adults. Bornholm disease is myositis and is also called Pleurodynia. It is characterized by paroxysms of stabbing pain in the chest muscles and abdomen muscles

Subacute sclerosing panencephalitis (SSPE) is a serious, late, and rare neurological complication occurring 1-10 years after recovery from measles. This fatal disease is characterized by a very slow replication and spread of measles virus in the brain. Patients with SSPE do not show a high number of measles viruses in the brain, but they demonstrate unusually high levels of measles antibody in the blood and cerebrospinal fluid. Many years after recovering from measles, patients develop changes in personality, behavior, and memory; those symptoms are followed by myoclonic jerks, blindness, and spasticity.

Orthoreovirus mostly causes asymptomatic or mild infections in human.

Persistent infection with Hepatitis B can develop into chronic hepatitis, cirrhosis, and hepatocellular carcinoma.

Papillomavirus is associated with skin warts, Condyloma acuminatum, genital malignancies, respiratory papillomatosis, and focal epithelial hyperplasia.

Parvovirus B19 is the etiological agent of erythema infectiosum primarily seen in children. Parvovirus B19 is also associated with chronic anemia in immunodeficient patients. Infection with this virus during pregnancy can cause anemia and congestive cardiac failure in the fetus and can lead to miscarriage or stillbirth.

The Epstein Barr virus causes infectious mononucleosis associated with the Burkitts lymphoma in East African children. The virus is found in human oropharynx and B lymphocytes. It is transmitted primarily by saliva. The infection begins in the pharyngeal epithelium, spreads to the cervical lymph nodes, then travels through the blood to the liver and spleen.

Hepatitis B virus is the DNA virus that is part of the Hepadnaviridae family. The characteristic feature of the virus from this family is that the genome consists of a circular DNA that is part double stranded and part single stranded. The virions are spherical particles with an envelope. Hepatitis B virus consists of icosahedral core within a closely adherent capsid that contains cellular lipid, glycoproteins, and a virus-specific surface antigen called Hepatitis B surface antigen (HBsAg). Respiratory syncytial virus is RNA virus that has linear single stranded nonsegmented RNA.Lassa fever virus has a circular single stranded RNA in 2 segments. Varicella-zoster virus and Epstein-Barr virus consist of a linear double stranded DNA.

Hepatitis B is an example of a chronic carrier infection where a carrier state can follow an asymptomatic infection, as well as actual disease. Neonatal rubella virus, cytomegalovirus, retrovirus, and togavirus do not cause chronic carrier infection.

Laryngotracheobronchitis, commonly known as croup, is one of the serious manifestation of parainfluenza virus infection in infants and young children. Parainfluenza type 1 is a common cause of croup, which results in subglottal swelling and airway obstruction. Major clinical manifestations include hoarseness, "barking" cough, tachypnea, tachycardia, and suprasternal retraction.

Cold sore is a recurrent mucocutaneous infection caused by herpes simplex virus (HSV). The individual retains HSV-1 DNA in the trigeminal ganglion for life following recovery from primary oropharyngeal HSV infection. Cold sores, also known as herpetic labialis, are manifested as a result of activation of HSV from the trigeminal ganglia. Cold sores are characterized by development of a cluster of vesicles around the mucocutaneous junction of the lips.

Rotaviruses can survive the acidic environment in stomach. The virus infects the small intestine and damages the epithelial cell lining the villi. The virus causes permeability changes and cell lysis, leading to malabsorption with water and electrolyte imbalance. Rotaviruses are a major cause of diarrhea in young children and are associated with outbreaks in preschool and day care-centers. Rotaviruses cause extensive tissue damage, leading to serious fluid and electrolyte loss.

Lassa fever virus is an Arenavirus associated with hemorrhagic fever. Lassa fever virus is enzootic in the West African peridomestic rodent. The rodent transmits the virus to the human by contaminating the house with urine. The infection is characterized by fever, headache, malaise, coagulopathy, petechiae, vomiting, pharyngitis, and occasional visceral hemorrhage. Serious manifestations include carditis, hepatitis, encephalopathy, pneumonitis, conjunctivitis, etc. Cardiovascular collapse results in death in 20% of the hospitalized cases.

Hand, foot, and mouth disease is a vesicular exanthem caused by coxsackievirus A16. It is characterized by ulcerating vesicles on hand, foot, mouth, and tongue along with mild fever. The disease subsides in a few days on its own.

Parvovirus B19 is a member of the family Parvoviridae and is the causative agent of erythema infectiosum (fifth disease). The hallmark symptom of erythema infectiosum is a mild rubella-like erythematous rash that produces arthropathy, especially in women. The disease has two separate components. The first component is the lytic phase where the lytic action of the virus replication in erythroid precursors gives rise to a transient arrest of erythrocytic production. This can result in a slight drop in hemoglobin. Hemoglobin levels will substantially drop in those patients with chronic hemolytic anemia. This is the viremic stage, and mild flu-like symptoms with pyrexia and chills are not uncommon. These flu-like symptoms can last for 1 to 3 days. One week after the viremia peak, the second phase occurs where the virus is rarely detectable. The second phase is where the erythematous maculopapular rash and arthropathy occur. The characteristic rash produces a lace-like appearance on the trunk and extremities and a “slapped-cheek” appearance on the face. Erythema infectiosum infections in pregnant women can induce fetal loss (5-20%), especially if the infection occurs at less than 20 weeks.

Herpes simplex type 1 (HSV-type 1) belongs to the family Herpesviridae and causes an infection that characteristically presents as an eruption of vesicles that are restricted to areas around the mouth, lips, and nostrils. The infection can also occur in the genital area, thought HSV-type 2 is more commonly associated with genital infections, called herpes labialis. Patients usually can predict the onset of an eruption due to a prodromal stage of itching or other sensations that can occur a few hours to a few days prior to the eruption of vesicles. HSV-type 1 also causes primary infections of the oral mucous membranes in children and herpetic eye infections. Eruptions can occur at any time and depend on the immunological status of the host, health, and various other factors that vary from host to host.

Herpes simplex type 2 (HSV-type 2) belongs to the family Herpesviridae and causes an infection that characteristically presents as an eruption of vesicles that are restricted to areas around the genital area. Multiple vesicles in females appear on the vulva, in the vagina, and on the portio. Multiple vesicles in men are found often on the sulcus of the glans and the preputium but can be found on any part of the penis. Duration and severity of the eruptions are usually more severe in females than in males. HSV-type 1 can also be found to cause genital eruptions but at a significantly lower rate. HSV-type 2 causes 75% of all neonatal herpes (a severe complication of genital HSV infection) where the newborn acquires the virus by contamination through the birth canal. Eruptions can occur at any time and depend on the immunological status of the host, health, and various other factors that vary from host to host.

Epstein-Barr virus belongs to the family Herpesviridae and is the causative agent of infectious mononucleosis (IM), Burkitt's Lymphoma, and undifferentiated nasopharyngeal carcinoma. IM characteristically produces a marked lymphocytosis involving almost all of the lymphoreticular tissues. This leads to hepatomegaly, splenomegaly, lymphadenopathy, and lymphoid hyperplasia of the oronasopharynx. The peripheral blood smear contains atypical lymphocytes of the Downey II type. It is generally a self-limiting disease; however, it can cause a severe protracted illness that can at times prove to be fatal. Patients with an unusual immuno-defect known as the X-linked lymphoproliferative syndrome frequently have overwhelming EBV primary infections, which can be fatal in the majority of the cases.

Cytomegalovirus (CMV) belongs to the family Herpesviridae and causes cytomegalovirus mononucleosis, cytomegalic inclusion disease, and cytomegalovirus infection in the immunocompromised. CMV resembles infectious mononucleosis in that atypical lymphocytosis, fever, and malaise are characteristic symptoms to both. Pharyngitis is present as a symptom, though less severe in CMV than in infectious mononucleosis. The heterophile antibody test is also negative in CMV. Toxoplasmosis may also mimic CMV and infectious mononucleosis and thus must be considered in the differential diagnosis in those patients with a negative heterophile antibody test and mono-like symptoms. Transmission of CMV from mother to fetus may occur at any time during the pregnancy.  Fetal loss is less likely than congenital CMV infection, which – in its most severe form – is manifested as hepatosplenomegaly, microcephaly, chorioretinitis, hearing loss, and thrombocytopenia.  The mortality rate is high.  

Human papillomaviruses are small DNA viruses. These viruses replicate in the nuclei of differentiated keratinocytes and are the cause of tumors of the skin and mucosa. The genome of human papillomaviruses is circular and contains approximately 8,000 base pairs.