The majority of infectious vomiting and diarrhea in infants and young children is viral in origin, with the most commonly implicated virus being rotavirus. Norovirus is  another common cause of viral gastroenteritis in individuals of all ages, though it is not as common in young children as rotavirus. 

In most children and adults, Zika virus causes a mild fever characterized by myalgia, fatigue, and headache. The population most at risk for serious complications from the disease is unborn fetuses. Exposure to Zika virus before birth has been associated with microcephaly, a frequently fatal disorder of abnormal skull and brain development.

Each of these viral families or groups has an RNA genome and envelope. The Paramyxoviruses are structurally the most closely related to influenza, since both are negative sense RNA viruses and many of the paramyxoviruses contain a neuraminidase and hemagglutinin. There are some notable differences, however. In the paramyxoviruses, both neuraminidase and hemagglutinin functions contained in a single glycoprotein on one type of spike, whereas in influenza, these functions are accomplished by two separate glycoproteins which on two types of spikes (except for Influenza C, which has both functions on a single glycoprotein). In addition, the genome is segmented in influenza, but not in the paramyxoviruses. The viruses in the Togaviridae and Coronaviridae families differ from the Influenza viruses in that they have a positive sense RNA genome. Viruses in the Rhabdoviridae family, which includes the vesicular stomatitis virus and the rabies virus, are bacilliform negative-stranded RNA viruses.

Paramyxoviruses possess hemagglutinin and neuraminidase that are present on the same spike. This is in contrast to the orthomyxoviruses that possess hemagglutinin and neuraminidase on different spikes.

The influenza virus is a member of the orthomyxovirus group and is an enveloped ss-RNA virus. Lentiviruses are a group of retroviruses which include HIV-1. Parainfluenza virus and respiratory syncytial virus (RSV) belong to the paramyxovirus group.

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.

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.