The invasion of an organism's body tissues by viruses leading to cellular damage or death, immunopathology or cell transformation (e.g. into a cancer cell).  Flu caused by influenza viruses is the best known viral disease. 

Viruses are spread (transmitted, mostly from other humans but also via- or  from animals) in various ways. They can be swallowed, inhaled, spread by the bites of insects, such as mosquitoes, certain biting flies, or ticks, spread sexually or during transfusion of contaminated blood.
Common viral infections (flu, measles, rubella, chickenpox) may be diagnosed based on symptoms.

species of curved, rod-shaped, non-spore forming, Gram-negative microaerophilic (requires small amounts of oxygen to survive) bacteria, causing food poisoning (gastroenteritis), most often from poultry, but also other incorrectly prepared meat,   contaminated drinking water and unpasteurized milk. Typical symptoms are abdominal pain, diarrhea, fever, and malaise. Severe cases (accompanying fevers, blood in stool, prolonged symptoms) may require ciprofloxacin, erythromycin, azithromycin or norfloxacin. 

 Zika virus (ZIKV) is a member of the Flaviviridae virus family. 
The Flaviviridae are a family of positive, single-stranded, enveloped RNA viruses. They are found in arthropods, (primarily ticks and mosquitoes), and can occasionally infect humans. Zika is a disease caused by Zika virus that is spread to people primarily through the bite of an infected Aedes species mosquito, such as A. aegypti. Other mosquito-transmitted viruses include Yellow Fever, Dengue Fever, Japanese encephalitis, West Nile viruse.

The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week. Severe disease requiring hospitalization is uncommon. During the first week of infection, Zika virus can be found in the blood and passed from an infected person to another person through mosquito bites. An infected mosquito can then spread the virus to other people. To help prevent others from getting sick, avoid mosquito bites during the first week of illness.
See your health care provider if you are pregnant and develop a fever, rash, joint pain, or red eyes within 2 weeks after traveling to a country where Zika virus cases have been reported as Zika might be responsible for birth defects such as microcephaly - a condition when babies are born with abnormally small heads and underdeveloped brains. In January 2016, CDC on Friday advised pregnant women avoid travel to a number of countries and territories around the world, primarily in the Americas: Bolivia, Brazil, Cape Verde, Colombia, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, St. Martin, Suriname, Samoa, Venezuela, and Puerto Rico.

Streptococci are spherical bacteria (cocci) that occur in pairs or chains. They belong to the phylum Firmicutes and are normal inhabitants of human flora - eyes (conjunctiva, mucous membrane that covers the front of the eye and lines the inside of the eyelids), respiratory tract, stomach, and intestines. 
Streptococci can be benign, opportunistic or pathogenic. 
Streptococcus. thermophilus, for example, is found in fermented milk products, and is generally used in the production of yogurt, helping to increase populations of Lactobacilli. Streptococcus sanguinis lives in the mouth is protects from cavities but might be associated with halitosis. Other halitosis-related streptococci include Streptococcus salivarius, Streptococcus parasanguinis, Streptococcus mitis, and Streptococcus oralis. Streptococcus pneumoniae lives in the in the area extending from the back of the nasal cavity to the throat of healthy individuals and turns into an invader when the individual's immune system weakens or microbiota gets disrupted. In addition to pneumonia, it can cause bronchitis, rhinitis, acute sinusitis, ear infection (otitis media), pink eye (conjunctivitis), meningitis, bacteremia, sepsis, osteomyelitis, joint infection (septic arthritis), heart issues (endocarditis), peritonitis, pericarditis, cellulitis, and brain abscess. 

The invasion of an organism's body tissues by bacteria leading to their multiplication, and the reaction of host tissues to these bacteria and their toxins  resulting in illness. 

In many cases it is difficult to determine if the illness is caused by bacteria or a virus. Antibiotics are medications that fight bacterial infections. They work by disrupting the processes necessary for bacterial cell growth and proliferation. Overuse and misuse of antibiotics has led to a rise in antibiotic resistance

See Aurametrix summaries for Infections.