If an animal strain reassorts with a human strain, then a novel strain can emerge that is capable of human-to-human transmission. This has caused pandemics, but only a limited number have occurred, so it is difficult to predict when the next will happen. Mechanism
Transmission
People who are infected can transmit influenza viruses through breathing, talking, coughing, and sneezing, which spread respiratory droplets and aerosols that contain virus particles into the air. A person susceptible to infection can then contract influenza by coming into contact with these particles. Respiratory droplets are relatively large and travel less than two meters before falling onto nearby surfaces. Aerosols are smaller and remain suspended in the air longer, so they take longer to settle and can travel further than respiratory droplets. Inhalation of aerosols can lead to infection, but most transmission is in the area about two meters around an infected person via respiratory droplets that come into contact with mucosa of the upper respiratory tract. Transmission through contact with a person, bodily fluids, or intermediate objects (fomites) can also occur, such as through contaminated hands and surfaces since influenza viruses can survive for hours on non-porous surfaces. If ones hands are contaminated, then touching ones face can cause infection.Influenza is usually transmissible from one day before the onset of symptoms to 5–7 days after. In healthy adults, the virus is shed for up to 3–5 days. In children and the immunocompromised, the virus may be transmissible for several weeks.
Pityriasis amiantacea is an eczematous condition of the scalp in which thick tenaciously adherent scale infiltrates and surrounds the base of a group of scalp hairs. It does not result in scarring or alopecia. : 647 Pityriasis amiantacea was first described by Alibert in 1832. Pityriasis amiantacea affects the scalp as shiny asbestos-like (amiantaceus) thick scales attached in layers to the hair shaft. The scales surround and bind down tufts of hair. The condition can be localised or covering over the entire scalp. Temporary alopecia and scarring alopecia may occur due to repeated removal of hairs attached to the scale. It is a rare disease with a female predilection. Diagnosis
Pityriasis amiantacea can easily be misdiagnosed due to its close resemblance to other scalp diseases such as psoriasis, seborrhoeic dermatitis or lichen planus. However, in pityriasis amiantacea the scales are attached to both the hair shaft and the scalp. Pityriasis amiantacea may be present with other inflammatory conditions such as atopic dermatitis or seborrhoeic dermatitis and sebaceous scales and alopecia can occur. According to Bolognias textbook "Dermatology," this rare condition is most often combined with psoriasis, but it may also develop as secondarily infected atopic dermatitis, seborrheic dermatitis, and/or tinea capitis. Treatment
The bacteria staphylococci are present in the majority of cases. Treatment with systemic antibiotics and coal tar shampoo can completely clear the condition when Staphylococcus aureus bacteria are found. Fungal infections such as tinea capitis are known to mimic the symptoms of the condition  and can be cleared with antifungal treatment.