were found to be immunogenic and well tolerated against HPIV-3 in phase I trials. HPIV-1 and -2 vaccine candidates remain less advanced. Vaccine techniques which have been used against HPIVs are not limited to intranasal forms, but also viruses attenuated by cold passage, host range attenuation, chimeric construct vaccines and also introducing mutations with the help of reverse genetics to achieve attenuation. Maternal antibodies may offer some degree of protection against HPIVs during the early stages of life via the colostrum in breast milk. Medication Ribavirin is one medication which has shown good potential for the treatment of HPIV-3 given recent in-vitro tests (in-vivo tests show mixed results). Ribavirin is a broad-spectrum antiviral, and as of 2012, was being administered to those who are severely immuno-compromised, despite the lack of conclusive evidence for its benefit. Protein inhibitors and novel forms of medication have also been proposed to relieve the symptoms of infection. Furthermore, antibiotics may be used if a secondary bacterial infection develops. Corticosteroid treatment and nebulizers are also a first line choice against croup if breathing difficulties ensue. Interactions with the environment Parainfluenza viruses last only a few hours in the environment and are inactivated by soap and water. Furthermore, the virus can also be easily destroyed using common hygiene techniques and detergents, disinfectants and antiseptics. Environmental factors which are important for HPIV survival are pH, humidity, temperature and the medium within which the virus is found. The optimal pH is around the physiologic pH values (7.4 to 8.0), whilst at high temperatures (above 37 °C) and low humidity, infectivity reduces. The majority of transmission has been linked to close contact, especially in nosocomial infections. Chronic care facilities and doctors' surgeries are also known to be transmission 'hotspots' with transmission occurring via aerosols, large droplets and also fomites (contaminated surfaces). The exact infectious dose remains unknown. Economic burden In economically disadvantaged regions of the world, HPIV infection can be measured in terms of mortality. In the developed world where mortality remains rare, the economic costs of the infection can be estimated. Estimates from the US are suggestive of a cost (based on extrapolation) in the region of $200 million per annum. References Further reading Human Parainfluenza Viruses (HPIVs) External links Human Parainfluenza Viruses – information provided by the CDC Respiratory diseases Rubulaviruses Paramyxoviridae Viral respiratory tract infections Atypical pneumonias