In the context of World Antibiotic Awareness week last week (November 14-20) and efforts to raise the awareness of infectious diseases in New Zealand, it is useful to include a discussion on viruses.
Although few treatments and vaccines are currently available for their control, the burden of disease in terms of personal affliction, loss of work or school days, hospitalisation and death is substantial. The viruses that cause human respiratory infections provide a window into the wider issues that we are dealing with regarding infectious diseases in New Zealand at present.
There are over 150 known respiratory viruses which by and large cause mild respiratory symptoms, the most common of which are the Rhinoviruses which infect the upper respiratory tract causing the common cold. Respiratory Syncytial Virus (RSV) is an important cause of more severe lower respiratory tract infections in young children, such as bronchiolitis and pneumonia, resulting in increased numbers of hospital admissions during the winter and spring months when this virus circulates in New Zealand annually. Fortunately a vaccine will be available in the near future for this virus.
Influenza is another respiratory virus which affects New Zealander’s annually. Four viruses are currently circulating: Influenza A(H3N2), A(H1N1)pdm09, Influenza B/Yamagatta and B/Victoria. Typical winter outbreaks and epidemics result in substantial illness, visits to general practitioners, school and workplace absenteeism and hospitalisation of especially young children and the elderly.
Effective interventions against influenza are available, with annual vaccination the most effective for preventing influenza infection. Vaccination needs to be annual as these viruses continue to evolve, undergoing antigenic drift, requiring frequent vaccine composition review and virus composition updating. Vaccines cannot be used in children under 6 months of age, and the best way to protect them is through vaccination of the mother before child birth. The elderly are also an issue as their immune systems are less active and they respond less vigorously to the vaccine. Regardless, vaccination is the most effective way we currently have to protect individuals against influenza.
Antivirals are effective for the treatment of influenza infections, especially if given early after the onset of symptoms. The Neuraminidase inhibitors (Tamiflu and Relenza) are the most common antivirals available. Unlike the use of antibiotics against bacterial infections, where unnecessary use contributes to the development of resistance, misuse of antivirals in general does not drive the development of antiviral resistance and other genetic mechanisms are involved when influenza viruses have developed resistance in the past.
In recent years novel respiratory viruses have caused global concern and have resulted in countries, including New Zealand establishing pandemic preparedness plans. The most recent influenza pandemic was due to the A(H1N1)pdm09 virus which emerged from pigs in Mexico in 2009. Characteristically influenza pandemics have been associated with high mortality (3% of the world’s population died during the Spanish 1918-19 pandemic) and substantial illness. However the 2009 virus was related to a virus that had circulated prior to 1957 and caused generally milder infections. Regardless, the circulation of this new virus did place substantial pressure on our health system over 2009 and the winter of 2010.
The emergence of the avian influenza A(H5N1) virus in Hong Kong in 1997, then re-emergence and spread amongst domestic poultry from late 2003 in many parts of the world remains a concern. Although human infections are rare, they are consistently associated with a 50% mortality rate. Should this virus develop the ability to be transmitted between humans, the outcome would be devastating. Another more recent avian A(H7N9) virus in poultry and other avian species in China, and the associated human infections, is also of concern.
Other novel respiratory viruses that have emerged recently are the SARS virus in China in 2003 and MERS-CoV, first identified in Saudi Arabia in 2012. Both viruses are Coronaviruses with origins in wild animal species (especially bats). Fortunately SARS was brought under control largely by vigorous implementation of hospital infection control measures. However MERS-CoV continues to cause severe human infections, largely in the Arabian Peninsula, with exposure to camels being a significant risk factor.
Although New Zealand is an island nation, it is very much part of the global community, especially with an economic focus on tourism drawing travellers from all parts of the world. For this reason we need to be aware of infectious diseases and what we can do to work towards their control and ensure that the treatments we have remain effective.
Lance Jennings is the Clinical Virologist for the Canterbury District Health Board. He is also a Clinical Associate Professor in the Pathology Department, University of Otago, Christchurch. He has an interest in the diagnosis of clinically relevant human viral infections and the epidemiology, treatment and control of influenza and other respiratory virus infections.
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