Outbreak of Measles!!

Over the past few weeks, communicable disease surveillance teams and public health professionals have been on alert due to the increasing number of isolated measles cases in Central Canada. As of today, 4 cases of measles in Alberta and 10 cases in Saskatchewan been have been confirmed since the start of 2014.^1,2

Now, 4 and 10 cases seem like a very small number compared to hundreds of cases of sexually transmitted infections and influenza; why do we make such a big deal when the cases are measles related? In order to understand the situation, we must look at the background and epidemiology of the disease.

Background of Measles

            Measles is a highly contagious infectious disease caused by the virus Morbillivirus of the Paramyxoviridae family. The culprit is a spherical, non-segmented, negative sense RNA virus that zoonotic in origin.³ It is believed that cross-species transmission of the virus may have occurred approximately 10, 000 years ago.  The first documented case of measles dates back to ~900CE, where Muhammad ibn Zakariya ar-Razi, a Persian philosopher and physician, published a book that attempted to distinguish measles from smallpox.⁴ In 1757, a Scottish physician named Francis Home discovered that measles arose from an infectious agent by transmitting measles to healthy individuals. He inoculated the blood of infected patients to the skin of health people and transferred the virus to 10 out of 12 health individuals. Finally, in 1954, the virus was isolated by Dr. Thomas Peebles In Boston, USA.⁵

           The virus is transmitted by contact with aerosolized droplets from infected individuals. Once infected by the virus, the incubation is around 10 days.  Infection is initiated when the virus enters the cells of the respiratory tract, oropharynx or conjunctivae.³ Two to four days following infection, the virus proliferates in the respiratory mucosa and spreads through the lymphatic system. The virus then enters the bloodstream and affects major target organs. It is at this point, around 7-10 days post infection, when symptoms such as cough, runny nose, sore throat, red eyes, fever, malaise and light sensitivity begin to appear.⁶ These initial symptoms progressively worsen for the next fours days and small white spots, known as Koplik’s spots, become visible inside the mouth and throat. About 2 weeks after the infection, characteristic rash of measles will appear starting from behind the ears, neck, hairline towards the face, trunk, arms and finally the legs and feet.³ The rash arises as a result of the immune response to the replicating virus and fades slowly in the progressive order. Measles infection can result in complications such as bronchitis (inflammation of the lungs), pneumonia (bacterial infection of the lung), ear infection and encephalitis (acute inflammation of the brain).³

          There is no specific treatment for measles. Treatment often involves Tylenol, bed rest, humidified air and vitamin A supplements in some children.⁶ Most people recover and develop long-term immunity against the virus. ³However, those that do die of measles are often vulnerable people such as children and immunocompromised individuals. In developed countries, less than 1 in 1000 children die of measles, however in endemic areas of developing regions the case-fatality rate is an astounding 5-10%.³

Epidemiology and Public Health

            Measles is one of the most highly contagious infectious diseases and can only be maintained if a continuous supply of susceptible persons exists.³ Measles is most prevalent in endemic regions and outbreaks typically occur in the late winter and early spring due to greater congregation of people.³ Rate of contact with infected people, amount of protective maternal antibody and vaccination status are the factors that determine the average age at which measles contraction occurs. In urbanized and densely populated regions with low vaccination coverage, infants and children and most susceptible to the disease. As the population density decrease and vaccination coverage rates increase, the age group most burdened by measles continues to increase.³

            According to the World Health Organization, measles is still the leading cause of death amongst vaccine-preventable diseases in children.⁷ In 2010, measles related mortality have been reduced from 535, 300 to 139, 000, a matter of 74% in 10 years.³ In the WHO region of Americas, endemic measles haves been completely eradicated as of 2002 and there has been no indigenous case of measles in Canada since 1997.⁸ Imported cases of measles still occur and therefore, public health professionals are conscientious of the current measles outbreak in the Philippines that is slowly emanating into Canada.⁹

            Measles is vaccine-preventable. The first live attenuated vaccine was licensed in the United States in 1963 and a more attenuated version was developed in 1968.⁵ The measles virus is antigenically monotypic, meaning that the surface proteins that induce the host’s immune system have retained its structure through time.³ This is great news for public health because this feature indicates that vaccines developed in the past still remains protective worldwide. In Canada, measles vaccine (MMR) is combined with other attenuated virus such as mumps and rubella and the first dose of vaccination is recommended at 12 months of age, once newborns lost their passively acquired maternal antibody against the virus.¹⁰ Two doses of vaccine are recommended to ensure complete protection.

            Unfortunately, vaccine coverage has been decreasing due to a paper published by Wakefield et al. in 1998 that claimed a relationship between MMR vaccine and autism.⁵ In 2004, it was found that a lawyer with a conflict of interest against vaccine manufacturers had recruited some of the study subjects. Nonetheless, some people still remain convinced and vaccine rates have decreased; resulting in an increased incidence of measles.⁵

What can we do?

            The best way to reduce measles prevalence is to increase vaccine coverage. Increased compliance to vaccination is necessary and proper containment of existing measles cases is required. Currently, new methods of vaccination, such as aerosolized administration, are being developed to increase rate of vaccination.¹¹ Furthermore, organizations such the WHO, Center for Disease Control, Public Health Agency of Canada, and the National Advisory Committee on Immunization, are releasing statistical data and information to educate the public on the effectiveness and safeness of MMR and reduce the stigma around the vaccines.^7-8,12-14 Lastly, some organization such as the Alberta Health and Wellness has developed a 10-year strategy to increase immunization coverage. Some point in this strategy include, providing publicly funded immunization programs, reviewing adult immunization status, providing booster vaccination and targeting vaccination to the vulnerable population.¹⁵

Reference:

1. http://regina.ctvnews.ca/regina-health-region-expands-list-of-places-where-measles-may-have-spread-1.1673982
2. http://www.calgaryherald.com/news/calgary/case+measles+reported+Calgary/9482060/story.html
3. http://accessmedicine.mhmedical.com.ezproxy.library.ubc.ca/content.aspx?bookid=331&sectionid=40726951
4. http://www.news-medical.net/health/Measles-History.aspx
5. http://www.historyofvaccines.org/content/timelines/measles
6. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002536/
7. http://www.who.int/mediacentre/factsheets/fs286/en/index.html
8. http://www.phac-aspc.gc.ca/im/vpd-mev/measles-rougeole-eng.php
9. http://www.thestar.com/life/health_wellness/2014/02/10/measles_outbreak_in_philippines_slowly_spreading_to_canada.html
10.  http://www.phac-aspc.gc.ca/im/ptimprog-progimpt/table-1-eng.php
11. Diaz-Ortega JL, Bennett JV, Castaneda D, Martinez D, de Castro JF. Aerosolized MMR vaccine: evaluating potential transmission components to vaccine administrators and contacts of vaccines. Biologicals. 40;4:278-281.
12.  http://www.cdc.gov/measles/
13.  http://immunize.cpha.ca/en/diseases-vaccines/measles.aspx
14.  http://www.immunize.org/catg.d/p4026.pdf
15.  http://www.health.alberta.ca/documents/Immunization-Strategy-07.pdf