Environmental and global health issues

Measles, Sars, Air Quality

Global Health Issues

Global Health Issues: Measles, SARS, and Air Quality

Global Health Issues: Measles, SARS, and Air Quality

Global Health Issues: Measles

Measles is caused by a single-stranded negative-sense RNA virus and is easily transmitted through aerosols or secretions generated by respiratory tract activity (reviewed by De Vries, Mesman, Geijtenbeek, Dubrex, and de Swart, 2012). Following exposure to the virus, a high fever will develop after approximately 10 to 12 days (Dardis, 2012). Other symptoms include coughing, runny nose, and red watery eyes. Small white spots will develop inside the mouth and a rash will become visible on the upper neck and face. This rash will spread down the trunk and across the limbs to the hands and feet, and will last a little less than a week. Once infected, there is no treatment, but an effective vaccine has been available for decades.

While most children and adults will survive a measles infection without any lasting problems, the risk of complications is a serious matter. These include blindness, otitis media, encephalitis, seizures, severe diarrhea, and pneumonia, with the latter killing 60% (Dardin, 2012) of all who succumb to the immunosuppressive effects (reviewed by De Vries, Mesman, Geijtenbeek, Dubrex, and de Swart, 2012) of a measles infection. In addition, pregnant women without immunity run the risk of complications. If the fetus survives, the chances that it will have a low birthweight are increased significantly.

Once thought to infect epithelial cells lining the respiratory tract, recent research findings reveal that the measles virus infects subsets of lymphocytes, dendritic cells, activated Langerhans cells, and macrophages expressing the CD150 cellular receptor (reviewed by De Vries, Mesman, Geijtenbeek, Dubrex, and de Swart, 2012). Sequence conservation studies reveal that this mode of entry is conserved with canine distemper virus and rinderpest virus. Although epithelial cells do eventually become infected, it is through the basally-expressed Nectin-4 adherens junction protein rather than apically. The primary mode of entry for the measles virus is therefore the immune system, which would explain why an infection suppresses immunity.

To better understand the health threat that measles represents, this report will review a recent measles outbreak that happened in France.

The Lyon, France Measles Outbreak

The World Health Organization (WHO), in collaboration with other health organizations, has been spearheading a measles initiative to reduce or eliminate measles infections in many locations around the world (WHO, 2009). Due to these efforts, deaths due to measles dropped by 78% between 2000 and 2008; however, the WHO predicted in 2009 that resurgence was possible because of a funding shortfall of about $60 million for 2010. Accordingly, large outbreaks were reported in Europe, Africa, Asia, and the Middle East in 2011 (Perry, Gacic-Dobo, Dabbagh, Strebel, and Okwo-Bele, 2013).

In the city of Lyon, France, 407 confirmed measles cases were diagnosed between 2010 and mid-2011 (Huoi, 2012). A slight majority of cases occurred in children under the age of 1 (32%) and the next biggest group infected was adults between 17 and 29 years of age (31%).

In 2010, a 17 and 29-year-old would have been born in 1993 and 1981, respectively. In France, a national measles vaccination program was begun in 1983 and the vaccine administered between the ages of 12 and 15 months, but a booster dose, administered between the ages of 11 and 13, was not introduced until 1996 (reviewed by Huoi, 2012). The following year, in 1997, the booster dose was moved to 3-6 years of age. In 2005, the recommended measles vaccination schedule was changed to a first dose at 12 months and a second dose within the next year. The 2010-2011 measles outbreak in Lyon, France can therefore be explained in part by adults who may not have received a vaccination or never received the second dose at an older age. When the vaccination records were examined for two thirds of the patients, only 4% had received two doses and 18% one dose. All others (78%) were unvaccinated. A recent study found that measles vaccination efficacy using the current vaccination schedule with a third dose at age 5 is 94% effective at age 7-10 years (Gans et al., 2013). The outbreak in adults 17 and older is therefore probably due to a combination of factors, including no measles vaccination history, having received only a single dose, and individuals who did not acquire measles immunity despite being vaccinated.

The median age of all measles cases in children below the age of 16 during the 2010-2011 Lyon, France outbreak was 1 year, which suggests that half of all infections in children occurred prior to the recommended age of the first dose (Huoi, 2012). This represents a shift in the age of measles infections to infancy, which has been occurring more often in countries having a robust vaccination program. Prior to widespread implementation of measles vaccination, maternal antibodies against the measles virus and herd immunity provided some protection for infants and infections rarely occurred until later childhood (Gans et al., 2013). In contrast, the maternal antibodies generated by the vaccine are not as effective in protecting infants from infection, which explains the shift in the age of child infections to below 12 months of age. This explains the recent measles outbreaks in Europe in children less than 1 year of age.

Given the international status of France, it would be easy to imagine the export of measles across its borders (see graphic above). Such a scenario is currently believed to be occurring as measles is being transported via airports and other modes of mass transportation (Gans et al., 2013). Such outbreaks would impact any community with poor vaccination compliance, including developed and developing areas of the world. In the United States, the demographic most vulnerable to measles would be infants under the age of 12 months since current guidelines recommend vaccination at 12 months of age.

SARS Reporting

Based on guidelines issued by the U.S. Centers for Disease Control and Prevention, the reporting of SARS cases can be divided into two main groups: (1) patients with severe respiratory illness and who are at risk for having been exposed to SARS-CoV (2) patients with known or suspected contact with other SARS patients (CDC, 2004). Patients belonging to the first group will have had a chest X-ray confirming pneumonia and have been inside a health clinic with poor infection-control measures, ridden frequently in taxis, or had a meal in a public place (Wu et al., 2004). Alternatively, a patient's laboratory test could have been positive for SARS-CoV (CDC, 2004). In the latter case, the positive result should be immediately reported to the state or local health department by telephone and the appropriate control procedures implemented, including patient isolation and all contacts identified, evaluated, and monitored. Any cluster of pneumonia patients should also be reported to the health department, since these could represent a SARS outbreak.

The reporting of patients who fit within the second group follow similar guidelines as the first group, but with modification to represent the existence of ongoing SARS outbreaks somewhere in the world (CDC, 2004). The additional criteria are travel to any location with confirmed SARS cases or contact with a person with SARS within the past 10 days, for patients with fever or lower respiratory illness.

Once reported to the state or local health department, these organizations are required to report suspected or confirmed cases of SARS to the CDC (CDC, 2004). The CDC will in turn report the same to the WHO.