According to the Washington Post, Mexican border officials and health authorities are worried about the spread of measles out of the United States and into Mexico:

As Republican lawmakers suggest that undocumented immigrants crossing the southern border may be responsible for bringing measles and other diseases into the country, Mexican health authorities are warning people traveling to the United States about the risk of infection here following an outbreak of measles at Disneyland last month that has sickened dozens of people in several states.

It's a remarkable reversal that demonstrates how far public health in Latin America has advanced in the past few decades -- especially in contrast to measles's alarming return in the United States.

Measles's [sic] new reality is at odds with the warnings given by some G.O.P. lawmakers, such as Rep. Mo Brooks (R-Ala.), who recently suggested that the southern border was a risk to public health in the United States. 'I don't think there is any health care professional who has examined the facts who can honestly say that Americans have not died because the diseases brought into America by illegal aliens who are not properly health care screened as lawful immigrants are,' he said.

Unfortunately, the Post's article glosses over a number of key points that would otherwise support the concerns held by Republican lawmakers.

According to the same World Health Organization (WHO) dataset used in the Post's article, measles immunization coverage among one-year-olds in the United States has been constant at between 90 and 93 percent since the mid-1990s.  There is no sign of a declining trend in measles immunization coverage for the U.S., including and especially in recent years.  The measles immunization coverage among one-year-olds in 2010, 2011, 2012, and 2013 (the latest year of data) was 92, 92, 92, and 91 percent, respectively.  Coverage was 90 percent in 2009.  A major anti-vaxxing trend is not apparent in the WHO dataset the Post cited.

One must also be cautious believing claimed immunization coverage in quasi-third-world nations such as Mexico and the Central American countries.  These countries often have a very poor understanding of their population base, making assessments over immunization coverage fraught with potential error and political bias.  Regardless, there does appear to be a significant decline in measles immunization coverage among one-year-olds for some important players below the U.S. southern border.

Between 2012 and 2013, Guatemala saw its immunization coverage drop from 93 percent to just 85 percent – its lowest level since the 1990s.  The coverage in Honduras has declined 10 percent since 2009 and is also now below that of the United States.  Panama's coverage dropped six percent from 2012 to 2013, and Mexico's declined 10 percent over this one-year period to 89 percent.

Lawmakers, and not just those within the GOP, should be very concerned about the apparent rapid decline in measles immunization rates in Mexico and some Central American countries during recent years when coupled with the illegal immigration problem.

Of course, measles is not the only infectious disease.  Costa Rica has only 78 percent BCG immunization coverage (for tuberculosis) among one-year-olds.  Panama (85 percent) and Honduras (88 percent) have relatively low diphtheria tetanus toxoid and pertussis (DTP3), hepatitis B (HepB3), and Haemophilus influenzae type b (Hib3) immunization coverage among this same age group.  Both nations are also below 90 percent coverage for polio immunization.

Rates of leprosy are much higher (up to 3.3-fold in the case of Mexico) in Costa Rica, Mexico, Nicaragua, and Panama than in the United States – meaning these nations can act as a potential net source of the disease.  Mumps case rates in Mexico and Central America are astronomical compared to the U.S., ranging from 9-fold higher in Belize and Costa Rica up to 65-fold higher in Mexico and 76-fold higher in El Salvador.  During 2012 – the latest year available – these countries collectively had 6,485 mumps cases compared to just 229 in the United States, even though their population is just one-half that in the U.S.

In 2013, Mexico had an outbreak of cholera with 159 confirmed cases.  As the Centers for Disease Control and Prevention (CDC) notes, "the vaccine to prevent cholera is not available in the United States."

There were twice as many cases of neonatal tetanus in Honduras (pop. 8 million) than in the United States (pop. 314 million) during 2012.  Tetanus rates are much higher throughout the region than in the U.S. – up to 18-fold higher in Honduras and more than 22-fold higher in Panama.  Tuberculosis is rampant as well.  Compared to the low levels in the United States, rates are 3-fold higher in Costa Rica, more than 5-fold higher in Mexico, 7- and 8-fold higher in Guatemala and Belize, 10-fold higher in El Salvador, 12- and 13-fold higher in Honduras and Panama, and nearly 15-fold higher in Nicaragua.

There are very real health risks to American citizens via illegal immigration from Mexico and Central America, in large measure because the rates of many infectious diseases are higher in these regions than among the U.S. citizenry.