Acapulco today is known as a major Mexican tourist center but in the seventeenth and eighteenth centuries, it was the principal port for Spanish ships carrying silks and spices gathered from Asia and the Western Pacific. For over 250 years, a yearly trading operation, known as the Manila-Acapulco Galleon,  traveled between Acapulco and the Philippine Islands. Today there is a particular strain of TB known as the Manila strain. The Manilastrain is endemic to the Philippines and is currently found in several parts of the world where there are numerous Filipino immigrants. But there are few recent Filipino immigrants in Acapulco. The presence of the Manila strain of TB in Acapulco is best explained by its having resided there for centuries.

Understanding how tuberculosis (TB) is transmitted takes on special importance in places where there is a good deal of migration, either from outside a country or from rural to urban areas of the same country. Most immigrants to Acapulco today are people from the rural areas of Guerrero State where TB is also endemic.

One key to understanding patterns of transmission is the ability to identify and locate different genetic strains of the bacterium. Using a DNA fingerprinting technique called spoligotyping (short for spacer oligonucleotide typing), Dr Elizabeth Nava of CIETmexico inAcapulco analyzed 300 TB cases gathered in the city and its suburbs during 2001 and 2002.

Dr Nava identified 85 strains, 50 of which had not been previously reported. The five most common spoligotypes accounted for 55% of the tuberculosis cases. One cluster of 70 patients (26.2%) produced a single spoligotype, the Manila strain. This strain accounted for one in every four cases of TB in her sample.

Clustering of strains is generally understood to be a sign of recent TB transmission. Thus it appears that the ancient Manila strain, among others, is being transmitted in the overcrowded dwellings and gathering places of Acapulco’s poorest residents where recent migrants tend to settle. But the migrants are not so much bringing TB to Acapulco as they are contracting it there. Some migrants might be bringing active or latent TB with them when they migrate, but they are being reinfected, and with more virulent strains, in the back alleys of Acapulco.

Further details about these projects can be obtained from the doctoral thesis of Elizabeth Nava Aguilera, Epidemiología molecular de tuberculosis pulmonar: Factores de riesgo asociados a transmisión reciente de Mycobacterium Tuberculosis en Guerrero, México,available from the library.

See also: 

Nava-Aguilera E, López-Vidal Y, Harris E, Morales-Pérez A, Mitchell S, Flores-Moreno M, Villegas-Arrizón A, Legorreta-Soberanis J,Ledogar R, Andersson N. Clustering of Mycobacterium tuberculosis Cases in Acapulco: Spoligotyping and Risk Factors, Clinical and Developmental Immunology, vol. 2011, Article ID 408375, 12 pages, 2011. doi:10.1155/2011/408375. Available at: http://www.hindawi.com/journals/cdi/2011/408375.html.