Possible Link between the Severe Respiratory Illness Outbreak in Mexico and Swine Flu in Southwestern United States?
Mark J. Cameron, Ph.D., JIDC Regional Office Canada.
Thomas Rowe, University of Toronto, Canada.
David J. Kelvin, Ph.D., JIDC Regional Office, Shantou University Medical College, China.
DOI: 10.3855/jidc.17
Eerily reminiscent of the Severe Acquired Respiratory Syndrome (SARS) outbreak during the spring and fall of 2003, an outbreak of Severe Respiratory Illness (SRI) in Mexico has world health officials in a state of "Heightened Concern". The concern centers around the fact that as of April 24, 2009 over 134 cases (see Figure 1) have been reported with an associated 20 (and possibly more, some estimates place mortality figures at 60) deaths (http://www.health.gov.on.ca/english/providers/program/emu/health_notices/ihn_042309.pdf). Case fatality rates range from 11 to 29% in central and southern Mexico. What is most alarming is that the deaths have occurred in healthy young adults.
Seasonal influenza, which usually subsides by late spring in North America and Mexico, does not seriously affect healthy young adults but can cause serious illness in the very young and the very old. In contrast, the 1918 influenza pandemic caused severe illness in healthy young adults. The symptoms observed in afflicted patients from the recent outbreak in Mexico have similarities to symptoms of the 1918 pandemic. Infected people first display flu-like symptoms, including fever, cough, sore throat, muscle joint pain, and possible shortness of breath. The illness progresses to SRI within five days.
Health officials in Mexico have reported SRI cases from central and northern Mexico. Several of the recent SRI deaths have been reported in Mexican states that border the US states of Texas and California, where the Centers for Disease Control and Prevention (CDC) has recently been investigating an outbreak of swine flu. As of today, the CDC report 7 human cases of swine flu in Texas and California (http://www.cdc.gov/flu/swine/investigation.htm). Interestingly, the first two confirmed cases of swine flu had no direct contact with pigs. The link between cases in Mexico and the United States appears to be swine influenza as Mexican Health Minister Jose Angel Cordova told the Televisa network. Indeed, Mexican officials now state that some of the samples taken from ill patients are positive for swine flu.
The alarming aspect of the Mexican SRI, which is possibly caused by swine flu, is that it appears to be contagious and easily transmitted outside of an intermediary pig host. If this is the case, then person to person contact may spread the illness. In an attempt to limit person to person transmission, Mexico City has cancelled classes at all levels of schools including Universities. Furthermore, they have recommended that people not gather in large groups.
The swine flu viruses isolated by the CDC from the two individuals who were ill in late March and early April in Southern California have not been previously seen [1]. Furthermore, the isolates from these two cases were found to be closely related and were identified as a novel swine influenza A (H1N1) strain. Even though the majority of the genes were similar to swine flu viruses circulating in the United States since 1999, two of the genes (the neuraminidase and the matrix proteins) were found to be similar to genes from viruses of swine flu Eurasian linage [2]. This finding suggests that the swine flu virus causing illnesses in the United States, and possibly Mexico, is a new virus recombined from different strains. Although H1N1 is not a new subtype of influenza A in humans, the new swine virus isolated from these cases is substantially different from existing human H1N1 viruses. Therefore, a large proportion of the population may be susceptible to infection with this new form of H1N1 influenza.
Since travel is extensive throughout Mexico and the US, North American public health officials are on alert for possible outbreaks. Anyone seeking medical attention for having flu-like symptoms, plus travel to Mexico, should be observed for onset of severe respiratory problems and possible infection with swine flu. Additionally, healthcare professionals in North, Central, and South America should be on the lookout for patients presenting with flu-like illness who have had recent contact with swine. This outbreak highlights the need for closer collaborations between investigators (in both human and animal pathogens) and front-line health care professionals in developing countries and their counterparts in other countries in order to coordinate resources and expertise in zoonotic emerging infectious diseases. This will aid in the design of rapid responses to emerging respiratory infections in humans, a gaining of a better understanding of the epidemiological and host factors of the disease, and the development of potential intervention strategies.
Bibliography
Swine Influenza A (H1N1) Infection in Two Children - Southern California, March - April 2009. MMWR Morb Mortal Wkly Rep, 2009. 58((Dispatch)): p. 1-3.
Vincent, A.L., et al., Characterization of an influenza A virus isolated from pigs during an outbreak of respiratory disease in swine and people during a county fair in the United States. Vet Microbiol, 2009.
Original Article appeared on The Journal of Infection in Developing Countries