Tuesday, January 13, 2015

Lax Industrial Controls Contribute to Spread of Chikungunya Virus in Some Latin American Countries

Chikungunya does not often result in death, but the joint pain may last for months or years and may become a cause of chronic pain and disability. There is no specific treatment for chikungunya infection, nor any vaccine to prevent it. Pending the development of a new vaccine, the only effective means of prevention is to protect individuals against mosquito bites.  -Pan American Health Organization (PAHO)

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The word chikungunya comes from the African Makonde language and means “bent over in pain.”  The disease is not usually fatal (unless the patient has other health problems), but an infection can result in crippling pain. Chikungunya is transmitted by the bite of two species of mosquito: the Aedes aegypti  (which can also transmit dengue and yellow fever, and is present in the tropics and sub-tropics of the Americas), and the Aedes albopictus mosquito (found in more temperate areas, extending from the east coast and southeast of the United States to the provinces of northern Argentina). "These mosquitoes are easily recognized by the white stripes around their legs; when they bite a person with chikungunya, the transmission cycle begins," said the Pan American Health Organization (PAHO). 

There was very little mention of the disease in Latin America and the Caribbean until December 2013, when the first non-imported case was confirmed in the region. There were more than 22,000 cases in the region as of Dec. 29,  2014, including 131 in Mexico.  (Read more in the latest issue of SourceMex).  According to PAHO, the numbers continued to increase in the region, reaching  24,071 cases as of Jan. 9, 2015.

So the why is just now that the disease is appearing in the Americas?  Haven't the aedes aegypti  and Aedes albopictus mosquitoes been around a while? Those mosquito species have been responsible for the spread of dengue fever, but the virus was not present until recently. There have been several cases where humans who traveled to infected areas came home sick.  But the disease is not transmitted from one human to another. So then, what is behind its spread into the Americas?  A closer look at the 2013-2014 data, released by the Pan American Health Organization (PAHO), reveals that climate and human travel do not have much to do with the spread of the disease. A bigger factor are national and local policies on international shipping, industrial infrastructure and health-care response systems. Furthermore, the species of mosquitos that transmit the virus, it turns out, do not actually depend on tropical and subtropical climates, as they are able to and have in the past bred successful populations in cold climates, even in snowy areas.

Case Studies: Cuba and El Salvador
The impact of industry on the spread of chikungunya are illustrated in the cases of Cuba and El Salvador. While many major Caribbean islands have experienced an outbreak of the viral disease, Cuba--which differs from its neighbors in terms of trade embargos, security levels of shipping ports and availability of health care services--has not reported a single domestic case. Cuba has only reported 20 cases in total, all of which were imported by human travelers.

On the other hand, while El Salvador does not actually contain a Caribbean coastline, it is one of the most highly affected Latin American nations with over 135,000 suspected cases, and nonetheless reports the vast majority of its cases in regions along its Pacific Coast urban areas, where its industry and shipping ports are most active and concentrated. This, too, is true for Guatemala and Nicaragua (Central America’s other highly affected nations) where the vast majority of cases are not found in its Caribbean regions that are dominated by protected wildlife refuges and tourist oases, but rather in Pacific urban areas rife with shipping and industrial activity.

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Used tires serve as a conduit
This pattern is further solidified by the history of the disease in Australia and New Zealand, which despite being in the middle of one of chikungunya’s most historically active regions, has been affected very little by the virus due to stringent regulations on port control and inspections, which are highly effective procedures for limiting the number of the two species of chikungunya-host mosquitos that tend to migrate in used tires and other industrial containers.

A recent special report on Chikungunya in the Dominican Republic published in the Pan American Journal of Public Health, also suggests that preventing the outbreak of the virus has everything to do with limiting the conditions in which the Asian Tiger Mosquito tends to breed. Evidently, these conditions have much to do with shipping ports, industrial materials and containers of standing water, and little to do with human travel.

Another characteristic of the mosquito might explain why chikungunya virus has spread so much more rapidly in countries like Venezuela, Nicaragua, El Salvador, Guatemala and French Guiana than it has in the US, Mexico, Brazil and Costa Rica: the Asian Tiger Mosquito feeds primarily during the day as opposed to night, and outdoors as opposed to indoors. What we see in cities such as Escuintla, Guatemala; Managua; San Salvador, Santo Domingo; and Caracas are conditions in which the indoor/outdoor separation between homes and workplaces is often very fluid, allowing the Asian Tiger Mosquito to spend its days in outdoor conditions, even when inside a home at dawn or dusk.

Also what we see in these cities are nearby commercial seaports and streets littered with containers, the bottles, cans and tires with little bits of liquid hanging at the bottom. Where there is litter, seaports, structures built of provisional materials and outdoor markets, there is often poverty, little access to health care and, most importantly, hordes of warm blooded mammals spending their days outside.

-Jake Sandler

Also in LADB on Jan. 7-9

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