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Biological Health Hazard – Public Health Risk/Roving Invasive Pathogens: Human-to-Human Dissemination


The World Health Organization announced its 1st list of antibiotic-resistant “priority pathogens” on [Mon 27 Feb 2017], detailing 12 families of bacteria that agency experts say pose the greatest threat to human health and kill millions of people every year.

The list is divided into 3 categories, prioritized by the urgency of the need for new antibiotics. The purpose is to guide and promote research and development of new drugs, officials said. Most of the pathogens are among the nearly 2-dozen antibiotic-resistant microbes that the US Centers for Disease Control and Prevention warned in a 2013 report could cause potentially catastrophic consequences if the United States didn’t act quickly to combat the growing threat of antibiotic-resistant infections. –Antibiotic resistance (02): WHO, priority pathogens Archive Number: 20170301.4871299 via Washington Post (2017) [edited]

Published Date: 2017-07-21 12:20:36
Subject: PRO/AH/EDR> Pathogen dissemination
Archive Number: 20170721.5193184

Date: Tue 18 Jul 2017 1:03 PM
Source: Reuters [edited]

Human travelers are much more likely than stowaway mosquitoes to import illnesses like Zika, yellow fever, malaria, and dengue to a new part of the world via airplane, researchers say.

Based on calculations of how many mosquitoes get onto commercial aircraft, how many are infected, and how many survive long enough at the destination to bite someone, the study estimates human travelers are 200 times more likely to spread dengue virus and 1000 times more likely to introduce _Plasmodium falciparum_, the parasite that causes malaria.

“Pathogens such as the Zika and chikungunya [viruses] have drawn a lot of interest lately and are showing up in travelers,” said senior study author Michael Johansson, a biologist at the US Centers for Disease Control and Prevention Division of Vector-Borne Diseases in San Juan, Puerto Rico.

Insects that transport disease, such as mosquitoes, have been introduced via airlines to geographic areas where they didn’t previous live, the authors write in PLoS Neglected Tropical Diseases. Airports have insect-elimination, or “disinsection,” policies mandated by the UN’s International Health Regulations. They typically use insecticides to try to kill insects in bags, cargo, containers, and conveyor belts, but infections still occur.

“We’ve had disinsection policies for a long time, which are targeted at mosquito species and agricultural pests,” Johansson told Reuters Health in a phone interview. “But we need to focus on ways to prevent the spread through humans.”

The study team assessed scenarios for the spread of mosquito-borne diseases, focusing on areas where either malaria or dengue are “endemic,” or widespread, and places where the diseases are not endemic, but conditions are favorable for them to establish themselves.

Based on past studies, the researchers calculated how many mosquitoes would likely be on any given plane, and how many of them would be infected with disease. For instance, the largest number of mosquitoes ever detected on a plane in past research is 17 _Anopheles gambiae_ mosquitoes, the primary transmitters of malaria, the researchers note. For the current study, they estimated a 0.25 probability of any mosquito on a given flight, or an average of one mosquito on every 4th plane.

They also calculated the infection rates for human travelers, likelihood of mosquito bites at the destination, and probability of disease transmission to a new person.

Even in the absence of mosquito control or disinsection on planes, humans were hundreds of times more likely to spread the diseases through travel. Overall, the probability that an airplane traveling from a mosquito-heavy area would lead to infection was extremely low.

“We expected to find this, but we were surprised by the magnitude,” Johansson said. “We didn’t think it would be so obvious, and this was focusing on the worst-case scenarios.”

Future studies should focus on preventing human transmission, he added. Policies around preventing the transportation of infected mosquitoes won’t likely work, the study authors conclude.

“There may be a misperception about how pathogens disperse globally,” said Moritz Kraemer of Harvard Medical School in Boston, who wasn’t involved in the study. “With the increase in travel globally, infectious diseases spread quickly from one location to another,” he told Reuters Health by email.

Kraemer, who recently published a study in the journal Nature about the multiple introductions of Zika virus to Florida (, suggests creating maps of the geographic areas where people are infected and their airports to better target disease. Pathways and directionality is also important, he added.

“One aspect that is still difficult to assess is which travelers are at highest risk of infection,” he said. “The most exciting thing about this study is that it shows the differences between dengue and malaria and the risk of mosquito versus human-driven importation.”

[Byline: Carolyn Crist]

Communicated by:
ProMED-mail from HealthMap Alerts

[The reference for the PLoS Neglected Tropical Diseases study cited above is Mier-Y-Teran-Romero L, Tatem AJ, Johansson MA. Mosquitoes on a plane: Disinsection will not stop the spread of vector-borne pathogens, a simulation study. PLoS Negl Trop Dis. 2017; 11(7): e0005683. doi: 10.1371/journal.pntd.0005683. eCollection 2017 Jul;

Both dengue and Zika viruses have been imported into Florida, USA by viremic individuals, with resulting ongoing transmission by _Aedes aegypti_ mosquitoes. The travel of 11 Chinese workers infected with yellow fever virus from Angola to China was a serious wake up call and illustration of the risk of infected individuals bringing the virus into areas where the vector is present. Fortunately, in that case, it was during the colder season when the vectors, mosquitoes, were not active. An example of where an individual infected with chikungunya virus in India, sparked an outbreak after he traveled to an area in Ramini, Ravenna province in north-eastern Italy in 2007, where _Aedes albopictus_, a competent vector mosquito, was abundant enough to initiate on-going transmission. Transport of infected mosquitoes cannot be completely dismissed. The introduction of West Nile virus into New York city in 1999 was likely due to transport of an infected mosquito in a commercial aircraft, since human viremias are not sufficient to provide infectious blood meals for mosquitoes. – Mod.TY]

[Spread of diseases by mosquitoes hitch-hiking in airplanes is rare if we look at reported cases of so-called “airport malaria”. A recent study from Spain analyzing more than 10 000 reported malaria cases could only identify 2 cases of airport malaria (Velasco E et al. Non-imported malaria in non-endemic countries: a review of cases in Spain. Malar J. 2017; 16(1): 260. doi: 10.1186/s12936-017-1915-8; Thus, we agree with the study that microorganisms travel with people not mosquitoes. – Mod.EP]

See Also

Antibiotic resistance (02): WHO, priority pathogens 20170301.4871299

Zika virus (62): Americas, Asia, Europe, research, observations 20161207.4680914
Dengue/DHF update (17): Americas 20160605.4266936
Yellow fever – China (09): ex Angola 20160424.4179477

Chikungunya – Italy (Emilia Romagna) (08) 20071210.3980

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

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