As we reported on BioNews Texas last Friday, a retrospective study by researchers at the Baylor College of Medicine National School of Tropical Medicine in Houston, published on October 9 in the journal Vector-Borne and Zoonotic Diseases and covering three years of blood and cerebrospinal fluid samples submitted for West Nile virus testing in the Houston area has also found that 47 of the samples tested positive for dengue fever virus.
Our report cited Dr. Kristy Murray, associate professor and associate vice chair of research in the department of pediatrics at BCM and director of the Laboratory of Viral and Zoonotic Diseases at Texas Children’s Hospital in Houston and a member of the National School of Tropical Medicine commenting in a BCM release that “We started with dengue virus since it was highest on the list of possible transmission here in Houston because we have the right kind of mosquitoes and a very large, densely populated city full of frequent travel to endemic areas, including Mexico and Central and South America.”
Outbreaks of dengue fever, the most common viral disease transmitted to humans through the bite of infected mosquitoes — particularly species Aedes aegpyti and Aedes albopictus — have been reported in both Texas and Florida this year. Dengue-carrying mosquitoes, which breed in standing water and are often found in urban and semi-urban areas, and Dengue has become a major international public health concern. McClatchy Foreign Staffer Tim Johnson, in a report published Oct.14, notes that 2013 has been a particularly bad year for dengue in the Western Hemisphere, with the Pan American Health Organization reporting 1.4 million cases, and that the Florida Department of Health issued an alert in late August amid an outbreak there, with the state reporting 19 cases by mid-September, happily none lethal.
The World Health Organization (WHO) says Aedes albopictus, popularly referred to a the “Asian tiger mosquito,” and a secondary Dengue vector in Asia, has also spread to North America and Europe largely due to the international trade in used tires (a breeding habitat) and other goods (e.g. lucky bamboo). They note that Ae. albopictus is highly adaptive and therefore can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats.
The WHO also warns threat of a possible outbreak of dengue fever now exists in Europe, and local transmission of Dengue was reported for the first time in France and Croatia in 2010 with imported cases detected in three other European countries. In 2012, an outbreak of dengue on Madeira Islands of Portugal resulted in over 2,000 cases and imported cases were detected in 10 other countries in Europe apart from mainland Portugal. In the past decade, Dengue has been identified in Hawaii, south Florida and along the Texas-Mexico border, and in 2013, cases have occurred in Florida and in China’s Yunnan province. In Asia, Singapore has reported an increase in cases after a lapse of several years and outbreaks have also been reported in Laos.
Evidently, the best efforts of scientists and governments have been achieving only spotty results at best against proliferation of Dengue, which is estimated to affect some 100 million people and cause 20,000 deaths annually, with no known specific drug treatment or vaccine available. The Aedes aegypti mosquito, originally native to Africa, spread throughout the world following World War II, and is now found in over 110 countries. As a result, incidence of dengue fever has reportedly risen 30-fold in the last 50 years, and now costs the world an estimated $5.6 billion Addressing the mosquito control challenge, researchers at Oxford University in the U.K. have developed strains of genetically modified mosquitoes aimed at eradicating Dengue, but this new weapon in the mosquito control arsenal is proving controversial.
Attempts to halt the disease’s spread have relied — with little success — on pesticides and education to control the Aedes aegypti mosquito. An Oxford research note says that decades ago, U.S. scientists experimented with producing sterilized male insects in the hope that their introduction to the wild would reduce the number of offspring and decrease incidence of dengue. The theory was revolutionary, proving successful against some agricultural pest insects, but the radiation used to achieve sterility had adverse effects on mosquitoes.
The Proposed Weapon Against the Spread of Dengue Fever
However, inspired by that pioneering concept, Inspired by the concept, Prof. Luke Alphey, from the Department of Zoology at the University of Oxford in the U.K., has developed a genetic modification technique which blocks reproduction of the mosquitoes.
Dr. Alphey’s main research focus is on the use of modern genetic methods to improve the Sterile Insect Technique (SIT), and another area of interest in genetic control is the “refractory insect” strategy, which is based on (i) the production in the laboratory of a strain of insects refractory to transmission of a disease agent (e.g. malaria or dengue fever) and (ii) the introgression of this refractory gene into the wild population, so that the disease-transmitting insect population is rendered harmless. He reports that he and his team have devised new approaches to the introgression problem, and are currently modeling these to explore their advantages and disadvantages, as well as trying to construct the required genetic systems.
In order to develop beyond larval stage, offspring of Dr. Alphey’s modified male mosquitoes require an antibiotic called tetracycline, which is impossible to obtain from natural sources in their habitat. When released into the wild, these genetically modified males mate with females, but their offspring never develop into adults, resulting in a targeted and gradual decline in populations of the Aedes aegypti species wherever it is introduced. The concept was patented in 1999, and Dr. Alphey has also established a commercial spin-off company, Abingdon, England based Oxitec Ltd., which is a Member of WHO Scientific Working Group on Dengue, and of the NAPPO Expert Working Group on RSPM 27 (“Importation and Confined Release of Transgenic Arthropods in NAPPO Member Countries”). One of Oxitec’s first products is a new method to control Aedes aegypti.
Oxitec has conducted field trials in in Brazil, Malaysia, and the Cayman Islands, and reports great success, with the process earning itself the title of BBSRC Innovator of the Year in 2009 and winning the Wellcome Trust Translational Award in 2011. In a demonstration conducted in Mandacaru, Brazil, the level of Dengue-carrying mosquitoes was reduced by 96 percent within 6 months, and it was shown that the reduction could be maintained for many months including through the time of the year when normally mosquito levels would be at their peak.
Oxitec plans to extend the trials, with the the long-term goal the company has set for itself to reduce populations of disease-carrying mosquitoes by over 80% for as little as £3 per person per year in areas where Dengue-carrying mosquitos are endemic or invasive. Oxitec’s method can also cost less than spraying, and eliminates the potentially hazardous and destructive effects of disseminating purpose-made toxic chemicals into the environment.
However, not everyone is convinced that introducing genetically modified insect species to the environment is a good idea.
McClatchy’s Tim Johnson cites Dr. Helen Wallace, executive director of GeneWatch UK — a British genetic science watchdog organization — suggesting that if Oxitec’s method succeeds in reducing Aedes aegypti mosquito populations, there is nothing to prevent some other type of mosquito from moving in and to carry the virus, and Chile-based French-trained biosecurity expert Camilo Rodriguez-Beltran, arguing that gene-altered mosquitoes could cross international boundaries, violating international treaties on biosafety.
In an article entitled: “Can GMO Mosquitoes Save You From Dengue?”, Mother Jones Senior Editor Kiera Butler cites Eric Hoffman, who tracks genetic engineering issues for the environmental group Friends of the Earth, commented that “This technology hasn’t been properly tested, nor is it clear that it’s going to work. “The public isn’t being told the whole truth.” Hoffman echoes Dr. Wallace in arguing that no one quite knows what will happen to an ecosystem suddenly devoid of Aedes aegypti. Suppose a worse mosquito species takes over he suggests such as the aforementioned so-called Asian tiger mosquito, which is one of the most invasive mosquito species — and a potential dengue carrier — that breeds extremely rapidly and may require great quantities of pesticide to control.
Ms. Butler observes that Oxitec’s answer for that is the sterile mutant Asian tigers it has in the works, but notes Hoffman’s objection that some of the genetically modified the offspring don’t self-destruct, the company confirming that a small percentage of its altered mosquitoes, including biting females, can survive in the lab without tetracycline, and he contends that Introducing any new engineered species into the wild presents the possibility that we may be allergic to it.
Oxitec acknowledges that as with any GM technology nowadays, the company has received criticism. But the company contends that unlike other GM products, Oxitec’s modified mosquitoes don’t spread their genes down the family line or to other species, and that Oxitec remains confident that, as an alien, invasive species in most dengue-plagued countries, Aedes aegypti eradication does no harm to the ecosystem. Mother Jones’ Ms. Butler notes that Oxitec CEO Hadyn Parry sees his company’s product as a humanitarian triumph, and says that independent studies commissioned by Oxitec suggest that allergens won’t be an issue.
Be sure to check out our Dengue Fever info page at BioNews Texas