Predict the global spread of dengue with a new tool


Researchers at CSIRO, Australia’s national science agency, QUT and Queensland Health have developed a new tool to predict the global spread of human infectious diseases, like dengue, and track them to their source.

The tool draws on travel data from the International Air Transportation Association and dengue incidence rates from the Global Health Data Exchange to derive new insights about the spreading dynamics of dengue, a mosquito-borne disease.

Dr Jess Liebig, postdoctoral fellow at CSIRO’s data science arm Data61, said international travel significantly contributes to the rapid spread of dengue from endemic to non-endemic countries.

“According to the World Health Organisation, around half the world’s population is at risk of contracting dengue,” Dr Liebig said.

“By understanding the travel behaviour of infected individuals, we can estimate the number of infections that are imported into different countries each month.

“The tool also determines the infections’ country of origin and is able to uncover the routes along which dengue is most likely spread,”

In non-endemic countries such as Australia, local outbreaks are triggered by individuals who acquire the disease overseas and transmit the virus to local mosquitoes.

Professor Raja Jurdak, QUT, said that in many locations around the globe, infected individuals are not diagnosed, and dengue can be under-reported to health authorities, making it challenging to monitor risk and prevent the spread of infection.

“According to recent studies, around 92 per cent of symptomatic infections are not reported to health authorities mainly due to low awareness levels and misdiagnosis,” Professor Jurdak said.

“Our tool is one of the first to be able to forecast the absolute number of dengue importations, rather than the relative risk, at a global level.”

The tool identifies the travel route from Puerto Rico to Florida as having the highest predicted volume of dengue-infected passengers travelling to a non-endemic region.

“This provides a useful tool to assist public health authorities with dengue preparedness,” Dr Cassie Jansen, researcher at Queensland Health said.

“It can also help authorities to identify those locations where new dengue outbreaks may occur, following the arrival of infected passengers.”

The tool can be applied to other vector-borne diseases of global concern such as malaria, Zika and chikungunya.

It expands on previous work, which modelled how dengue infections from overseas might spread in Australia.

The research is part of the Disease Networks and Mobility (DiNeMo) project aimed at developing a real-time alert and surveillance system for human infectious diseases.

An earlier model was developed to predict the spread of dengue within Australia.

Learn more: New tool to predict the global spread of dengue



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A novel larvicide approach made from corn starch and thyme could help control Aedes aegypti mosquitoes

A system created in Brazil using cheap, biodegradable materials permits controlled release of larvicide and can be used in small amounts of water (photo: Ana Silvia Prata)

Corn starch, an abundant, cheap and biodegradable raw material, is the basis for a novel larvicide developed by researchers at the University of Campinas (UNICAMP) in São Paulo State, Brazil. The material is used in microcapsules for storage and controlled release of active compounds to kill larvae of Aedes aegypti, the mosquito that transmits dengue, zika, yellow fever and chikungunya.

A patent application has been filed via UNICAMP’s innovation agency (Inova). The methodology is described in an article published in Industrial Crops and Products.

The research and development was supported by FAPESP. The principal investigator was Ana Silvia Prata, a professor in the university’s Food Engineering School (FEA-UNICAMP).

The published paper describes a biodegradable controlled release system using thymol as the microencapsulated larvicide. Thymol, a key ingredient of essential oil derived from thyme (Thymus vulgaris), a plant widely used as a pharmaceutical and therapeutic agent, is also biodegradable and not harmful to humans in the concentration used by the researchers.

“We succeeded in obtaining a particle that behaves exactly like eggs laid by A. aegypti,” Prata said. “While the environment is dry, it remains inert and keeps the active agent protected. As soon as it comes into contact with water, it begins to swell up and release the larvicide. After three days, when the eggs hatch and the larval stage begins, the particle starts to release lethal quantities of the active principle into the water.”

The researchers set out to develop a system for controlled release of larvicide in backyards, gardens, utensils and other household objects that may contain water, including bottles, potted plants, old tires and rubble, all of which are breeding grounds for A. aegypti.

According to Prata, public health authorities in Brazil tend to focus on treating water tanks and other large reservoirs with larvicide, but epidemiological studies show that small containers account for 50% of mosquito breeding grounds.

“This is a low-cost larvicide, so the government can produce the particles and distribute them to the public for placement around the home where rainwater accumulates. The idea is to supplement educational and awareness campaigns against dengue,” she said.

In tests conducted at UNICAMP, the particles remained functional during approximately five rain cycles. After first contact with water, they released only 20% of the thymol. “In one of our tests, we let the material dry and then rehydrated it, after which the particles again released the larvicide normally,” Prata said.

She added that thymol, the key active ingredient in thyme essential oil, is an anti-microbial and blocks the proliferation of microorganisms in water containers, preventing rapid spoilage of the particles after they become wet.

Production method

The life cycle of A. aegypti comprises four stages: egg, larva, pupa, and adult mosquito. The development stage varies from five to ten days, becoming shorter as temperatures rise. The larval stage takes place in water and is considered strategic as far as combating the proliferation of the mosquito is concerned.

“Based on this information, we thought about how to produce the particle. One of our collaborators, Johan Ubbink [California Polytechnic State University, USA], suggested extrusion. This is the method used to produce breakfast cereals such as cornflakes and savory corn snacks,” Prata said.

The method consists of heating wet starch and forcing it through a small hole. The heat and pressure normally make the material expand after exiting the hole.

“We adapted the process by using a lower temperature and slower screw speed to avoid expansion of the material. If it swelled, the particle would dissolve too quickly on contact with water, releasing the active principle all at once,” Prata said.

Another challenge for the group was finding the right composition for the raw material. As Prata explained, starch from corn, wheat or any other plant consists mostly of amylose and amylopectin in varying proportions. The quantity of each substance determines properties such as viscosity and structure, influencing the material’s integrity when in contact with water.

“We tested formulations with proportions of amylose ranging from 1.8% to 76%, and in each case evaluated leaching [loss of solids by solubilization] and swelling in an aquatic environment,” she said.

At the same time as they evaluated these two aspects of the particle to dose the quantity of thyme essential oil released as a function of the water contact time, the researchers also observed the larvicidal activity of the active principle. This test consisted of measuring the “lethal concentration” (LC) required to kill 99% of the larvae, a parameter known as LC99.

“The LC99 of nonencapsulated thyme essential oil is approximately 70 micrograms per milliliter [µg/ml]. When we put the oil into the particle, it fell to 31 µg/ml. In other words, our controlled release system increased its larvicidal action,” Prata said.

Even so, the natural compound’s LC99 remained far lower than that of synthetic agents such as temephos. The main advantage of using thyme essential oil, according to Prata, is that the mosquito is unlikely to develop resistance to it because of its complex chemical composition, which includes other active molecules besides thymol.

The group also tested the method using paracress (Acmella oleracea) as a larvicide. The result was similar, but the cost was approximately 15 times that of thymol.

“Thyme essential oil is plentiful and commercially available. It corresponds to only 5% of the particle’s composition. The rest is corn starch, which is very cheap. We therefore consider the technique to be easily scalable,” Prata said.

The group is currently studying the possibility of using the same particles to encapsulate nitrogen-fixing bacteria, which assist plant growth. Theoretically, the material could reduce the amount of fertilizer needed in agriculture. “We plan to test this theory in a future project,” Prata said.

Learn more: Thyme essential oil in corn starch particles combats Aedes aegypti larvae


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A common bacterium called Wolbachia could block replication of viruses and break the cycle of mosquito-borne disease

Wolbachia bacteria (stained red) inside mosquito cells (with nuclei stained blue) IMAGE: CASSANDRA KOH / MONASH UNIVERSITY

Viruses, spread through mosquito bites, cause human illnesses such as dengue fever, Zika and yellow fever. A new control technique harnesses a naturally occurring bacterium called Wolbachia that blocks replication of viruses and breaks the cycle of mosquito-borne disease, according to an international team of researchers.

“Wolbachia is present in around 50 percent of all insects,” said Beth McGraw, professor and Huck Scholar in Entomology at Penn State, who did this research while at Monash University. “Interestingly it is not present in some of the major mosquito vectors (insects that transmit pathogens). After researchers put Wolbachia into mosquitoes, they found that, quite excitingly, Wolbachia effectively vaccinates mosquitoes, preventing viruses from replicating.”

Spread by Aedes aegypti mosquitoes, dengue virus affects millions of people each year. Symptoms include fever, body aches and nausea, although a more severe version, known as dengue hemorrhagic fever, can be fatal.

In the tropics and subtropics where Ae. aegypti resides, several large releases of Wolbachia are underway to test whether Wolbachia can reduce the incidence of human disease.

In a paper published recently in Virus Evolution, McGraw and her team report that dengue virus failed to evolve resistance to Wolbachia in controlled lab-based experiments. These findings show promise for the long-term efficacy of Wolbachia following field release.

“I am continually surprised by Wolbachia,” said McGraw. “I thought we would get dengue variants that would evolve resistance. Wolbachia is doing a better job than I expected at controlling virus replication in cells.”

The researchers took dengue virus and infected mosquito cells that either had Wolbachia or were free of bacteria. After five days, they collected the viruses that had been released from the cells and used them to infect fresh cells.

“Dengue takes over the machinery of the host cells, makes lots of copies of itself, and then it buds or burst out of the cell,” explained McGraw.

After nine rounds of passaging the virus through mosquito cells, the team found that the amount of virus released was stable in the Wolbachia-free cells. However, in the presence of Wolbachia, virus levels crashed — and in some cases, disappeared completely.

Dengue viruses grown with Wolbachia were also less effective at infecting mosquito cells and had reduced ability to replicate, compared to viruses grown without the bacterium.

Although this is good news for the control of dengue and other mosquito-transmitted diseases, the researchers note the study has limitations. The researchers used mosquito cells — which may not reflect what happens within the whole insect. And outside the lab, where mosquito populations are much larger, there may be more opportunities for the virus to develop resistance to Wolbachia.

“I think our study suggests that the evolution of resistance to Wolbachia in the virus is challenging,” said McGraw. “I don’t think it’s a guarantee that the virus is not going to evolve under field conditions because the natural system is much more complex. The real experiment is being done in the field right now, because Wolbachia has been released into communities in Australia, Indonesia and Brazil, among others. Monitoring in release areas will be needed to test for the emergence of resistance in the virus.”

Other control methods for dengue have largely been unsuccessful. Because Ae. aegypti is active during the day, bed nets are ineffective at reducing mosquito bites. Spraying of insecticides to control the mosquito and removing standing-water breeding sites have also been difficult to implement in urban environments where the mosquito thrives.

Wolbachia is an attractive control option because it blocks the replication of many disease-causing viruses. It is also self-spreading because of a curious effect, where Wolbachia-containing male mosquitoes cannot reproduce successfully with Wolbachia-free females. According to McGraw, this means that these males prevent Wolbachia-free females from reproducing. Because the bacterium is transmitted from mother to offspring, each generation has successively more mosquitoes containing Wolbachia.

Researchers are still unsure exactly how Wolbachia reduces virus replication in the mosquito.

“We think it might have to do with competition between Wolbachia and the virus for physical space (inside the cell) or for nutrition they both need from the mosquito,” said McGraw. “Or it could be that Wolbachia is increasing the immune capacity of the mosquito. There are a whole range of theories, none of which are entirely satisfying.”

Learn more: Combating mosquito-borne diseases with bacteria


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New mechanism could be a major advance for immunology

Eric Weaver, Assistant Professor in the School of Biological Sciences, Brigette Corder, graduate student in biology in glasses at right, and Brianna Bullard, graduate student in biology, are researching the Zika Virus. December 3, 2018. Photo by Craig Chandler / University Communication

University of Nebraska-Lincoln researchers may have identified a vaccine that would defend against Zika virus without producing antibodies.

Researcher Eric Weaver described the finding as exciting and novel. He and his team are confident that future experiments will yield significant findings that could have a profound impact on the field of vaccinology.

“If we can figure out the mechanism, we might be able to apply it to other vaccine strategies,” said Weaver, an assistant professor of biological sciences affiliated with the Nebraska Center for Virology. “This would be a huge leap for immunology and vaccine research.

Many studies show that antibodies against Zika virus can worsen Dengue virus infection, which, like Zika, is caused by a mosquito-borne virus. This phenomenon is referred to as antibody-dependent enhancement (ADE) of disease. This has been an obstacle to the development of effective and safe Dengue virus vaccines.

“If you have immunity to one of these viruses and get infected by a second one, the illness can be much worse,” Weaver said. “The body makes the wrong immune response.”

Weaver‘s team, which includes doctoral students Brianna Bullard and Brigette Corder, have been studying potential Zika vaccines since 2016, shortly after a Zika outbreak in Brazil that was declared a global public health emergency by the World Health Organization.

First discovered in Uganda’s Zika Forest in 1947, the virus initially was believed to cause only mild or asymptomatic infection in humans. However, outbreaks in Brazil in 2015 and 2016 resulted in abnormally high rates of congenital birth defects in babies born to infected mothers and an increase in the neurological disorder Guillain-Barré syndrome in adults.

In 2016, between 500,000 and 1.5 million suspected cases of Zika infection were reported worldwide, with 4,300 related cases of microcephaly, or abnormally small heads, in infants.

Bullard, then an undergraduate student at Truman State University, came to Nebraska in 2016 for an undergraduate summer research experience in virology (USREV) and returned to Nebraska as a graduate student because of her interest in fighting Zika.

Bullard, who is from St. Louis, developed a genetically altered version of Adenovirus while working with Weaver as an undergraduate – though she didn’t have enough time to test it before her summer program came to an end. She was eager to return to the project after she graduated from Truman State in December 2016.

“I’m interested in viruses in general and I want to do research in an applied, translational setting,” she said. “I’m most excited about making vaccines that can help people. We’re working on Zika right now, but we also have projects relating to influenza.”

In a study reported online Dec. 20 by Scientific Reports, the Nebraska scientists used two forms of weakened Adenovirus to serve as vectors to deliver the Zika vaccine. Adenoviruses, which typically cause mild illness such as the common cold, are modified so that they are replication-defective and incapable of causing disease. The modified viruses are regarded as safe and highly effective vaccine vectors capable of inducing long-lasting protective immune responses against infectious pathogens.

The researchers inserted structural genes of Zika into key areas of the Adenovirus Type 4 and Adenovirus Type 5 genomes. Tested in mice, both vaccines offered strong T-cell responses and substantial protection against Zika infection. However, the vaccine based on Type 4 Adenovirus induced strong T-cell responses with undetectable antibodies. T cells are a type of white blood cell that are at the core of the system that tailors the body’s adaptive immune response to specific pathogens.

“To our knowledge, this is the first report of a vaccine that uses the prM-E genes of Zika virus to induce protective immunity without inducing anti-Zika virus antibodies,” Weaver said. “The lack of antibodies may very well circumvent the potential risks of ADE, resulting in an effective and safer vaccine than those currently in clinical trials.”

Weaver said more studies are needed to determine why the two virus vectors yielded different results.

Learn more: Nebraska virologists discover safer potential Zika vaccine



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A new approach for controlling dengue fever and Zika virus

This is Alexander Raikhel in his office at UC Riverside.
I. Pittalwala, UC Riverside.

UC Riverside study uses gene-editing tool to disrupt serotonin receptor linked to egg production in Aedes aegypti mosquitoes

Mosquitoes are the world’s deadliest animals, killing thousands of people and causing millions of illnesses each year. To be able to reproduce and become effective disease carriers, mosquitoes must first attain optimal body size and nutritional status.

A pair of researchers at the University of California, Riverside, have succeeded in using CRISPR-Cas9, a powerful tool for altering DNA sequences and modifying gene function, to decrease mosquito body size, moving the research one step closer to eliminating mosquitoes that carry dengue fever and Zika virus.

The researchers succeeded in postponing mosquito development, shortening the animal’s lifespan, retarding egg development, and diminishing fat accumulation.

Alexander Raikhel, a distinguished professor of entomology, and Lin Ling, a postdoctoral scholar working with Raikhel, used CRISPR-Cas9 to disrupt the serotonin receptor Aa5HT2B in Aedes aegypti mosquitoes, the vectors of dengue fever, yellow fever, and Zika virus.

“Aa5HT2B controls insulin-like peptides,” Raikhel said. “We were able to uncover the different roles that these peptides play in controlling body size and metabolism, and disrupt the gene associated with this receptor.”

The team accomplished this, Raikhel said, by uncovering a key molecular pathway determining mosquito body size and metabolism.

“Mosquitoes of small size with diminished fat resources mature later and live shorter lives than nonmodified mosquitoes,” he said. “Thus, these genetically engineered mosquitoes have low reproductive capacity and ability to transmit disease pathogens. These features of CRISR-Cas9 mutant mosquitoes can be exploited for developing novel mosquito control approaches. Many challenges remain on the road, however, toward achieving this goal.”

Study results appear in the Proceedings of the National Academy of Sciences.

Raikhel, the UC Presidential Chair and the Mir Mulla Endowed Chair in the Department of Entomology and a member of the National Academy of Sciences, explained that disease-transmitting female mosquitoes require a vertebrate blood meal to produce their eggs because egg development occurs only after a diet change from carbohydrate-rich nectar to protein-rich vertebrate blood.

Blood feeding, Raikhel added, boosts serotonin concentration and increases the level of the serotonin receptor Aa5HT2B in the “fat-body,” the insect analog of vertebrate liver and adipose tissue. A target for hormones, the fat-body is the main nutrient sensor in insects. It links nutritional state, metabolism, and growth.

“Our study provides for the first time a link — the serotonin receptor Aa5HT2B — between blood feeding and the serotonin signaling that is specific to the fat-body,” he said. “Aa5HT2B mediates serotonin action. Until now, the mechanisms of serotonin action specific to the fat-body were poorly understood. Understanding regulatory mechanisms that underlie determination of body size and metabolism is important for developing novel approaches to control mosquito populations and the diseases they carry.”

One important question for further research is how CRISPR-Cas9 gene modification could be introduced into the wild mosquito population.

“This question is a topic of intense research in other laboratories,” Raikhel said. “At UCR, we are continuing our efforts in identifying other key processes important for mosquito development that could be exploited for mosquito control.”

Learn more: Researchers identify new approach for controlling dengue fever and Zika virus



The Latest on: Mosquito control

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