Category: Uncategorized

Post by: Eli Fenichel

What is the cost of a vector borne disease? It is not simply the sum of medical bills from treatment. People incur costs to avoid getting sick. Economic theory says that on the margin people are expected to equalize there incremental expenditures or forgone benefits on avoidance with their expected incremental costs of illness. In a 2018 study, published in Environmental and Resource Economics, we estimate the behavioral risk avoidance response to Lyme Disease in the Northeast United States, and use that to estimate the avoidance costs. We find that the average individual in the average Northeast US county spends nearly nine and half fewer hours outdoors per year. For reference the average outdoor activity lasts 73 minutes. This amounts to the average individual taking nearly 8 fewer trips outside per year or just over one billion lost trips. These trips can be valued at between $2.74 to $4.91 per trip – these are largely trips to things like local parks. All told this means that the cost of defensive actions to avoid Lyme Disease are on the order of $2.8 billion to $5.0 billion a year (we used 2006 dollars for our analysis). This suggests that if Lyme could be eradicated permanently and with perfect certainty, then that would merit an expenditure of up to $40 billion, using the US Office and Management’s 7% discount rate.

There are challenges to doing a study like this. First, there is getting the data. Second, is addressing bias, because behavior itself likely effects Lyme cases. We use two primary sources of data, supplemented with a few others. The core behavioral data comes from the American Time Use Survey (ATUS), which is collected and made public by the US Bureau of Labor Statistics. The ATUS asks a stratified random sample of the Current Population Survey to keep a minute-by-minute diary of all activities and locations of activities for a 24 hour period. The survey has been run every day since January 1, 2003. However, in our study we only use the first decade of observations. The survey tracks nearly 400 activity codes and 25 location codes (types of locations not exact coordinates). The data can be aggregated to the county level, though in many locations the data are more granular. We merge these data with year-by-county Lyme Disease case reports from the CDC. Additionally, we use some weather data and geographic data.

There are potential concerns with the data and with the process of simply regressing time spent outside on Lyme Disease cases. First, there could be challenges with the ATUS data, but BLS puts a lot of effort into the randomization and recruiting process, and these data are used in the context of many important economic and policy decisions. Second, there is concern that reporting of Lyme Disease may go down as Lyme becomes endemic. If this is the case, then the behavioral response we measure should be a lower bound and underestimate the cost. Regressing Lyme Disease cases on time spent outside using an ordinary least squares regression is likely biased because time spent outside is an important input into contracting Lyme. This sort of feedback problem is common in economic statistics, and economists and econometricians have developed a number of regression techniques to address these problems. Standard ordinary least squares regressions finds no effect of Lyme Disease cases on time spent outdoors, our econometric regression that accounts for the feedback (an Arellano-Bond estimator) finds a strong significant reduction in time spent outdoors that attenuates with increasing Lyme Disease cases in a county. Our estimates condition on population, minimum humidity, minimum temperature, precipitation, percent wilderness, percent city parks, maximum humidity, and maximum temperature. Overall, the estimate of the marginal effect of Lyme Disease cases on time spent outdoors is highly robust to model specification.

We believe that most researchers studying vector borne disease do so because they are concerned about social outcomes and public health. We are too. Yet, public health is not an end to itself, it is an important input into broader wellbeing. Quantifying the tradeoffs people make around avoiding getting sick can provide a credible lower bound to the cost of a vector borne disease and help policy makers better assess the tradeoffs involved in reducing vector borne infections. Increasingly, available data on human behavior makes these analyses possible. We encourage vector disease scientists to work with economists to further place the important science of vector borne pathogens in a social context.

Dear RCN Members,

As part of the upcoming meeting, we will have a Working group on Vector Traits, with the goal of further improving the VecTraits database, which we are developing as a global resource for functional traits in disease vectors. To get an idea about where we (or at least some of us!) are coming from and how we envisage the role of vector Traits in VBD research, please see this preprint.

We are looking for 2-3 more members, who have experience with collecting, managing, or generally meddling around with vector traits, to join the VecTraits workshop team. If you are interested, please email me (s.pawar@imperial.ac.uk).

Exciting times ahead!

Best wishes

Samraat

Blog post by Senay Yitbarek

What has the working group been doing?

The coinfection group is focused on incorporating vector behavior into multiple pathogen dynamics across plants, animals, and human systems. Our group has been working to identify relevant traits from the empirical literature that can help explain coinfection patterns in vector populations. The vector traits of interest have primarily focused on arthropod vectors including mosquitos, ticks, and aphids. For each vector group (~ 5 member/per group), we have appointed a group leader that is responsible for disseminating progress and updates to the general working group body. Furthermore, we have been working on a general theoretical framework that explores the consequences of vector traits for the epidemiology of vector-borne diseases. A separate working group is currently working on a vector borne model.

Any progress made?

The vector groups have recently completed a literature survey on relevant traits pertaining to coinfection dynamics. In the aphid group, seasonality and life stages have been found to play a key role in transmission events. For instance, the wingless-aphid morphs transmit at higher rates early in the season. Aphid preferences for infected and uninfected plants can also affect transmission efficiency of multiple viruses. In the tick group, we focused on two major species and found that ticks are likely to acquire pathogens at each life stage resulting in higher coinfection rates in adults. However, it takes ticks up to 3 years to complete a life cycle requiring hosts at each stage without which they die. Depending on the specific pathogen involved, seasonality generally increases transmission risk. However, transmission risk varies considerably with some pathogens showing annual stability while others peak during the summer months. In the mosquito group, we have examined the role of vector competence in transmitting arboviruses. While A. aegypti mosquitos are highly susceptible to multiple pathogens, vector competence shows preferential transmission to vertebrae hosts. For instance, A. aegypti mosquitos are highly permissive and competent for mono-infection and coinfection with Zika and Dengue, including co-transmission. However, Zika grows to higher titers and more efficiently infects hosts. Thus, vector competence in mosquitos is a critical component that needs to be accounted for in coinfection dynamics. With this in mind, the modeling group is developing a general coinfection model that incorporates vector traits. We are currently expanding on a classical vector-borne disease model by incorporating multiple pathogens and vector traits such as density, fecundity, searching efficiency, handling time, and life-stages. We will explore the effects of vector traits on the basic reproduction ratio of pathogens.

Future goals of this group?

We plan on submitting a manuscript in the form of a review paper that addresses our current knowledge and challenges in understanding the drivers of vector behavior and their consequences for coinfection dynamics. Several groups leaders from our working group will be attending the Vectorbite conference in Asilomar, California. As part of the workshop training, we hope to utilize the population dynamics database to fit some of the vector parameters to our coinfection model. Following the Vectorbite conference, we will reconvene a meeting on the UC Berkeley campus with several group members.

Blog post written by Marta Shocket.

Last month my friend and lab mate Meghan Howard gave a talk at a global health conference and got one of those questions: a question not directly related to her research, but fundamental, big, and interesting. The kind of question that you might hear from a civilian (non-scientist) friend or a relative around the Thanksgiving table.

The question was: How important are mosquitoes for ecosystems? What, if any, calamities would befall the Earth if we could somehow engineer their disappearance? Meghan was quick on her feet and gave a great answer (1). However, our whole lab was having the same nervous reaction in the audience: we knew it was a question that she hadn’t prepared for, and none of us were quite sure how we would answer it in her place. Discussing her improvised answer over lunch, we decided that at our next open lab meeting we would split into teams and tackle popular topics in vector biology. That way, the next time one of us was in the hot seat, we’d be more prepared.

Even though the question about the ecological importance of mosquitoes caught me off guard, it wasn’t a new question for me. I’d been interested enough to bookmark some popular science articles on that exact topic—but of course, not enough to actually read them.

Since others in the vector ecology community might be in a similar boat, this entry will be the first of three blog posts covering the topics we researched for our lab meeting: the role of mosquitoes in ecosystem functioning, Wolbachia bioengineering, and other types of vector bioengineering. Each post will have a short summary of the topic, links to popular and scientific articles if you want to dig deeper, and hopefully some fun and unexpected facts (including the one behind this post’s click-bait title).

So, how important are mosquitoes? The general consensus among scientists is that with a few exceptions, mosquitoes are not very important for ecosystem functioning. Many animals eat mosquitoes, but they only comprise a significant proportion of biomass in the arctic tundra. The migratory birds that breed there would definitely miss them as a food source if they disappeared (2,3). Little Forest Bats in Australia also depend mostly on adult mosquitoes for food (3), and larval mosquitoes are a critical food source for mosquitofish. Beyond these three examples, most other predators are probably generalist enough that they could subsist on other prey items (2).

Aside from being eaten (and of course, transmitting pathogens), mosquitoes have a couple other minor roles. Many mosquito species eat nectar, and some plants rely on them for pollination (2,3). Larval mosquitoes are important for structuring the communities of protists that live inside pitcher plants, and for recycling nutrients to make them available to the plants (2).

However, the most sensational use for mosquitoes was one I found in a relatively obscure article reviewing the potential use of spiders as biocontrol (4). They referenced a study showing that Evarcha culicivora, an East African jumping spider, specifically targets blood-fed Anopheles mosquitoes over sugar-fed ones. The reason for this preference: eating blood-fed mosquitoes gives both males and females a scent that makes them more sexually attractive to mates (5). Not exactly earth-shattering in terms of ecosystem services, but it definitely makes a salacious blog title, and could spice up next year’s conversation around the Thanksgiving table.

A caveat to end: magically disappearing all mosquitoes is an interesting thought-experiment, but not very realistic. The biotech strategies being developed to drive down mosquito populations all target single species that spread infections to humans. These villains account for a tiny proportion of the 3,500 described species of mosquitoes, so the mosquitofish and pitcher plants don’t need to worry too much.

Sources:

(1) You can watch her talk about mosquito communities across a land use gradient in Costa Rica on youtube <https://www.youtube.com/watch?v=38xcapLLB7s>. The question in question occurs at around 12:22.

(2) https://www.nature.com/news/2010/100721/full/466432a.html

(3) https://theconversation.com/why-dont-we-wipe-mosquitoes-off-the-face-of-the-earth-54005

(4) http://www.dipterajournal.com/pdf/2018/vol5issue1/PartA/4-6-15-487.pdf

(5) Jackson RR, Cross FR. Mosquito-terminator spiders and the meaning of predatory specialization. Journal of Arachnology. 2015; 43:123-142. PDF

Marta Schocket is a post-doc in the Mordecai lab at Stanford University and a member of VectorBite.

Hello folks,

Looking forward to seeing many of you at VectorBiTE 2018.

Matt Watts has made great progress with VecDyn – please visit vectorbyte.org. We will be integrating VecDyn into the training in this meeting.

The new Ecoinformatics Working Group for VBite 2018 will focus on VecTraits, though we will also have some discussions about VecDyn and how to develop it further. Let me know if you have any thoughts or suggestions.

Thanks,

Samraat

We are now accepting applications for an Open Session of VectorBiTE 2017.

The Open Session is available for any RCN members who would like to participate, regardless of participation in the rest of the meeting. The Open Session will take place on:

Thursday 27 July 2017 from 8:45am to noon
in the Moore Auditorium at the Royal Holloway University. 

In person attendance to the session is capped (due to maximum occupancy of the room) so we will allocate places in the order requests are received.

We also intend to allow remote participation in the open session. If that would be your preference, please indicate this under the “special requests” section of the application.

Hello VectorBiTE members,

We are preparing for VBite 2017 and are now accepting applications for new working groups. We have had an extremely strong response from the exiting groups and many of them have proposed Open meeting activities (meaning that if you apply to the meeting you could join one of these groups). We will therefore be accepting a very small number (1-2) of new working groups.  If you would like to propose a new working group please send a 1 page summary containing the following information.  We would like these by Feb 20th.

• Proposed activities/objectives- Why do you need to meet? What do you hope to accomplish?
• Proposed group members- What composition of group members do you need to accomplish these objectives?  This may be only one or two people at this stage.
• Funding requirements of the group- Accommodation is covered for all attendees automatically. In order to ensure we can maximize the number of folks who can attend we are asking that if funding for alternative travel is available that people use this. Some attendees last year mentioned they would be willing to draw on these alternative sources for travel funding if it meant others could attend. However, it will not count against an application if all attendees need travel funds.
• What if you are not funded? Even if proposals are not chosen we are open to creating a virtual working group through the VectorBiTE website to help develop community ideas. Let us know if you would like us to arrange for this in the event that you are not funded and who the admin should be for your group.
• Open or Closed Enrollment? All new working groups must be Open to new members

Some additional notes: We want to balance participation across early stage and late stage career researchers, theoretical and empirical focus, and geographic region.  We would be especially interested in increasing participation from early career UK scientists. We are also specifically interested in a group to look at the effect of vector age on transmission.

Please submit your 1 page summary by emailing vectorbitercn@gmail.com

Best,
Vectorbite Board

The second annual meeting will take place this summer at Imperial College in London, UK.