Reducing Risks of Wildlife/Livestock Parasite Transmission

Progress report for GNE20-244

Project Type: Graduate Student
Funds awarded in 2020: $14,907.00
Projected End Date: 08/31/2022
Grant Recipient: University of Maine
Region: Northeast
State: Maine
Graduate Student:
Faculty Advisor:
Anne Lichtenwalner, DVM PhD
University of Maine
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Project Information


White-tailed deer (Odocoileus virginianus; WTD) pose a risk to livestock health due to a parasite, meningeal worm (Parelaphostrongylus tenuis; P. tenuis) also called brainworm. Farms where livestock grazing systems overlap with WTD habitat (P .tenuis definitive host) and that harbor high numbers of terrestrial gastropods (P. tenuis intermediate hosts) face elevated risk of brainworm infection. The parasite often causes severe neurologic disease or death in livestock, primarily to small ruminants (sheep, goats, llamas and alpacas)¹. Small-scale farmers face a large risk of production loss due to meningeal worm, as even a small increase in mortality can have a large financial impact. 

The objectives of this project include; 1) establishing baseline abundance for brainworm on Maine farms 2) estimating risk of P. tenuis infection to small ruminants in overlapping grazing systems with WTD; 3) proposing risk management and preventive applications to producers. During the first year of the study and in preliminary work, gastropods and WTD fecal samples were collected from two different Maine farms; 17 out of 21 WTD fecal samples and 4% of snails carried P. tenuis larvae. The study collated information from a survey for United States farmers about their pasture systems and if they have had P. tenuis related symptoms or deaths. In the coming year, WTD fecal samples, as well as gastropods will be collected on Maine farms to determine meningeal worm prevalence in pasture systems. Producer education will be developed to minimize risk, to aid early detection, and to direct producers to seek appropriate veterinary treatment.  Several abstracts have been produced in the first year, and additional educational materials will be disseminated via Extension publications, a recorded presentation, and a peer-reviewed publication.

Although we began the project in 2020, due to increased Covid-19 restrictions in the field and in the laboratory we did not make the anticipated progress. However, in this interim report, we describe additional preliminary findings as well as survey conclusions. Our objectives have been modified in regards to establishing a diagnostic test. In contrast to our expectations we did not have the expertise available. This task no longer seems feasible and will no longer be part of this project. However, we have added objectives which include an undergraduate project evaluating ducks as gastropod control, as well as assessing pastured poultry and mowing as control measures on working farms. 

Since the original proposal, we evaluated an additional 795 gastropods from two farms. In 2019, with the overall brainworm prevalence was 4.07%; the 2020 preliminary sampling season found a prevalence of 2.9%. Dry weather and high temperatures, in addition to mowing in July, decreased gastropod population numbers dramatically. Random sampling in October 2020 found no gastropods, compared to the wet and warm October 2019 when 172 were collected. 

Survey responses identified small ruminant farmers with an interest in being part of the on-farm study.  However, due to pandemic restrictions, we have been constrained in travel, so have focused on the University’s Witter Farm and the PI’s farm so far.  We expect these restrictions to be removed in the coming summer, but if not, we will continue to concentrate on our current study areas, and to focus on producing educational materials from the work.

Project Objectives:

Changes and updates in this report are indicated by bold text. 

1) Assess the prevalence of P. tenuis on Maine’s agricultural landscape

Results from our nation-wide survey will give general insight to the perceived incidence of P.tenuis on farms. Examining fecal samples and gastropods in the lab will indicate the prevalence of brainworm on Maine farms. Necropsy, followed by histology, of animals showing neurologic symptoms before death will be performed as appropriate using the UMaine VDL resources

2) Establish the risk factors associated with brainworm to determine likelihood of infection to livestock.

Farmers across the north east utilize various grazing strategies which often overlap with WTD habitat. This, in combination with high gastropod numbers,creates risk of livestock brainworm infection on a farm. Weather trends, grass height, wetness, topography, and woody debris may change gastropod behavior or abundance. These factors, once quantified, can be entered into a statistical model to determine the likelihood of infection to animals exposed to different grazing systems, climatic events, and preventive treatments. These factors will be explored across several farms in Maine where pastures support deer and small ruminant livestock, such as sheep and goats. This study will be the first evaluation of P.tenuis on Maine livestock farms.

3) Create management strategies for farmers.

After analyzing the risk factors associated with increased prevalence of brainworm, preventive measures to combat the parasite will be suggested in project publications. In a closely related project, integrated pest management using poultry (ducks, other species) is being explored by an undergraduate member of the Lichtenwalner lab.  This additional project has been funded via 2 internal grants and the IACUC approval is in place.


The purpose of this project is to evaluate risk of brainworm to domestic livestock, and to evaluate risk management techniques. Brainworm infection of small ruminants often causes death, resulting in emotional and financial difficulties for small farmers. Diagnostic serologic tests are not optimized for use in livestock, and diagnostic fecal examinations don’t work for livestock, as the worm cannot reproduce in any species other than the white-tailed deer (Odocoileus virginianus; WTD).  Additionally, preventive practices for agriculture have not been well documented. The results of this project will inform future outreach efforts to producers about risk assessment, preventive steps, and recognition/treatment for this deadly infection in livestock.


Problem 1: Diagnosis.

Currently, diagnosis of P. tenuis in livestock is neither easy nor cost-efficient but is important due to zoonotic and very serious “look-alike” diseases, like rabies, eastern equine encephalitis (EEE), listeriosis, polioencephalomalacia (PEM), scrapie, and bacterial meningitis¹.  While infection can be confirmed by histology of the spinal cord and brain post-necropsy, this is time-consuming and expensive. Recently, a serologic test has been developed for brainworm detection in moose, but is not validated for small ruminants.  As well, response to larvicidal treatment may assist with diagnosis, but may enhance anthelmintic resistance on small ruminant farms, a serious problem for farmers.


Problem 2: Risk Evaluation and Risk Management.

In natural grazing systems, P. tenuis risk to livestock is not well documented. Farmers in the North East who graze their animals in WTD habitat would be expected to face an increased risk of brainworm exposure, as approximately 84% of WTD are infected with brainworm² ³ ⁴. Environmental conditions and frequent mild winters/early springs increase deer survival, resulting in escalated production of larvae². Additionally, gastropod abundance might be expected to increase under these conditions. Height of vegetation, wet fields, and woody debris may also increase gastropod presence⁵.

This project seeks to quantify the variables associated with risk of infection within different livestock grazing strategies in high deer population areas. Implementation of this goal will include visiting several farms across Maine to quantify the different risk factors. Observations will include measuring and identifying vegetation in grazing plots, documenting climate and weather trends, assessing deer abundance and movement with the use of game cameras, identifying infected gastropod species, and counting infected gastropods within the study sites. These variables may create a model that could assist farmers or consultants with preventive grazing strategies.


Problem 3: Producer Knowledge.

By deploying a nationwide survey, we will gain insight about producer knowledge of the disease and quantify the perceived infections across the United States. Questions also focus on grazing systems and WTD habitat overlap with livestock. This survey will help identify future study sites in the state of Maine, as well as risk perception areas of need. This and project results will create educational opportunities that can help with risk management and reducing infection in livestock.


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  • Joshua Hatley (Educator)


Materials and methods:

Establish the risk factors associated with brainworm to determine likelihood of infection to livestock.

To establish the risk factors associated with brainworm, visits to working farms is necessary. Sampling will be held over ten weeks between May- August for two seasons.

  1. Study locations: From voluntary recruitment, six farms in Maine will be selected at random based off of project criteria: forty or more small ruminants (goats, sheep, alpacas, and/or llamas), an abundant and active deer population, and observation of gastropods. Farms will be mapped to document areas of wetness, forest, field, rockiness, and man-made influence (driveways, barns, etc.). It has been advised that a control, like the originally proposed dairy farm observation, may not be necessary in this experimental study, rather an evaluation of additional preventative strategies could be of more use to producers. 
  2. Sample sites: One grazing field per farm will be chosen randomly based on time of grazing when animals are about to be, or are currently, grazing. Sampling sites within the field will be stratified random samples on two different transects, 15m apart. 45cm x 90cm corrugated cardboard and 45cm x 90cm white plastic sheeting will be used for two sites on the transect on ground level. The remaining site will be a piece of cardboard and plastic sheeting angled up to appeal to climbing gastropods. Sample sites will be fenced-in so animals do not ingest materials.
  3. Vegetation within the field, on the field’s fence line or boundary line, 10m out of the grazing area, will be mapped. Land use type (agricultural, forest, commercial) will be documented in a 1mile (1.6km) radius of the field site. The grazing system which sample sites are located will be recorded (rotational, permanent pasture, dry lot, etc.). Within the grazing system, vegetation density, height, and species will be recorded.
  4. When visiting sample sites, climatic data such as ambient air temperature, precipitation, wind direction, and humidity will be recorded.
  5. Game cameras will be deployed on habitat buffers (field edges) to record deer movement and visitation to the field. Deer abundance is related to increased brainworm within gastropods, since deer feces carry the infective larval form that must gestate within the gastropod intermediate host

During the summer of 2020, some of these methods were implemented. From analysis of the research this summer using both cardboard and visual collection, in addition to several research papers highlighting the disadvantages of introduced materials (Boag, 1982; McCoy, 1998; Capinha et al., 2014), we have decided to conduct natural collections without artificial interference. This eliminates the need for fencing in the study site. With this change, pvc piping will be used to create 45cm x 90cm portable grids for the sample sites. 

Document prevalence of brainworm on Maine farms.

To establish the baseline of prevalence of brainworm we will experiment on gastropod and deer fecal samples from the farms, mentioned above, in the laboratory. A survey, made by an undergraduate in our project group, that encompasses risk perception questions will be sent to producers across the country.

  1. A survey will be sent nationwide to assess producer knowledge of brainworm. This survey will help identify future study sites in the state of Maine, as well as risk perception areas of need. Questions also focus on grazing systems and WTD habitat overlap with livestock.
  2. Collection of deer fecals: fecal samples from deer will be collected within the field while the livestock are grazing. As deer fecal pellets look similar to that of sheep and goat, we may have to choose deer fecal pellets from areas adjacent to the field or slightly before livestock are introduced to the pasture.
  3. Examination of fecal pellets for P. tenuis: grouped deer feces from sample fields will be placed in a Baermann apparatus to extract stage 1 larvae.
  4. Collection of terrestrial snails and slugs: gastropods will be collected in transects (mentioned above). Different materials will be offered for longevity and moisture-holding ability. “Traps” staked to the ground will provide shelter from brisk mornings or weather events. Cardboard or plastic at a slight vertical angle may provide shelter for climbing species and those less dominant. Three 1m x 1m plots will be chosen randomly each farm visit to account for free-living gastropods in the field.
  5. Gastropod movement: Travel of snails will be a subproject to determine the migratory behavior of common land snails. A mark-recapture method will be utilized by an undergraduate member of our project.
  6. Examination of gastropods for P.tenuis: Gastropods will be placed in an artificial digest to entice the third-stage larvae out of the host tissue. These will be quantified, measured, and genetically tested.
  7. Necropsy will be performed on up to six deceased individuals from these farms that had neurologic symptoms leading to death.
  8. Diagnosis in livestock will be confirmed via necropsy of deceased animals from project farm sites at the UMaine VDL. 

Create management strategies for farmers.

Creating management strategies for farmers will first require statistical analysis of significant risk factors found from the study. Response variables include animal health indices (eg. behavioral analysis, symptomatic response, or death) after ingesting meningeal worm larvae. Modeling risk will include the factors that increase likelihood of infection. Management strategies will be informed from the results of this study and broadcasted to a wide audience (see Outreach section). Organic control methods of pastured poultry and mowing will be examined on two farms to assess before and after gastropod population numbers at one week intervals. In exploring the gastropod-borne helminths on Maine’s farmed landscapes, we may uncover other harmful parasites in addition to P. tenuis.

    1. Duck effectiveness in a lab setting: Members of our group for an undergraduate capstone project (not part of this proposal) will be testing the effectiveness of ducks as “snail grazers”. Some ducks will be experimentally infected with tenuis at different levels to test if the ducks readily ingest gastropods, if they become infected, if their enteric tract kills the infective larvae, or if they expel viable P. tenuis larvae in their feces.
  • Pastured poultry effectiveness: Large-scale organic poultry growth operations often place poultry on their fields to manage for insect pests, rejuvenate the soils, and substitute feed. We will examine the before-and-after poultry flock foraging gastropod numbers on two rotational pasture poultry operations to assess the effectiveness of poultry management.
  • Mowing effectiveness: Although many producers use pasture as primary feed sources, and are eager to get small ruminants out onto lush spring pastures, mowing pastures may significantly reduce gastropod numbers. Before-and-after population densities of gastropods will be measured to determine the effectiveness of mowing on gastropod control. 


Boag DA. Overcoming sampling bias in studies of terrestrial gastropods. Canadian journal of zoology. 1982;60(6):1289-92.

McCoy KD. Prevalence of Parelaphostrongylus tenuis in gastropod populations: Ecological and behavioural factors affecting transmission [dissertation]. ProQuest Dissertations Publishing; 1998.

Capinha C, Rödder D, Pereira HM, Kappes H. Response of non-native European terrestrial gastropods to novel climates correlates with biogeographical and biological traits. Global ecology and biogeography. 2014;23(7/8):857-66.

Research results and discussion:

Due to Covid-19, the University of Maine has implemented research restrictions, including field research. Currently, we are in the process of submitting a form to seek allowance to perform on farm research for 2021. If denied, we are preparing alternative collection methods which includes farmer submitted gastropods and increased citizen science efforts. 

In the 2020 season, methodology for measurements and gastropod collections were tested. Two sample pastures were gridded and mapped. In one pasture with abundant gastropod activity, mean populations dropped from 134 snails per 4,050cm² in July to 48 per 4,050cm² in August (64% reduction in one month), and to 20 per 4,050cm² in the following month (85% reduction by September). This was attributed to a regional drought in combination with field mowing prior to the July count. Brainworm prevalence in the collected gastropods decreased in relation to the prior year (4% in 2019 to 2.9% in 2020).  In 2021, these collection efforts will be expanded if University pandemic restrictions allow these field and lab efforts to continue.

Based on the 21 WTD fecal samples evaluated to date, there is 85% prevalence of brainworm larvae in WTD fecal samples collected on the two Maine farms studied. Our procedures were based on microscopic assessments of gastropod samples after enzymatic digestion, but did not extend to molecular identification of all larval samples.  Based on morphology, we found more than one type of nematode larva of probable small ruminant health significance in gastropods.  Work in the final year of the project will more accurately identify the larvae, providing a better risk assessment for farms. Although the farm outreach was limited due to the pandemic, and no animal deaths were investigated, we plan necropsy of small ruminant livestock followed by histology  as appropriate, using UMaine VDL resources in the remainder of the study.

So far, we have received 65 responses to our nation-wide survey. Our conclusions are that producers are aware of brainworm as a risk to their livestock (95%), with 41% of farmers saying they experienced brainworm related illness on their farm. Survey data is currently being further analyzed. Several respondents from Maine contacted us to volunteer their farms for research. Communication with farmers is a current effort. Some notable results from the survey include:

  • Hobby farming/ pet livestock consist of 29%, partial income 55%, total income 9%, and other 7%.
  • Farmer respondents have diverse livestock, including cattle (8%), sheep (19%), pigs (7%), goats (13%), horses (8%), alpacas or llamas (30%), and other (15%).  Brainworm has been documented in several of these mammalian species.
  • Different grazing systems seem to be used across the same farm, especially with alpacas/llamas and sheep. 
    • Use of continuous grazing (one pasture all the time) is most common for alpacas/llamas and is followed by goats.  
    • Use of rotational grazing and dry lots is most common in alpacas/ llamas and is followed by sheep. 
  • 95% of survey participants had heard of brainworm prior to the survey.
  • 41% of producers said they had suspected or confirmed cases of brainworm on their farm.
  • 98% said their farm was near white-tailed deer habitat, and 88% said that deer were observed near their livestock grazing system. 
  • 82% of farmers said their poultry share pasture or housing with livestock. 

Poultry as control against gastropods, along with mowing, has been recommended in abstracts, presentations, and newsletters. Abstracts and presentations were given at the online University of Maine Student Symposium, the University of Maine Cooperative Extension’s newsletter “Cows and Crops”, the Extension Risk Management Education National Conference (abstract accepted and travel award granted, but conference cancelled in 2020), and the online Everyday Farmers Conference. These methods will be revised and updates published in 2021, and after the projects and analysis have been completed.

Participation Summary

Education & Outreach Activities and Participation Summary

5 Consultations
4 Webinars / talks / presentations

Participation Summary:

Education/outreach description:

Farmer involvement with the project is integral to its success, and farmer networks will be utilized to design, implement and share experimental information. In-progress results will be shared via Extension websites, direct-to-farmer workshops, webinars, a “Brainworm Blog”, 4H and FFA youth workshops, and peer-reviewed publications. The project is designed to assist primarily small-scale or beginning farmers, but may also assist wildlife managers who seek to advise the public on the dangers of wildlife feeding.

  1. Farmer surveys will be distributed via UMaine Extension social media accounts (including livestock owners and the Beginning Farmers Resource Network); responding farmers will be contacted for potential recruitment into the study (in progress).
  1. Participating farmers will be visited up to 10 times yearly, at each visit, risk factors and small ruminant health will be discussed.
  2. Survey and other in-progress study results will be posted on the UM VDL website ( ) as a “Brainworm Blog”.
  1. Online or in-person Extension Small Ruminant Workshops are held 1 to 2 times yearly in Maine; these presentations reach both sheep and goat farmers. This project’s interim and final results will be shared with these audiences. Additional presentations will be made to the Maine Sheep Breeders Association during the Maine Agricultural Trade Show (yearly in January; Augusta, Maine).
  2. One webinar will be held yearly to engage a national audience on this topic; the event will be publicized on eXtension and other sheep and goat websites (e.g,,
  1. At least one publication will be shared with a wildlife biologist audience via a regional meeting (North East Association of Fish and Wildlife Agencies), as well as the NorthEast Wildlife Disease Cooperative (NWDC), of which the UMaine Veterinary Diagnostic Lab is a member.
  1. Both 4H and Future Farmers of America (FFA) youth workshops on veterinary science are held yearly at the UMaine Veterinary Diagnostic Lab; this project’s findings will provide case-report discussions for teaching purposes.
  2. Final results will be reported to SARE, and will be submitted as peer-reviewed publications to both Extension journals (Extension Risk Management Education and the Journal of Extension), and an open-access journal (such as Small Ruminant Research, a One Health journal, and/or a wildlife journal). Further outreach to farmers will consist of a follow-up survey to evaluate impacts of the study, and will be designed to best address preferences indicated by the study. For instance, farmers may prefer to engage in online educational efforts about reducing parasite risks, versus engaging in workshops. Farmers may be interested in using innovative methods, such as working with drone-based farm risk assessment to design livestock holding/pasture areas. The educational products of this study will impact the small ruminant farming community at the student level, such as 4H and FFA students, at the beginning farmer level via BFRN ( ), and at the practicing small farmer level via direct involvement. Information shared with the wildlife management community may also have the effect of informing policy about deer population management, and creating a bridge between the farmer and local/regional wildlife managers.

In the past year, several presentations and educational abstracts were produced related to this project. At the University of Maine’s Student Symposium, the presentations, “Risk management solutions for brainworm (Parelaphostrongylus tenuis) on farms with domestic livestock,” and , “Control of a Ruminant Pathogen, Parelaphostrongylus tenuis, Using Poultry: Effects of Gastropod Diets on Ducks,” were presented. In the University of Maine Cooperative Extensions newsletter “Cows and Crops,” the article, “Managing Pastures to Reduce Risk of Meningeal Worm ("Brainworm" or Parelaphostrongylus tenuis) Infection in Ruminants,” was included. The abstract and poster titled, “ Grazing with White-tailed Deer: Simple Solutions to Complex Problems,” was displayed at the 2020 Extension Risk Management Education National Conference and can be found on their website. In January 2021, the Everyday Farmers online conference included a presentation about ruminant health, including the threat of brainworm, the lifecycle of the worm, and potential ways of mitigation. 

We were unable to present at the online Maine Ag Trade Show in Jan. 2021, but plan to reach out to the MSBA and Maine goat organizations, as well as regional camelid organizations, to discuss the project.  An additional outreach to goat producers, whose animals are often at high risk of brainworm, is anticipated in spring and summer 2021.

Project Outcomes

2 Grants applied for that built upon this project
2 Grants received that built upon this project
$840.00 Dollar amount of grants received that built upon this project
5 New working collaborations
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.