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finish questions on the pdfThe diultion effect Page 1“The Dilution Effect” by Stein and Pardini NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE How Biodiversity Can Affect Human Health by  Claudia Stein and Eleanor A. Pardini Department of Biology Washington University in St. Louis, MO The Dilution Effect: Introduction Today you will learn information and examine data to piece together a fascinating story of how forest fragmentation  and biodiversity loss can seriously affect the risk of Lyme disease transmission to humans. Diseases can be transmitted  by biological vectors, such as mosquitos, flies, and ticks. Vectors feed on hosts, which can vary in their quality as a  reservoir (their probability of infecting a vector with a pathogen) and in their quality as a host (their probability that a  vector attempting a blood meal successfully feeds and survives). In the case of Lyme disease, ticks are the vectors that  carry the disease-causing bacterium.  Lyme disease is an infectious disease transmitted via  the bite of an infected tick. It is named after Lyme,  Connecticut, the town in the United States where  the first cases were described in 1975. It is the most  frequently reported vector borne disease in the United  States. In 2013 there were about 36,000 confirmed  or probable cases of Lyme disease. Symptoms of  Lyme disease include fever, headache, fatigue, and a  characteristic “bullseye” rash. Lyme disease is easily  treated with antibiotics soon after infection, but if left  untreated, infection can spread to the joints, heart, and  nervous system (CDC, 2015). Lyme disease in North  America is mainly caused by the spirochete bacterium  Borrelia burgdorferi that is vectored by the black-legged  tick (genus Ixodes). Larval ticks are born uninfected,  but by taking a blood meal from an infected host they  can become infected with the bacterium and transmit  the disease to other hosts including humans.  This case study consists of a figure set in which each  data figure represents one piece of a puzzle that will  fit together to tell the whole story. Different figures  will be assigned to different groups, so each group  will become an expert on one figure. After becoming  experts on the different figures, we will come together  as a class to share data and put the whole story together. The lifecycle of blacklegged ticks generally lasts two years and they go  through four life stages. After the eggs hatch, the ticks need a blood meal  at each stage of their life cycle to survive. Source: www.cdc.gov/lyme/ transmission/ blacklegged.html. http://www.cdc.gov/lyme/transmission/blacklegged.html NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE Page 2“The Dilution Effect” by Stein and Pardini Part I – Examine the Data Puzzle Pieces To work on your assigned figure, please follow the directions below:  • To begin, choose one spokesperson and one note-keeper in your group. Each group will be asked to explain  some element of your figure to the class during the class discussion. The spokesperson will share a brief  explanation of your study’s methods and your interpretation of the results with the class. • First, look at the figure on your own. Read through the figure legend to orient yourself to the study. Then orient  yourself to the graph (examine the parameters and scale on each axis, and the symbols). Then examine the  overall pattern in the result (i.e., the basic trend, shape, relative values). Then attempt to interpret the results  (i.e., determine how the pattern indicated in the results relates to the original hypothesis). • After each person in your group has finished doing this, carefully discuss each figure together and answer the  questions. Talk to make sure that each person truly understands the data, the axes, the symbols, the pattern, and  your interpretations.  • Now decide how to explain these graphs to other students who will not have seen them before. What confused  you at first? Show and explain these aspects. What are the most important points you need to make? Make sure  you can explain these clearly. Anticipate problems and questions other students may have.  References Allan B.F., Keesing F., and Ostfeld R. S. 2003 Effect of forest fragmentation on Lyme Disease Risk. Conservation Biology 17:267–272. CDC. 2015. Lyme Disease. The Centers for Disease Control and Prevention, 4 March 2015. Retrieved from http://www.cdc.gov/ lyme/ on July 7, 2015. Keesing, F., J. Brunner, S. Duerr, M. Killilea, K. LoGiudice, K. Schmidt, H. Vuong,  and R.S. Ostfeld. 2009. Hosts as ecological  traps for the vector of Lyme disease. Proc R Soc B 276, 3911–3919. Kremen C. and R.S. Ostfeld. 2005. A call to ecologists: measuring, analyzing, and managing ecosystem services. Front Ecol  Environ 3 (10), 540–548. Krohne, D.T. and G.A. Hoch. 1999. Demography of Peromyscus leucopus populations on habitat patches: the role of dispersal.  Canadian Journal of Zoology. 77: 1247–1253. LoGiudice, K., R.S. Ostfeld, K.A. Schmidt, and F. Keesing. 2003. The ecology of infectious disease: effects of host diversity and  community composition on Lyme disease risk. Proc. Natl Acad. Sci. USA 100, 567–571. Extra Resources • The Centers for Disease Control and Prevention (CDC) has a comprehensive site with information about Lyme disease  transmission and symptoms, preventing tick bites, tick removal, treatment, post-treatment Lyme disease syndrome, and  data on incidence: http://www.cdc.gov/lyme/ • Learn more about Lyme disease symptoms, tests, and treatments from Mayo Clinic:   http://www.mayoclinic.org/diseases-conditions/lyme-disease/basics/definition/con-20019701 • The National Science Foundation special report on ecology and evolution of infectious disease has a useful graphic  explaining how forest fragmentation is related to Lyme disease risk:  http://www.nsf.gov/news/special_reports/ecoinf/lyme.jsp • The National Science Foundation also has an article on “ten things you always wanted to know about ticks, but maybe were  afraid to ask” at: http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=131439  • Post-treatment Lyme disease syndrome (PTLDS) has been controversial. It is not directly relevant to the ecological concepts  presented in the case, but it is a subject that has increasingly been in the news media. There is some information about it on  the CDC site above. This news article from the Portland Press Hearld (June 29, 2015) discusses how Maine is dealing  with medical treatment of this syndrome:   http://www.pressherald.com/2015/06/29/maine-legislature-clears-way-for-long-term-lyme-disease-treatment/  • The New Yorker published an article (“The Lyme wars,” 2013) about the increasing Lyme disease infection rate and the battle  over how to treat it. Some of the authors of the scientific papers in this case study are interviewed. An interesting point  highlighted by Dr. Rick Ostfeld is that there are still many unknowns in this area of science, such as the impact of co- infections by multiple tick-borne pathogens, and the way to treat advanced Lyme disease.  http://www.newyorker.com/magazine/2013/07/01/the-lyme-wars http://www.cdc.gov/lyme/ http://www.cdc.gov/lyme/ http://www.mayoclinic.org/diseases-conditions/lyme-disease/basics/definition/con-20019701 http://www.nsf.gov/news/special_reports/ecoinf/lyme.jsp http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=131439 http://www.pressherald.com/2015/06/29/maine-legislature-clears-way-for-long-term-lyme-disease-treatment/ http://www.newyorker.com/magazine/2013/07/01/the-lyme-wars NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE “The Dilution Effect” by Stein and Pardini Figure 1 – Host Quality Larval ticks feed on a wide variety of vertebrate host species, including mammals, birds and reptiles. To determine if  species differ in their quality as a host, Keesing et al. (2009) captured individuals of six different host species in upstate  New York, USA and conducted a larval tick feeding experiment in the laboratory. After a 72-hour pre-test period, they  infected each individual with 100 larval ticks and then recorded how many ticks fed in a 96-hour period. Feeding  success of a tick is defined as a larval tick getting a blood meal from the host and surviving. Feeding success was  compared using ANOVA with host species as the treatment and individual hosts as replicates. Examine the data below. Questions 1. Does the feeding success of larval ticks differ among different host species? If yes, how? 2. What are possible reasons why feeding success could differ among host species? 3. Based on this information, what are options to minimize the abundance of larval ticks? Figure 1. The proportion of larval ticks that fed success- fully on six species that are common hosts for larval  blacklegged ticks in upstate New York, USA. Hosts were  captured in the field and held in the laboratory until  ticks naturally feeding on them had fed to repletion and  dropped off. Hosts were then reinfested with 100 larval  ticks and monitored to determine the proportion of  those ticks that fed successfully. Lowercase letters indicate  results that were significantly different (ANOVA; p

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NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
The Dilution Effect:
How Biodiversity Can Affect Human Health
by
Claudia Stein and Eleanor A. Pardini
Department of Biology
Washington University in St. Louis, MO
Introduction
Today you will learn information and examine data to piece together a fascinating story of how forest fragmentation and biodiversity loss can seriously affect the risk of Lyme disease transmission to humans. Diseases can be transmitted by biological vectors, such as mosquitos, flies, and ticks. Vectors feed on hosts, which can vary in their quality as a reservoir (their probability of infecting a vector with a pathogen) and in their quality as a host (their probability that a vector attempting a blood meal successfully feeds and survives). In the case of Lyme disease, ticks are the vectors that carry the disease-causing bacterium.
Lyme disease is an infectious disease transmitted via the bite of an infected tick. It is named after Lyme, Connecticut, the town in the United States where the first cases were described in 1975. It is the most frequently reported vector borne disease in the United States. In 2013 there were about 36,000 confirmed or probable cases of Lyme disease. Symptoms of Lyme disease include fever, headache, fatigue, and a characteristic “bullseye” rash. Lyme disease is easily treated with antibiotics soon after infection, but if left untreated, infection can spread to the joints, heart, and nervous system (CDC, 2015). Lyme disease in North America is mainly caused by the spirochete bacterium Borrelia burgdorferi that is vectored by the black-legged tick (genus Ixodes). Larval ticks are born uninfected, but by taking a blood meal from an infected host they can become infected with the bacterium and transmit the disease to other hosts including humans.
This case study consists of a figure set in which each data figure represents one piece of a puzzle that will fit together to tell the whole story. Different figures will be assigned to different groups, so each group will become an expert on one figure. After becoming experts on the different figures, we will come together as a class to share data and put the whole story together.
The lifecycle of blacklegged ticks generally lasts two years and they go through four life stages. After the eggs hatch, the ticks need a blood meal at each stage of their life cycle to survive. Source: www.cdc.gov/lyme/ transmission/ blacklegged.html.

The diultion effect Page 1“The Dilution Effect” by Stein and Pardini NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE How Biodiversity Can Affect Human Health by Claudia Stein and Eleanor A. Pardini...

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