Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in the inset, among red blood cells), which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term if not treated.
Why is Lyme disease on the rise in eastern North America?
Newly hatched ticks do not harbor B. burgdorferi. Rather, they pick it up from certain hosts that are reservoirs of the bacterium. When a larval tick crawls onto a host, it may get groomed off and killed by the host, or it may feed successfully, in which case it may or may not then become infected with B. burgdorferi. Felicia Keesing and others measured the rate of tick feeding and infection on different hosts.
What percentage of ticks on mice were infected with B. burgdorferi? What percentage of ticks on opossums were groomed off and killed?

Verified step by step guidance

1. Examine the graph provided. The y-axis represents the proportion of larval ticks that fed, while the x-axis lists the host species. The graph is divided into two categories: ticks infected with Borrelia burgdorferi (red bars) and ticks not infected (blue bars).
2. To determine the percentage of ticks on mice infected with Borrelia burgdorferi, focus on the red bar for the white-footed mouse. Note the proportion value of the red bar and multiply it by 100 to convert it into a percentage.
3. To determine the percentage of ticks on opossums that were groomed off and killed, consider the proportion of ticks that did not feed successfully. Since the graph only shows ticks that fed, subtract the total proportion of ticks that fed (sum of red and blue bars for opossums) from 1. Multiply this value by 100 to convert it into a percentage.
4. Ensure you account for any error bars in the graph when interpreting the data. Error bars indicate variability in the measurements, so the exact values may slightly vary within the range shown.
5. Summarize the findings by stating the calculated percentages for ticks infected on mice and ticks groomed off on opossums, based on the graph data.

Key Concepts

Lyme Disease Transmission

Lyme disease is primarily transmitted to humans through the bite of infected ticks, specifically the Ixodes scapularis species. The ticks acquire the bacterium Borrelia burgdorferi from feeding on infected hosts, which serve as reservoirs. Understanding this transmission cycle is crucial for grasping why Lyme disease is prevalent in certain areas, particularly where these ticks and their hosts are abundant.

Reservoir Hosts

Reservoir hosts are species that harbor pathogens without suffering from the disease themselves, allowing the pathogen to persist in the environment. In the case of Lyme disease, small mammals like mice are significant reservoirs for Borrelia burgdorferi. The interaction between ticks and these hosts is vital for the spread of Lyme disease, as ticks become infected when they feed on these animals.

Tick Grooming Behavior

Grooming behavior in host animals can significantly impact tick populations and the transmission of Lyme disease. Hosts like opossums are known to groom off and kill ticks, reducing the number of ticks that can become infected and subsequently transmit the bacterium. Understanding the dynamics of tick grooming helps explain variations in infection rates among different host species and the overall rise of Lyme disease in certain regions.