Transmission time for Lyme Bacteria: how long does it take for ticks to infect a host?

Introduction to a debated topic

The length of time it take for most ticks to pass pathogens to a host has been debated for many years, due in large part to poor communication by public health officials and (justified) mistrust of those health officials by countless individuals affected by Lyme disease and other tick-borne illnesses. That poor communication stems from an effort to simplify a very messy topic into digestible and memorable guidelines for practitioners, but along the way extensive research has been flattened and nuance has been lost. As a result, many people and their doctors have been left with a false sense of security in the risk posed by a tick bite, and many tick-borne illnesses are likely going untreated in their earliest and most curable stages. In this post and those that follow (which we’ll link to as they are published) we will do our best to sort through what is known, what isn’t, and how doctors and patients can direct their investigations following a tick bite.

Note: Parenthetical citations (1) point to peer-reviewed research we recommend for further reading, and those sources are listed at the bottom of this post.

How do people contract Lyme disease?

Lyme disease is an illness caused by the bacterial pathogens Borrelia burgdorferi and, less commonly, Borrelia mayonii, Borrelia azfelii, and Borrelia garinii (1, 2). Borrelia species transmit via the bite of an infected tick, most commonly Ixodid ticks such as Ixodes scapularis and Ixodes pacificus in the United States, Ixodes ricinus in Europe, or Ixodes persulcatus and Ixodes granulatus in Asia (1). Human infection rates for Lyme disease are highest in Western Europe, Eastern Asia, Central Europe, and the northeast part of the United States, but Lyme can be contracted from a tick bite across a large portion of our planet (4, 5).

How long do ticks feed?

Most ticks that people encounter attempt to feed on a single host without interruption for 4-10 days depending on species and stage. Immature ticks (i.e., nymphal and larval) ticks will complete their feeding process faster than the larger and sexually mature adult stage. While nymphs and larvae feed in order to molt into the next stage, adult female ticks engorge to convert the bloodmeal to eggs; the resources needed to produce thousands of viable eggs are much greater than those needed for molting between life stages. Adult males do not engorge like their female counterparts and only feed upon necessity (e.g. when nutrients are required for reproduction).

How long does it take for a tick to transmit Lyme?

According to the Centers for Disease Control and Prevention (CDC):

“In most cases, a tick must be attached for 36 to 48 hours or more before the Lyme disease bacterium can be transmitted. If you remove a tick quickly (within 24 hours), you can greatly reduce your chances of getting Lyme disease.”

This isn’t the whole story and such phrasing leads to common misconceptions that can have serious consequences for our health. Common public health messaging takes highly complex processes and flattens them into short and hopefully memorable messages. Key phrases such as “in most cases” and “greatly reduce your chances” are often left out of the important takeaways, which can lead both patients and healthcare providers to believe a tick can only transmit Lyme disease if it has been attached for at least 36 hours and infection is certain after 48 hours. The reality is much more complex and varied, and a range of factors that researchers have already identified, as well as many others that we are still learning about, can change that timeline significantly.

What factors influence transmission times of Lyme bacteria?

The simple length of time a tick has been feeding is the most important factor to consider when gauging the risk of exposure to the causative agents of Lyme disease; however, there are other important factors to consider as well (6).

“Co-feeding":” feeding by multiple infected ticks at once

In some studies, rodents were shown to become infected with B. burgdorferi at a faster rate when they were bitten by multiple, simultaneously feeding nymphal ticks compared to just a singular nymph. The main mechanism at work here is neatly described by the adage “the dose makes the poison.” The more spirochetes that move from an infected tick to a host, the more likely there will be enough bacteria present to evade the host’s immune system and cause an infection. Multiple ticks each delivering a less-than-infectious volume of bacteria individually can add up to an adequate bacterial load to cause an infection.

Figure 1 and Table 1 below combine and condense results from several similar published studies that can be found in the citations below.

Figure 1. Figure 1 shows the transmission of B. burgdorferi by infected I. scapularis nymphs in relation to duration of hours attached (7-14). While the evidence shows B. burgdorferi can be transmitted within 24 hours, it is much more common for infection to result from longer feeding times. Also important to note is that even when ticks feed to repletion, transmission is not guaranteed and some bites from infected ticks may never cause infection in the host. As evident above, even when the infected nymphs were allowed to feed to completion, approximately 5% of rodents did not contract B. burgdorferi infection. The variation in successful Lyme transmission during tick feeding indicates there is no hard timeline for pathogen acquisition and even an extremely long feeding time by an infected tick should not be treated as a diagnosis of infection in and of itself.

Table 1.

Cumulative number of rodents contracting B. burgdorferi after exposure to a single or multiple, simultaneously feeding infected I. scapularis nymphs (7-14).

Tick life stage: differences in size and feeding between larvae, nymphs, and adults

As aforementioned, nymphs and larvae finish engorging sooner than the adults. In addition, they are much smaller and more abundant. As a result, nymphal ticks are believed to be the most likely to transmit Lyme as larvae rarely have the opportunity to acquire the causative agents of Lyme so early in their lifecycle while adults are more noticeable due to their size and thus more likely to be removed in the early stages of feeding (1, 15). While our own passive surveillance since 2006 through TickReport.com shows that adult stage ticks are no means found and removed immediately in all cases, it is certainly plausible that on average, immature ticks feed more often and for longer durations than adults before being removed.

Partial feeding on more than one host

It has also been proposed that pathogen transmission times could happen sooner after a bite if the tick as already partially fed on a different host. Shih and Spielman (1993) found that infected I. scapularis nymphs were able to transmit Lyme disease at a faster rate following reattachment to a new host even if feeding on an initial host for only 24 hours. In this situation, the Lyme spirochetes have had a head start in their migration from the midgut to the salivary glands and the tick is farther along in its feeding process and may need to dispose of excess waste sooner than it normally would.

It is important to note that while this risk has been tested in a lab environment, the likelihood of being bitten by a partially fed tick is quite low. Ticks that find a host to feed on have already “beaten the odds” once. Doing so again stretches their chances further. Early removal is also not usually by choice: in most cases these ticks are detached through grooming or scratching, a process that can easily cause irreparable damage to the tick so it cannot feed even if it finds another host.

Learn more from our earlier post on partial feeding and the risk it poses for us and those near us.

Variations in tick and pathogen species

Two more important factors to consider are the tick species and the specific strain and species of Borrelia. For example, instead of a 100% infection rate, only two-thirds of white mice were infected with B. mayonii by I. scapularis nymphs upon feeding to completion after four days (Figure 2, Table 2)(16, 17). On the other hand, I. ricinus nymphs were able to infect four out of six gerbils with one particular strain of B. burgdorferi within 18 hours (18).

Figure 2. Cumulative number of rodents contracting B. mayonii after exposure to a single or multiple, simultaneously feeding infected I. scapularis nymphs (16, 17).

Table 2.

Cumulative number of rodents contracting B. mayonii after exposure to a single or multiple, simultaneously feeding infected I. scapularis nymphs (16, 17).

Key Takeaways

The transmission of Lyme disease is a complex process influenced by various factors, which can sometimes lead to confusion in understanding how it spreads. Most importantly, even if all variables are accounted for, the likelihood of transmission is only based on averages. Outliers are certainly possible on both the shorter and longer ends of the feeding duration, so symptoms should always lead the way in diagnosis and treatment. It’s also important to note that the transmission times observed in these cited studies show whether or not a host was infected at the pre-determined sampling time. A study animal that was found to be infected after 72 hours of feeding may have acquired the infection at 60, 48, or even fewer hours of feeding, but the study design had predesignated that subject to be tested at 72 hours. More studies with a greater sample size, particularly focusing on shorter feeding times, will improve our statistics. At present, the trends in infection over time do allow reasonable inferences about the feeding times that are most likely to lead to infection.

So what can I do to learn about my risk of Lyme exposure?

Assessing the risk of exposure based on elements like feeding status can be challenging, especially given the fact that the exact attachment time is not always known. As such, we recommend a few tactics to minimize your risk of contracting Lyme disease. Starting with regular tick checks and appropriate outdoor attire can greatly reduce your chances of being bitten. When you discover a tick, it's crucial to place it in a clear bag, labeled with the removal date and any pertinent information, such as where it was found – both geographically and on the host’s body. This practice not only benefits the patient but also aids healthcare providers and tick-testing labs in the event of any potential tick-borne illness symptoms emerging in the future. We always recommend testing after a bite so that you can fully assess your risk of exposure and use that information to formulate treatment plans with your doctor. Arrange tick testing at TickReport.com or learn more about tick testing from one of our earlier blog posts here or here.

References

1. Centers for Disease Control and Prevention. (2023). Lyme Disease. Retrieved from https://www.cdc.gov/lyme/index.html.

2. Stone, B. L., Tourand, Y., & Brissette, C. A. (2017). Brave new worlds: the expanding universe of Lyme disease. Vector-borne and zoonotic diseases, 17(9):619-629. DOI: 10.1089/vbz.2017.2127

3. Johnston, D. Kelly, J., Ledizet, M., Lavoie, N., Smith, R., Parsonnet, J., Schwab, J., Stratidis, J., Espich, S., Lee, G., Maciejewski, K., Deng, Y., Majan, V., Zheng, H., Bonkoungou, S., Stevens, J., Kumar, S., Krause, P. (2022). Frequency and Geographic Distribution of Borrelia miyamotoi, borrelia burgdorferi, and Babesia microti Infections in New England Residents. Clinical Infectious Disease, ciac107. DOI:10.1093/cid/ciac107

4. Dong Y., Zhou G., Cao W., Xu, X., Zhang, Y., Ji, Z., Yang, J., Chen, J., Liu, M., Fan, Y., Kong, J., Wen, S., Li, B., Yue, P., Liu, A., Bao, F. (2022) Global seroprevalence and sociodemographic characteristics of Borrelia burgdorferi sensu lato in human populations: a systematic review and meta-analysis. BMJ Global Health;7:e007744. DOI:10.1136/bmjgh-2021-007744

5. Ji, Z., Jian, M., Yue, P., Cao, W., Xu, X., Zhang, Y., Pan, Y., Yang, J., Chen, J., Liu, M., Fan, Y., Su, X., Wen, S., Kong, J., Li, B., Dong, Y., Zhou, G., Liu, A., & Bao, F. (2022). Prevalence of Borrelia burgdorferi in Ixodidae Tick around Asia: A Systematic Review and Meta-Analysis. Pathogens, 11(2):143. DOI:10.3390/pathogens11020143

6. Eisen, L. (2018). Pathogen transmission in relation to duration of attachment by Ixodes scapularis ticks. Ticks and tick-borne diseases, 9(3):535-542. DOI: 10.1016/j.ttbdis.2018.01.002

7. Piesman, J., Mather, T., Sinsky, R., Spielman, A. (1987). Duration of tick attachment and Borrelia burgdorferi transmission. Journal of Clinical Microbiology, 25:557-558. DOI:10.1128/jcm.25.3.557-558.1987

8.  Des Vignes, F., Piesman, J., Hefferman, R., Schulze, T., Stafford, K., Fish, D. (2001). Effect of tick removal on transmission of Borrelia burgdorferia and Ehrlichia phagocytophila by Ixodes scapularis nymphs. Journal of Infectious Disease, 183:773-778. DOI: 10.1086/318818

9. Piesman, J. & Dolan, M. (2002). Protection against Lyme disease spirochete transmission provided by prompt removal of nymphal Ixodes scapularis (Acari: Ixodidae). Journal of Medical Entomology, 39:509-512 DOI:10.1603/0022-2585-39.3.509.

10. Hojgaard, A., Eisen, R., Piesman, J. (2008). Transmission dynamics of Borrelia burgdorferi s.s. during the key third day of feeding by nymphal Ixodes scapularis (Acari: Ixodidae). Journal of Medical Entomology, 45:732-736. DOI:10.1603/0022-2585(2008)45[732:TDOBBS]2.0.CO;2

11. Piesman, J. (1993). Dynamics of Borrelia burgdorferi transmission by nymphal Ixodes dammini ticks. Journal of Infectious Disease, 167:1082-1085. DOI:10.1093/infdis/167.5.1082

12. Shih, C. & Spielman, A. (1993). Accelerated transmission of Lyme disease spirochetes by partially fed vector ticks. Journal of Clinical Microbiology, 31:2878-2881. DOI:10.1128/jcm.31.11.2878-2881.1993

13. Ohnishi, J., Piesman, J., de Silva, A. (2001). Antigenic and genetic heterogeneity of Borrelia burgdorferi populations transmitted by ticks. Proc. National Academy of Science USA, 98:670-675. DOI:10.1073/pnas.98.2.670.

14. Piesman, J., Maupin, G. O., Campos, E. G., & Happ, C. M. (1991). Duration of adult female Ixodes dammini attachment and transmission of Borrelia burgdorferi, with description of a needle aspiration isolation method. Journal of Infectious Diseases, 163(4):895-897. DOI:10.1093/infdis/163.4.895

15. Ostfeld, R. S. (2011). An Overview of Tick-Borne Diseases. In Critical Needs and Gaps in Understanding Prevention, Amelioration, and Resolution of Lyme and Other Tick-Borne Diseases: The Short-Term and Long-Term Outcomes: Workshop Report (pp. 15-23). The National Academies Press. DOI:10.17226/13134.

16. Dolan, M., Hojgaard, A., Hoxmeier, J., Replogle, A., Respicio-Kingry, L., Sexton, C., Williams, M., Pritt, B., Schriefer, M., & Eisen, L. (2016). Vector competence of the blacklegged tick, Ixodes scapularis for the recently recognized Lyme borreliosis spirochete Candidatus Borrelia mayonii. Ticks and Tick-Borne Disease, 7:665-669. DOI:10.1016/j.ttbdis.2016.02.012.

17. Dolan, M., Breuner, N., Hojgaard, A., Boegler, K., Hoxmeier, J., Replogle, A., & Eisen, L. (2017). Transmission of the Lyme disease spirochete Borrelia mayonii in relation to duration of attachment by nymphal Ixodes scapularis (Acari: Ixodidae). Journal of Medical Entomology, 54:1360-1364. DOI:10.1093/jme/tjx089.

18. Kahl, O., Janetzki-Mittmann, C., Gray, J. S., Jonas, R., Stein, J., & de Boer, R. (1998). Risk of Infection with Borrelia burgdorferi sensu lato for a Host in Relation to the Duration of Nymphal Ixodes ricinus Feeding and the Method of Tick Removal. Zentralblatt Für Bakteriologie, 287(1-2):41–52. DOI:10.1016/s0934-8840(98)80142-4