Can ticks bite more than one host? Partial feeding explained.

Originally published by MedZulabs.org

How long does a tick typically feed?

An Ixodes scapularis tick engaging in questing, a host-seeking behavior. It attaches itself to a piece of grass with its third and fourth leg set while outstretching the first, waiting to grab and climb onto a host.

Hematophagous arthropods are those that feed on blood. This includes – but is not limited to – ticks, mosquitoes, and bedbugs. During their blood meal, mosquitoes and bedbugs are known to feed with interruption either between hosts or bites, respectively. On the other hand, most Ixodid ticks that people encounter attempt to feed continuously on a single host for 4-10 days depending on species and stage. Immature ticks (i.e., nymphs and larvae) prefer to feed to engorgement and molt into the next stage while adult female ticks engorge with the goal of converting the blood meal to eggs.

Why would a tick detach before its fully fed?

Though ticks usually prefer to complete their blood meal on the same host within a single feeding session, this is not always the case. Feeding may be interrupted for a number of reasons. The host may engage in natural anti-tick behaviors (e.g., grooming, shaking, scratching), the tick may drop off spontaneously, or the tick may detach due to host immune response, host death, or mating behaviors in males. If this detachment happens before the tick has taken enough of a blood meal, the tick may engage in host-seeking behavior again if it is able.

How successful are partially fed ticks at resuming their blood meal?

In a lab setting:

Beginning as early as 1912 and expanding in the 1960s (Tahir et al. 2020), there has been evidence for partially fed ticks successfully reattaching to a new host. Under laboratory conditions, Ixodes and Dermacentor ticks were shown to successfully reattach to a new host after careful removal from its initial host. After sixteen hours of uninterrupted feeding on an initial host, nine out of ten Ixodes scapularis nymphs successfully reattached to a new host. It is important to note that longer uninterrupted feeding times and higher chances of reaching critical mass on an initial host are associated with lower rates of successful attachment to a new host (Shih and Spielman 1993, Sonenshine and Roe 2013).

In nature:

Additional evidence from field observations indicates the ability of ticks to reattach. In some instances, two or more vertebrate hosts’ DNA was detected in field-collected adults and nymphs throughout Europe and the United States in Ixodes ricinus, Ixodes scapularis, and Amblyomma americanum. The presence of at least two individual hosts from different species or genera indicates ticks’ ability to feed from more than one host in the same life stage. The bacterium that causes Lyme disease has also been detected in I. ricinus larvae during active surveillance studies, further supporting the notion of partial feeding and reattachment. It is important to note the drawbacks of host-identification using a tick’s bloodmeal such as potential underreporting due to detection limitations (e.g., unable to differentiate multiple hosts from the same species or genera) and remnant DNA from the previous life stage’s bloodmeal (Leger et al. 2015).

The direct laboratory findings and indirect field observations indicate immature and mature ticks have the potential to detach from their host during feeding and successfully finish their blood meal on a separate host.

“What might prevent partially fed tick from reattaching to a new host?”

A tick that has detached from its host and not completed its bloodmeal may once more quest for a new host; however, questing for a new host does not always equate to successful re-attachment. By finding and successfully attacking to its initial host, the tick has already “beaten the odds” to a certain extent. Successful re-attachment to a second host requires the tick to face the same probability challenge, possibly with additional complicating due to physical damage or a hostile environment.

Even if a tick manages to find a second host, it may be physically unable to attach. In some cases, forced detachment may damage the parts of the tick (i.e., the hypostome) necessary for attachment and feeding, rendering it unable to reattach even if finding a second host. A dog may scratch at a tick with a hind leg and break the fragile hypostome; if the dog scratches the tick off while indoors, the climate-controlled house typically presents a poor environment for the tick to maintain hydration. On the other hand, if the dog is sitting in a lap or on a couch next to a human, the tick may be fortunate enough to be delivered to a ready (and unaware)

What risks do partially fed ticks pose if they do reattach?

The ability of a pathogen to be successfully transmitted from vector to host correlates with how long the attachment period lasts. A longer duration of tick attachment increases the probability of a tick-borne pathogen being transmitted. It has been proposed that pathogen transmission times are shortened when ticks detach during initial feeding then reattach to a new host and feed to completion. Shih and Spielman (1993) found a 100% transmission rate for I. scapularis nymphs infected with Lyme disease – Borrelia burgdorferi sensu lato (s.l) spirochetes – that were allowed to reattach and feed for 48 hours on a new host following an interrupted bloodmeal of at least a day. However, infected nymphs were able to transmit spirochetes to a new host only four out of five times within 24 hours of reattachment following a 24-hour uninterrupted feeding. In addition, following detachment from a Lyme-positive host after 24 hours of feeding, the initially uninfected nymphs were then able to transmit spirochetes successfully within three to five days intrastadially (i.e., within the nymphal life stage). Transmission efficiency is dependent on a tick’s ability to acquire spirochetes early in feeding – including the number of spirochetes acquired by the feeding tick from an infected host - and on its reattachment ability.

Full Citation

Leger, E., Liu, X., Masseglia, S., Noel, V., Vourc'h, Bonnet, S., McCoy, K. (2015). Reliability of molecular host-identification methods for ticks: an experimental in vitro study with Ixodes ricinus. Parasites & Vectors, 8, 433. https://doi.org/10.1186/s13071-015-1043-7.

Shih, C. & Spielman, A. (1993). Accelerated transmission of lyme disease spirochetes by partially fed vector ticks. Journal of Clinical Microbiology 31(11): 2878-2881. https://doi.org/10.1128/jcm.31.11.2878-2881.1993.

Sonenshine, D. & Roe, R. (2013) Biology of Ticks (2nd ed., Vol 1.). Oxford University Press.

Tahir, D., Meyer, L., Fourie, J., Jongejan, F., Mather, T., Choumet, V., Blagburn, B., Straubinger, R.K. & Varloud, M. (2020). Interrupted Blood Feeding in Ticks: Causes and Consequences.  Microorganisms, 8:910. https://doi.org/10.3390/microorganisms8060910.