It is possible to get Lyme disease from a tick that is not engorged, but the risk is lower compared to an engorged tick. Ticks need to be attached for at least 36-48 hours before they can transmit Lyme disease. An unengorged tick has likely not been attached long enough to transmit Lyme bacteria. However, there is still a small risk of transmission even from an unengorged tick because the Lyme bacteria can be present in the tick’s saliva from the time it starts feeding.
What is Lyme Disease?
Lyme disease is an infectious disease caused by the bacterium Borrelia burgdorferi. It is transmitted to humans through the bite of infected ticks that carry the bacteria in their stomachs. Common symptoms of Lyme disease include fever, headache, fatigue and a characteristic skin rash called erythema migrans. If left untreated, the infection can spread to the joints, heart and nervous system. Lyme disease is diagnosed based on symptoms, physical findings and laboratory testing. It is treated with antibiotics, typically doxycycline, amoxicillin or cefuroxime axetil.
How is Lyme Disease Transmitted?
Lyme disease is transmitted through the bite of an infected tick. In the United States, the blacklegged tick (or deer tick, Ixodes scapularis) is the main vector responsible for Lyme transmission. Ticks get infected with Lyme bacteria when they feed on infected hosts, such as mice, deer and other small mammals. The bacteria live in the tick’s stomach. During the next feeding, the tick regurgitates the bacteria into the new host, infecting the host with Lyme disease.
Lyme Transmission Timeline
For a tick to transmit Lyme bacteria, it generally needs to be attached and feeding on the host for 36-48 hours. This allows time for the bacteria to migrate from the tick’s stomach to its salivary glands, where it can then be injected into the host through the tick’s saliva. The longer a tick is attached, the higher the risk of Lyme transmission.
Can an Unengorged Tick Transmit Lyme?
An unengorged tick is one that has not fed long enough to become noticeably swollen with blood. Since Lyme bacteria reside in the tick’s midgut or stomach, an unengorged tick has likely not been feeding long enough to pose a major risk of Lyme transmission.
However, there is still a small chance of getting Lyme disease from an unengorged tick for the following reasons:
While most Lyme bacteria are in the tick’s midgut, some bacteria can also be present in the salivary glands and saliva. When an infected tick starts feeding, it injects saliva containing Lyme bacteria into the host’s skin. So bacterial exposure starts once feeding starts, even before the tick becomes engorged.
Variable Transmission Time
While 48 hours of feeding is required on average for a tick to transmit Lyme, the exact time varies. Some studies have shown Lyme bacteria in unfed tick salivary glands, and transmission in less than 24 hours of tick attachment in animal models.
An unengorged tick may have actually fed for over 24 hours before being noticed and removed. Even if it does not appear engorged, partial prolonged feeding increases Lyme risk.
High Bacterial Load
Ticks with higher bacterial loads in their salivary glands can transmit Lyme faster. An unengorged tick with a high bacterial level has higher transmission potential than one with lower bacterial levels.
Likelihood of Transmission from an Unengorged Tick
While possible, transmission risk from an unengorged tick is still considered low. Studies estimate the risk to be approximately 1-3% from an unengorged tick, compared to 10-20% from a fully engorged nymphal tick. The longer a tick is attached, the higher the risk as more bacteria migrate to the salivary glands. An unengorged tick simply has not fed long enough to pose a major transmission threat.
One study exposed lab mice to Lyme-infected unengorged nymphal ticks for 4, 24 or 48 hours. Only mice exposed for at least 24 hours developed Lyme infections. Another study found no transmission from unengorged larval ticks after 72 hours of exposure. While these lab models do not perfectly replicate real-world conditions, they demonstrate the lower transmission risk from unengorged ticks.
If you find an attached tick that has not engorged, and are concerned about possible Lyme transmission, you can have the tick tested for Lyme bacteria. The tick can be sent to a lab where it is directly tested for Borrelia burgdorferi DNA through polymerase chain reaction (PCR) analysis. This can provide definitive evidence whether the tick carried Lyme bacteria or not.
Advantages of Tick Testing
– Provides definitive answer if the tick was infected or not
– May provide peace of mind if test is negative
– Helps guide treatment decisions if test is positive
Disadvantages of Tick Testing
– Does not guarantee you were not infected, since exposure can occur rapidly
– Can be expensive, often >$100 per tick test
– Results take time, 1-2 weeks, delaying potential treatment
Discuss tick testing options with your healthcare provider to determine if it makes sense in your situation.
Prevention of Lyme Disease
The best way to avoid Lyme disease is to prevent tick bites. Prevention strategies include:
Avoid Tick Habitats
Ticks reside in wooded, brushy or grassy habitats. Avoid such areas when possible or stay in the center of trails.
DEET, picaridin or oil of lemon eucalyptus repels ticks. Treat exposed skin and clothing.
Wear Protective Clothing
Wear long sleeves, long pants, hats and closed toe shoes when in tick areas. Tuck pants into socks.
Conduct Tick Checks
Check your whole body for ticks after being outdoors. Shower soon after coming inside.
Dogs and outdoor pets can bring ticks indoors. Use veterinarian recommended tick preventives.
Clear brush and leaf litter from lawn edges and create tick-safe zones.
While the risk of getting Lyme disease from an unengorged tick is low, around 1-3%, it is still possible in some cases. Ticks can transmit Lyme bacteria in their saliva when they first start feeding, before they become swollen with blood. However, an unengorged tick has likely not been attached long enough to pose a major Lyme threat. The longer a tick feeds, the higher the transmission risk. To definitively determine if an unengorged tick carried Lyme bacteria, you can have it tested through PCR analysis. The best prevention against Lyme is to avoid tick bites by using repellents, protective clothing and prompt tick removal.