Larval ticks may be a threat after all ─ insights based on study of Borrelia miyamotoi
The tiny larval tick has never been considered a threat to humans. Experts had long believed that an adult female tick could not pass on any infections to the eggs and larvae. As a result, ticks in the larva stage were thought to be free from carrying diseases and therefore, harmless. But that may not necessarily be the case, according to a case series by Philip Molloy, MD and colleagues, published in the Annals of Internal Medicine. 
When ticks hatch from eggs, they’re called larva. At this stage, they have only six legs. After taking their first blood meal, the larvae molt into 8-legged nymphal ticks. Most studies have identified blacklegged ticks in the nymph stage as posing the greatest threat to humans. But Dr. Molloy now raises concerns that these newly hatched larvae, which are microscopic in size, may be just as dangerous.
While investigating the clinical spectrum and effectiveness of laboratory testing for Borrelia miyamotoi disease (BMD), one of the newer tick-borne infections, Dr. Molloy found that most cases occurred in July and August. These are the months when larvae ticks are most active, compared with nymphal ticks, which are most abundant in June and early July.
The timing of BMD peak incidence in Dr. Molloy’s case series suggests that infection might be transmitted by unfed larval ticks that acquired it by transovarial transmission from the infected female tick.
“Bites from larval deer ticks have not been considered a health threat, but this needs to be reevaluated,” writes Peter J. Krause, MD, from the Yale School of Public Health and Alan G. Barbour, MD, from the University of California – Irvine, in an accompanying editorial.
The authors also did not dismiss the possibility of acquiring Borrelia miyamotoi through blood transfusions. ”Human-to-human transmission by blood transfusion is theoretically possible, but a transfusion associated case has not been reported to date.”
How do we know if we are ill with BMD if we cannot detect a larval tick during a tick check? In the Molloy case series, BMD was clinically similar to human Anaplasmosis, including abnormal aminotransferase levels, leukopenia, and thrombocytopenia. The blood smear, PCR, and/or antibody determination used to diagnose BMD for the study are not available in most commercial laboratories.
Until reliable tests for BMD are available, physicians will need to diagnose the disease based on a patient’s clinical presentations. Unfortunately, symptoms are similar to other tick borne diseases and acute viral infections, and can include fever, fatigue and headaches.
Read more about the need for laboratory developed tests to assist in diagnosing emerging tick borne diseases, like Borrelia miyamotoi. “Where is the FDA test for relapsing fever spirochete, Borrelia miyamotoi?”
Dr. Molloy writes, “a patient presenting with an acute ‘summer fever’ and no rash and testing positive by the whole cell antigen serologic test for Lyme disease could actually be infected with Borrelia burgdorferi, Borrelia miyamotoi, or both.”
A clinical diagnosis is tough when we do not know the full spectrum of the disease. The Molloy study only included patients who were treated acutely. The case series definition was limited to patients “who were acutely symptomatic with features or, whose laboratory findings were suggestive of a possible tick borne infection (typically fever, myalgia, flu-like illness, headache, or rash).”
“Larval transmission of Borrelia miyamotoi has implications for checking for ticks and
continuing tick precautions even after the risk of Lyme disease has abated.”
— Peter Krause, MD, Yale University School of Public Health
The outcome of treatments remains uncertain when recommendations are made based on acute cases. Doxycycline or other tetracyclines, amoxicillin, or cefuroxime were effective based on a few case reports and a case series of acute cases. Zithromax was also presumed to be effective. The study was not designed to assess the long-term outcome of individuals with BMD who are treated acutely or those who are not.
Dr. Krause points out the importance of monitoring emerging infections, such as Borrelia miyamotoi. “On the basis of the current report and previous data, the frequency of Borrelia miyamotoi infection seems to be similar to that of Anaplasma phagocytophilum and Babesia microti.”
- Molloy PJ, Telford Iii SR, Chowdri HR et al. Borrelia miyamotoi Disease in the Northeastern United States: A Case Series. Ann Intern Med, (2015).
- Krause PJ, Fish D, Narasimhan S, Barbour AG. Borrelia miyamotoi infection in nature and in humans. Clin Microbiol Infect, (2015).
People talk as of larval ticks are microscopic….well magnification is needed to identify them morphologically but they are definitely visible on the body with the naked eye…but you have to be looking quite closely. If you see a red area with a black spot in the center it may well be a larval tick embedded. You will need the finest pointed tweezers to remove it. I have also considered just excising the tissue it is on.
Thanks for your insight.
Driving back from a hike last Friday (I was in northeast Mississippi), I found a horde of seed ticks traveling up my leg. We pulled over and I removed as many as I could see, pulled off my clothes, and when I got home I showered and scrubbed as best I could. On the drive home I kept finding them crawling up my leg—they are so small and they don’t come off easily! Now, six days later, I have found four (what I believe to be) tick bites on my left leg. Initially I was not concerned about Lyme disease because most of the literature says larval ticks don’t have the bacteria in them as later-stage ticks do. After reading this article though, I am concerned. What should I do?
Not every tick leads to an illness. I advise my patients to be evaluated particularly if they have symptoms within 2 months of the bite.
Conclusions were based on data collected at the Cary Institute of Ecosystem Studies. The 2,000-acre research campus sits at an epicenter for tick-borne disease. Ecologist Dr. Richard Ostfeld says that nearly two decades of data revealed climate warming trends correlated with earlier spring feeding by nymphal ticks, sometimes by as much as three weeks. If this persists, Ostfeld says we will need to move Lyme Disease Awareness Month from May to April.
Late this morning I spotted some blood near the top base of my thumb. It resembled a small cut but I could not recall cutting myself. After lunch, with the blood somewhat washed off, I looked at the cut area with a magnifying glass. It looked as if there were tiny dots in the wound. I took out my tick kit with description leaflet and there I found the larva picture. Looked similar. I used the tweezer with attached magnifier and tried to pick off the five to
Eight tiny specks which I wondered were larva. I had never seen such a thing! I collected them with a damp tissue from off the small table where I had been working in the sunlight and threw tissue in toilet. I poured rubbing alcohol On the area of my hand, covered it with a tiny bandaid, and will keep an eye on the spot.
I then looked up deer tick larva on Internet and read your article with interest. Have had many tick encounters over
Larval ticks are even smaller than nymphal tick. Most people don’t see them. Most larval ticks are not infected but there are exceptions particularly co-infections. Call the office at 914 666 4665 if you have any questions.
I think that transovarial transmission was shown in tick-borne Anaplasma marginale a few years back. I worked as a grad student with the USDA Hemoparasitic Research Group in southern Idaho in the early 1980s. Then we did not have the tools we do now but I drop in on literature now and again on the issue and find stuff out. I had fun studying the life cycle of the ticks in the area by trapping rodents in two 144 trap grids over a spring season and counting the larval, nymph and adult ticks in the area over time and rodent species caught.