Tick Talk 2015

By Ann A. Kiessling, PhD

TT-1Tick season is in full swing for 2015 and New England is the hottest spot in the country for tick-borne diseases.  The big questions:  How do we estimate the risk of infection of Bedford residents?  How do we reduce that risk to the much lower levels of the 1980’s?

Tick-borne diseases are estimated to be under-reported by a factor of 10, according to the Special Commission to study Lyme Disease in Massachusetts.  The under-reporting is due to lack of good surveillance methods because persons with symptoms of a tick-borne disease are usually prescribed medication before they actually test positive for the infection. Read the Lyme Disease Commission’s Final Report of 28 Feb 2013.

Middlesex Tick Task Force

Another surveillance method to attempt to determine disease risk is to analyze tick populations for the presence of the organisms that cause disease.  The Middlesex Tick Task Force, a group of public health staff members and residents from 32 Massachusetts towns, including Acton, Bedford, Carlisle, Concord, Lexington, Lincoln and Waltham was formed in September, 2012, to confront the serious public health issue posed by tick-borne diseases.

The group, headed up by Heidi Porter of the Bedford Board of Health, received a $111,000 Community Innovation Challenge Grant that provided free testing of approximately 100 ticks in each of the 32 towns last summer.

Click chart to enlarge it for easier reading
Click chart to enlarge it for easier reading

The Middlesex Tick Task Force took advantage of an existing tick testing program in the Laboratory of Medical Zoology at the University of Massachusetts Amherst (https://www.tickdiseases.org/medical-zoology/cic/) directed by Dr. Stephen Rich.   The Laboratory of Medical Zoology began testing ticks submitted from all over the country for 11 tick borne diseases in 2006.

In the first four years of testing, 2006 through 2009  (https://www.tickreport.com/stats/search_results), 886 ticks from Massachusetts were tested, with 29% testing positive for Borrelia burgdorferi (Lyme Disease), 4.5% testing positive for Anaplasma phagocytophilum (anaplasmosis), and 1.9% testing positive for Babesia microti (babesiosis).   In the next five years (2010 through 2014), 5,655 ticks were tested, with 31% testing positive for B burgdorferi, 4.3% positive for A phagocytophilum, and 4.5% testing positive for B microti.   Many ticks test positive for more than one organism.

In 2014, when the Tick Task Force testing program was in effect, 100 ticks from Bedford were tested, 33% were positive for B burgdorferi, 2% were positive for A phagocytophilum, 2%  were positive for B microti, and14% tested positive for another Borrelia species, B miyamotoi.

In the same time period, 179 ticks were submitted by Carlisle residents:  52% tested positive for B burgdorferi, 7% were positive for A phagocytophilum, 9% were positive for B microti, and none were positive for B miyamotoi.

Lincoln submitted 113 ticks: 40% tested positive for B burgdorferi, 3% positive for A phagocytophilum, 9% positive for B microti and 38% of those tested for B miyamotoi were positive.

Concord residents submitted 176 ticks for testing: 35% tested positive for B burgdorferi, 3.6% positive for A phagocytophilum, 4% positive for B microti, and 12% were positive for B miyamotoi.

Country-wide, from 2013, 7% of ticks have tested positive for B miyamotoi, a newly described cousin to the Lyme disease agent B Burgdorferi, that causes a different type of infection without the characteristic “bulls-eye” wheel.

Do tick surveillance numbers relate to disease in humans? No.

But tick surveillance numbers don’t relate directly to disease in humans bitten by ticks because, although the infectious agents reside in the salivary glands of ticks, and can be detected by sensitive lab methods, they are not present in sufficient amounts to transmit disease until the ticks have had a warm blood meal.  The warmth allows the infectious agents to multiply, and finally enter the blood stream of the host being bitten.  According to a report from Israel (New England Journal of Medicine, 2006), this takes at least 24 to 48 hours of attachment by the tick infected with B burgdorferi.  The same report illustrated that one or two doses of doxycycline prevented Lyme disease if taken within 48 to 96 hours of tick attachment.

Caption
Anaplasma phagocytophilum

Anaplasma phagocytophilum causes anaplasmosis, previously termed human granulocytic ehrlichiosis because it infects one type of human white blood cell and can change its appearance.  Skin rash is rare with anaplasmosis; symptoms (fever, headache, muscle ache, fatigue) usually appear about two weeks after infection by tick bite.  According to the Centers for Disease Control, “The diagnosis of anaplasmosis must be made based on clinical signs and symptoms and can later be confirmed using specialized confirmatory laboratory tests.  Treatment should never be delayed pending the receipt of laboratory test results, or be withheld on the basis of an initial negative laboratory result.”  Standard treatment is two weeks of doxycycline. https://www.cdc.gov/anaplasmosis/symptoms/index.html

TT-3Babesia microti is a tiny parasite that infects red blood cells and may cause no symptoms, and therefore infection may go unnoticed.   Babesiosis has become the Number One blood transfusion transmitted disease in the U. S. today.

Infected mice are the intermediate host that infects the deer tick, probably in the nymph stage when they are so small (about the size of a poppy seed) they are difficult to see.   Effective treatments are available if the infected person is symptomatic.

Although tick researchers in the U.S. have known about B Miyamotoi infections since 2001 in the same tick species that transmit Lyme disease, the first report of human infection was in Russia in 2011, with three identified in the U.S. in 2013.  The symptoms are fever, chills and muscle aches, and the infection is successfully treated by two weeks of the doxycycline.   https://www.cdc.gov/ticks/miyamotoi.html

This information presents a conundrum for health care providers because of the current concern about the over-use of antibiotics, many health care providers are reluctant to prescribe doxycycline in the absence of the characteristic rash (“erythema migrans”) or other symptoms commonly associated with tick-borne diseases.

These considerations highlight the obvious importance of minimizing the risk of tick-borne diseases, through protective measures, and by reducing the numbers of tick hosts, such as deer.

Caption
Life cycle of a deer tick

The life cycle of Ixodes scapularis, the deer tick that carries these four diseases spans two years.  The animal host for the first year, the nymph stage, is the field mouse.  The animal host for the second year, the egg-laying year, is the deer.  The highest incidence of infection in Massachusetts is now, June and July, principally by being bitten by the tiny nymph.  The marked increase in the deer population, secondary to the reversion of farm land to forests in Massachusetts, has led to the marked increase in hosts for the egg-laying stage of the larger, adult ticks. The deer blood meal supports the laying of millions of fertilized eggs by the adult I. scapularis, that winter-over, becoming larvae the following spring, which again winter over, becoming nymphs the following spring that feed on infected field mice and humans.

 

What to do to avoid tick bites

All tick experts agree:

  1. Deer populations need to be controlled
  2. Tick control on mouse populations needs to be included
  3. The use of DEET (a deterrent, but not a pesticide) and pymethrin (a pesticide) on clothing and in mouse nests, careful body searches after exploring leafy forests and grassy meadows, and consultation with your health care provider after tick removal are all personal protective measures that will diminish the risks of acquiring a tick borne disease.

Some thoughts on controlling the tick population

Some Massachusetts communities are attempting to reduce tick populations by reducing deer populations in accordance with prior reports of success in Massachusetts (Telford SR, 1993).   The Dover Board of Health formed a Lyme Disease Committee that implemented a controlled deer reduction program that involved 58 qualified bow hunters in 2012 and was based on Massachusetts Wildlife experience and guidance.  The impact of the program on tick and Lyme disease incidence is under study.   2012 DMP Dover MA Hunting Report

Placing pymethrin-soaked cotton balls in small cardboard tubes (e.g. toilet paper roll tubes) near mouse habitats has been reported to reduce tick populations in mouse hosts.

Ticks die when dehydrated which is why they are found in damp leaf litter and tall grassy areas.  Removing such areas from backyards, and using DEET when walking in damp woodsy areas will reduce risk of picking up ticks.  Remembering that the nymph is tiny, the size of a poppy seed, when doing a body search may reveal more ticks.

New pymethrin-coated clothing – Insect Shield — is a recent advance in tick avoidance that claims to reduce the threat of tick-borne infections.   https://www.insectshield.com/ourTechnology/


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