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June 2

Drawing the lines in the Lyme disease battle

Angry patients question treatment — or lack of it — yet with tests often inconclusive, some doctors think the condition is overdiagnosed. And the split is widening.

Deer ticks that carry the bacteria Borrelia burgdorferi can infect people with Lyme disease. Most, but not all, people will develop a bull's-eye rash. Fever, headache, fatigue, muscle and joint aches can follow. Untreated, the infection can cause facial paralysis, heart palpitations, dizziness, other rashes, memory issues, and arthritis in large joints.
Life
cycle
Seasonal Activity
Relative sizes
Feeding method
Disease spread

Life cycle of deer ticks

A tick needs a blood meal to progress through each stage of its two-year life.

First year

May-June
Adult females lay eggs and die.
July-Oct.
Larvae hatch and seek a blood meal, typically on a small rodent or bird. Larvae are born disease free and acquire pathogens from an infected host.
Oct.-April
Larvae molt into nymphs, stay dormant over winter.
Females typically lay 2,000-3,000 eggs in leaf litter.
FIRST BLOOD MEAL
White-footed mice often carry the Lyme bacteria.

Second year

May-Sept.
Nymphs become active and try to grab hold of a passing person or animal. Ticks can detect hosts through odors, body heat, moisture, vibrations, and visual cues.
When infected nymphs feed, bacteria can migrate from tick to host; in most cases the tick must be attached for at least 36 hours to transmit pathogens. After feeding, nymphs drop off and molt into adults.
Sept.-Dec.
Females seek to feed once more before mating.
Jan.-Feb.
Adults remain active all winter on warm days.
Mar.-April
Adults that did not feed in the fall continue to seek a host.
SECOND BLOOD MEAL
Infected nymphs pass pathogens to humans.
THIRD BLOOD MEAL
A deer can carry a tick for miles.

SOURCES: TickEncounter.org; Kirby Stafford III, Connecticut Agricultural Experiment Station; US Centers for Disease Control and Prevention

David Butler/Globe Staff

Active months

The actual number of ticks present can vary from place to place and year to year.
Chart shows when each stage is most prevalent wherever deer ticks are found.
Adults: Possibly infected but large enough to be seen
Nymphs: Tiny and infected
Larvae: Possibly infected
Adults: Possibly infected but large enough to be seen
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
JAN
Most likely time to catch Lyme disease
SOURCE: Kirby Stafford III, Connecticut Agricultural Experiment Station

Relative sizes

Larvae
Nymph
Adult male
Adult female
Engorged female

Enlarged

Larvae
Nymph
Adult male
Adult female

SOURCES: TickEncounter.org; US Centers for Disease Control and Prevention

David Butler/Globe Staff

Feeding

Ticks can attach to any part of the human body but are often found in hard-to-see areas such as the groin, armpits, and scalp.
1.
The tick inserts its barbed feeding tube (right) through the outer layer of skin.
2.
The tick secretes a cement-like substance to stay firmly attached.
Detail of mouth parts
3.
Tick saliva contains an anesthetic property that keeps the host from feeling the bite.
4.
Pathogen can be exchanged when tick saliva and blood from the host mingle at the bite site.
5.
After feeding for several days, the tick drops off and molts into its next stage of life.

SOURCES: Kirby Stafford III, Connecticut Agricultural Experiment Station; US Centers for Disease Control and Prevention

David Butler/Globe Staff

Blood pool
Tick embedded in skin

Lyme disease cases in the United States

Each dot represents a confirmed case in the county where the patient lives.

1979

2001

2011

SOURCES: Allen C. Steere (1979); US Centers for Disease Control and Prevention (2001, 2011)

David Butler/Globe Staff

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