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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