Page 214 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 24 Spirochetes
203
suspected exposure, and serologic follow-up of infected
individuals and their contacts. The presence of any sexually
transmitted disease makes testing for syphilis mandatory,
because several different infections are often transmitted
simultaneously. There is no vaccine against syphilis.

2. Nonvenereal Treponematoses
These are infections caused by spirochetes that are virtually
indistinguishable from those caused by T. pallidum. They
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are endemic in populations and are transmitted by direct
contact. All these infections result in positive (nontrepone-
mal and treponemal) results on serologic tests for syphilis.
None of these spirochetes have been grown on bacterio-
logic media. The diseases include bejel in Africa, yaws
(caused by T. pallidum subspecies pertenue) in many humid
tropical countries, and pinta (caused by Treponema cara-
teum) in Central and South America. All can be cured by
penicillin.

BORRELIA

Borrelia species are irregular, loosely coiled spirochetes that
mebooksfree.com mebooksfree.com mebooksfree.com FIGURE 24–5 Ixodes tick. Nymph form of tick with head bur- mebooksfree.com
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stain readily with Giemsa and other stains. They can be
cultured in bacteriologic media containing serum or tissue
extracts. They are transmitted by arthropods. They cause
ied in skin surrounded by an erythematous macular rash. (Reproduced
two major diseases, Lyme disease and relapsing fever.
with permission from Wolff K, Johnson R. Fitzpatrick’s Color Atlas & Synopsis of Clinical
Dermatology. 6th ed. New York: McGraw-Hill, 2009. Copyright © 2009 by The
McGraw-Hill Companies, Inc.)
1. Borrelia burgdorferi
Disease
incidence of disease on the West Coast. The main reservoir
Borrelia burgdorferi causes Lyme disease (named after a
4
town in Connecticut). Lyme disease is also known as Lyme
white-footed mouse, upon which the nymphs feed.
borreliosis. Lyme disease is the most common tick-borne
Large mammals, especially deer, are an obligatory host
in the tick’s life cycle but are not an important reservoir of
disease in the United States. It is also the most common of the organism consists of small mammals, especially the
vector-borne disease in the United States. Approximately
the organism.
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20,000 cases each year are reported to the Centers for Dis-
The nymphal stage of the tick transmits the disease more
often than the adult and larval stages do. Nymphs feed pri-
ease Control and Prevention, and that number is thought to
be significantly less than the actual number.
of disease during the months of May to September.
Important Properties
The tick must feed for 24 to 48 hours to transmit an
infectious dose. This implies that inspecting the skin after
Borrelia burgdorferi is a flexible, motile spirochete that can
being exposed can prevent the disease. However, the
be visualized by dark field microscopy and by Giemsa and
nymphs are quite small and can easily be missed. There is
silver stains. It can be grown in certain bacteriologic media,
no human-to-human spread.
but routine cultures obtained from patients (e.g., blood,
The disease occurs worldwide. In the United States, three
spinal fluid) are typically negative. In contrast, culture of
regions are primarily affected: the states along the North
the organism from the tick vector is usually positive.
Atlantic seaboard, the northern midwestern states (e.g.,
Transmission & Epidemiology
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Approximately 80% of the reported cases occurred in four
Borrelia burgdorferi is transmitted by tick bite (Figures
states: New York, Connecticut, Pennsylvania, and New Jersey.
24–5 through 24–7). The tick Ixodes scapularis is the vector
on the East Coast and in the Midwest; Ixodes pacificus is
involved on the West Coast. The organism is found in a
4
In California, the wood rat is the main reservoir, and a second tick,
much higher percentage of I. scapularis (35%–50%) than I.
Ixodes neotomae, perpetuates the infection in the wood rat but does not
pacificus (approximately 2%) ticks. This explains the lower
transmit the infection to humans.
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