types of this infection, caused by differ-
ent bacteria. The symptoms include
inflammation at the site of the bite and
in nearby lymph nodesand vessels,
bouts of fever, a rash, and, in one type,
painful joint inflammation. Treatment
for both types is with antibiotic drugs.
Rabies virus can be transmitted by the
bites of infected rats. Lassa fever, also a
viral disease, may be contracted from
the urine of rats in West Africa. Rats
also carry the viral infection lympho-
cytic chorio-meningitis, as well as the
bacterial infection tularaemia.
Raynaud’s diseaseA disorder of the
blood vessels in which exposure to cold
causes the small arteries supplying the
fingers and toes to contract suddenly.
This cuts off blood flow to the digits,
which become pale. The fingers are
more often affected than the toes. The
cause is unknown, but young women
are most commonly affected.
On exposure to cold, the digits turn
white due to lack of blood. As sluggish
blood flow returns, the digits become
blue; when they are warmed and normal
blood flow returns, they turn red. During
an attack, there is often tingling, numb-
ness, or a burning feeling in the affected
fingers or toes. In rare cases, the artery
walls gradually thicken, permanently
reducing blood flow. Eventually painful
ulceration or even gangrenemay devel-
op at the tips of the affected digits.
Diagnosis is made from the patient’s
history. Treatment involves keeping the
hands and feet as warm as possible.
Vasodilator drugsor calcium channel
blockersmay be helpful in severe cases.
(See also Raynaud’s phenomenon.)
Raynaud’s phenomenonA circulatory
disorder affecting the fingers and toes
that shares the mechanism, symptoms,
and signs of Raynaud’s diseasebut re-
sults from a known underlying disorder.
Possible causes include arterial diseases,
such as atherosclerosis; connective tissue
diseases, such as rheumatoid arthritis;
and various drugs, such as beta-blocker
drugs. The disorder is an occupational
disorder of people who use pneumatic
drills, chain saws, or vibrating machin-
ery; it is sometimes seen in typists,
pianists, and others whose fingers suffer
repeated trauma. Treatment is the same
as for Raynaud’s disease, along with
treatment of the underlying disorder.
reactive arthritisInflammation of the
joints due to an abnormal immune res-
ponse that occurs after an infection of
the genital tract, such as chlamydial
infection, or of the intestinal tract, such
as gastroenteritis. If there is additional
inflammation elsewhere in the body,
such as in the eyes, the condition is
known as Reiter’s syndrome.
reagentA term for any chemical sub-
stance that takes part in a chemical
reaction. The term usually refers to a
chemical or mixture of chemicals used
in chemical analysis or employed to
detect a biological substance.
reboxetineAn antidepressant drug that
blocks the reuptake of noradrenaline
(norepinephrine) within the nervous
system. Side effects include insomnia,
sweating, and dizziness on standing.
receding chinUnderdevelopment of the
lower jaw. The condition can be corrected
by the use of orthodontic appliances
used in the growth spurt at adolescence
or by cosmetic surgery.
receding gumsWithdrawal of the gums
from around the teeth, exposing part of
the roots. The teeth may be sensitive to
hot and cold substances, and the attach-
ment of the tooth in the socket may
weaken, causing the tooth to become
loose. Severe cases of receding gums
are usually a signs of gum disease (see
periodontitis; gingivitis).
receptorA general term for any sensory
nerve cell (one that converts stimuli
into nerve impulses). The term is also
used to refer to structures on the sur-
face of a cell that allow chemicals to
bind with the cell.
recessiveA term used in genetics to
describe one of the ways by which a gene
is passed from parent to offspring. Many
characteristics are determined by a sin-
gle pair of genes, 1 of each pair being
inherited from each parent. A recessive
gene is overridden by an equivalent dom-
inantgene. For example, the gene for
blue eye colour is recessive; therefore, if
a child inherits the gene for brown eyes
from 1 parent and the gene for blue
eyes from the other, the “blue eye” geneRAYNAUD’S DISEASE RECESSIVE
R