Encyclopedia of Health and Medicine

human ehrlichiosis 335
compromise the immune system, aggressive treatment
with a regimen called HAART (highly active
antiretroviral therapy), which combines three or
more medications taken daily, can delay the progression
of infection. Three factors influence the
decision to begin HAART:
• CD4 count (the number of CD4 T-lymphocytes
in the blood circulation) below 350 cells per
cubic millimeter (mm 3 )
• viral load (the number of copies of HIV in the
blood circulation) above 100,000 per milliliter
(ml)
• presence of symptoms or an AIDS-defining
clinical condition
Doctors wait to start HAART until these conditions
exist because the antiretroviral drugs have
potentially serious side effects, necessitating a
careful balance between benefit and risk, and
because once started, treatment is lifelong.
ANTIRETROVIRAL DRUGS TO TREAT HIV/AIDS (HAART)
Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs)
delavirdine efavirenz nevirapine
Nucleoside Reverse Transcriptase Inhibitors (NRTIs)
abacavir didanosine emtricitabine
lamivudine stavudine tenofovir
zalcitabine
zidovudine
Protease Inhibitors (PIs)
amprenavir atazanavir fosamprenavir
indinavir lopinavir nelfinavir
ritonavir saquinavir tipranavir
Fusion Inhibitors
enfuvirtide
Regular blood tests to monitor CD4 counts and
viral load determine how well a particular drug
combination is working. Because drug toxicity and
resistance are both problems with long-term
HAART, it is sometimes necessary to change regimens.
Risk Factors and Preventive Measures
Numerous risk factors exist for HIV/AIDS. Key
among them are
• unprotected vaginal intercourse, anal intercourse,
or oral sex
• multiple sexual partners
• intravenous drug use with shared needles
• infection with SEXUALLY TRANSMITTED DISEASES
(STDS) that have open sores, such as SYPHILIS and
GENITAL HERPES
• vaginal intercourse during MENSTRUATION
Use of condoms with all sexual activity reduces
the risk for spreading the virus but does entirely
prevent infection. Pregnant women who are HIVpositive
should discuss prophylactic treatment
during PREGNANCY and for the infant after birth.
See also ANTIBODY; ANTIBODY-MEDIATED IMMUNITY;
HIV/AIDS PREVENTION; SEXUAL HEALTH; SEXUALLY TRANS-
MITTED DISEASE (STD) PREVENTION.
human ehrlichiosis Any of several illnesses
resulting from INFECTION with various species of
Ehrlichia BACTERIA. Human ehrlichiosis infection
spreads via tick bites. The tick species and the
Ehrlichia species vary by geographic region.
Ehrlichia bacteria infect white BLOOD cells. The two
main forms of human ehrlichiosis in the United
States are human granulocytic ehrlichiosis (hGE),
in which the infection involves granulocytes (primarily
neutrophils), and human monocytic ehrlichiosis
(hME), in which the bacteria infect
monocytes and macrophages. hME is about twice
as common as hGE.
The INCUBATION PERIOD for human ehrlichiosis is
5 to 10 days, after which symptoms appear that
are flulike in nature. Symptoms may include
• FEVER
• HEADACHE and general sense of not feeling well
(malaise)
• JOINT PAIN and MUSCLE aches
• NAUSEA, VOMITING, and DIARRHEA
The diagnostic path includes blood tests to evaluate
blood cell counts. The bacteria are also apparent
with microscopic examination of a blood
sample. Ehrlichia bacteria are highly sensitive to
doxycycline, an antibiotic in the tetracycline family
of ANTIBIOTIC MEDICATIONS. Because blood test
results may take a week or longer, responsiveness