SEXUALLY TRANSMITTED
VIRAL INFECTIONS
Herpes simplex
Genital herpes simplex transmission is usually sexual (vaginal,
anal,
orogenital or oro–anal), but perinatal infection of the neonate
may
also occur.
Human
papillomavirus (HPV)
Of the many subtypes of human papillomavirus (HPV), genotypes
6, 11, 16 and 18 most commonly infect the genital tract through
sexual transmission.
Genotypes HPV-6 and 11 cause benign anogenital warts.
Genotypes such as 16 and 18 are associated with dysplastic
conditions
and cancers, but not benign warts. Anogenital warts are the
result of HPV-driven hyperplasia and usually develop after an
incubation
period of between 3 mths and 2 yrs. Local treatment with
cryotherapy or podophyllotoxin may help, and condoms offer some
protection. Vaccines are highly effective in preventing cervical
neoplasia
and are in routine use in several countries.
HUMAN IMMUNODEFICIENCY
VIRUS INFECTION
The acquired immunodeficiency syndrome (AIDS) is caused by the
human immunodeficiency virus (HIV-1) and was first recognised in
1981. HIV-2 causes a similar but less aggressive illness occurring
mainly in West Africa. AIDS has become the second leading cause
of disease worldwide and the leading cause of death in Africa
(causing > 20% of deaths). Immune deficiency
arises from continuous
HIV replication leading to virus- and immune-mediated destruction
of CD4
lymphocytes.
Global epidemic and regional patterns
In 2011, the WHO estimated that there were 34.2 million people
living with HIV/AIDS, 2.5 million new infections and 1.7 million
deaths. Globally, new infections have declined by 20% in the past
10 yrs, although incidence is still increasing in Eastern Europe,
Central Asia, the Middle East and North Africa particularly in
injection
drug-users. Expansion of access to combination antiretroviral
therapy (ART) has resulted in improved life expectancy and a 24%
decline in global AIDS-related deaths since 2005. Despite this,
HIV
remains important and has caused over 30 million deaths since the
start of the epidemic.
HIV is transmitted:
● By sexual contact.
● By exposure to blood or blood products (e.g.
drug users, patients with haemophilia or occupationally in
healthcare
workers).
● Vertically from mother to child
in utero, during birth
or by breastfeeding.
In the Americas and Western Europe, the epidemic has until
now predominantly affected men who have sex with men (MSM),
whereas in Eastern Europe, Central Asia, the Middle East and Southeast
Asia, IV drug use also causes many infections. In sub-Saharan
Africa, the Caribbean and Oceania, most transmission is
heterosexual.
Worldwide, the major route of transmission is heterosexual.
A high proportion of patients with haemophilia had been infected
through contaminated blood products by the time HIV antibody
screening was adopted in the USA and Europe in 1985. Screening
of blood products has virtually eliminated these as a mode of
transmission in developed countries; however, the WHO estimates
that 5–10% of blood transfusions globally are with HIV-infected
blood.
Virology and immunology
HIV is an enveloped RNA retrovirus of the lentivirus family. The
different stages of the viral replication process offer
opportunities
for drug therapy. A small percentage of T-helper lymphocytes
enter a post-integration latent phase and represent sanctuary
sites from antiretroviral drugs, which only act on replicating
virus. This prevents current ART from eradicating HIV. Latently
infected CD4 cells also evade CD8 cytotoxic T lymphocytes.
Diagnosis and initial testing
HIV infection is detected by testing for host antibodies; most
tests
are sensitive to antibodies to both HIV-1 and HIV-2. Global trends
are towards more widespread testing. Counselling is essential both
before testing and after the result is obtained.
Following diagnosis, the CD4 lymphocyte count should be
determined.
This indicates the degree of immune suppression and is used
to guide treatment. Counts between 200 and 500/mm3 have a low risk
of major opportunistic infection; below 200/mm3 there is a high
risk of AIDS-defining conditions. Quantitative PCR of HIV-RNA,
known as viral load, is used to monitor the response to ART.
Natural history and classification of HIV
Primary infection
Primary infection is symptomatic in > 50% of cases and usually
occurs 2–4 wks after exposure. The major clinical manifestations
resemble
infectious mononucleosis:
● Fever.
● Pharyngitis with lymphadenopathy.
● Myalgia/arthralgia.
● Headache.
● Diarrhoea.
● Mucosal ulceration.
● Oral and genital ulceration.
The presence of a maculopapular
rash or mucosal ulceration suggests
HIV rather than the other causes
of infectious mononucleosis.
Lymphopenia with oropharyngeal
candidiasis may occur. Symptomatic
recovery normally takes 1–2 wks
but may take up to 10 wks,
and parallels the return of the
CD4 count and the fall in viral load.
In many patients the illness is
mild and is only identified by retrospective
enquiry.
Diagnosis is made by detecting
HIV-RNA in the serum by PCR,
as antibody tests may be negative
in the early stages. The differential
diagnosis includes:
● Acute Epstein–Barr virus.
● Cytomegalovirus.
● Streptococcal pharyngitis.
● Toxoplasmosis.
● Secondary syphilis.
Asymptomatic infection
This lasts for a variable period,
during which the infected individual
remains well with no evidence of
disease, except for persistent generalised
lymphadenopathy (defined as
enlarged glands at ≥2
extrainguinal
sites). Viraemia peaks during
this phase and high viral
loads predict a more rapid rate
of decline in CD4 count .
The median time from infection to
development of AIDS in adults
is 9 yrs
AIDS-defining diseases
• Oesophageal candidiasis
• Chronic cryptosporidial diarrhoea
• Chronic mucocutaneous herpes simplex
• Pulmonary or extrapulmonary TB
• Progressive multifocal leucoencephalopathy
• Recurrent non-typhi Salmonella septicaemia
• Invasive cervical cancer
• Kaposi’s sarcoma
• HIV-associated wasting
• Primary cerebral lymphoma
• Cryptococcal meningitis
• Cytomegalovirus (CMV) retinitis or colitis
• Pneumocystis
jirovecii pneumonia (PJP)
• Disseminated Mycobacterium avium intracellulare (MAI)
• Cerebral toxoplasmosis
• Extrapulmonary coccidioidomycosis
• Extrapulmonary histoplasmosis
• Non-Hodgkin’s lymphoma
•
HIV-associated dementia
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