Sexually transmitted diseases; types and treatment

 

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