. Primary HIV Infection

The risk of HIV transmission is largely dependent upon direct transfer of infected secretions (e.g. semen) or blood that include high copy numbers of HIV.
HIV is much less infective than many other viral infections such as hepatitis B.
Genital secretions and blood have the highest HIV copy numbers per ml and pose the greatest risk of transmission.
Breast milk also has high HIV copy numbers, and may be a potential source of transmission between mother and child, although the risk is lower compared to that associated with either genital secretions or blood.
Cerebrospinal fluid also contains high HIV copy numbers, but is unlikely to be the cause of HIV transmission.
Saliva, tears, sweat, urine or faeces have low copy numbers of HIV and pose a low risk of transmission.
HIV infection spreads rapidly from the point of inoculation and:
Many CD4 positive T-lymphocytes (T-helper cells) are infected.
Some macrophages become infected.
In the first few weeks there is massive HIV replication that results in:
A marked viraemia (e.g. 5000 infectious HIV particles per ml) at which stage:
The patient is highly infectious.
Antibodies against HIV have yet been formed, so an HIV test would be negative.
Dissemination of HIV infection throughout the lymphoid tissue and many other cell types.
As many as 250 billion cells may become infected at this time.
Within a few weeks a specific immune response against HIV controls the viraemia and copy numbers of HIV drop dramatically.
CD4 positive lymphocyte numbers, which have been reduced by HIV viral replication, return to normal.
Seroconversion occurs and antibodies against HIV antigens are produced for the first time, and persist thereafter.
Although the viraemia ends, HIV is not eliminated from the body.
The infectious risk to others diminishes with resolution of the viraemia, but is still present.
Clinical symptoms experienced during the primary phase of infection are extremely variable.
In many patients this phase is subclinical and they are free of symptoms.
Others, perhaps up to 50% experience a Glandular Fever-Like Syndrome.
During the acute phase the severity of symptoms varies from patient to patient.
There may be little more than a mild flu-like illness.
Symptoms may include
Sore throat.
Fever.
Lymphadenopathy (tender, enlarged lymph nodes).
General malaise.
Headache.
Muscle aching.
Erythematous rash involving the trunk.
Most of the symptoms subside in a few weeks
But, lymphadenopathy and general malaise do persist for several months in some patients.
A small proportion of patients become clinically immunocompromised at this stage (due to HIV replication killing large numbers of CD4 positive cells) and may present with:
Minor infections such as oral or vaginal thrush, or herpes.
AIDS-defining opportunistic infections such as oesophageal candidiasis or pneumocystis pneumonia.