HIV superinfection (also called HIV reinfection) is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. The HIV superinfection strain (a recombinant strain) appears when a person becomes simultaneously infected by two different strains, allowing the two viruses to exchange genetic material, resulting in a new unique strain that can possess the resistances of both previous strains. This new strain co-exists with the two prior strains and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.

People with HIV risk superinfection by the same actions that would place a non-infected person at risk of acquiring HIV. These include sharing needles and forgoing condoms with HIV-positive sexual partners. For many years superinfection was thought to occur mainly in high-risk populations. Research from Uganda published in 2012 indicates that HIV superinfection among HIV-infected individuals within a general population remains unknown. Further research from "The Journal of Infectious Diseases" indicates that there have been 16 documented cases of superinfection since 2002.

The initial period following the contraction of HIV is called acute HIV, primary HIV or acute retroviral syndrome. Many individuals develop an influenza-like illness or a mononucleosis-like illness 2–4 weeks post exposure while others have no significant symptoms. Symptoms occur in 40–90% of cases and most commonly include fever, large tender lymph nodes, throat inflammation, a rash, headache, and/or sores of the mouth and genitals. The rash, which occurs in 20–50% of cases, presents itself on the trunk and is maculopapular, classically. Some people also develop opportunistic infections at this stage. Gastrointestinal symptoms, such as vomiting or diarrhea may occur. Neurological symptoms of peripheral neuropathy or Guillain–Barré syndrome also occurs. The duration of the symptoms varies, but is usually one or two weeks.

Due to their nonspecific character, these symptoms are not often recognized as signs of HIV infection. Even cases that do get seen by a family doctor or a hospital are often misdiagnosed as one of the many common infectious diseases with overlapping symptoms. Thus, it is recommended that HIV be considered in people presenting an unexplained fever who may have risk factors for the infection.

There are three main stages of HIV infection: acute infection, clinical latency and AIDS.

The co-epidemic of tuberculosis (TB) and human immunodeficiency virus (HIV) is one of the major global health challenges in the present time. The World Health Organization (WHO) reports 9.2 million new cases of TB in 2006 of whom 7.7% were HIV-infected. Tuberculosis is the most common contagious infection in HIV-Immunocompromised patients leading to death. These both diseases become dreadful in combination as HIV declines the human immunity while tuberculosis becomes progressive due to defective immune system.This condition becomes more severe in case of multi-drug (MDRTB) and extensively drug resistant TB (XDRTB), which are difficult to treat and contribute to increased mortality. See Multi-drug-resistant tuberculosis. Tuberculosis can occur at any stage of HIV infection. The risk and severity of tuberculosis increases soon after infection with HIV. A study on gold miners of South Africa revealed that the risk of TB was doubled during the first year after HIV seroconversion. Although tuberculosis can be a relatively early manifestation of HIV infection, it is important to note that the risk of tuberculosis progresses as the CD4 cell count decreases along with the progression of HIV infection. The risk of TB generally remains high in HIV-infected patients above the background risk of the general population even with effective immune reconstitution with ART maintaining high CD4 cell counts.

Characteristics of a viral infection can include pain, swelling, redness, impaired function, fever, drowsiness, confusion and convulsions.

The most common diseases caused by chronic viral infections are subacute-sclerosing panencephalitis, progressive multifocal leukoencephalopathy, retrovirus disease and spongiform encephalopathies.

A Transfusion transmitted infection (TTI) is a virus, parasite, or other potential pathogen that can be transmitted in donated blood through a transfusion to a recipient. The term is usually limited to known pathogens, but also sometimes includes agents such as Simian foamy virus which are not known to cause disease.

Preventing the spread of these diseases by blood transfusion is addressed in several ways. In many cases, the blood is tested for the pathogen, sometimes with several different methodologies. Donors of blood are also screened for signs and symptoms of disease and for activities that might put them at risk for infection. If a local supply is not safe, blood may be imported from other areas. Human immunodeficiency virus (HIV) leads to the best known of the transfusion transmitted diseases, acquired immune deficiency syndrome (AIDS).

Blood that is processed into medications by fractionation is treated in a multi-step process called pathogen inactivation that is analogous to pasteurization: it destroys most viruses and bacteria in the blood. Donors are still screened and tested.

The signs and symptoms of a vertically transmitted infection depend on the individual pathogen. It may cause subtle signs such as a influenza-like illness and may not even be noticed by the mother during the pregnancy. In such cases, the effects may be seen first at birth.

Symptoms of a vertically transmitted infection may include fever and flu like symptoms. The newborn is often small for gestational age. A petechial rash on the skin may be present, with small reddish or purplish spots due to bleeding from capillaries under the skin. An enlarged liver and spleen (hepatosplenomegaly) is common, as is jaundice. However, jaundice is less common in hepatitis B because a newborn's immune system is not developed well enough to mount a response against liver cells, as would normally be the cause of jaundice in an older child or adult. Hearing impairment, eye problems, mental retardation, autism, and death can be caused by vertically transmitted infections. The mother often has a mild infection with few or no symptoms.

The genetic conditions of Aicardi-Goutieres syndrome are possibly present in a similar manner.

AIDS-related complex, or ARC, was introduced after discovery of the HIV (Human Immunodeficiency Virus) when the medical community became aware of the inherent difficulties associated with treating patients suffering from an advanced case of HIV which gave rise to the term Acquired Immune Deficiency Syndrome (AIDS). The necessity for doctors to quickly and accurately understand the special needs of unknown patients suffering from AIDS in an emergency room situation was addressed with the creation of the term ARC.

ARC is "A prodromal phase of infection with the human immunodeficiency virus (HIV). Laboratory criteria separating AIDS-related complex ( ARC) from AIDS include elevated or hyperactive B-cell humoral immune responses, compared to depressed or normal antibody reactivity in AIDS; follicular or mixed hyperplasia in ARC lymph nodes, leading to lymphocyte degeneration and depletion more typical of AIDS; evolving succession of histopathological lesions such as localization of Kaposi's sarcoma, signaling the transition to the full-blown AIDS."

Clinical use of this term was widely discontinued by the year 2000 in the United States after having been replaced by modern laboratory criteria.

A small proportion of humans show partial or apparently complete inborn resistance to HIV, the virus that causes AIDS. The main mechanism is a mutation of the gene encoding CCR5, which acts as a co-receptor for HIV. It is estimated that the proportion of people with some form of resistance to HIV is under 1%.

A vertically transmitted infection is an infection caused by pathogens (such as bacteria and viruses) that uses mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. It can occur when the mother gets an infection as an intercurrent disease in pregnancy. Nutritional deficiencies may exacerbate the risks of perinatal infection.

The early (prodromal) symptoms in adolescents and adults are nausea, loss of appetite, aching muscles, and headache. This is followed by the characteristic rash or oral sores, malaise, and a low-grade fever that signal the presence of the disease. Oral manifestations of the disease (enanthem) not uncommonly may precede the external rash (exanthem). In children the illness is not usually preceded by prodromal symptoms, and the first sign is the rash or the spots in the oral cavity. The rash begins as small red dots on the face, scalp, torso, upper arms and legs; progressing over 10–12 hours to small bumps, blisters and pustules; followed by umbilication and the formation of scabs.

At the blister stage, intense itching is usually present. Blisters may also occur on the palms, soles, and genital area. Commonly, visible evidence of the disease develops in the oral cavity and tonsil areas in the form of small ulcers which can be painful or itchy or both; this enanthem (internal rash) can precede the exanthem (external rash) by 1 to 3 days or can be concurrent. These symptoms of chickenpox appear 10 to 21 days after exposure to a contagious person. Adults may have a more widespread rash and longer fever, and they are more likely to experience complications, such as varicella pneumonia.

Because watery nasal discharge containing live virus usually precedes both exanthem (external rash) and enanthem (oral ulcers) by 1 to 2 days, the infected person actually becomes contagious one to two days before recognition of the disease. Contagiousness persists until all vesicular lesions have become dry crusts (scabs), which usually entails four or five days, by which time nasal shedding of live virus ceases.

The condition usually resolves by itself within a couple of weeks. The rash may, however, last for up to one month. Chickenpox is contagious starting from one to two days before the appearance of the rash and lasts until the lesions have crusted.

Chickenpox is rarely fatal, although it is generally more severe in adult men than in women or children. Non-immune pregnant women and those with a suppressed immune system are at highest risk of serious complications. Arterial ischemic stroke (AIS) associated with chickenpox in the previous year accounts for nearly one third of childhood AIS. The most common late complication of chickenpox is shingles (herpes zoster), caused by reactivation of the "varicella zoster" virus decades after the initial, often childhood, chickenpox infection.

In 1994, Stephen Crohn became the first person discovered to be completely resistant to HIV in all tests performed. In early 2000, researchers discovered a small group of sex workers in Nairobi, Kenya who were estimated to have sexual contact with 60 to 70 HIV positive clients a year without signs of infection. Researchers from Public Health Agency of Canada have identified 15 proteins unique to those virus-free sex workers. Later, however some sex workers were discovered to have contracted the virus, leading Oxford University researcher Sarah Rowland-Jones to believe continual exposure is a requirement for maintaining immunity.

AIDS dysmorphic syndrome, also called HIV embryopathy, is a cluster of facial malformations seen in children with perinatal HIV infection. Its status as a syndrome is disputed by the research community. Common symptoms of perinatal HIV infection include candidiasis, lymphocytic interstitial pneumonitis, hepatosplenomegaly, and lymphadenopathy.

Long-term nonprogressors (LTNPs), sometimes also called "elite controllers", are individuals infected with HIV, who maintain a CD4 count greater than 500 without antiretroviral therapy with a detectable viral load. Many of these patients have been HIV positive for 30 years without progressing to the point of needing to take medication in order not to develop AIDS. They have been the subject of a great deal of research, since an understanding of their ability to control HIV infection may lead to the development of immune therapies or a therapeutic vaccine. The classification "Long-term non-progressor" is not permanent, because some patients in this category have gone on to develop AIDS.

Long-term nonprogressors typically have viral loads under 10,000 copies RNA/ml blood, do not take antiretrovirals, and have CD4+ counts within the normal range. Most people with HIV not on medication have viral loads which are much higher.

It is estimated that around 1 in 300 people with HIV are long-term nonprogressors. Without the symptoms of AIDS, many LTNP patients may not know they are infected.

Genetic traits that confer greater resistance or more robust immune response to HIV are thought to explain why LTNP patients are able to live much longer with HIV than patients who are not LTNP. Some LTNP are infected with a weakened or inactive form of HIV, but it is now known that many LTNP patients carry a fully virulent form of the virus. Genetic traits that may affect progression include:

- Gene mutation. A mutation in the FUT2 gene affects the progression of HIV-1 infection. 20% of Europeans who have that mutation are called "non secretor" because of their absence of a certain type of antigen that also provides strong resistance against norovirus.

- Mitochondrial DNA. Different mitochondrial DNA haplotypes in humans may increase or decrease rates of AIDS progression. Haplotypes associated with more loosely coupled mitochondrial respiration, with reduced ATP and ROS generation, have been associated with faster progression and vice versa.

- Receptor mutations. A low percentage of long-term nonprogressors have been shown to have inherited mutations of the CCR5 receptor of T cell lymphocytes. HIV uses CCR5 to enter these cells. It is believed that the Δ32 (delta 32) variant of CCR5 impairs HIV ability to infect cells and cause disease. An understanding of this mechanism led to the development of a class of HIV medicines, the entry inhibitors. The presence of this mutation, however, is not a unifying theme among LTNPs and is observed in an exceedingly small number of these patients.

- HLA type has also been correlated with long-term non-progressor cohorts. In particular, strong correlations have been found between possessing the class 1 HLA-B*5701, HLA-B*5703, and/or HLA-B*2705 alleles and ability to exert control over HIV.

- Antibody production. All individuals with HIV make antibodies against the virus. In most patients, broadly neutralizing antibodies do not emerge until approximately 2–4 years after the initial infection. At this point, the latent reservoir has already been established and the presence of broadly neutralizing antibodies is not enough to prevent disease progression. In some rare patients, these antibodies emerge earlier and can result in a delayed disease course. These patients, however, are not typically classified as LTNPs, but rather as slow progressors, who will eventually develop AIDS. Induction of broadly neutralizing antibodies in healthy individuals is a potential strategy for a preventive HIV vaccine, as is the elicitation of these antibodies through rationally designed immunogens. Direct production of these antibodies in somatic tissue through plasmid transfection also pose a viable method for making these antibodies available in a large number of humans.

- APOBEC3G protein production. In a small number of people infected with HIV, the virus is naturally suppressed without medical treatment. These people may carry high quantities of a protein called APOBEC3G that disrupts viral replication in cells. APOBEC3G, or "A3" for short, is a protein that sabotages reverse transcription, the process HIV relies on for its replication. This process involves the virus transcribing its singe-stranded RNA genome into double-stranded DNA that is incorporated into the cell's genome. A3 usually stops dormant viruses in the human genome, called endogenous retroviruses, from reawakening and causing infections.

In microbiology, coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with Hepatitis B virus and Hepatitis D virus, which can arise incrementally by initial infection followed by superinfection.

Global prevalence or incidence of coinfection among humans is unknown, but it is thought to be commonplace, sometimes more common than single infection. Coinfection with helminths affects around 800 million people worldwide.

Coinfection is of particular human health importance because pathogen species can interact within the host. The net effect of coinfection on human health is thought to be negative. Interactions can have either positive or negative effects on other parasites. Under positive parasite interactions, disease transmission and progression are enhanced and this is also known as syndemism. Negative parasite interactions include microbial interference when one bacterial species suppresses the virulence or colonisation of other bacteria, such as "Pseudomonas aeruginosa" suppressing pathogenic "Staphylococcus aureus" colony formation. The general patterns of ecological interactions between parasite species are unknown, even among common coinfections such as those between sexually transmitted infections. However, network analysis of a food web of coinfection in humans suggests that there is greater potential for interactions via shared food sources than via the immune system.

A globally common coinfection involves tuberculosis and HIV. In some countries, up to 80% of tuberculosis patients are also HIV-positive. The potential for dynamics of these two infectious diseases to be linked has been known for decades. Other common examples of coinfections are AIDS, which involves coinfection of end-stage HIV with opportunistic parasites and polymicrobial infections like Lyme disease with other diseases.

HIV in pregnancy is the presence of the HIV virus in a woman while pregnant. There are concerns because women diagnosed with HIV/AIDS may transmit the infection to their child during pregnancy. The infection be transmitted to the infant during the pregnancy, childbirth, or breastfeeding. However, the risk of mother-to-child transmission of HIV may be reduced by the use of HIV medications known as antiretroviral therapy (ART). These medications may be used by women before, during, and after pregnancy. After delivery, children are also given the medication to reduce the risk of infection. Because HIV may be spread through breast milk, mothers with the infection are encouraged to avoid breastfeeding.

Infection with HIV/AIDS is not a contraindication to pregnancy. Women with the disease may choose to become pregnant if they desire, however, they are encouraged to talk with their doctors beforehand. Some women are unaware they have the disease until they become pregnant. In this case, they should begin antiretroviral therapy as soon as possible. With the appropriate treatment, the risk of mother-to-child infection can be reduced to below 1%. Without treatment, the risk of transmission is 15-45%.

There are approximately 1.4 million HIV positive women who become pregnant and contribute to more than 300,000 neonatal and fetal deaths each year. With the use of ART, transmission of HIV from the mother to child has decreased according to reports by the World Health Organization (WHO). In 2009, there were an estimated 400,000 children born with HIV and by 2013, there were 240,000. Countries in Southern Africa are worst affected by the HIV/AIDS pandemic. In 2010, 30% of all pregnancies in the region were affected by HIV. In 2011, HIV was responsible for 50% of the deaths for children below the age of 5. In the United States, fewer than 200 babies are born with HIV every year.

As of 2015, Cuba has become the first country in the world to eradicate mother-to-child transmission of HIV. In 2010, the WHO partnered with the Pan American Health Organization (PAHO) to implement an initiative that would provide early prenatal care and HIV testing for all pregnant women in the country. For women who tested positive, ART was provided for both the mother and child, cesarean sections were performed, and alternatives to breastfeeding were provided. In implementing these measures, the country was successfully able to eradicate HIV transmission during pregnancy.

Many of these viruses are controlled through laboratory screening tests. These fall into three basic varieties: antibody tests, nucleic acid tests (NAT), and surrogate tests. Antibody tests look for the immune system's response to the infection. Nucleic acid tests look for the genetic material of the virus itself. The third variety are tests that are not specific to the disease but look for other related conditions.

High risk activities for transfusion transmitted infections vary, and the amount of caution used for screening donors varies based on how dangerous the disease is. Most of the viral diseases are spread by either sexual contact or by contact with blood, usually either drug use, accidental needle injuries among health care workers, unsterilized tattoo and body piercing equipment, or through a blood transfusion or transplant. Other vectors exist.

Whether a donor is considered to be at "too high" of a risk for a disease to be allowed to donate is sometimes controversial, especially for sexual contact. High risk sexual activity is defined in many different ways, but usually includes:

- Sex in exchange for money or drugs.

- Men who have sex with men, the most controversial criterion.

- A recent history of sexually transmitted disease.

- Sex with a person who has had a positive test or was at high risk for a disease that can be spread in blood transfusions.

Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab over. It usually starts on the chest, back, and face then spreads to the rest of the body. Other symptoms may include fever, tiredness, and headaches. Symptoms usually last five to seven days. Complications may occasionally include pneumonia, inflammation of the brain, and bacterial skin infections. The disease is often more severe in adults than in children. Symptoms begin 10 to 21 days after exposure to the virus.

Chickenpox is an airborne disease which spreads easily through the coughs and sneezes of an infected person. It may be spread from one to two days before the rash appears until all lesions have crusted over. It may also spread through contact with the blisters. Those with shingles may spread chickenpox to those who are not immune through contact with the blisters. The disease can usually be diagnosed based on the presenting symptom; however, in unusual cases it may be confirmed by polymerase chain reaction (PCR) testing of the blister fluid or scabs. Testing for antibodies may be done to determine if a person is or is not immune. People usually only get chickenpox once. Although reinfections by the virus occur, these reinfections usually do not cause any symptoms.

The varicella vaccine has resulted in a decrease in the number of cases and complications from the disease. It protects about 70 to 90 percent of people from disease with a greater benefit for severe disease. Routine immunization of children is recommended in many countries. Immunization within three days of exposure may improve outcomes in children. Treatment of those infected may include calamine lotion to help with itching, keeping the fingernails short to decrease injury from scratching, and the use of paracetamol (acetaminophen) to help with fevers. For those at increased risk of complications antiviral medication such as aciclovir are recommended.

Chickenpox occurs in all parts of the world. In 2013 there were 140 million cases of chickenpox and herpes zoster worldwide. Before routine immunization the number of cases occurring each year was similar to the number of people born. Since immunization the number of infections in the United States has decreased nearly 90%. In 2015 chickenpox resulted in 6,400 deaths globally – down from 8,900 in 1990. Death occurs in about 1 per 60,000 cases. Chickenpox was not separated from smallpox until the late 19th century. In 1888 its connection to shingles was determined. The first documented use of the term "chicken pox" was in 1658. Various explanations have been suggested for the use of "chicken" in the name, one being the relative mildness of the disease.

It is unknown what aspects of the natural immune response to HIV may protect someone from superinfection, but it has been shown that cytotoxic lymphocyte responses do not seem to be protective. In addition, it has been demonstrated that superinfection can occur in individuals that demonstrate a robust anti-HIV antibody response. The anti-HIV antibody response broadens and strengthens in individuals post-superinfection.

Taken with the finding that super-infection is common and occurs within and between HIV subtypes it has been suggested that the immune response elicited by primary infection may confer limited protection and raises concerns that HIV-vaccine strategies designed to replicate the natural anti-HIV immune response may have limited effectiveness in preventing new infections. However at the same time, HIV-infected individuals at high risk for super-infection who do not become superinfected may also provide a very interesting avenue for new vaccine research.

Breastfeeding by HIV-infected mothers is the practice of breastfeeding of HIV-infected mothers and include those who may want to or are currently breastfeeding . HIV can be transmitted to the infant through breastfeeding. The risk of transmission varies and depends on the viral load in the mother's milk. A infant can be infected with HIV throughout the duration of the pregnancy or during childbirth (intrapartum).

Human immunodeficiency virus salivary gland disease (abbreviated to HIV-SGD, and also termed HIV-associated salivary gland disease), is swelling of the salivary glands and/or xerostomia in individuals infected with human immunodeficiency virus.

HIV drug resistance occurs when microevolution causes virions to become tolerant to antiretroviral treatments.

Erythema infectiosum or fifth disease is one of several possible manifestations of infection by parvovirus B19.

The name "fifth disease" comes from its place on the standard list of rash-causing childhood diseases, which also includes measles (1st), scarlet fever (2nd), rubella (3rd), Dukes' disease (4th, however is no longer widely accepted as distinct) and roseola (6th).

HIV-SGD may be the presenting sign of HIV infection. There may also be xerophthalmia (dry eyes) and arthralgia (joint pain), similar to Sjögren syndrome.