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.

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.

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.

Many viral infections of the central nervous system occur in seasonal peaks or as epidemics, whereas others, such as herpes simplex encephalitis, are sporadic. In endemic areas it is mostly a disease of children, but as the disease spreads to new regions, or nonimmune travelers visit endemic regions, nonimmune adults are also affected.

Prophylactic vaccination is available against poliomyelitis, measles, Japanese encephalitis, and rabies. Hyper immune immunoglobulin has been used for prophylaxis of measles, herpes zoster virus, HSV-2, vaccine, rabies, and some other infections in high-risk groups.

The virus that causes AIDS is the best known of the transfusion-transmitted infections because of high-profile cases such as Ryan White, a haemophiliac who was infected through factor VIII, a blood-derived medicine used to treat the disease. Another person who died of medically acquired HIV/AIDS was Damon Courtenay, who died in 1991 due to a bad batch of factor VIII.

The standard test for HIV is an enzyme immunoassay test that reacts with antibodies to the virus. This test has a window period where a person will be infected but not yet have an immune response. Other tests are used to look for donors during this period, specifically the p24 antigen test and nucleic acid testing.

In addition to the general risk criteria for viruses, blood donors are sometimes excluded if they have lived in certain parts of Africa where subtypes of HIV that are not reliably detected on some tests are found, specifically HIV group O. People who have been in prison for extended periods are also excluded for HIV risk.

Babies can also become infected by their mothers during birth. Some infectious agents may be transmitted to the embryo or fetus in the uterus, while passing through the birth canal, or even shortly after birth. The distinction is important because when transmission is primarily during or after birth, medical intervention can help prevent infections in the infant.

During birth, babies are exposed to maternal blood, body fluids, and to the maternal genital tract without the placental barrier intervening. Because of this, blood-borne microorganisms (hepatitis B, HIV), organisms associated with sexually transmitted disease (e.g., "Neisseria gonorrhoeae" and "Chlamydia trachomatis"), and normal fauna of the genitourinary tract (e.g., "Candida albicans") are among those commonly seen in infection of newborns.

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.

Bacteria, viruses, and other organisms are able to be passed from mother to child. Several vertically transmitted infections are included in the TORCH complex, which stands for:

1. T – Toxoplasmosis / "Toxoplasma gondii"

2. O – Other infections (see below)

3. R – Rubella

4. C – Cytomegalovirus

5. H – Herpes simplex virus-2 or neonatal herpes simplex

"Other infections" include:

- Coxsackievirus

- Chickenpox (caused by varicella zoster virus)

- "Chlamydia"

- HIV

- Human T-lymphotropic virus

- Syphilis

- Zika fever, caused by Zika virus, can cause microcephaly and other brain defects in the child.

Hepatitis B may also be classified as a vertically transmitted infection, but the hepatitis B virus is a large virus and does not cross the placenta, hence it cannot infect the fetus unless breaks in the maternal-fetal barrier have occurred, such as can occur in bleeding during childbirth or amniocentesis.

The TORCH complex was originally considered to consist of the four conditions mentioned above, with the "TO" referring to "Toxoplasma". The four-term form is still used in many modern references, and the capitalization "ToRCH" is sometimes used in these contexts. The acronym has also been listed as TORCHES, for TOxoplasmosis, Rubella, Cytomegalovirus, HErpes simplex, and Syphilis.

A further expansion of this acronym, CHEAPTORCHES, was proposed by Ford-Jones and Kellner in 1995:

- C – Chickenpox and shingles

- H – Hepatitis, C (D), E

- E – Enteroviruses

- A – AIDS (HIV infection)

- P – Parvovirus B19 (produces Hydrops faetalis secondary to aplastic anemia)

- T – Toxoplasmosis

- O – Other (Group B Streptococcus, Listeria, Candida, Lyme disease)

- R – Rubella

- C – Cytomegalovirus

- H – Herpes simplex

- E – Everything else sexually transmitted (gonorrhea, "Chlamydia" infection, "Ureaplasma urealyticum", human papillomavirus)

- S – Syphilis

HIV/AIDS may be vertically transmitted from a mother to her child. This means the infection may be spread during pregnancy, labor, delivery, or breastfeeding. 70% of transmissions are believed to occur during delivery when the baby comes into direct contact with the mother's infected blood or genital secretions/fluid in the birth canal. 30% of infections occur in utero during the pregnancy with 66% occurring within the last 14 days of a pregnancy. The mechanism for in utero infection is not well understood, but the current belief is that infected maternal secretions may cross the placenta during the pregnancy.

The risk of HIV transmission from a mother to child is most directly related to the plasma viral load of the mother. Untreated mothers with a viral load >100,000 copies/ml have a transmission risk of over 50%. For women with a viral load < 1000 copies/ml, the risk of transmission is less than 1%. In general, the lower the viral load the lower the risk of transmission. For this reason, ART is recommended throughout the pregnancy so that viral load levels remain as low as possible and the risk of transmission is reduced.

Women with an established diagnosis of HIV often begin ART before becoming pregnant to treat the infection. It is recommended that all pregnant women begin ART regardless of CD4 counts or viral load to reduce the risk of transmission. The earlier ART is initiated, the more likely the viral load is to be suppressed by the time of delivery. Some women are concerned about using ART early in the pregnancy as babies are most susceptible to drug toxicities during the first trimester. However, delay in ART initiation may prove less effective in reducing infection transmission.

Antiretroviral therapy is used at the following times in pregnancy to reduce the risk of mother-to-child transmission of HIV:

- During pregnancy: pregnant women infected with HIV receive an oral regimen of at least three different anti-HIV medications.

- During labor and delivery: pregnant women infected with HIV and already on triple ART are recommended to continue to their oral regimen. If their viral load is >1,000 copies or there is question about whether medications have been taken consistently, then intravenous zidovudine (AZT) is added at the time of delivery. Pregnant women who have not been on ART prior to delivery should also be given intravenous zidovudine (AZT).

In couples where the male and female are both HIV positive, conception may occur normally without concern for disease transmission. However, in couples where only one partner is HIV positive, there is risk of transmitting the infection to the uninfected partner. These couples, known as serodiscordant couples, are advised not to engage in unprotected intercourse. Instead, assisted reproductive methods are recommended. In all serodiscordant couples, the infected partner is advised to begin ART so that levels of the infection are undetectable prior to attempting conception.

In couples where the woman is HIV negative and the man is HIV positive, sperm is collected from the male partner using a technique called sperm washing. This process is then followed by intrauterine insemination (IUI) or in vitro fertilization (IVF). Couples may also use donor sperm from a non-infected male if desired.

In couples where the woman is HIV positive and the man is HIV negative, artificial insemination is recommended.

In areas where assisted reproductive techniques such as IUI or IVF are not available, techniques to reduce the transmission of HIV during conception can be attempted to reduce, but not eliminate, the risks. Most importantly, the HPTN 052 trial showed that when HIV infected partners were on ART there was 96% less transmission of HIV and none from partners with undetectable viral loads.

Many serodiscordant couples use pre-exposure prophylaxis (PrEP) to limit transmission of the infection to the uninfected partner. Daily use of PrEP has been shown to decrease transmission of the infection by an average of 63-75%. However, use of PrEP during pregnancy has not yet been studied and its long-term effects are unknown and should not be the only safety feature in the prevention process.

Although assisted reproductive techniques are available for serodiscordant couples, there are still limitations to achieving a successful pregnancy. Women with HIV have been shown to have decreased fertility which can affect available reproductive options. Women with HIV are also more likely to be infected with other sexually transmitted diseases, placing them at higher risk for infertility. Males with HIV appear to have decreased semen volume and sperm motility which decreases their fertility. Antiretroviral drugs may also affect both male and female fertility and some drugs can be toxic to newly developed embryos. Additionally, there have been cases where an HIV-negative partner was infected with the disease despite using processed artificial insemination.

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.

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 is transmitted by three main routes: sexual contact, significant exposure to infected body fluids or tissues, and from mother to child during pregnancy, delivery, or breastfeeding (known as vertical transmission). There is no risk of acquiring HIV if exposed to feces, nasal secretions, saliva, sputum, sweat, tears, urine, or vomit unless these are contaminated with blood. It is possible to be co-infected by more than one strain of HIV—a condition known as HIV superinfection.

When HIV-negative children take isoniazid after they have been exposed to tuberculosis, their risk to contract tuberculosis is reduced. A Cochrane review investigated whether giving isoniazid to HIV-positive children can help to prevent this vulnerable group from getting tuberculosis. They included three trials conducted in South Africa and Botswana and found that isoniazid given to all children diagnosed with HIV may reduce the risk of active tuberculosis and death in children who are not on antiretroviral treatment. For children taking antiretroviral medication, no clear benefit was detected.

Herpes simplex virus is commonly found in humans, yet uncommonly results in systemic manifestations. Suppression of HIV with antiretroviral medications, careful monitoring of immunosuppressive medications are important means of prevention. Antiviral prophylaxis such as daily acyclovir in immunocompromised individuals may be considered.

HIV can be transmitted from mother to child during pregnancy, during delivery, or through breast milk, resulting in the baby also contracting HIV. This is the third most common way in which HIV is transmitted globally. In the absence of treatment, the risk of transmission before or during birth is around 20% and in those who also breastfeed 35%. As of 2008, vertical transmission accounted for about 90% of cases of HIV in children. With appropriate treatment the risk of mother-to-child infection can be reduced to about 1%. Preventive treatment involves the mother taking antiretrovirals during pregnancy and delivery, an elective caesarean section, avoiding breastfeeding, and administering antiretroviral drugs to the newborn. Antiretrovirals when taken by either the mother or the infant decrease the risk of transmission in those who do breastfeed. However, many of these measures are not available in the developing world. If blood contaminates food during pre-chewing it may pose a risk of transmission.

If a woman is untreated, two years of breastfeeding results in an HIV/AIDS risk in her baby of about 17%. Treatment decreases this risk to 1 to 2% per year. Due to the increased risk of death without breastfeeding in many areas in the developing world, the World Health Organization recommends either: (1) the mother and baby being treated with antiretroviral medication while breastfeeding being continued (2) the provision of safe formula. Infection with HIV during pregnancy is also associated with miscarriage.

Specific age groups, persons who participate in risky sexual behavior, or those have certain health conditions may require screening. The CDC recommends that sexually active women under the age of 25 and those over 25 at risk should be screened for chlamydia and gonorrhea yearly. Appropriate times for screening are during regular pelvic examinations and preconception evaluations. Nucleic acid amplification tests are the recommended method of diagnosis for gonorrhea and chlamydia. This can be done on either urine in both men and women, vaginal or cervical swabs in women, or urethral swabs in men. Screening can be performed:

- to assess the presence of infection and prevent tubal infertility in women

- during the initial evaluation before infertility treatment

- to identify HIV infection

- for men who have sex with men

- for those who may have been exposed to hepatitis C

- for HCV

"Mycobacterium" Tuberculosis is the most common cause of Tuberculosis disease (TB). Airborne transmission typically causes TB infection in both immunocompetent and immunocompromised hosts.

Tuberculosis, is categorized into two types of infection: latent infection or active TB disease.

After penetration into the respiratory tract, the "Mycobacterium" bacilli infect macrophages. T-lymphocytes start producing many cytokines (interferon gamma, interleukin-2, tumour necrosis factor alpha, and macrophage colony-stimulating factor) to activate macrophages and cytotoxic cells to inhibit their intracellular growth.

- Latent TB infection occurs when the immune system is successful in controlling the infection. Latent infection is usually asymptomatic and non contagious.

- Active TB disease appears when immune response is not sufficient in limiting the growth of infection. TB disease is symptomatic and contagious.

In those infected, there is a 5-10% chance that latent TB infection will progress into active tuberculosis disease. If proper treatment is not given in case of active disease, then death rate is about 50%. See Tuberculosis

HIV infection is a lifelong illness with three stages of disease. Medicine to treat HIV can slow or prevent progression from one stage to the next. Treatment can also reduce the chance of transmitting HIV to someone else.

- Stage 1 occurs in the first 2 to 4 weeks after infection. When people have acute HIV infection, they have a large amount of virus in their blood and are very contagious. People with acute infection experience a flu-like illness and are often unaware that they’re infected.

- Stage 2 is sometimes called asymptomatic HIV infection or chronic HIV infection. In this stage, HIV is still active but reproduces at very low levels. This stage varies between individuals but can last a decade or longer. By taking medicine to treat HIV (ART) the right way, this stage can last for several decades. HIV transmission can still occur in this stage. If not on medication, a person’s viral load starts to go up and the CD4 cell count begins to go down.

- Stage 3 of HIV infection is AIDS. Patients with AIDS have severely damaged immune systems increasing number of severe illnesses they contract (called opportunistic illnesses). Without treatment, people with AIDS typically survive about 3 years. People with AIDS can have a high viral load and be very infectious. See HIV

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%.

Many STIs are (more easily) transmitted through the mucous membranes of the penis, vulva, rectum, urinary tract and (less often—depending on type of infection) the mouth, throat, respiratory tract and eyes. The visible membrane covering the head of the penis is a mucous membrane, though it produces no mucus (similar to the lips of the mouth). Mucous membranes differ from skin in that they allow certain pathogens into the body. The amount of contact with infective sources which causes infection varies with each pathogen but in all cases a disease may result from even light contact from fluid carriers like venereal fluids onto a mucous membranes.

Some STIs such as HIV can be transmitted from mother to child either during pregnancy or breastfeeding.

Healthcare professionals suggest safer sex, such as the use of condoms, as a reliable way of decreasing the risk of contracting sexually transmitted diseases during sexual activity, but safer sex cannot be considered to provide complete protection from an STI. The transfer of and exposure to bodily fluids, such as blood transfusions and other blood products, sharing injection needles, needle-stick injuries (when medical staff are inadvertently jabbed or pricked with needles during medical procedures), sharing tattoo needles, and childbirth are other avenues of transmission. These different means put certain groups, such as medical workers, and haemophiliacs and drug users, particularly at risk.

It is possible to be an asymptomatic carrier of sexually transmitted diseases. In particular, sexually transmitted diseases in women often cause the serious condition of pelvic inflammatory disease.

Congenital toxoplasmosis is a specific form of toxoplasmosis in which an unborn fetus is infected via the placenta. Congenital toxoplasmosis is associated with fetal death and abortion, and in infants, it is associated with neurologic deficits, neurocognitive deficits, and chorioretinitis. A positive antibody titer indicates previous exposure and immunity, and largely ensures the unborn fetus' safety. A simple blood draw at the first prenatal doctor visit can determine whether or not a woman has had previous exposure and therefore whether or not she is at risk. If a woman receives her first exposure to "T. gondii" while pregnant, the fetus is at particular risk.

Not much evidence exists around the effect of education before pregnancy to prevent congenital toxoplasmosis. However educating parents before the baby is born has been suggested to be effective because it may improve food, personal and pet hygiene. More research is needed to find whether antenatal education can reduce congenital toxoplasmosis.

For pregnant women with negative antibody titers, indicating no previous exposure to "T. gondii", serology testing as frequent as monthly is advisable as treatment during pregnancy for those women exposed to "T. gondii" for the first time dramatically decreases the risk of passing the parasite to the fetus. Since a baby's immune system does not develop fully for the first year of life, and the resilient cysts that form throughout the body are very difficult to eradicate with antiprotozoans, an infection can be very serious in the young.

Despite these risks, pregnant women are not routinely screened for toxoplasmosis in most countries, for reasons of cost-effectiveness and the high number of false positives generated; Portugal, France, Austria, Uruguay, and Italy are notable exceptions, and some regional screening programmes operate in Germany, Switzerland and Belgium. As invasive prenatal testing incurs some risk to the fetus (18.5 pregnancy losses per toxoplasmosis case prevented), postnatal or neonatal screening is preferred. The exceptions are cases where fetal abnormalities are noted, and thus screening can be targeted.

Pregnant women should avoid handling raw meat, drinking raw milk (especially goat milk) and be advised to not eat raw or undercooked meat regardless of type. Because of the obvious relationship between "Toxoplasma" and cats it is also often advised to avoid exposure to cat feces, and refrain from gardening (cat feces are common in garden soil) or at least wear gloves when so engaged. Most cats are not actively shedding oocysts, since they get infected in the first six months of their life, when they shed oocysts for a short period of time (1–2 weeks.) However, these oocysts get buried in the soil, sporulate and remain infectious for periods ranging from several months to more than a year. Numerous studies have shown living in a household with a cat is not a significant risk factor for "T. gondii" infection, though living with several kittens has some significance.

In 2006, a Czech research team discovered women with high levels of toxoplasmosis antibodies were significantly more likely to have baby boys than baby girls. In most populations, the birth rate is around 51% boys, but women infected with "T. gondii" had up to a 72% chance of a boy. In mice, the sex ratio was higher in early latent toxoplasmosis and lower in later latent toxoplasmosis.

HIV infection rates in central Africa are generally moderate to high.

Antivirals such as acyclovir, famciclovir, or valacyclovir may be used. Intravenous acyclovir is reserved for individuals who cannot swallow due to the pain, individuals with other systemic manifestations of herpes or severely immunocompromised individuals.

Cryptococcosis is a defining opportunistic infection for AIDS, and is the second-most-common AIDS-defining illness in Africa. Other conditions that pose an increased risk include certain lymphomas (e.g., Hodgkin's lymphoma), sarcoidosis, liver cirrhosis, and patients on long-term corticosteroid therapy.

Distribution is worldwide in soil. The prevalence of cryptococcosis has been increasing over the past 20 years for many reasons, including the increase in incidence of AIDS and the expanded use of immunosuppressive drugs.

In humans, "C. neoformans" causes three types of infections:

- Wound or cutaneous cryptococcosis

- Pulmonary cryptococcosis

- Cryptococcal meningitis.

Cryptococcal meningitis (infection of the meninges, the tissue covering the brain) is believed to result from dissemination of the fungus from either an observed or unappreciated pulmonary infection. Often there is also silent dissemination throughout the brain when meningitis is present. "Cryptococcus gattii" causes infections in immunocompetent people (fully functioning immune system), but "C. neoformans v. grubii", and "v. neoformans" usually only cause clinically evident infections in persons with some form of defect in their immune systems (immunocompromised persons). People with defects in their cell-mediated immunity, for example, people with AIDS, are especially susceptible to disseminated cryptococcosis. Cryptococcosis is often fatal, even if treated. It is estimated that the three-month case-fatality rate is 9% in high-income regions, 55% in low/middle-income regions, and 70% in sub-Saharan Africa. As of 2009 there were globally approximately 958,000 annual cases and 625,000 deaths within three months after infection.

Although the most common presentation of cryptococcosis is of "C. neoformans" infection in an immunocompromised person (such as persons living with AIDS), the "C. gattii" is being increasingly recognised as a pathogen in what is presumed to be immunocompetent hosts, especially in Canada and Australia. This may be due to rare exposure and high pathogenicity, or to unrecognised isolated defects in immunity, specific for this organism.