Human immunodeficiency virus replication

After integration, the first virus particles are detectable after approximately 12 h; i. Because the viral RT has no proofreading activity, statistically one incorrect nucleotide per transcription round is incorporated into the proviral DNA.

If HIV replication is unrestricted a daily turnover of 10 8 9 viral particles is expected, i. Assuming a mutation rate of 1 in 10 4 nucleotides per genome during one replication cycle, a broad spectrum of various quasispecies can therefore develop in a patient in the course of time.

Since epitopes for neutralising antibodies are also affected by mutation, these quasispecies are able to continually evade the immune system, infect new cells and therefore maintain HIV production [ 25 , 29 ]. Not all nucleotide changes result in the exchange of an amino acid. However, mutations in essential regions of the structural proteins or influencing active centres of enzymes give rise to replication-incompetent HIV mutants.

Infected T lymphocytes are eliminated with a half-life of days from the blood of an HIV-infected person by cytotoxic HIV components, lysis of virus-producing cells or by cytotoxic T lymphocytes as part of the immune response [ 48 , 49 ]. Since HIV-infected T helper cells are also lysed and the production of such cells is inhibited simultaneously, a gradual decline of T helper cells is observed.

HIV-specific proteins like Nef and Tat are responsible for insufficient maturation and replacement of T helper cells [ 29 ].

Therefore, part of the newly produced T helper lymphocytes do not develop normal functions [ 47 ]. After a long-lasting HIV infection the continuous loss of T helper lymphocytes results in immunodeficiency. HIV integrated into the host genome of long-lived cells like macrophages, astrocytes or memory T cells can persist in the latent stage for several years half-life of certain target cells is 7 years.

Activation of such cells results in the production of infectious HIV particles. The lipid envelope primarily characterises the stability of HIV. HIV is stable for several hours at a pH between 3 and 10 [ 50 , 51 ]. HIV is sensitive against disinfectants. HIV is stable over several hours against the influence of physical conditions like ultraviolet light, gamma irradiation or ultrasonic waves [ 53 , 54 ].

In contrast to other viruses, treatment of platelet concentrates with UVC light reduced HIV titres only slightly [ 55 ]. Therefore in a blood donation only a titre reduction of 1. Taking into consideration that one human infectious dose HID corresponds to approximately , HIV particles, a small amount of transfused blood is sufficient to transmit an HIV infection, although exceptions were observed occasionally [ 58 ].

The infectivity of HIV particles in lymphocytes is variable. It has to be assumed that processed HIV in lymphocytes is inactivated more rapidly than in plasma. In dendritic cells HIV can remain infectious for several weeks [ 41 ]. In lyophilised plasma or factor concentrates, HIV is stable at room temperature for years in the presence of high protein concentrations.

HIV is able to enter the body via intact mucous membranes, eczematous or injured skin or mucosa and by parenteral inoculation. When transmitted by sexual contact, HIV attaches first to dendritic cells e. HIV is taken up by macrophages and replicated [ 60 ] as shown for M cells in the mucosa [ 61 ]. HIV exposure to blood cells can result in the direct infection of T helper cells and the transmission of R5 and X4 viruses using CXC4 receptor as a co-receptor [ 62 ].

As mentioned above, 1 HID is equivalent to approximately , HIV particles, with a higher dose required for infection via mucous membranes compared to infection via the bloodstream, e. The majority of new HIV infections are still transmitted sexually. Another epidemiologically relevant route is parenteral administration of drugs and also snorting of drugs with epistaxis.

One to two days after infection HIV can be detected in regional lymphatic tissue [ 63 ] and within days in regional lymph nodes. After days post infection HIV can be detected in the whole body, including the nervous system. Differences in the rate of dissemination of HIV in the body have been observed, depending on the primary target cells infected, e.

Within an infected organism, distinct compartments can be distinguished by means of virus concentration; however, no correlation between virus concentrations in the different compartments is obvious. HIV-relevant compartments are blood and the cerebrospinal and genital systems ejaculate or vaginal secretion [ 65 , 66 ].

Transmission of HIV via blood or transplanted organs, including bone, is possible from about days after infection of the donor. HIV can be transmitted via breast milk [ 68 ]. These symptoms are non-specific and are also found in other viral infections such as EBV- and CMV-induced mononucleosis or influenza.

Acute neuropathy is common in the acute phase. The symptoms persist for weeks. This initial symptomatic phase is usually followed by an asymptomatic phase or one with occasional symptoms which can last for many years. Therefore blood donations are highly infectious during this phase. However, in this phase blood and cervicovaginal secretions or seminal fluids of infected persons are still infectious. Diagram of the temporal course of an untreated HIV infection. The time scale is initially weeks acute phase , then months and finally years stages 2 and 3.

The key feature of viraemia is the undulation after the initial uninhibited HIV replication. The CD4 cell count decreases over time despite repeated recovery phases. HIV antibodies remain measurable for life, and the decrease of antibody response in stages 2 and 3 results from loss of core antibodies anti p55, p24 and p The overall interval from infection with the virus to the onset of AIDS may vary without therapy from 2 to 25 years or longer.

Depending on the immune response and the test systems used, the commercially available antibody screening tests are able to detect HIV-specific antibodies in the plasma approximately as of the third week post infection, typically after weeks and in the case of a delayed immune response after 8 weeks see 1.

At the beginning of the immune response low titres of IgM and IgG antibodies are detectable that are mainly directed against p24 and the surface glycoproteins gp and gp Subsequently, high-avidity IgG antibodies against all HIV proteins are developed, typically within weeks. A specific T-cell response is induced against a variety of epitopes of HIV proteins [ 76 ].

Like in other virus infections, the early immune response leads to an IgM antibody response that can persist for months [ 5 ]. A high portion of the neutralising antibodies is directed against the V3 loop of gp Such antibodies are strain-specific and are not able to sufficiently eliminate all HIV quasispecies which are continuously produced in the infected individual [ 25 , 77 , 78 ]. Under the pressure of the immune response, viruses with a variable V3 loop are selected.

The V3 loop is the region of the gp protein hypervariable region in which high numbers of mutations are observed, resulting in amino acid exchanges. No serologic subtype differentiation is possible, but this can be achieved by determining the subtype-specific amino acid sequences of the C2V5 region of gp [ 8 ]. In the course of the HIV infection and depending on the number of CD4 cells, at first unspecific symptoms can be observed.

These can include short episodes of fever, diarrhoea, malaise, fatigue and loss of weight symptoms of the so-called AIDS-related complex, ARC. Characteristic features of an HIV infection are periods of good health followed by periods of illness which become more frequent and longer-lasting in the course of the infection [ 79 , 80 ].

Time to occurrence of apparent symptoms of immunodeficiency varies from 2 to 25 years or more fig. As mentioned above, impairment of neurologic and cerebral functions can emerge at any stage of infection.

Frequently occurring opportunistic pathogens are Toxoplasma gondii , Cryptosporidium parvum , Pneumocystis jirovecii , Mycobacterium tuberculosis and atypical mycobacteria, Salmonella spec. Patients with HIV infections lasting for years develop marasmus which is a characteristic outward manifestation of untreated patients [ 5 ].

Concurrent infection with hepatitis C virus HCV results in faster progression of both virus-induced diseases [ 81 , 82 , 83 ]. Some HIV-infected patients develop characteristic atrophic skin alterations or seborrhoeic eczema that are visible manifestations of the HIV infection.

Likewise at an early stage of the infection changes of the oral mucosa are detectable, with gingival retraction and deep periodontal lesions as well as hairy leucoplakia on the lateral rim of the tongue or on the buccal mucosa [ 84 ]. Subdivision includes the CD4 cell count. According to present knowledge, the spread of HIV started at the beginning of the 20th century [ 4 , 86 ]. HIV-2 was transmitted zoonotically from sooty mangabey Cercocebus atys to human in West Africa around [ 87 ].

Molecular genetic analyses suggest that HIV-1 was exported to Haiti probably in and arrived in North America approximately 2 years later [ 4 , 88 ]. Since the mids the different HIV-1 M subtypes have been spreading, leading to a global pandemic. Globally, an estimated 35 million people were living with HIV in [ 89 ]. Since the number of new infections has been decreasing continuously, and for a number of 1.

About three quarters of HIV-infected persons live in Sub-Saharan Africa, and also about two-thirds of the reported new infections originate from this region. The data on the HIV epidemic in Germany are mainly based on the implemented obligatory reporting system.

Reporting must be performed by the diagnosing laboratory also the diagnosing blood establishment. The physician submitting the specimen receives a copy of the reporting form. The physician is required to supply demographic, anamnestic and clinical data which are not available to the laboratory. The completed reporting form is sent directly to the Robert Koch Institute. The available surveillance instruments provide data on specific aspects of the HIV epidemic.

Therefore, the Robert Koch Institute regularly generates estimations of the course of the HIV epidemic, taking into account the available data and information from the various sources. Determination of the number of new HIV infections per time unit HIV incidence by means of official reporting data is not possible because the reports of HIV diagnoses do not allow direct conclusions about the date of infection. HIV incidence and HIV prevalence cannot be measured directly but only estimated by means of model projections.

At first, the estimated number of new HIV infections in all age groups has decreased significantly in the course of time up to the end of the s, with peak values in the mids. From to around a significant increase of HIV infections was observed, with a plateau since Approximately women In addition, HIV infections were observed in about 9. The trends in the three main groups affected in Germany proceeded differently: the first peak of infections occurred simultaneously in the groups of MSM and IVD in the mids.

In the following years up to the beginning of the s, the number of new HIV infections decreased significantly in both groups. This trend continued in the group of IVD up to with a largely constant low level of new infections since Also in the group of MSM significantly fewer infections occurred during the s. However, in the period between and a significant increase in HIV infections in MSM was observed and reached a considerably higher plateau in The number of those infected via heterosexual contacts hetero-domestic in Germany has been rising significantly slower in the course of the epidemic than in the MSM and IVD groups.

Since the number of new infections in heterosexually infected persons has remained on a constant level. Autonomous heterosexual infection chains have a minor impact on the spread of the HIV epidemic in Germany.

Considering the number of reported new infections, large regional differences can be observed. Especially in densely populated urban areas among others Rhine-Ruhr, Rhine-Main and major cities, the incidence of new diagnoses is much higher than in the remaining regions.

In , the ratio of men to women in the group of new infections was 3. Since the percentage of newly diagnosed cases has been rather stable. In Eastern Europe i. Newly diagnosed HIV infections and modes of transmission in different European countries in www. The molecular epidemiologic data show that HIV-1 group M subtypes have different regional prevalence patterns.

The prevalence of HIV-1 subtypes and HIV-2 in European countries reflects the historic connection of these countries to the corresponding endemic regions in Africa [ 12 , 17 , 93 ]. Africa is the continent that is affected most by HIV infections. The estimated HIV prevalence in Africa varies widely and lies between 0. Heterosexual contacts are the main route of infection in Africa, and sex work and sexual violence contribute significantly to the spread of the disease. Approximately one third of those infected with HIV received antiretroviral therapy in [ 89 ].

In Asia, about 1. The epidemic is concentrated in distinct groups with a high risk of exposure, such as MSM, sex workers, drug users and transsexuals [ 89 ]. This is a further indication for the continuous evolution of HIV-1 group M in humans. The main mode of transmission is sexual contact among men [ ]. At the beginning of the epidemic the prevalent subtype B strain had a defect in Nef and a lower pathogenicity [ ].

Approximately 1. The main route of transmission is sexual contact between men. About one third of all persons infected with HIV receive antiretroviral therapy [ ]. In Canada, 2, new HIV infections were reported in , the lowest number determined since introduction of the reporting system in In Canada also, MSM represent the mainly affected group. In Latin America, approximately 1. Further recombinants are found in Brazil and in neighbouring countries [ 16 ].

A general distinction can be made between two principles of detection: antibody and virus detection. HIV antibody screening tests are used for the primary diagnosis followed by a confirmation test in the case of a reactive result in the screening assay. In addition to the ELISA enzyme linked immunosorbent assay or variants of this test system, particle agglutination tests are used. Depending on the manufacturer, additional antigens derived from the reverse transcriptase and the p24 protein are included in the test systems [ 11 , , , ].

Depending on the immune response and the antibody titre, an infection can be detected serologically after 3 weeks but usually after weeks [ ]. In rare cases, HIV-infected individuals with complete immunosuppression might be HIV antibody-negative, but they have HIV-typical clinical symptoms and measurable virus titres in the blood [ ]. Because ELISAs were developed also for the detection of low antibody levels with the highest sensitivity, false-positive results occur, especially when immune complexes are present in the serum, e.

Furthermore, false-positive results were reported for individuals with autoimmune diseases or allergies and for pregnant women. Mistakes in pre-test conditioning can lead to false-positive screening tests, e. Since the information about a positive HIV finding has far-reaching consequences for the infected individual, it is recommended in cases of a positive result in the initial analysis to test a second, independently taken blood sample.

In the same sample the amount of viral genomes viral load should also be determined using NAT in order to identify the need for antiviral treatment [ , ]. Virus isolation in cell culture takes approximately 6 weeks and is often unsuccessful and costly. For diagnostics in blood establishments virus isolation is of no relevance. The p24 protein forms the inner capsid. Each virus particle contains approximately 2, p24 molecules [ ]. Detection of p24 antigen is performed using a combination of polyclonal or monoclonal antibodies, following the principle of the sandwich ELISA technique.

In the course of the infection, free or particle-bound p24 can be found in plasma. In some AIDS patients, high levels of p24 antigen can be observed. There is no direct correlation between the number of HIV particles determined by NAT and the p24 antigen concentration in plasma, because p24 is shed from infected cells without associated viral nucleic acid.

A positive p24 antigen test result must also be confirmed. Most of the HIV-1 p24 antigen tests react also with the HIV-2 p25 antigen, but in some systems with reduced sensitivity. Screening of blood donations for p24 protein in addition to HIV antibodies is not mandatory in Germany [ ]. For analysis of the viral load and the presence of HIV in blood donations, RNA is extracted from virus particles in plasma.

Genome detection can be done either via direct amplification of defined target sequences or through the use of probes with subsequent signal amplification. One genome equivalent ge equals 1. In plasma pools, virus particles can be concentrated, e. For quality control and quantification, standard materials are available [ , , ].

NAT systems have been developed and made commercially available that use primers binding preferentially and stringently to the genome of HIV-1 M:B; therefore, with a few exceptions, viruses of the type HIV-1 M:B are detected with the highest sensitivity. Depending on the test design and the target sequence, e. Taking into account the genetic variability of the HIV genome, it is advantageous and therefore has become compulsory for Germany in to use so-called dual-target amplification techniques, i.

At present, only tests from a few manufacturers are used in Germany for the screening of blood donations with commercial NAT tests. However, since several blood establishments and manufacturers of plasma derivatives have developed their own HIV amplification assays, so-called homemade or in-house assays [ , , ]. In case a test system is sufficiently sensitive, e. In order to avoid contamination of the NAT assays, fully automated processing systems have been established [ ].

For quantitative HIV-2 genome detection, commercial tests have become available in [ 38 ]. For quality control and quantification, an international standard for HIV-2 has been developed [ ].

In Germany, every year approximately 7. The HIV prevalence among new donors has been largely stable since 6. However, an upward trend of seroconversions was observed in repeat donors from 2.

This increase is almost entirely due to an increase in HIV infection among male repeat donors. Most of these donors have both a reactive antibody test and a positive NAT. Almost in all cases there was a sexual exposure; nearly half of the infected men indicated sexual contacts with men as the most likely route of infection. Almost all of the HIV-positive donors MSM and heterosexuals would have been deferred from blood donation on the base of their risk of exposure.

In previous years, it was noticed that a significantly higher proportion of HIV-infected persons was found in the population of plasma donors compared to whole blood donors. This difference is becoming increasingly larger in the population of repeat donors. Whereas the HIV incidence in the group of repeat whole blood donors increased between and from 1. The reasons for this increase are unclear.

The site of plasma donation centres in cities may play a role as well as the higher proportion of young male plasma donors.

The trend described for Germany is not observed in other countries [ ]. Criteria are defined for the permanent or temporary deferral from donation with respect to the transmission of HIV. Permanently deferred from donation are the following:. From a scientific perspective it appears to be justified to implement a temporary deferral for those persons with a high-risk sexual behaviour that they have verifiably changed. There is currently an intensive discussion on a national and international level whether lifetime deferral of MSM and of sex workers could be replaced by a sufficient temporary deferral, taking into account the last sexual contact between men or in sex work, respectively [ , , ].

Reactive screening test results must be followed by a serologic confirmation test or a NAT assay. An additional second blood sample has to be investigated for confirmation of an HIV infection see 1. Until the results are clarified, the donation is separated and should be preserved for additional investigations. The donor is deferred until the final results are available [ ].

According to current knowledge, the vast majority of reactive HIV antibody screening test results of blood donors are non-specific, i. The diagnostic window period, which is between 3 and 6 weeks for antibody screening tests, can be shortened by application of NAT. Depending on the level of viraemia, the sensitivity of the assay used and the infecting HIV, an infection can be detected as early as about 11 days post infection see also 1. Reference materials for the detection of different HIV-1 genotypes are available [ ].

Despite the high labour input and costs, screening with NAT is justifiable, because the majority of potential HIV transmissions by cellular blood components have been prevented through NAT in recent years [ , , , , , , ]. In view of the high costs of NAT and the currently low incidence in blood donors, the financial investment for the elimination of infectious, but still HIV antibody-negative donations is high, but justified.

The costs are estimated to be about EUR 7. In several cases, NAT tests containing only primers directed against only one genome region were not able to detect HIV with mutations in the target region of the primers.

To increase safety, it has been made mandatory to use at least two different target regions for donor screening dual target NAT [ , ]. Sequence analysis of several genome regions can be used to clarify reliably an etiologic relationship of an HIV transmission by the donation [ , , ]. According to the haemotherapy guidelines, the state of health and pre-existing relevant diseases have to be assessed by using a donor history questionnaire and a confidential interview.

This can help to identify and defer persons whose donation could represent a health risk to themselves or could be associated with the risk of transmitting a disease to others. For further queries and explanations a physician has to be available.

The medical history should cover all issues of the donor selection criteria exclusion criteria of the haemotherapy guidelines. These constitute a legally binding basis for decision-making in selecting donors. Since an updated standardised donor history questionnaire is available www. Using quantitative assays for analyzing HIV-1 core stability in vitro, we identified point mutations in CA that either reduce or increase the stability of the HIV-1 core without impairing conical core formation in virions.

Alterations in core stability resulted in severely attenuated HIV-1 replication and impaired reverse transcription in target cells with only minimal effects on viral DNA synthesis in permeabilized virions in vitro. We conclude that formation of a viral core of optimal stability is a prerequisite for efficient HIV-1 infection and suggest that disassembly of the HIV-1 core is a regulated step in infection that may be an attractive target for pharmacologic intervention.

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