1 INTRODUCTION

Human immunodeficiency virus (HIV) is classified into two main types: HIV-1, which is closely related to a simian immunodeficiency virus (SIV) in chimpanzees, and HIV-2, which is closely related to an SIV in sooty mangabeys (SIVsmm) [1, 1, 3, 1. HIV-2 has a number of subtypes but only groups A and B have become epidemic [2, 2, 2. HIV-2 is a much less common HIV type than HIV-1; the exact prevalence is unknown, but an estimate has been made of 1–2 million people living with HIV-2 worldwide, including those with dual HIV-1 and HIV-2 infection [2, 2, 2. There are few current reliable prevalence estimates and the widely used rapid testing methods for HIV do not distinguish between HIV-1 and HIV-2 [3, 3. Although endemic in West Africa, the distribution of HIV-2 is limited and low prevalence in most settings, which means that understanding and experience of HIV-2, relative to HIV-1, among clinicians are often lacking. In addition, the majority of cohort and treatment studies quoted below, relate only to group A, adding to clinical uncertainty. Since HIV-2 was first recognised, evidence has accumulated regarding pathogenicity and prognosis. Although HIV-2 was initially considered non-pathogenic, it is now known that most untreated individuals with HIV-2 will experience disease progression, albeit at a slower rate compared to those with HIV-1 [4. Diagnosis, monitoring and management of HIV-2 remain challenging. Antiretroviral drugs are mostly developed for activity against HIV-1 group M, therefore many are inactive against HIV-2 and there are limited in vitro data for those drugs that may be used. To date, there have been no published randomised controlled trials of antiretroviral therapy (ART) for HIV-2 and our understanding is based on cohort studies and observational data.

There are important differences in natural history between HIV-1 and HIV-2. HIV-2 carries a lower risk of horizontal and vertical transmission related to much lower plasma viral load, which is often undetectable without ART [1, 1, 3, 1. There is a slower CD4 T-cell decline but some AIDS-defining illnesses may develop at higher CD4 counts [4. The disease trajectory of HIV-1 and HIV-2 is almost identical but progresses at approximately half the rate in HIV-2 so that a prolonged asymptomatic phase is more common. However, disease progression is likely eventually to occur in the majority of individuals with HIV-2 in the absence of ART [4. Clinical disease due to HIV-2 is indistinguishable from that due to HIV-1. Resistance mutations in protease and reverse transcriptase can develop commonly in HIV-2 as the resistance barrier is lower and their effect on treatment efficacy is less well clinically characterised than in HIV-1 [5.

HIV-2 infection does not protect against HIV-1 infection and dual infection may occur. One study has shown that HIV-2 prior to acquisition of HIV-1 in dual infection delays clinical progression, compared to HIV-1 mono-infection [6.

1.1 Origin of HIV-2

HIV-2 was initially isolated in 1986 [7 and the first sequence published in 1987 [8. It had been observed that some individuals had an unusual serological profile, more closely related to simian lentiviruses than HIV-1; it was subsequently shown that the animal origin of HIV-2 is SIVsmm [9. Sooty mangabeys are native to the forests of coastal West Africa where a high prevalence of SIVsmm has been demonstrated, are hunted for food and are often kept in captivity as pets. It has been estimated that species jump into humans occurred between 1905 and 1942 for HIV-2 group A and between 1914 and 1945 for group B (which has been less extensively studied) [1, 10, 11, 1, 3, 1.

Nine distinct lineages of HIV-2 have been identified, termed groups A to I. Only HIV-2 groups A and B are endemic; all other HIV-2 groups have been identified in only one or two individuals. HIV-2 group A is more common and has a distinct geographical origin from group B. There do not seem to be clinical differences between groups A and B, but data are lacking. Each of the nine HIV-2 groups is thought to represent a single cross-species viral transmission. The non-endemic groups are considered to be ‘dead-end’ infections representing continuing transmissions of SIVsmm to humans. In contrast to HIV-1, recombination events are rare; only one circulating recombinant and one unique recombinant form have been described.

1.2 Epidemiology of HIV-2

HIV-2 is mainly restricted to West Africa. The highest prevalence has been observed in Guinea-Bissau, The Gambia, Senegal, Cape-Verde, Côte d'Ivoire and Sierra Leone, which all reported >1% general population prevalence in the 1980s. Guinea-Bissau had the highest reported prevalence at 8% in adults and up to 20% in individuals aged over 40 years in 1987 [12. HIV-2 is also found in Ghana, Burkina Faso and Mali and has dispersed to Angola, Mozambique, Brazil, India and Europe. A significant increase in the number of new HIV-2 infections in Guinea-Bissau in the mid-1960s is attributable to the war of independence (1963–1974) and is linked to the expansion and dissemination of HIV-2 to Portugal and its former colonies [1, 1, 3, 1. HIV-2 is increasingly recognised in parts of India, especially those with previous connections to Portugal such as Goa and Maharashtra states. Relatively high prevalence in some areas is thought to be driving a significant prevalence of dual HIV-1 and HIV-2 infections in India [13. Portugal and France have the highest number of people living with HIV-2 in Europe with approximately 2000 and 1000 people respectively [14. HIV-2 has been reported in a number of other countries, including Spain, Germany, the UK and the USA [15-18.

Studies from Guinea-Bissau, The Gambia and Senegal have shown a recent rapid decrease in the prevalence of HIV-2 resulting in speculation that the infection may become extinct by the middle of the 21st century [19-21. The decreasing prevalence of HIV-2 may be due to its lower transmission risk, changes in risk behaviours, reduced risk of healthcare-associated infections and/or competition with HIV-1 [22, 23. Notable in these studies is the finding that HIV-2 prevalence has declined more among women than men, while older women seem to maintain a higher risk of acquiring infection than older men [22, 24.

1.3 Guideline development process

Full details of the guideline development process, including conflict of interest policy, are outlined in the British HIV Association (BHIVA) guideline development manual which was last updated in 2020 (see https://www.bhiva.org/file/jgCacHqmuxZFL/GuidelineDevelopmentManual.pdf). The scope, purpose and guideline topics were agreed by the writing group. Questions concerning each guideline topic were drafted and an independent systematic literature review carried out. For the current guidelines, Medline, Embase and the Cochrane Library were searched for English language publications between January 2016 and September 2019 using the search terms HIV-2 or HIV2; animal studies were excluded. Abstracts from selected conferences (BHIVA, Conference on Retroviruses and Opportunistic Infections, IAS Conference on HIV Science, International AIDS Conference and HIV Drug Therapy Glasgow) were also searched for the same period.

For each topic, evidence was identified and evaluated by writing group members with expertise in the field. Using the modified Grading of Recommendations Assessment, Development and Evaluation (GRADE) system (see Appendix 1), writing group members were responsible for assessing and grading the quality of evidence for predefined outcomes across studies and developing and grading the strength of recommendations. Good practice points (GPPs) are recommendations based on the clinical judgment and experience of the working group. GPPs emphasise an area of important clinical practice for which there is not, nor is there likely to be, any significant research evidence, but where the aspect of care is regarded as such sound clinical practice that healthcare professionals are unlikely to question it and where the alternative recommendation is deemed unacceptable.

Before final approval by the writing group, the guidelines were published online for public consultation and external peer reviews were commissioned.

A full review of these guidelines is due in September 2026, with interim updates only if recommendations need updating in line with new data.

2 SUMMARY OF RECOMMENDATIONS 3 Supporting people living with HIV-2 We recommend that the same principles for involving people with HIV-1 in their care are followed for those with HIV-2. (GPP) In providing treatment and peer support, particular care must be taken to give accurate information, given the differences between HIV-1 and HIV-2. (GPP) Adherence support is particularly important, owing to limited treatment options. (GPP) 4 Clinical standards We suggest that the BHIVA clinical standards [25 are likely to be appropriate for people living with HIV-2. (Grade 2D)

5 Diagnosis of HIV-2 infection

5.1 Laboratory diagnosis of chronic HIV-2 infection We recommend that an initial diagnosis of chronic HIV-2 infection should be made using a total of three CE-marked serology tests (i.e. tests conform to EU health and safety requirements) performed in an ISO 15189-accredited laboratory. There must be reactivity in two CE-marked fourth-generation tests for HIV-1 and HIV-2, followed by differentiation of HIV-2 by a third CE-marked antibody-only test. (Grade 1A) Clinicians should consider revisiting a previous diagnosis of HIV-1 by repeating HIV-2 serology and molecular tests in individuals with an undetectable HIV-1 viral load in the absence of ART, but a falling CD4 count. This is in order to detect the possibility of missed HIV-1 and HIV-2 dual infection. (GPP) Similarly, in those with diagnosed HIV-2 with an undetectable viral load in the absence of ART, clinicians should consider repeating HIV-1 diagnostic tests, if their CD4 count falls. This is to investigate the possibility of HIV-1 superinfection. (GPP) 5.2 Laboratory diagnosis of acute primary HIV-2 infection We recommend that investigation for acute or very recent HIV-2 infection should start as for diagnosis of chronic HIV-2 infection. A negative HIV-2 screening result on a blood sample taken within 3 months of the likely exposure should be further investigated at 6 weeks and 3 months, with parallel testing for HIV-2 viral RNA and, if necessary, HIV-2 proviral DNA. (Grade 1A) 5.3 Indeterminate HIV-1 or HIV-2 serology: how to investigate further We recommend that any HIV-1 or HIV-2 serology that does not fit into a clear pattern of a confirmed laboratory diagnosis is fully investigated for the presence or absence of HIV-2 infection, and that this should be established by PCR for HIV-2 proviral DNA. (Grade 1A) 5.4 Measuring HIV-2 viral load People with HIV-2 should have viral load measured at baseline and then repeated at appropriate intervals (see Section 8 Monitoring). (Grade 1A) 5.5 Resistance testing Resistance testing should be performed at diagnosis, prior to treatment initiation and at virological failure, if the HIV-2 viral load meets the threshold of ≥500 copies/mL. (Grade 1C) 6 When to start treatment It is essential that the risks and benefits of initiating ART are discussed with all individuals with HIV-2. (GPP) We suggest that all people with HIV-2 start ART. (Grade 2C) We recommend that people with HIV-2 start ART in the following circumstances: If there is dual HIV-1 and HIV-2 infection; (Grade 1A) When a diagnosis is made during primary HIV-2 infection; (Grade 1C) If there is co-infection with hepatitis B (HBV); (Grade 1C) In pregnancy (see Section 9.1 Pregnant women); (Grade 1C) If there is detectable HIV-2 viraemia; (Grade 1B/C) If the CD4 count is below 500 cells/mm3; (Grade 1B) In advanced HIV disease, or if there are opportunistic infections; (Grade 1B) If there are symptoms, or an indicator condition for HIV-1 and/or HIV-2, regardless of CD4 count or viral load. (Grade 1C) We suggest that additional consideration is given to starting ART if there are significant comorbidities. (Grade 2D) 6.1 Chronic infection We suggest that people with HIV-2 start ART. (Grade 2C) 6.2 Individuals with dual HIV-1 and HIV-2 infection We recommend that people with dual HIV-1 and HIV-2 infection start ART, with a regimen selected to provide full suppression for both viruses. (Grade 1A) 6.3 Treatment of primary HIV-2 infection We recommend that people diagnosed with HIV-2 during primary HIV-2 infection start ART. (Grade 1C) 6.4 Individuals with HBV co-infection We recommend that all people with HIV-2 who are co-infected with HBV are treated with fully suppressive ART that provides activity against both viruses. (Grade 1C) 6.5 Individuals with a detectable HIV-2 viraemia We recommend that people with HIV-2 start ART if there is detectable HIV-2 viraemia. (Grade 1B) 6.6 Individuals with a CD4 cell count below 500 cells/mm3 We recommend ART initiation for all people with HIV-2 with a CD4 cell count below 500 cells/mm3. (Grade 1C) 6.7 In advanced HIV disease or the presence of opportunistic infections We recommend that all people with HIV-2 who have advanced HIV disease or a current or previous opportunistic infection start ART. (Grade 1B) 6.8 In the presence of an indicator condition for HIV We recommend that all people with HIV-2 who are symptomatic or have a current or previous indicator condition for HIV start ART. (Grade 1C) 6.9 Comorbidities We suggest that additional consideration is given to starting ART if there are significant comorbidities. (Grade 2D) 7 What to start It is recommended that people with HIV-2 start ART containing two NRTIs plus one of the following: a second-generation INSTI or a ritonavir-boosted PI (PI/r). (Grade 1C) Two-drug regimens currently in use for treatment of HIV-1 are not recommended. (Grade 1D) NNRTIs are not recommended in the treatment of HIV-2. (Grade 1C) 7.2 Which NRTI backbone We recommend that tenofovir disoproxil (DX) with emtricitabine is the preferred NRTI backbone. (Grade 1C) Tenofovir alafenamide (AF) with emtricitabine is a suggested alternative NRTI backbone if there are clinical reasons to prefer it over tenofovir DX. (Grade 2C) Abacavir with lamivudine is another suggested alternative NRTI backbone if there are clinical reasons to avoid both tenofovir prodrugs. (Grade 2D) 7.3 Which third agent We recommend that therapy-naïve individuals start ART containing dolutegravir or darunavir/r as the preferred third agent. (Grade 1C for both) Bictegravir is a suggested alternative INSTI if clinically appropriate. (Grade 2D) Cobicistat is an alternative pharmacokinetic enhancer if clinically appropriate. (Grade 2D) Raltegravir is a suggested alternative INSTI if clinically appropriate. (Grade 2C) Cobicistat-boosted elvitegravir is a suggested alternative INSTI if clinically appropriate. (Grade 2C) We suggest that lopinavir/r should be reserved for those who cannot tolerate either darunavir/r or dolutegravir or when there are clinical reasons to avoid the other third agents listed above. (Grade 2C) 8 HIV-1 and HIV-2 co-infection Consider the viral load and resistance profiles for both viruses when selecting treatment. (GPP) We recommend that, if there is a clinical reason to start treatment before a definitive diagnosis is made, treatment is started as for HIV-2 using twice daily dosing of either dolutegravir or boosted darunavir. (Grade 1D) 9 Monitoring In individuals who are not on treatment, CD4 cell counts should be measured at 3- to 6-month intervals depending on the baseline value and rate of decline of CD4 count. (Grade 1B) In individuals who are not on treatment, the viral load should be measured at baseline and every 6 months. (Grade 1C) Baseline testing for NRTI, PI and INSTI resistance should be performed prior to starting ART; a sample should be retained if resistance testing is not possible. (Grade 1C) In those who are taking ART, the CD4 cell count should be measured at 1, 3 and 6 months after starting or changing ART and 3–6 monthly thereafter depending on the nadir CD4 cell count. (Grade 1C) If the pre-treatment viral load was detectable, the viral load should be measured at 1, 3 and 6 months after starting or changing ART and then 3–6 monthly. (Grade 1C) If the pre-treatment viral load was undetectable, the viral load should be measured at 1 month and then 6 monthly. (Grade 1C) The HIV viral load should be repeated in those on ART where the HIV-2 RNA has been maximally suppressed and becomes detectable. (Grade 1D) Testing for drug resistance should be performed in those on ART where the HIV-RNA has been maximally suppressed and becomes repeatedly detectable. (Grade 1C)

10 Pregnant women and neonatal post-exposure prophylaxis

10.1 Pregnant women We recommend that pregnant women with HIV-2 should initiate ART, if they are not already established on an effective regimen. (Grade 1C) We recommend that an effective ART regimen already established at conception should be continued. (Grade 1C) We recommend tenofovir DX with emtricitabine as the preferred NRTI backbone. (Grade 1C) We recommend darunavir/r as the preferred third agent. (Grade 1C) Dolutegravir may be used or continued as a preferred third agent, taking into consideration the possible risks and benefits for the woman. (Grade 1C) Case discussion with experts with experience of managing HIV-2 is recommended for all pregnant women. (Grade 1D) Women with HIV-2 who wish to conceive should be informed about the possible risks associated with dolutegravir use around the time of conception. (GPP) 10.2 Neonatal post-exposure prophylaxis Infants who are defined as being at very low or low risk of vertical transmission should receive zidovudine monotherapy. (Grade 1D) We suggest that the duration of zidovudine monotherapy should be 2 weeks and 4 weeks for very low-risk and low-risk infants, respectively, stratified as per the BHIVA HIV-1 pregnancy guidelines. (Grade 2D) Infants who are defined as being at high risk of vertical transmission should receive triple therapy with zidovudine/lamivudine/raltegravir. (Grade 1D) 11 Managing treatment failure Genotypic resistance testing should be attempted in the event of virological rebound. (Grade 1C) Algorithmic resistance mutation analysis should be utilised if resistance is detected. (Grade 1D) We suggest that specialist advice is sought from a clinician with experience in managing HIV-2. (Grade 2D) Fully active agents should be used to construct a second-line regimen in the case of resistance, though it may be necessary to continue partially active agents in order to maximise overall regimen activity. (Grade 1D) 12 PEP and pre-exposure prophylaxis for sexual exposure to HIV-2 We suggest that PEP after sexual exposure and pre-exposure prophylaxis (PrEP) used for HIV-1 are likely to be effective against HIV-2. (Grade 2D) 3 SUPPORTING PEOPLE LIVING WITH HIV-2 Recommendations We recommend that the same principles for involving people with HIV-1 in their care are followed for those with HIV-2. (GPP) In providing treatment and peer support, particular care must be taken to give accurate information, given the differences between HIV-1 and HIV-2. (GPP) Adherence support is particularly important, owing to limited treatment options. (GPP)

Rationale

Although there may be many similarities in the way HIV-1 and HIV-2 are treated and managed, there are also significant differences that need to be clearly understood. In the UK, HIV-1 is by far the more common diagnosis, and almost all of the available patient information is written for people living with HIV-1. As a result, the differences between HIV-1 and HIV-2 may be poorly understood, and so special effort must be made to inform people living with HIV-2 and their partners about these differences, as they affect important aspects of diagnosis, treatment and ongoing management.

Most people living with HIV-2 in the UK either have West African ancestry or have migrated from there, or from France or Portugal (due to their former colonial connections with West Africa). This means that there may be greater language/communication needs in this patient group than for those with HIV-1.

Clinical practice after diagnosis of HIV-1 has a robust and broad evidence base with clear recommendations around treatment and its positive effects. This is not the case for HIV-2, where there are only limited data on the value of diagnostic tools, monitoring and treatment. Thus, it is very difficult to make recommendations on the basis of high-quality evidence (using the GRADE system). Nonetheless, it can be assumed that general principles will apply. For example, it can be assumed that for those on ART, undetectable = untransmittable (U=U) will apply for people with HIV-2, even though there is no direct evidence. However, it is hard to express the same confidence for those who have an undetectable viral load in the absence of ART. Similarly, much of the good practice and advice around adherence discussed in guidelines for HIV-1 can be assumed to apply for HIV-2 [26. There are some significant differences between HIV-1 and HIV-2 that are highlighted in these guidelines. These need to be clearly understood and communicated to patients, in the context of involving people in their care and supporting adherence.

3.1 Testing and diagnosis

Testing for and diagnosis of HIV-2 are more challenging compared with HIV-1. Standard HIV antibody screening tests detect both HIV-1 and HIV-2. This can lead to misunderstandings; people may assume that they have been diagnosed with HIV-1 or not realise that there are different types of HIV, and it may be several weeks before confirmation of HIV-2 is obtained. This can cause uncertainty and confusion.

Likewise, viral load and resistance testing are performed at specialised centres and it takes longer to receive results. HIV-2 groups are so distinct from each other that it is common for resistance tests, and even viral load assays, to fail to amplify which causes further delay in treatment decisions.

3.2 Treatment

Disease progression of HIV-2 is slower compared to HIV-1. Many people living with untreated HIV-2 have undetectable (or very low) viral loads for many years and may not experience a significant decline in CD4 count. This makes decisions about when to start ART for HIV-2 less clear-cut than for HIV-1. Deferral of treatment with continued monitoring may sometimes be an appropriate course of action for HIV-2, though there are many circumstances (described below) when starting ART is recommended. Nonetheless, in these guidelines we suggest that ART should be routinely offered when a new diagnosis of HIV-2 is made.

Low viral loads may mean that the risk of onward transmission of HIV-2 to sexual partners is significantly lower than for HIV-1. People may have been living with asymptomatic HIV-2 for longer than is usual for HIV-1, but they may still face the same levels of stigma and discrimination.

As well as the complexity of deciding when to start ART, it should be noted that HIV-2 is ‘harder to treat’ than HIV-1. Most antiretroviral agents were developed for HIV-1 and HIV-2 has intrinsic resistance to some of these drugs. There is some concern about the barrier to resistance and durability of treatment for HIV-2. The limited choice of effective agents also means that there are fewer switch options, and fewer options remaining if resistance develops. This makes adherence a particularly key issue for people living with HIV-2, and more support may be needed. Although peer support organisations can provide invaluable advice about stigma and adherence, the low numbers of people living with HIV-2 in the UK may mean that peer organisations have limited experience of counselling about HIV-2, its treatment and the lived experience of people with HIV-2. Caution is needed, because information relevant to HIV-1 (for example, on when to start ART, or the option of switching to other antiretroviral drugs to help with side effects) may not be directly translatable to HIV-2.

Treatment for HIV-2 may need to be more closely monitored than for HIV-1, to minimise the risk of resistance developing. There is some evidence to suggest that resistance may develop more easily. The low or undetectable viral loads in people with HIV-2 may mean that CD4 is monitored more frequently in people with HIV-2, compared with HIV-1. The CD4 count might be the most useful marker of health status and response to treatment.

3.3 General support for people with HIV-2

The differences between HIV-2 and HIV-1, and the resulting uncertainties, mean that more support for people with HIV-2 is needed. Explaining these complexities, particularly immediately after diagnosis when people are emotionally vulnerable, and especially if there are language or comprehension barriers, may be time-consuming and difficult. Although peer support is often advocated at these times, this may need to be more carefully considered or supplemented with additional information in the case of HIV-2, as most of the lived experience in the UK is of HIV-1.

Decisions about when to start ART, and what drugs to start, may need more discussion than might be the case for HIV-1. Given the possible increased risk of developing resistance, special emphasis on adherence may be appropriate, with extra support and more frequent monitoring. There are fewer switch options, so switching because of intolerance to antiretroviral drugs is less of an option than for HIV-1. This may necessitate more support for drug intolerance.

4 CLINICAL STANDARDS Recommendation We suggest that the BHIVA clinical standards [25 are likely to be appropriate for people living with HIV-2. (Grade 2D)

There is very little research to guide standards for clinical care in HIV-2. From a clinical perspective the same principles as for HIV-1 broadly apply with respect to treatment, monitoring and support. The gaps in our understanding of HIV-2 and its relative rarity suggest that a specialist multi-disciplinary team approach is particularly important. Care should be taken in communicating with other health professionals and people providing support for people with HIV-2 who may have little understanding of the differences compared with HIV-1.

5 DIAGNOSIS OF HIV-2 INFECTION 5.1 Laboratory diagnosis of chronic HIV-2 infection Recommendations We recommend that an initial diagnosis of chronic HIV-2 infection should be made using a total of three CE-marked serology tests (i.e. tests conform to EU health and safety requirements) performed in an ISO 15189-accredited laboratory. There must be reactivity in two CE-marked fourth-generation tests for HIV-1 and HIV-2, followed by differentiation of HIV-2 by a third CE-marked antibody-only test. (Grade 1A) Clinicians should consider revisiting a previous diagnosis of HIV-1 by repeating HIV-2 serology and molecular tests in individuals with an undetectable HIV-1 viral load in the absence of ART, but a falling CD4 count. This is in order to detect the possibility of missed HIV-1 and HIV-2 dual infection. (GPP) Similarly, in those with diagnosed HIV-2 with an undetectable viral load in the absence of ART, clinicians should consider repeating HIV-1 diagnostic tests, if their CD4 count falls. This is to investigate the possibility of HIV-1 superinfection. (GPP)

Rationale

Chronic HIV-2 is the development of persistent infection following the acute phase of primary infection. Accurate testing for HIV-2 chronic infection depends on a laboratory diagnosis, made using at least one venous blood sample. Positive results from tests using other strategies for convenience, such as point-of-care tests (POCTs) or self-sampling and testing schemes, must be followed up with results from a laboratory accredited for HIV testing under ISO 15189 by the UK Accreditation Service (UKAS).

In the UK, the first-line approach to the diagnosis of HIV-2 chronic infection is well established and should follow the HIV-1 and HIV-2 serology pathway presented in the UK Standards for Microbiology Investigation guidance [27.

The approach to patient testing for HIV-2 follows the pathway for HIV-1 diagnosis. A sensitive fourth-generation screening test for HIV-1 and HIV-2 is performed: any samples showing reactivity are subjected to a further two tests, preferably from separate manufacturers, including one that can differentiate between HIV-1 and HIV-2.

For chronic HIV-2 infection, specific reactivity in all three tests is required to confirm the presence of HIV-2 antibodies in the sample.

As with HIV-1, the patient identity for HIV-2 diagnosis is not confirmed until a second sample from the patient has consistent reactive results. This step is essential to allow for clinic or laboratory errors, which can result in misdiagnosis.

Where a POCT or self-sampling test has been performed prior to the laboratory test, this is considered as one of the two samples. Therefore, one POCT-reactive sample plus one laboratory-reactive sample with differentiation for HIV type is considered adequate for confirmation of identity and HIV-2 infection.

A recently licensed qualitative HIV-1/HIV-2 reverse transcriptase (RT)-polymerase chain reaction (PCR) test may be helpful in confirming the diagnosis of HIV-2 [28.

5.2 Laboratory diagnosis of acute primary HIV-2 infection Recommendation We recommend that investigation for acute or very recent HIV-2 infection should start as for diagnosis of chronic HIV-2 infection. A negative HIV-2 screening result on a blood sample taken within 3 months of the likely exposure should be further investigated at 6 weeks and 3 months, with parallel testing for HIV-2 viral RNA and, if necessary, HIV-2 proviral DNA. (Grade 1A)

Rationale

Diagnosis of acute primary HIV-2 infection can only be made on the basis of HIV-2 antibody seroconversion.

The need to test for a suspected acute HIV-2 infection is rare [29, 30, but the context of managing a needle-stick incident, sexual exposure or other potential transmission event, or clinical presentation, may necessitate consideration of the principles.

Fourth-generation serology tests (see Appendix 2) have become the mainstay of HIV diagnosis, but their development has resulted in bias towards the timely detection of HIV-1 infection. The inclusion of p24 antigen detection in some tests is designed to be specific for HIV-1 only; so in terms of HIV-2 diagnosis, the ‘antibody/antigen’ test format is solely an antibody test and can justifiably be regarded as equivalent to third-generation tests. A negative result in a screening test must therefore be interpreted with consideration of the ‘window’ period in which a genuine HIV-2 infection may not be detected by antibody alone.

The window period for HIV-2 antibody detection is considered to be at least as long as for HIV-1. The BHIVA/BASHH/BIA Adult HIV Testing guidelines strongly recommend using a test at a time point at which it has a 99% probability of detecting infection [31. For third-generation tests, the cumulative probability of a false-negative HIV test result is 5%, 1% and 0% by 40, 85 and 99 days post-exposure, respectively [32. Applying this reasoning to HIV-2 antibody detection, the window period can be established as approximately 90 days from exposure.

HIV-1 avidity tests cannot be used to determine recent HIV-2 infection. The US Food and Drug Administration has approved the Roche cobas® HIV-1/HIV-2 qualitative RT-PCR test for diagnosis, which may be helpful in identifying acute infection [28.

5.3 Indeterminate HIV-1 or HIV-2 serology: how to investigate further Recommendation We recommend that any HIV-1 or HIV-2 serology that does not fit into a clear pattern of a confirmed laboratory diagnosis is fully investigated for the presence or absence of HIV-2 infection, and that this should be established by PCR for HIV-2 proviral DNA. (Grade 1A)

Rationale

Because of the close genetic relationship between HIV-1 and HIV-2, reactivity in combined serological tests may reflect cross-reactivity to either antibody or antigen. Historically, there may also have been some non-specific detection in viral load assays. However, such cross-reactivity should not be considered to indicate that the patient has dual HIV-1 and HIV-2 infection. It is also important to remember that a patient may have had an initial diagnosis of HIV decades previously, when the availability and specificity of diagnostic tests for HIV-2 were not as good as at present.

A fuller investigation of suspected cross-reactive serology should normally include an HIV-2 western blot analysis, to better compare the range of the patient's serological responses to HIV-1 and HIV-2 antigens. Unfortunately, HIV-2 western blot diagnostic tests are not performed in the UK, so the specialist confirmation of HIV-2 infection depends on molecular testing.

The next step on the diagnostic path would normally be an HIV-2 viral load test, but because a significant proportion of patients with HIV-2 do not have a detectable HIV-2 viral load, a negative result can be misleading. Though not quantitative, the Roche cobas® HIV-1/HIV-2 qualitative RT-PCR test has a very low estimated limit of detection and may be helpful in resolving indeterminate serology or identifying dual infection [28.

If RNA is not detected, the next test to confirm or refute HIV-2 infection in the context of indeterminate serology is investigation for the presence of HIV-2 proviral DNA. This test is more exacting in terms of sample requirement, which must be sent to the laboratory within a relatively short time period because it requires white cells to be separated from whole blood. Nevertheless, the test is capable of reliably and specifically detecting HIV-2 DNA that has been integrated into human lymphocytes.

5.4 Measuring HIV-2 viral load Recommendation People with HIV-2 should have viral load measured at baseline and then repeated at appropriate intervals (see Section 8 Monitoring). (Grade 1A)

Rationale

Detection of viraemia in HIV-2 varies with time since diagnosis. In studies in West Africa, the proportion of ART-naïve individuals with viral load <50 copies/mL varied between 25% and 40% [33-35. However, viral load will vary according to time since acquisition and clinical progression as well as between individuals. Measurement of viraemia allows baseline genotypic testing, monitoring of response to treatment or detection of disease progression in those who do not start treatment.

If detectable, the plasma viral load of HIV-2 can be correlated with clinical progression for individual patients [34, 36. A proportion of HIV-2 patients who do not initially have a detectable viraemia may still deteriorate clinically without a newly detectable or increasing plasma viral load. Recommendations for management of these patients are given in Section 5 When to start treatment.

Quantification of HIV-2 subtype B viral load is more problematic than of subtype A, probably due to a relatively wider variation across the viral genome, including the RT-PCR primer-binding sites. This may result in under-quantification, and partly explain the discordance between viral load and clinical progression more regularly observed in subtype B infections.

Almost all methods to measure HIV-2 viral load are based on RT-PCR. These have steadily improved over the years to overcome problems with natural variation in critical primer-binding sites, and limits of both quantification and detection. In addition, almost all HIV-2 quantitative assays are non-commercial ‘in-house’ tests, although one commercial HIV viral load assay which offers a different methodology is the Cavidi ExaVir assay which measures the polymerase activity of plasma virions. Although the Cavidi ExaVir assay is less sensitive than the better molecular RT-PCR assays (~500 vs 100 copies/mL) [37, and cannot distinguish between HIV-1 and HIV-2 load in co-infected patients, it has shown promise in single-sample limited comparisons with RT-PCR assays [38.

Availability of HIV-2 viral load testing is limited in the UK; at the time of writing there are only two diagnostic centres (see Appendix 2 for details). Both centres use methods developed in-house that have been published in peer-reviewed journals, and the development teams are part of the ACHIEV2E international collaboration (http://etudes.isped.u-bordeaux2.fr/achiev2e/). This collaboration has taken steps to document the variation in assay limits of detection and quantification [37, 39, and recommends standards for interpretation of HIV-2 viral load data with relevance to clinical progression [39.

5.5 Resistance testing Recommendation Resistance testing should be performed at diagnosis, prior to treatment initiation and at virological failure, if the HIV-2 viral load meets the threshold of ≥500 copies/mL. (Grade 1C)

Rationale

Genotypic HIV-2 resistance testing is the only available method for determining drug resistance; there are no phenotypic assays that can be routinely used to inform clinical decisions about treatment. Only one specialist laboratory centre in the UK performs an accredited HIV-2 resistance test (see Appendix 3). Quality assurance is provided by in-house and international schemes.

The limit of HIV-2 viral load for which sequencing can be performed reliably is 500 copies/mL. Prior to requesting HIV-2 resistance testing, the viral load should be determined at one of the two specialist centres providing this assay (see Appendix 3). If the HIV-2 viral load is detected but below the limit of quantification, it may still be possible to attempt resistance testing after discussion with the sequencing laboratory.

The classes of HIV drugs for which resistance testing may be performed are the protease inhibitors (PIs), nucleos(t)ide reverse-transcriptase inhibitors (NRTIs) and integrase strand transfer inhibitors (INSTIs). HIV-2 is naturally resistant to all non-nucleos(t)ide reverse-transcriptase inhibitors (NNRTIs), and the fusion inhibitor enfuvirtide (see Section 6 What to start).

The basic methodology for genotypic HIV-2 resistance testing is similar to that used for HIV-1: extraction of viral RNA from plasma, then reverse transcription of RNA to complementary (c)DNA, followed by nested PCR amplification of specific regions of this cDNA. After checking for amplification, the product is then sequenced, scanned for quality of sequence, and analysed for the presence of mutations that are predicted to confer drug resistance [40. Lists of mutations used in the scanning process are updated regularly and available from international databases and are based on peer-reviewed clinical research [41.

At the time of writing, HIV-2 sequencing is performed using conventional Sanger methodology, which has a limit of sensitivity for point mutations in viral population sequencing of approximately 15%. Thus, any mutations present in a viral population at a proportion less than this are unlikely to be reliably detected, though whether these will have clinical consequences for antiviral control of HIV-2 infection is largely unknown.

6 WHEN TO START TREATMENT Recommendations It is essential that the risks and benefits of initiating ART are discussed with all individuals with HIV-2. (GPP) We suggest that all people with HIV-2 start ART. (Grade 2C) We recommend that people with HIV-2 start ART in the following circumstances: If there is dual HIV-1 and HIV-2 infection; (Grade 1A) When a diagnosis is made during primary HIV-2 infection; (Grade 1C) If there is co-infection with hepatitis B (HBV); (Grade 1C) In pregnancy (see Section 9.1 Pregnant women); (Grade 1C) If there is detectable HIV-2 viraemia; (Grade 1B/C) If the CD4 count is below 500 cells/mm3; (Grade 1B) In advanced HIV disease, or if there are opportunistic infections; (Grade 1B) If there are symptoms, or an indicator condition for HIV-1 and/or HIV-2, regardless of CD4 count or viral load. (Grade 1C) We suggest that additional consideration is given to starting ART if there are significant comorbidities. (Grade 2D)

The rationale for these recommendations is considered in detail in the sections below.

6.1 Chronic infection