Evidence for Mother-to-Child Transmission of HIV-2 in Uganda: A Retrospective Analysis
Authors: Kushemererwa Grace Esther , Sam Acellam , Kemigisha Oreen , Nabitaka Linda Kisakye , Namulindwa Christine , Katureebe Cordelia , Nabadda Susan , Ssewanyana Isaac 
Published: January 2024

Background

HIV-2 prevalence is poorly understood outside its West African epicenter, contributing to gaps in global epidemiolocal understanding. Cases have been identified in countries like India, Europe, and the Americas, largely due to migration and travel. With a clinical presentation marked by lower viremia and reduced transmission risk, HIV-2 progresses to AIDS more gradually than HIV-1. However, it can still lead to significant health issues. The overlap in diagnostic profiles for HIV-1 and HIV-2 often results in the under-recognition of the latter in areas where HIV-1 is dominant. This under-detection poses challenges in eradicating the epidemic, as current testing protocols may not adequately differentiate between the two strains. In Uganda, we recently transitioned to the Roche Cobas 8800/6800 using the Cobas®HIV-1/HIV-2 Qualitative nucleic acid test, for the early infant diagnosis of HIV. The platform has the ability to differentiate between HIV-1 and HIV-2 to detect presence of HIV-2 in DBS, Serum, Plasma and whole blood samples. This represents a pivotal shift toward refining early infant diagnosis and underscores the need for nuanced surveillance to address the distinct epidemiology of HIV-2.

Method

Twenty-four thousand six hundred and nineteen (24,619) Dry blood spots (DBS) collected from infants under 18 months old, all born to mothers living with HIV AIDs in Uganda were tested according to the Uganda consolidated guidelines for HIV prevention and treatment. These were tested for routine early infant diagnosis (EID) at the centralized reference lab as per the Uganda national HIV consolidated guideline. Testing was performed using the Cobas®HIV-1/HIV-2 Qualitative nucleic acid test for use on the Cobas®5800/6800/8800 Systems. This advanced testing method not only detects HIV but also differentiates between HIV-1 and HIV-2, which is crucial for accurate diagnosis and treatment. It’s a reliable test, with a specificity confirmed to be 100% (95% confidence limit: ≥ 99.5%) and it is both FDA approved and WHO Pre-qualified.

Results

Of the 24,619 DBS tested between May and November 2023, 466 were confirmed positive (1.9%). Four (4) of the 466 (0.9%) were confirmed HIV-2. These 4 are from Kampala (1), Kagadi (1), Namutumba (1), and Oyam (1) districts. The HIV-2 positive samples had higher CT values (39.2, 40.33, 40.35, 44.62) compared to the average less than 30 for the HIV-1 positive samples and are representative of the 95thpercentile. The significance of the CT (cycle threshold) values obtained for HIV-2 positive samples is crucial for understanding the viral load and transmission risk. Compared to HIV-1, HIV-2 is generally associated with lower viral loads, as indicated by higher CT values in PCR testing. This lower viral load is a key factor in the reduced transmissibility of HIV-2 compared to HIV-1. In the context of mother-to-child transmission, the CT values can provide insights into the risk of transmission from mother to infant. Typically, a higher CT value (indicating a lower viral load) would suggest a lower risk of MTCT for HIV-2. This distinction is important for tailoring prevention and treatment strategies specifically for HIV-2, considering its unique virological characteristics compared to HIV-1.

Discussion

This study marks a pioneering report on the possible transmission of HIV-2 from mother to child in Uganda, with 4 cases identified between May to November 2023. The HIV-2 positive samples exhibited high CT values, indicative of low viral load that is characteristic for HIV-2. Further investigations are ongoing to gather more details about the HIV-2 positive infants and to perform alternative tests to rule put non-specificity.