A study led by Catalan researchers aims to identify the main vulnerability factors to HIV in the population of Madagascar, a country that has had a low prevalence until now but has seen an increase in infections in recent years. The goal is to analyze why the infection could transition from being limited to specific vulnerable populations to becoming widespread.

The first cases of AIDS were described in San Francisco (USA) in 1981, and its infectious nature, isolation of the causative agent, HIV, and transmission mechanisms were soon determined. At that time, the world became aware that the infection was already widespread in sub-Saharan Africa, where most infections still occur today, specifically in southern Africa with a pattern of generalized epidemic, where the majority of cases are detected in the general population with a prevalence above 2 or 3%. In contrast, a concentrated epidemic is one where most cases occur in well-identified at-risk populations, such as sex workers, men who have sex with men, or injectable drug users.

Dr. David Alonso, a researcher at the Center for Advanced Studies of Blanes (CEAB-CSIC) and article’s coauthor, comments: “Determining the factors influencing the transition from a concentrated HIV epidemic to a generalized one is essential for establishing prevention measures and avoiding this generalization, as well as understanding why some countries or regions in sub-Saharan Africa show different epidemic patterns.”

Xavier Vallès, doctor in A team of doctors and researchers from various hospitals and research centers, including the Foundation Fight against Infections (PROSICS. Catalan Institute of Health, and Germans Trias i Pujol Research Institute) and David Alonso, researcher the Center for Advanced Studies of Blanes (CEAB-CSIC), explores in the study titled “A potential transition from a concentrated to a generalized HIV epidemic: the case of Madagascar” (published in the Infectious Diseases of Poverty Journal) these mechanisms. They analyze vulnerability factors present in Madagascar along with available epidemiological data and the specific cultural, geographical, and political factors of the country.

Difference between a concentrated and a generalized epidemic from a public health perspective

From a health perspective, the shift from a concentrated to a generalized epidemic is a paradigm shift for HIV and AIDS control and prevention. In a concentrated epidemic, public health actions can be focused to contain it in well-defined vulnerable groups, and if controlled in this population, it protects and may even recede in the general population. In other words, the epidemic cannot persist if controlled in these population segments. On the other hand, if we have a generalized epidemic, it will persist despite focused actions on the most vulnerable groups, and there will no longer be an opportunity to contain it with many fewer resources and very targeted actions, such as promoting the use of sterile syringes among injectable drug users or Pre-Exposure Prophylaxis (PreP) and condoms in other groups. Preventing this transition is, therefore, crucial.

Madagascar as a case study

This research uses Madagascar as a case study to determine the epidemiological transition of HIV. The island of Madagascar is located off the east coast of Africa, near Mozambique and South Africa, with a population of approximately 30 million people. In contrast to southern Africa, Madagascar shows, according to official data, a low HIV prevalence in the general population (less than 1%), along with a high HIV prevalence among vulnerable populations on the island (above 10 or 15% in many cities). Therefore, it fits the model of a concentrated epidemic, which is surprising considering that in Madagascar, well-known risk factors associated with HIV acquisition are widespread: erratic and inconsistent condom use is prevalent in the young population, along with a high prevalence of multiple sexual relationships, the increasingly widespread practice of transactional sex among young girls fueled by poverty, and the very high incidence of Sexually Transmitted Infections (STIs). Since the 90s, previous studies had predicted that Madagascar was close to the epidemiological turning point, and therefore, the country would transition from a concentrated infection in the at-risk population to a generalized epidemic in a few years. The fact is that this transition has not yet occurred to this day; why has this not happened? This scenario is very interesting to explore these transition mechanisms and, above all, find answers to justify and implement appropriate control and prevention measures if this risk is confirmed.

In recent years, doctors and health workers across the country have been warning of an increase in infections in the general population. This fact should alert health authorities.

So why do we not yet observe a generalized epidemic like in neighboring countries? The study suggests that the late introduction of HIV to the island and the traditional practice of male circumcision, which protects against HIV transmission, could have slowed or delayed the spread of HIV in the country. However, the study also points out that considering this increase in infections in recent years and the interaction of risk factors associated with young women, along with the effect of acute HIV infections on epidemiological dynamics, neither the protective effect of circumcision nor the late introduction of the virus into the country are sufficient to contain the disease’s expansion in Madagascar. Therefore, it is considered a plausible scenario that the epidemic will generalize in the coming years.

Work Methodology

This is a modeling study that has used all available epidemiological and demographic data in Madagascar, as well as an exhaustive literature search for risk and protective factors in the country. All this information has been parameterized with necessary and plausible assumptions based on HIV knowledge in other better-studied contexts. This allowed the creation of a mathematical model that replicates how all the evaluated factors interact (circumcision, dates of virus introduction to Madagascar, general population behavior, and specifically that of younger women, interaction between sex workers and the general population, HIV infectivity at different stages of the disease, etc.).

Conclusion: Madagascar may experience a silent transition of the HIV epidemic

In conclusion, the study determines that at this moment, there is not enough empirical evidence to specify the current epidemiological situation of HIV in Madagascar due to the weakness of the epidemiological surveillance system. Still, the results very clearly suggest that Madagascar may be very close to a change that points to a high epidemic prevalence in the general population similar to neighboring countries like South Africa or Mozambique in a few years. This generalization would have serious consequences in an already impoverished country with a very weak healthcare system. It also highlights gender vulnerability and poverty at the root of this possible generalization. The most important conclusion is that in this scenario, action is needed at two levels: strengthening the response to HIV and implementing a more robust epidemiological surveillance system to better determine the real situation and act accordingly. The study also provides a comprehensive model that includes biological, behavioral, cultural, and even geographical factors that can help better study the epidemiological dynamics of HIV in other countries.

Dr. Xavier Vallès, a researcher at the Foundation Fight against Infections and one of the researchers who led the study along with Dr. David Alonso from the Center for Advanced Studies of Blanes (CEAB-CSIC), emphasizes: “Our research highlights the need for more qualitative and quantitative data to understand the current dynamics of HIV/AIDS in Madagascar. This lack of information should urge the leaders of the country’s public health and international agencies that fund and support HIV responses in low- and middle-income countries to increase efforts to gather more data and improve infection diagnostics. Our research aims for nothing more than drawing attention to a probable public health crisis and helping lay the groundwork

This study shows how collaboration between disciplines and centers is often the key to obtaining significant results.