At least 60 percent of people living with HIV in Sub-Saharan Africa, including Zimbabwe, are becoming resistant to the key anti-retroviral drug, Tenofovir, raising fears among scientists that a strain of virus resistant to drugs might have developed.
The scientists, whose research was carried out in 36 countries between 2012 and 2015, said another possible cause of the resistance could be due to poor administration of the drug.
The study results showed that the 60 percent of people living with HIV continued to have an uncontrolled virus despite being treated with medications, including Tenofovir, compared to 20 percent in Europe.
The results further revealed that treatment failure as a result of drug resistance was common in people with a lower CD4 count due to HIV progression, and that the treatment worked best when begun with a high CD4 count.
The research, led by the University College London, looked at around 2 000 HIV patients worldwide over the four-year period.
Tenofovir is the common component in HIV treatment in most countries, including Zimbabwe.
In a paper published in The Lancet Infectious Diseases journal last week, co-author Dr Ravi Gupta said the figure of the HIV positive people resistant to drugs was likely to rise to 75 percent in the near future.
Dr Gupta described the results as "extremely concerning" and required a global effort coupled with cash investment to provide better facilities and monitoring in many African countries.
He said the high number of Africans resistant to Tenofovir could have been due to poor administration of the drug or that they were infected by someone who already had a drug-resistant form of virus.
"If the right levels of the drug are not taken, as in they are too low, or not regularly maintained, the virus can overcome the drug and become resistant," said Dr Gupta.
"Tenofovir is a critical part of our armamentarium against HIV, so it is extremely concerning to see such a high level of resistance to this drug.
"We certainly cannot dismiss the possibility that resistant strains can spread between people, and should not be complacent. We are now conducting further studies to get a more detailed picture of how Tenofovir resistant viruses develop and spread."
Dr Gupta said although the availability of second-line drugs was increasing, they were more expensive and have more side effects associated with them.
Head of Aids and TB Unit in the Ministry of Health and Child Care Dr Owen Mugurungi said they were still waiting for local results on the prevalence of resistance to tenofovir.
"We conduct early warning indicator drug monitoring survey, which look at our quality of care in order to limit development of resistance," he said.
"We also conduct regular resistance surveys in selected clinics throughout the country."
Dr Mugurungi said the last resistance survey locally was in 2013 when the country was still administering Stalanev combination (another form of antiretroviral drug) to people living with HIV, and it showed a 6,3 percent resistance to treatment.
"We have since moved away from that combination to the Tenofovir-based combination and we are currently awaiting local results on resistance to Tenofovir," he said.
Dr Mugurungi said Zimbabwe used a standardised treatment protocol which emphasised on maintaining one drug regimen.
He said HIV positive people in Zimbabwe could only be moved to another combination of drugs when they began to show signs of resistance, unlike in other African countries which switch patients depending on availability of drug combinations.
According to World Health Organisation guidelines, drug resistance should be less than 5 percent.
An estimated 1,2 million people are living with HIV in Zimbabwe from which 63,4 percent of adults and 55 percent of children are on treatment.