Nikhil Prasad Fact checked by:Thailand Medical News Team Jul 16, 2026 1 hour, 14 minutes ago
Medical News:
New Study Reveals Some Drug-Resistant CMV Variants Can Compete and Thrive, Raising Concerns for Transplant Patients
A new study has uncovered worrying evidence that certain drug-resistant strains of cytomegalovirus (CMV) are not only able to survive treatment but can also compete successfully with normal virus strains. The findings suggest that these resistant viruses could become increasingly common in vulnerable patients, particularly those who have received stem cell or organ transplants.
Scientists have identified a highly competitive drug-resistant CMV strain that could become increasingly common
in transplant patients treated with letermovir
The research was conducted by scientists from the Rega Institute for Medical Research, Department of Microbiology, Immunology and Transplantation, KU Leuven, Belgium.
Why CMV Matters
CMV is a common virus that usually causes few problems in healthy people because the immune system keeps it under control. However, for individuals with weakened immune systems, especially transplant recipients, CMV can trigger severe infections affecting the lungs, liver, digestive system, eyes, and other organs.
One of the most important drugs used to prevent CMV after transplantation is letermovir, which targets a viral protein known as the UL56 terminase. Although the drug has significantly reduced CMV disease, scientists have become increasingly concerned that the virus may quickly develop resistance through only a few genetic changes.
Certain Resistant Mutations Show a Dangerous Survival Advantage
The researchers compared several CMV strains carrying different resistance mutations to determine how well they multiplied when competing directly against normal virus strains and against other resistant viruses.
The standout mutation was UL56 C325F. Unlike several other resistant mutations, this variant replicated almost as efficiently as the normal virus even without antiviral drugs. Once letermovir was introduced, however, the C325F strain rapidly gained a major advantage and became the dominant virus population.
Other mutations, including C325W and C325Y, were much weaker. Although they also caused resistance to letermovir, they reproduced less efficiently and struggled to compete with both the normal virus and the C325F variant. Another mutation, V236M, showed some increase in growth under drug pressure but still could not consistently match the strength of C325F.
Competition Experiments Reveal How Resistance Can Spread
In this
Medical News report, one of the study's most important discoveries came from direct competition experiments that closely mimic what may happen inside patients.
When C325F was grown together with wild-type CMV or with other resistant strains, it repeatedly became the dominant virus whenever letermovir was present. Even more concerning, C325F was able to outperform several CMV stra
ins carrying resistance to completely different antiviral drugs that target the virus's DNA polymerase.
The researchers also found that resistance to letermovir remained highly specific. These resistant viruses generally stayed sensitive to older antiviral drugs such as ganciclovir, cidofovir, and foscarnet, while DNA polymerase-resistant viruses continued to remain susceptible to letermovir. This means doctors still have treatment alternatives, although selecting the most appropriate drug becomes increasingly important.
Why These Findings Are Important
The study helps explain why the C325F mutation is the drug-resistant CMV strain most frequently detected in hospitals worldwide. It combines two dangerous characteristics: extremely high resistance to letermovir and excellent ability to continue reproducing. Viruses carrying weaker resistance mutations may appear temporarily, but C325F has the biological advantage needed to persist and spread whenever letermovir is widely used.
Conclusion
The findings highlight that not all drug-resistant CMV strains behave the same way. While many resistant viruses lose strength, the UL56 C325F variant remains highly competitive and can quickly dominate viral populations during letermovir treatment. Continued surveillance, routine genetic testing for resistance mutations, and careful selection of antiviral therapy will be essential to prevent treatment failure and improve outcomes for transplant recipients facing CMV infections.
The study findings were published in the peer reviewed journal: Viruses.
https://www.mdpi.com/1999-4915/18/7/779
For the latest on cytomegaloviruses, keep on logging to Thailand
Medical News.
Read Also:
https://www.thailandmedical.news/news/new-antiviral-compound-shows-promise-against-dangerous-cmv-virus
https://www.thailandmedical.news/news/new-genotypes-of-human-cytomegalovirus-causing-ocular-diseases
https://www.thailandmedical.news/news/human-cytomegalovirus-infection-and-breast-cancer-risk
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