In the Story of the Rubella Virus as a Source of Granulomas, the Plot Is Still Thickening

SAN DIEGO — Approximately 10 years ago in France, high throughput screening in a series of cases suggested that vaccine-derived rubella virus was the surprising cause of persistent cutaneous granulomas, but an update at the annual meeting of the American Academy of Dermatology suggests this phenomenon is not as rare as once supposed.

Based on accumulating evidence, the Centers for Disease Control and Prevention (CDC) through collaborations with others also recognized this in pediatric patients with inborn errors of immunity, and it is now appropriate for clinicians to consider this etiology when no other infectious agents can be identified, according to Karolyn A. Wanat, MD, professor of dermatology, Medical College of Wisconsin, Milwaukee, who spoke about rubella as a trigger in granulomatous disease at the meeting. “This is a huge evolving area of interest,” said Dr. Wanat, who has been the first author or coauthor on several published papers, including a review article published earlier this year.

In the earliest cases, including those reported in 2014, the cutaneous granulomas presumed to be causally related to vaccine-derived rubella virus were found only in those with a primary immunodeficiency. This is no longer the case. In a collaboration among US clinics, granulomas that had persisted for years in immunocompetent adults were identified, according to Dr. Wanat, the first author of a report on these findings in four adults in 2022. In addition, it now appears that wild-type rubella virus, like vaccine-derived rubella virus, can be the source of the antigenic response that underlies the development of rubella-associated cutaneous granulomas.

“These are the types of granulomas that we would be thinking infection. If tissue cultures are negative, we would probably repeat them,” she said, suggesting that suspicion of an infectious etiology would probably remain high even after multiple negative tests.

Of the cases accruing in the United States and elsewhere, most but not all have been linked to inborn errors of immunity. In a 2020 CDC review, the risk of granulomas caused by compromised immunity, such as defects in T cell function, was estimated to be in the range of 0.6% to 2.5%, Dr. Wanat said.

It is now known that primary immunodeficiency is not a prerequisite, but this should not change the perception that the rubella vaccine, which was introduced in 1979, is effective and safe, according to Dr. Wanat. The vaccine is associated with few serious adverse events and is so effective that rubella was eliminated from the United States in 2004 and from the Americas in 2015.

This makes cases of granuloma associated with wild-type rubella virus surprising, but they appear to be exceedingly rare. Whether caused by vaccine exposure or another source, the mechanism of latent development of cutaneous granulomas is consistent with other infectious sources, and is not well understood.

“Rubella is a sneaky virus that can persist in some immunoprivileged sites indefinitely,” Dr. Wanat said. These sites include the eyes, joints, and placenta.

Many initial cases of rubella-associated granulomas occurred on the arms, presumably where the vaccine was administered, despite long intervals between exposure and lesion growth. This interval is often measured in years.

With more cases, it is now understood that involvement of other organs does occur even if the skin is the most common site of antigenic response in patients with immunodeficiency. The liver and lymph nodes represent other tissues that have been affected. Even lesions in the brain have been seen on autopsy.

Based on the benefit-to-risk ratio of a highly effective and successful vaccine, however, the association with a risk of granulomas “should not raise questions” about the value of the vaccine itself, Dr. Wanat noted.

“The proportion of patients who develop these granulomas is very, very low. Yet, the vaccine provides life-long immunity,” she said.

The discovery of granulomas associated with wild type rubella infection was “shocking” based on the supposition that the rubella virus had been eliminated, but this is just one of the unexpected discoveries as the still-evolving science has traced the story of rubella-associated granulomas over the past 10 years.

Cases now include children and adults through advanced ages.

Shedding of the virus and risk of infection to others has been studied but so far, the risk — if it exists — is very low. The evidence includes the many patients who have lived with the granulomas for years, even decades, without any known spread to others.

As for ongoing work in this area, Dr. Wanat said that a histopathological case definition for rubella-associated granulomas is being developed, and she and other investigators are actively seeking new cases to better characterize the disease.

So far, optimal treatment is not well defined. A number of strategies have had limited success or are considered impractical for routine use. One example is a stem cell transplant. In a case Dr. Wanat cited, complete resolution of the skin lesions was achieved with a transplant.

“I am not suggesting that those with localized disease in the skin should undergo a transplant, but it does support the role of the immune system and the potential for a reboot to clear the skin,” she said.

Other therapies associated with benefit in at least some patients include tumor necrosis factor (TNF) inhibitors with dapsone and ribavirin. The risk of adverse events for the latter might again limit its use, Dr. Wanat said.

With awareness, the number of granulomas found to be associated with rubella virus is expected to grow. Dr. Wanat speculated that those areas of the country that not yet have documented a case will do so over time. For idiopathic cases of cutaneous granulomas, rubella should be kept in mind, she said.

Characterizing rubella-associated cutaneous granulomas as “a public health concern,” Dr. Wanat urged clinicians to consider this etiology in lesions that match the phenotype, particularly when other more common infectious agents cannot be identified.

Asked for his perspective, Jeffrey P. North, MD, managing director of the UCSF Dermatopathology, and professor of dermatology and pathology at the University of California, San Francisco, agreed that rubella should be considered as a source of granulomas with a suspected infectious etiology when a pathogen cannot be found.

“It is likely much more common than we know as it has only been recently described and testing for it is limited. I suspected there are a lot of undiagnosed patients suffering from this disease,” Dr. North said in an interview.

“One of the important points for clinicians to consider is that while this has been reported mostly in patients with some form of immunodeficiency, there have also been patients reported to have this condition with no immunodeficiency,” he added. Even though the association between rubella and granulomas was made 10 years ago, awareness is only now spreading, which means the frequency with which rubella leads to granulomas remains uncertain.

“I think we will start to get a better idea of how common this is as more people learn about and testing for it expands,” Dr. North said.

Dr. Wanat reports no potential conflicts of interest. Dr. North reports financial relationships with AdviNow and Kiniksa Pharmaceuticals.