First Case of Sexually Transmitted Dengue in Spain and Europe

Carla Nieto Martínez

November 15, 2019

MADRID - Spain confirmed the first case of sexually transmitted dengue, according to health ministry officials in Madrid. This is the first case of sexual transmission of the dengue virus described in Europe, and also the first case reported in men who have sex with men.

As reported by the Consejería de Sanidad, in September, Hospital Ramón y Cajal staff in Madrid notified Madrid’s Dirección General de Salud Pública of the two cases of dengue (one native and one imported) in two local men.

The first detected case was that of a 36-year-old man who had not left Spain in the 45 days prior to the onset of symptoms (fever, headache, back pain, myalgia, diarrhoea and rash).

His partner, a 41-year-old male, presented very similar clinical conditions with the onset of symptoms 10 days earlier. He had a history of travelling to Cuba and the Dominican Republic during the incubation period, so it was considered an imported case. Infection was suspected in the two men because of raised C-reactive protein in serum and urine, respectively, and diagnosis was later confirmed by the laboratory of the Spanish National Centre for Microbiology.

Mosquito Vector Ruled Out

Once the notification of both cases was received, responsive actions against vector-borne diseases were launched as stipulated in the surveillance protocols of the National Network for Epidemiological Surveillance and the National Plan for Preparedness and Response.

Dr Paz Sánchez-Seco, head of the Arbovirus laboratory at the National Centre for Microbiology at Carlos III Health Institute, in Madrid, told Medscape in Spanish that "the Community of Madrid has conducted active screenings to detect possible outbreaks of Aedes albopictus since 2017".

"In this particular case, once we became aware of this infection, entomological surveillance actions were carried out in the immediate vicinity of the places frequented by both patients, finding no indication of the presence of said mosquito."

In particular, entomological investigations were carried out at the homes of those affected, as well as in the immediate surroundings of the houses and in another municipality of the Community of Madrid that they had visited. The results were negative for Aedes albopictus, the mosquito vector of the disease present in Spain.

In both cases, partial sequencing of the virus and subsequent phylogenetic analysis confirmed that it was the dengue virus, and that the viral sequence obtained was identical in both patients. This was consistent with what had already been detected in other imported cases from Cuba that had been analysed at the Spanish National Centre for Microbiology.

The two male patients had unprotected sex within 3 days after the onset of symptoms of the imported case, so semen samples were requested for both.

Through direct laboratory techniques, "analysis confirmed the dengue virus infection in both patients. Subsequently, the dengue virus genome was detected in semen samples from said patients, and the sequence of the analysed fragment was determined to be identical," explained Dr Sánchez-Seco. Therefore, in the absence of data supporting a possible vector transmission, the sexual route was considered the most likely in this case.

Sexual Transmission Probably Uncommon, but Possible 

"Dengue virus is a virus that is transmitted through the bite of infected mosquitoes. However, this finding supports the possibility that the virus is capable of being transmitted sexually, although the risk at the population level is considered very low," said Dr Sánchez-Seco.

"Knowing that the sexual route is a possible way of transmitting the virus, it might be appropriate that this possibility is considered in the presence of new native and imported cases, as well as focusing on the prevention of vector mosquito bites," said the specialist.

Along the same lines, Dr Francesca Norman, deputy physician of the National Reference Unit of Tropical Medicine and Infectious Diseases of Ramón y Cajal University Hospital, IRYCIS, in Madrid, and a member of the Spanish Society of Infectious Diseases and Clinical Microbiology, told Medscape in Spanish that according to the World Health Organisation, worldwide, there are approximately 390 million annual infections due to dengue, and around 96 million are symptomatic.

"However, the possibility of the sexual transmission of the dengue virus had not been clearly described until now, although it is possible that some cases have gone unnoticed or have been attributed to a vector transmission."

On the recently reported case in Madrid, Dr Norman said that this supports the possibility that dengue virus can be transmitted sexually, although at this time that possibility is still considered rare.

Likewise, Dr Norman stressed the need to maintain epidemiological surveillance in non-endemic areas so that new cases of dengue can be detected, and their origin investigated if necessary. "At the moment, prevention measures are based on avoiding vector bites and precautions to prevent transmission by transfusion of blood products and organ transplantation.

"However, these recommendations may be revised in the future with the objective of preventing sexual transmission, although currently the available scientific evidence does not support that it is an important route of transmission of this virus."

More Cases and Other Routes of Transmission?

In scientific literature there is only one case described of a possible contagion of the dengue virus by sex, from 2013, in South Korea. The patient had no history of travelling to an endemic area; however, he contracted the disease after unprotected sex with a woman who had acquired the infection in Indonesia.

In both cases the dengue-1 virus serotype was detected, and genomic sequencing confirmed that it was the same virus. Unlike the cases in Madrid, in the area where these events occurred Aedes albopictus was present, so the vector transmission could not be completely ruled out.

While the case in South Korea is the first recorded sexually transmitted infection in a heterosexual relationship, that of Madrid is considered the first described in men who have sex with men.

The evidence of a possible transmission of dengue virus by means other than the bite of the infected vector mosquito makes it necessary to assess, for example, the potential risk of maternal-foetal transmission.

Dr Norman commented: "This possibility has been described infrequently, with vertical transmission rates varying with the gestation period (there is an increased transmission risk if maternal dengue infection occurs in the late peripartum period). Similarly, maternal dengue virus infection during pregnancy may be associated with premature delivery, low birth weight and foetal distress."

Dr Norman pointed out that the main control measures for dengue virus continue to focus on vector mosquito control and protection against bites. "Vaccines against dengue virus have been developed but are currently not marketed in non-endemic countries."

Low-Risk but Awareness Important

Madrid’s Ministry of Health pointed out that although the sexual transmission route is very rare and has a low epidemiological relevance, it is important that health professionals are informed of the possibility of this contagion mechanism. They should always notify dengue cases to the Department of Public Health to facilitate the detection and investigation of new cases, and also contemplate including in their recommendations the prevention of sexual transmission.

Regarding the need to raise public awareness about the risk of contagion of dengue virus, especially as a result of the notification of this case, Dr Sánchez-Seco said that society should be calm, and emphasised the importance of consulting specialists in case of visiting potentially endemic countries.

"Travellers should know that before going to areas with a possible risk of infection, they should contact specialised travel health centres, which can advise on how best to avoid infections by dengue virus and/or any other circulating pathogen in the area. Upon their return, if they are ill, they should attend a health centre and make clear their status as recent travellers."

On the current situation in the Spanish territory and the possible repercussions of climate change (especially in the light of recent heat waves), Dr Sánchez-Seco commented that "dengue virus is considered an emerging virus in Spain, with numerous cases, more than in previous years. The number of cases in travellers reflects what happens in the endemic areas where they come from.

"In fact, the Pan American Health Organisation quantifies an increase in the Americas of 101.5% compared with 2018, with Brazil being the country that reports the most cases.

"The high activity of the virus in endemic areas is favoured by an increase in competent vectors, which also depends on the weather. Meanwhile, in non-endemic areas such as Europe, climate change is producing an expansion of the Aedes albopictus vector. Since 2007, virtually every year there have been declared cases of autochthonous infection by dengue virus or similar viruses, such as zika or chikungunya; that is to say, global warming promotes higher quantities of mosquito vectors, which expand to zones with temperate weather. Hence the sporadic appearance of these infections in Spain and surrounding countries is likely", she concluded.

Doctors Sánchez-Seco and Norman have declared no relevant conflicts of interest.

Community of Madrid. Public Health Alerts. Caso de dengue autóctono de transmisión sexual en la Comunidad de Madrid. Published on November 8th 2019. Consulted in electronic version. Source.

Adapted and translated from Medscape Spanish Edition.


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