Recent developments in the field of infectious diseases have placed tick-borne rickettsioses (TBR) in the spotlight as an emerging threat to public health in mainland Portugal.

These neglected zoonoses stem from obligate intracellular α-proteobacteria of the spotted-fever group, predominantly represented by various strains of the genus Rickettsia. The Mediterranean Spotted Fever (MSF) caused by Rickettsia conorii is the most prevalent form in Europe, but it is not alone; tick-borne lymphadenopathy (TIBOLA) and Mediterranean spotted fever-like (MSF-like) diseases significantly endanger human health as well.

Understanding the Risks

Rhipicephalus sanguineus sensu lato ticks are not just primary vectors—they also act as reservoirs, sustaining the MSF pathogen through transstadial and transovarial transmission. Moreover, domestic dogs can contribute to the persistence of MSF in ecosystems.

Common symptoms include fever, rash, and an eschar at the tick bite site, particularly prevalent during the summer months when tick activity peaks.

A concerning development is the expanded recognition of TIBOLA, primarily linked to Rickettsia slovaca, R. raoultii, and Candidatus R. rioja. The association of these pathogens with human cases has been well-documented since the late 1990s, with symptoms such as neck lymphadenopathy mimicking other tick-borne infections. Other names like “Dermacentor-borne necrosis erythema lymphadenopathy” (DEBONEL) and “scalp eschar and neck lymphadenopathy” (SENLAT) are being used to describe similar clinical manifestations.

Multiple Vectors: A Growing Concern

The number of tick species that transmit rickettsial diseases continues to grow. Notably, Ixodes ricinus, commonly known as the castor bean tick, has been found to harbor several rickettsial agents including R. helvetica, which was termed the “Swiss agent” for many years before human pathogenicity was confirmed.

Despite initial ambiguity regarding its impact on human health, R. helvetica has been associated with severe cases, including fatal outcomes in Sweden.

Likewise, R. massiliae was identified for the first time from ticks in France and has been confirmed in Portugal, albeit without documented human cases. Lethargy and low platelet counts were observed in infected dogs, highlighting the potential risks to domestic animals.

The Call for Greater Awareness and Surveillance

In response to the escalating risks, recent studies conducted in Portugal have provided molecular evidence of several rickettsial species circulating among questing ticks. The study collected ticks from diverse ecological regions across mainland Portugal between 2018 and 2021, contributing invaluable data on the distribution and prevalence of these infectious agents.

One alarming finding revealed an overall rickettsial infection prevalence of 10.31% among pooled samples of nymphs, while adult ticks yielded a separate prevalence determined via standard testing.

However, estimates may still be undervalued, and continuous surveillance programs are mandated to safeguard both human and animal health.

Moreover, specific findings included the presence of R. helvetica in ticks, although no human cases have yet been recorded in Portugal. The detection of R. slovaca and Candidatus R. rioja also raises red flags, as these pathogens are crucial causes of TIBOLA, and recently reported cases underscore the urgent need for public health interventions.

Conclusion: Stay Informed and Prepared

The growing body of research paints a vivid picture of the complex interplay between ticks and rickettsial diseases in Portugal. With vectors emerging and changing, it is essential for the public and health authorities to stay informed.

Awareness campaigns, strict tick surveillance, and prompt disease reporting will be vital to addressing the threats posed by tick-borne rickettsioses. Protect yourself by avoiding tick-infested areas, using insect repellent, and promptly checking for ticks after outdoor activities—because in this battle for health, knowledge and preparation are your best allies!