Rocky Mountain spotted fever: researchers seek vaccine against disease

Developing a vaccine requires time and scientific rigor. Safety and efficacy are priorities throughout the research and development process

Rocky Mountain spotted fever, a tick-borne disease, has worried health officials and experts for decades. Caused by the bacteria Rickettsia rickettsii , the disease can lead to serious complications and even death if not treated early. Despite the seriousness and the number of cases that have occurred in recent months, especially in the interior of São Paulo and Minas Gerais, its occurrence is relatively sporadic when compared to other infectious diseases, even those caused by insect vectors, such as dengue, Chikungunya and Leishmaniasis. According to the Ministry of Health, from 2012 to 2022, 2,157 cases and 753 deaths from Rocky Mountain spotted fever were confirmed .

So far, there is no vaccine available to prevent Rocky Mountain spotted fever and treatment is based on the use of antibiotics. Professor of Clinical Parasitology at the School of Pharmacy at the Federal University of Ouro (UFOP), Dr. Alexandre Reis, one of the most influential scientists in the area of ​​Immunology in Brazil, believes that it would be more rational to think about the development of a vaccine to combat ticks in domestic and wild animals in risk areas than a vaccine to protect against infection by the bacteria. Rickettsia rickettsii .

According to the professor, a future vaccine against tick infestation may reduce the chance of these hosts carrying the vector, that is, the star tick. “For example, a vaccine that uses salivary antigens may make it more difficult for ticks to infest, since some work as a ‘Trojan horse’ for various pathogens (including Ricketis ) . If they are neutralized, the ticks lose or have their vector competence diminished”, warns Dr. Kings.

Studies seek pathways to vaccines

A study by the Institute of Biomedical Sciences at the University of São Paulo (ICB-USP) identified a way to reduce the growth of the bacteria that cause Rocky Mountain spotted fever in ticks and make them more resistant to infection. Knowledge of this mechanism of interaction between host and bacteria makes it possible to advance methodologies for vaccine development. The article, entitled “ Tick Immune System: What Is Known, the Interconnections, the Gaps, and the Challenges ” , published in 2021, in the journal Parasites & Vectors, demonstrated the possibility of silencing the gene of the main protein responsible for preventing programmed death of cells, called apoptosis, in the star tick. The research builds on previous studies that showed that Rickettsia rickettsii ,inhibits the death of tick cells, which favors the growth of the animal, giving more time for the bacteria to proliferate and infect new cells.

The Doctor. Erol Fikrig, a researcher at the Yale School of Medicine, and his group, have been developing a vaccine for Lyme disease, also transmitted by ticks ( Ixodes scapularis ). The strategy of this immunizer employs 19 antigens from Ixodes scapularis , most of which are from the saliva of this tick. Recently, this group of researchers tested an mRNA vaccine that was capable of inducing resistance in ticks and preventing the transmission of the etiologic agent of Lyme disease, Borrelia burgdorferi . Immunization of guinea pigs was able to induce immunity and prevent Borrelia burgdorferi infection .

Although it is a goal of the Pan American Health Organization (PAHO)  to encourage basic scientists to develop effective vaccines against Rickettsiosis and Ehrlichiosis, we are still far from having a vaccine against spotted fever in the short and medium term. “I see that we are still far from a promising vaccine and we also have no way of evaluating what the immunization strategies would be, the targets, if we are going to think about a vaccine to prevent thetick infestations,” emphasizes Dr. Kings. However, the researcher does not believe that a good strategy would be to vaccinate the capybaras with a tick vaccine. For him, carrying out population control can bring more effective and faster results than a vaccine itself. “On the other hand, a vaccine against the pathogen, Rickettsia sp , for a relatively low-prevalence disease, also does not make much sense from the point of view of public health, much less of corporate biotechnological investment”, he recognizes.

Lastly, Dr. Reis points out that until the development of a vaccine, information, training and dissemination of knowledge to sensitize health professionals and the population about Rocky Mountain spotted fever, how to carry out the diagnosis as quickly as possible and start medication as soon as suspicion arises of contact with ticks is defined, are the tools available against this serious and potentially fatal disease. The efforts of scientists and the collaboration between research institutions and governments are essential to boost the development and availability of a future vaccine, which will help protect people exposed to the risk of contracting Rocky Mountain spotted fever, especially thosewho work in rural and forested areas where exposure to ticks is more common. While we await research progress, it is critical to maintain awareness of the risks of the disease and adopt preventive measures, such as avoiding tick-infested areas, using repellents, and performing careful body checks after outdoor activities.

To learn more about Rocky Mountain spotted fever, check out the article published by the Brazilian Society of Tropical Medicine (SBMT) in February. Click here .

Access the Technical Note from the Ministry of Health : Epidemiological Surveillance Guidelines from the Ministry of Health to the State Health Secretariats for the period of seasonality of spotted fever in Brazil and other referrals.