By: Angel Morgan
Rocky Mountain Spotted Fever (RMSF) is a bacterial infection caused by Rickettsia rickettsii and can be transmitted by a variety of tick species depending on the geographical region. For instance, the brown dog tick (Rhipicephalus sanguineus) is primarily
responsible for RMSF transmission in Arizona and Mexico [2,3]. Clinical manifestations of RMSF include fever, headache, rash, edema, and myalgia setting in 3-12 days after an infected bite [1,2]. The greatest number of RMSF cases and highest fatality
rates are seen in Native American tribal lands of Arizona, Baja California, and La Laguna, Mexico with a fatality rate up to 44% [2]. Combining nonspecific symptoms and a lack of a point of care diagnostic test makes RMSF difficult to diagnose [2].
Despite the disease being acknowledged for over a century and having a relatively high mortality rate, scientists have still not been able to develop an effective vaccine [2].
Dr. David Walker, who serves as the director for the Center for Biodefense and Emerging Infectious Disease (CBEID) and a professor in the Department of Pathology at the University of Texas Medical Branch (UTMB), and his collaborators have recently published an article in the Vaccines Journal that focuses on using a One Health approach to develop a vaccine against RMSF.
In their unique approach they seek to design a canine vaccine against R. rickettsii, rather than a traditional human vaccine. If effective, a canine vaccine would break the R. rickettsii zoonotic cycle, inhibiting rickettsial transmission in dogs. Infected
ticks would no longer be able to transfer R. rickettsii to humans, preventing numerous global RMSF cases a year. During an interview with Dr. Walker, he highlighted some of the obstacles for a vaccine rollout if one were to be developed. One of the
largest hurdles would be developing trusting and mutually beneficial collaborations across state and country lines to implement the vaccine globally. Another would be convincing pet owners to vaccinate their dogs. This is further complicated by the
fact “fluid ownership” exists in which pets are owned by a community rather than an individual, so the added challenge would be deciding who can give permission to vaccinate the dogs. This ownership style is common in rural parts of Mexico
or tribal lands of Arizona.
Dr. Walker believes UTMB is in a strong position to develop an RMSF canine vaccine given the availability of both the equipment and expertise needed to design a potentially commercial encapsulated mRNA vaccine. He and his team are also investigating the
possibility of using another bacteria from the Rickettsia genus, R. amblyommii, to induce proliferation of cross-reactive antibodies that can target R. rickettsii antigens [5]. R. amblyommii, which causes a subclinical infection, can be used as a "ready-made vaccine” against R. rickettsii and present a, “rapid approach to address this critical public health problem."UTMB is also home to many professors with previously established global collaborations that could aid
in the vaccine development and rollout process.
References:
Sexton, Daniel J., and Micah T. McClain. "Clinical manifestations and diagnosis of Rocky Mountain spotted fever." UpToDate May 18 (2016).
Walker, David H., et al. "A Vaccine for Canine Rocky Mountain Spotted Fever: An Unmet One Health Need." Vaccines 10.10 (2022): 1626.
“Rocky Mountain Spotted Fever (RMSF).” CDC, May 2019, Rocky Mountain Spotted Fever (RMSF) | CDC.
“Life cycle of Rhipicephalus sanguineus and the transmission of Rickettsia rickettsii (the causative agent of Rocky Mountain Spotted Fever.” Center for Global Health (U.S.). Division of Parasitic Diseases and Malaria. April 2017,
https://stacks.cdc.gov/view/cdc/53759
Blanton LS, Mendell NL, Walker DH, Bouyer DH. "Rickettsia amblyommii" induces cross protection against lethal Rocky Mountain spotted fever in a guinea pig model. Vector Borne Zoonotic Dis. 2014 Aug;14(8):557-62. doi: 10.1089/vbz.2014.1575. PMID:
25072985.