A new rickettsial pathogen causing severe illness has surfaced in Northern California. Learn all about this emerging tick-borne disease, from prevention and treatment to diagnostic challenges.
Researchers have identified a new bacterial species, Rickettsia sp. CA6269, responsible for causing severe illness similar to Rocky Mountain spotted fever. in Northern California. This new pathogen, discovered by the California Department of Public Health, has added another rickettsial pathogen to the list of those transmitted by ticks on the West Coast.
Discovery and Initial Findings:
Rickettsia sp. CA6269 was first identified in rabbit ticks (Haemaphysalis leporispalustris) collected in Northern California in 2018. The researchers have suggested naming this pathogen Candidatus Rickettsia lanei, honoring Dr. Robert S. Lane, a prominent researcher in tick-borne diseases. The discovery was made using advanced techniques like multilocus sequence typing, which revealed this pathogen's close resemblance to Rickettsia rickettsii, the bacterium that causes Rocky Mountain spotted fever.
Case Studies in Northern California:
Two severe cases of Rocky Mountain spotted fever-like illness caused by Rickettsia were documented in the San Francisco Bay Area nearly 20 years apart. In both cases, the patients did not recall being bitten by ticks, although one saw a tick crawling on his body. The first patient experienced high fever, severe headache, nausea, vomiting, and other symptoms after golfing in the area in July 2023. Despite being treated with antibiotics, he went into a coma and had severe complications, including gangrene.
The researchers then went back to old samples stored from 8 other Rocky Mountain spotted fever cases that had occurred over the years and discovered a second patient had also been infected with Rickettsia sp CA6269 in 2004. Thispatient, who had been camping, also developed severe symptoms and was hospitalized for 13 days i.The researchers then developed a specific test (real time PCR) that can distinguish this new Rickettsia pathogen from other Rickettsia species.
The researchers also tested ticks from the 5 golf courses that the first patient had played at prior to his illness. Out of the 197 ticks that they collected, none of them were rabbit ticks and nor were they infected with any Rickettsia species. Rabbit ticks also rarely attach to humans, so further studies are needed to determine the vectors that transmit this new Rickettsia species as well as its geographic location.
Diagnostic Challenges and Treatment:
Rickettsial infections are often under-diagnosed because of a lack of awareness and specific diagnostic tests. Early symptoms can be non-specific, such as fever and headache, making early diagnosis challenging. Usually within 2-4 days after developing a fever, 90% of individuals will develop a rash that looks like small pink or red like flat splotches on the forearms and legs before spreading to the rest of the body. However those who fail to develop a rash or have an atypical rash have an increased chance of being misdiagnosed.
Both patients were initially misdiagnosed and treated without doxycycline, the recommended antibiotic for rickettsial infections. After their conditions worsened, they were correctly diagnosed with rickettsial disease and treated with doxycycline, which led to gradual recovery.
Preventative Measures:
Rickettsial diseases, including Rocky Mountain spotted fever, are severe and can be life-threatening if not promptly treated. While Rickettsia species are rare in California, the incidence of spotted fever group rickettsioses in the USA has tripled since 2010. Therefore it is important for increased awareness among healthcare providers and the public. It's crucial to consider rickettsial infections in patients presenting with febrile illnesses, especially if they have a history of outdoor activities. Spotted fever group rickettsioses can occur across the United States as they can be spread through American dog ticks, the Rocky Mountain wood tick, and brown dog ticks. Over 60% of cases are reported in North Caroline, Oklahoma, Arkansas, Tennessee and Missouri.
To reduce the risk of rickettsial infections, individuals should take preventive measures against tick bites. This includes using insect repellents, wearing protective clothing, performing regular tick checks, and avoiding areas known to be infested with ticks. Early removal of ticks is essential as the risk of infection increases with the duration the tick is attached.
Concluding Thoughts:
Further research is needed to understand the epidemiology and ecological distribution of Rickettsia sp. CA6269. Identifying the full range of vectors and host species will help develop better preventive strategies and diagnostic tools. Continuous monitoring and public health efforts are essential to manage and control the spread of this newly recognized pathogen.
The discovery of Rickettsia sp. CA6269 highlights the complexity of tick-borne diseases and the need for comprehensive strategies to diagnose, treat, and prevent these infections. Increased vigilance and research are critical to improving patient outcomes and reducing the incidence of rickettsial diseases.
For more information, visit the CDC's page on Rocky Mountain Spotted Fever and related rickettsial diseases, and stay updated with the latest research and guidelines.
For more details on the symptoms, diagnosis, and prevention of rickettsial diseases, visit the CDC website
References
Probert WS, et al. Newly recognized spotted fever group Rickettsia as cause of severe Rocky Mountain spotted fever–like illness, Northern California, USA. Emerg Infect Dis. 2024 Jul;30(7). https://doi.org/10.3201/eid3007.231771
Eremeeva ME, et al. Detection and characterization of a novel spotted fever group Rickettsia genotype in Haemaphysalis leporispalustris from California, USA. Ticks Tick Borne Dis. 2018 May;9(4):814-818. doi: 10.1016/j.ttbdis.2018.02.023. Epub 2018 Mar 1. PMID: 29545107***
