Knowledge, Attitudes, and Practices Regarding Ticks, Tick-Borne Diseases, and Ethnomedicine Among an at-Risk Population in Kerala.

Tick and tick-borne diseases (TBDs) are increasing annually, and the study of ticks has gained importance after the outbreak of Kyasanur Forest disease (KFD) in the South Western Ghats of India. Wayanad district of Kerala, with the highest tribal population in South India, is a KFD endemic state, owing to the lack of knowledge, attitude, and practice studies on TBDs and ethnomedicines against ticks. This study was carried out to assess their baseline knowledge, attitude, and ethnomedicinal practice against ticks. A structured questionnaire was used to conduct a survey of 499 tribal members living in forest fringe areas. Logistic regression analysis was performed to identify the factors that influence the knowledge, attitude, and practice of tribes on TBDs. More than 70% of the population visit the forests on a regular basis, with 65.7% of the population regularly exposed to tick bites; however, only 47.7% were aware of TBDs. About 47.4% of the respondents took precautions like therapeutics and natural remedies to avoid tick bites. Ten species of medicinal plant belonging to eight different families have been identified from the survey. The tribal population use these plants to repel ticks as well as treat tick bites. From the study, we concluded that the limited in-depth knowledge displayed by the tribes can be strengthened by conducting community programs such as awareness classes on TBD and its control measures. The ethnobotanicals identified can be used to formulate novel tick repellents in the future.

Development of a Model for Preliminary Diagnosis of Human Granulocytic Anaplasmosis.

Background: Human granulocytic anaplasmosis (HGA) is a vector-borne natural focal disease that is not officially registered in Ukraine. The first 13 cases of HGA in adults in Ukraine were identified in 2007. The purpose of our study was to develop a predictive model of HGA based on clinical and laboratory characteristics to develop a three-level standard case definition of HGA. Materials and Methods: Researchers examined 498 patients with suspected tick-borne infections and carried out a retrospective clinical and epidemiological analysis of 60 cases recruited from Lviv regional infectious disease hospitals. Logistic regression was used to create a model of the probability of the diagnosis of HGA depending on the presence of certain clinical and laboratory factors that, when examined, together may help to confirm a case of HGA. For logistic regression, eight clinical and laboratory factors were selected: history of tick bite, hyperthermia, signs of pharyngitis, changes in chest X-ray picture (enhancement of the pulmonary pattern and enlargement of the lung root boundaries), increased bilirubin (˃21 µmol/L), increased alanine aminotransferase (ALT ˃36 U/L), erythema migrans, and detected Lyme disease. Results: In the presence of all eight factors, the probability of HGA is 95.7%. When the five main signs are absent-signs of pharyngitis, changes in chest X-ray picture, increased bilirubin and ALT, and a history of tick bite-the probability of HGA in the patient dramatically decreases to 6.8%, meaning that HGA might be excluded. Conclusions: Based on the analysis of epidemiological, clinical, and laboratory signs, criteria for establishing a suspected, probable, and confirmed diagnosis of HGA have been developed to improve diagnosis.

Investigation of a Symptomatic Tick Bite Patient Confirms Borrelia burgdorferi in Ixodes scapularis and White-Footed Mice in Ashe County, North Carolina.

In June 2021, a traveler to Ashe County, North Carolina, was bitten by an Ixodes scapularis tick. The patient experienced axillary lymphadenopathy and an erythematous rash near the bite site. We confirmed Borrelia burgdorferi sensu stricto through PCR testing and DNA sequencing in the attached tick and later from mice trapped inside the cabin where the patient stayed.

Haemaphysalis longicornis calreticulin is not an effective molecular tool for tick bite diagnosis and disruption of tick infestations.

BACKGROUND: Tick calreticulin (CRT) is a calcium-binding protein secreted into the host during blood feeding. It has been used as a biomarker of tick exposure and has potential as an anti-tick vaccine, but there is no information about these uses for Haemaphysalis longicornis CRT (HlCRT). We synthesized recombinant H. longicornis CRT (rHlCRT) and evaluated its potential for tick bite diagnosis and for disrupting tick infestations. METHODS: The responses of mice and rabbits exposed to H. longicornis ticks were measured with ELISA to determine the antibody level against rHlCRT. To evaluate the effects of rHlCRT-induced anti-tick immunity, engorgement weight, tick engorgement index (TEI), feeding duration, ecdysis rate, and egg weight per engorged tick were compared between ticks fed on immunized and normal mice. RESULTS: Mean anti-tick CRT antibody levels in sera collected from mice at 1 and 15 days after primary tick exposure were not significantly different from the mean antibody levels in negative control mice that were not bitten by ticks (all P values > 0.05). No significant anti-HlCRT IgG responses developed in mice after second exposure to tick bites compared with the level of anti-HlCRT antibody response in negative control mice (all P values > 0.25). For rabbits, no significant differences in the antibody levels were observed in animals before challenge infestation and after tick exposures, and in animals after two tick exposures (all P values > 0.10). There were no significant differences in the body weight of ticks fed on immunized and normal mice (all P values > 0.15). No significant differences in TEI were observed between ticks fed on immunized mice and normal control mice (all P values > 0.50). There were no significant differences in feeding duration for female ticks, and feeding duration and ecdysis rate for nymphs in the experimental and control groups (all P values > 0.10 for feeding duration and P value = 0.19 for ecdysis rate). We did not observe a significant difference in egg weight per tick in the rHlCRT-immunized and the control groups (P = 0.88). CONCLUSIONS: HlCRT in H. longicornis tick saliva proteins appears to be nonimmunogenic to mammalian hosts like mice and rabbits. Vaccination with rHlCRT did not generate effective immunity against parthenogenetic and bisexual H. longicornis nymphs or female ticks. These results indicate that HlCRT is not a suitable molecular candidate for H. longicornis tick bite diagnosis and not effective for the disruption of tick infestations.

Effectiveness of personal protection measures against Lyme disease: A review of epidemiologic studies from the United States.

Lyme disease, the most commonly reported vector-borne disease in the United States, is caused by the bacteria Borrelia burgdorferi and is transmitted through the bite of an infected blacklegged tick. In the absence of a licensed vaccine, the prevention of Lyme disease relies heavily on limiting tick exposure. Methods for limiting tick exposure include personal protection measures such as repellent use, wearing protective clothing, avoiding areas where ticks may be present, bathing after exposure to tick habitat and performing regular tick checks. Public health officials typically recommend all these personal protection measures; however, there is limited evidence to promote one behaviour or practice over another. The focus of this article is to review available literature that examines the effectiveness of recommended personal protection measures to prevent Lyme and other Ixodes-transmitted diseases in humans. Articles included in this review were identified through Google Scholar and PubMed searches using specific search terms. We identified over 56,000 articles using Google Scholar and PubMed searches. Of those, 16 studies fit our criteria for inclusion and were reviewed in their entirety. Among the personal protection measures evaluated, no intervention was predominantly or consistently effective across studies, demonstrating that, currently, there is no single best method for primary prevention of Ixodes-transmitted diseases in the United States. Frequently recommended practices such as tick checks, repellent use and protective clothing had mixed results across studies. Study design differences limited comparability among studies, and sample sizes for these studies may have been too small to detect statistically significant results even if a prevention method was effective. Though many of the reviewed personal protection measures are frequently recommended to the public, limited evidence demonstrates their ability to prevent tick-borne disease. Additional standardized studies are needed to evaluate personal protection measures.

Tick-borne encephalitis virus and West-Nile fever virus as causes of serous meningitis of unknown origin in Kazakhstan.

Flaviviruses are a family of viruses that cause many diseases in humans. Their similarity in the antigenic structure causes a cross-reaction, which complicates the precise diagnostic of disease causing agents. Tick-borne encephalitis virus (TBEV), a member of the flavivirus family, is the cause of tick-borne encephalitis (TBE). Worldwide the awareness of this disease is raising, however, in many countries such as the Republic of Kazakhstan (KZ) there is a lack of serological investigation of flaviviruses in humans. In our study, we focused on two TBE endemic regions of KZ (East Kazakhstan Oblast (EKO) and Almaty (AO)) and a region where TBE cases were registered only since 2010 (Akmola Oblast (AkO)). In KZ, up to 400 cases of serous meningitis of unknown origin were registered annually in the period from 2017 to 2019. Our goals were to calculate the prevalence of antibodies against TBEV in patients with suspected meningitis. We collected 179 sera and 130 cerebrospinal fluid (CSF) samples from patients and included a questionnaire with focus on socio-demographical factors and observed tick bites. The human samples were tested with TBEV and West-Nile fever virus (WNFV) IgM and IgG ELISA, by immunofluorescence assay using a flavivirus biochip, and TBEV-specific real-time RT-PCR. We found TBEV and WNFV antibodies in 31 samples by serological and molecular techniques. Seven serum samples out of 31 showed TBEV-specific antibodies, and three serum pairs had WNFV antibodies. Correlating the serological results with the information gained from the questionnaires it becomes apparent that the number of tick bites is a significant factor for a TBEV infection. This result has an impact on diagnostic in KZ and physicians should be aware that both flaviviruses play a role for serous meningitis of unknown origin in KZ.

Oxidative and local histopathological response on skin wound of horses due to Amblyomma sculptum tick parasitism.

Amblyomma sculptum is frequently observed parasitizing horses, responsible for economic losses, damage to the host''s skin and transmission of pathogens. The oxidative stress profile and inflammatory mechanisms involved in this parasitism remain poorly studied. Thus, this study aimed to assess the histopathological changes and oxidative profile responses of horses in the attachment site of A. sculptum to find variations that indicate resistance and susceptibility between the breeds to this tick, based on the hypothesis that resistant animals have a greater inflammatory response and lesser number of attached ticks. We analyzed female horses of two breeds, Mangalarga Marchador and Breton Postier, naturally infested by Amblyomma sculptum. The ticks were counted and full-thickness excisional skin wounds of 10 mm were made on the perineal region on the attachment site of partially engorged females for histological and biochemical analyzes. The occurrence of the tick on the skin caused an increase in cellularity, inflammatory infiltrate, mast cells, pyknotic nuclei, and changes in the fibrous components of the matrix. The negative correlation observed between tick infestation and inflammatory response indicated that animals with greater inflammatory response tend to have less tick infestation. The oxidative stress markers, MDA, PCN and NO not present great variation; however, between the antioxidant enzymes levels, SOD was higher in tick attachment of Breton Postier skin, this may mean that these animals had higher oxidative enzymatic activity and consequently less tissue damage, while the GST dropped in the attachment sites compared to the control, which may indicate that animals were in a state of significant oxidative stress or raises the question of the possibility of enzymatic sequestration by ticks. No significant differences were found in the resistance of the two breeds since most of the analyzes varied due to the presence or absence of the tick attached to the skin. We draw attention to the importance of studying characteristics of the animal's antioxidant responses to the tick and the action of tick saliva on antioxidant enzymes and ROS because these characteristics are interdependent with the inflammatory response.

First Data on Human Lyme Borreliosis in Kosovo: Prospective Evaluation of the Disease from a Tick Bite Perspective.

Purpose: Lyme borreliosis (LB) occurs throughout Europe. No clinical and seroprevalence studies for LB in Kosovo have been publicly available thus far. Therefore, this study aimed to investigate LB from a tick bite perspective in the Pristina region, Kosovo. Methods: This single-center prospective observational study enrolled consecutive adult participants (≥18 years of age) with tick bite (embedded tick in the skin), who were examined at the Clinic of Infectious Diseases, Pristina, between January 2015 and August 2018. At the first visit related to the index tick bite, ticks (the complete ticks or parts of the ticks) were removed from the skin, blood samples were taken for serological tests, and antibiotic treatment was started when deemed necessary. The complete, undamaged ticks removed were proceeded for entomological identification. Participants were followed up at 2 months (serological tests were repeated) and 6 months after the index event for the development of clinical manifestations of LB and/or seroconversion against Borrelia burgdorferi. Results: A total of 380 subjects were included in the study. Most cases were seen in May and June in all study years. All 117 preserved ticks were identified as Ixodes ricinus. Immunoglobulin G seroprevalence among subjects during the first visit in the study was 28/380 (7.4%). Erythema migrans (EM) was clinically diagnosed in 74/380 patients (19.5%, 95% confidence interval 15.6-23.8). Only 15 clinically diagnosed EM (in seronegative patients) were serologically confirmed with seroconversion (2 months later), 3.9% of all subjects included in the study. There were three cases with clinical manifestation between the second and third visit: EM recidivans, multiple erythema, or several nonspecific systemic symptoms. Doxycycline and amoxicillin were mainly used for the treatment of borrelial skin lesions. Conclusion: This assessment can help indicate the need for disease awareness and reinforce the importance of primary prevention measures, early diagnosis, and appropriate treatment.

Transcriptome analysis of Ehrlichia ruminantium in the ruminant host at the tick bite site and in the tick vector salivary glands.

Heartwater is a non-contagious tick-borne disease of domestic and wild ruminants. Data regarding the complex processes involved during pathogen-vector-host interaction during Ehrlichia ruminantium infection is lacking and could be improved with knowledge associated with gene expression changes in both the pathogen and the host. Thus, in the current study, we aimed to identify E. ruminantium genes that are up-regulated when the pathogen enters the host and before the disease is established. Identification of such genes/proteins may aid in future vaccine development strategies against heartwater. RNA-sequencing was used to identify E. ruminantium genes that were exclusively expressed at the tick bite site in sheep skin biopsies (SB) and in adult tick salivary glands (SG). RNA was extracted from pooled samples of the SB or SG collected at different time points during tick attachment and prior to disease manifestation. Ribosomal RNA (rRNA) was removed and the samples were sequenced. Several E. ruminantium genes were highly expressed in all the samples while others were exclusively expressed in each. It was concluded that E. ruminantium genes that were exclusively expressed in the SB or both SB and SG when compared to the transcriptome datasets from bovine elementary bodies (BovEBs) from cell culture may be considered as early antigenic targets of host immunity. In silico immunogenic epitope prediction analysis and preliminary characterization of selected genes in vitro using ELIspot assay showed that they could possibly be ideal targets for future vaccine development against heartwater, however, further epitope characterization is still required.

Tick saliva-induced programmed death-1 and PD-ligand 1 and its related host immunosuppression.

The tick Rhipicephalus microplus is a harmful parasite of cattle that causes considerable economic losses to the cattle breeding industry. Although R. microplus saliva (Rm-saliva) contains several immunosuppressants, any association between Rm-saliva and the expression of immunoinhibitory molecules, such as programmed death (PD)-1 and PD-ligand 1 (PD-L1), has not been described. In this study, flow cytometric analyses revealed that Rm-saliva upregulated PD-1 expression in T cells and PD-L1 expression in CD14+ and CD11c+ cells in cattle. Additionally, Rm-saliva decreased CD69 expression in T cells and Th1 cytokine production from peripheral blood mononuclear cells. Furthermore, PD-L1 blockade increased IFN-γ production in the presence of Rm-saliva, suggesting that Rm-saliva suppresses Th1 responses via the PD-1/PD-L1 pathway. To reveal the upregulation mechanism of PD-1/PD-L1 by Rm-saliva, we analyzed the function of prostaglandin E2 (PGE2), which is known as an inducer of PD-L1 expression, in Rm-saliva. We found that Rm-saliva contained a high concentration of PGE2, and PGE2 treatment induced PD-L1 expression in CD14+ cells in vitro. Immunohistochemical analyses revealed that PGE2 and PD-L1 expression was upregulated in tick-attached skin in cattle. These data suggest that PGE2 in Rm-saliva has the potential to induce the expression of immunoinhibitory molecules in host immune cells.

Severe Fever with Thrombocytopenia Syndrome Associated with Manual De-Ticking of Domestic Dogs.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease. SFTS is caused by the SFTS virus, a novel phlebovirus, and is spread by ticks. Methods: A 50-year-old man was admitted to our hospital with the chief complaint of fever and was diagnosed with confirmed SFTS. An epidemiological investigation was conducted, and immunofluorescent antibody assays (IFAs) were performed to determine the role of the patient's three dogs in the transmission. PCR assays were performed using ticks that were collected with the dragging and flagging method from the patient's dogs and home. Results: PCR results were positive, and IFA confirmed an increased antibody titer. Although the reverse transcription PCR results of the three dogs were negative for SFTS virus, one dog had an elevated SFTS IFA immunoglobulin G (IgG) titer of 1:1,024. Moreover, a number of ticks were observed in the area surrounding the dog cages. Based on the findings of the patient interview, the patient was likely to have acquired SFTS by blood splash because he removed or burst ticks from the dogs with his bare hands. Although no tick bites were reported, tick transmission could not be ruled out. Studies have shown that only one in three individuals with a diagnosis of SFTS recalls a tick bite; thus, a definite exclusion of tick transmission in this case was not possible. Conclusions: The epidemiological findings of our case suggest a possible relationship between tick infestation in domestic dogs and SFTS virus transmission to humans. However, there is no direct evidence supporting this viral transmission route. Future studies are needed to further investigate a potential route of SFTS transmission by exposure to engorged tick blood or pet dogs.

Genomes, expression profiles, and diversity of mitochondria of the White-footed Deermouse Peromyscus leucopus, reservoir of Lyme disease and other zoonoses.

The cricetine rodents Peromyscus leucopus and P. maniculatus are key reservoirs for several zoonotic diseases in North America. We determined the complete circular mitochondrial genome sequences of representatives of 3 different stock colonies of P. leucopus, one stock colony of P. maniculatus and two wild populations of P. leucopus. The genomes were syntenic with that of the murids Mus musculus and Rattus norvegicus. Phylogenetic analysis confirmed that these two Peromyscus species are sister taxa in a clade with P. polionotus and also uncovered a distinction between P. leucopus populations in the eastern and the central United States. In one P. leucopus lineage four extended regions of mitochondrial pseudogenes were identified in the nuclear genome. RNA-seq analysis revealed transcription of the entire genome and differences from controls in the expression profiles of mitochondrial genes in the blood, but not in liver or brain, of animals infected with the zoonotic pathogen Borrelia hermsii. PCR and sequencing of the D-loop of the mitochondrion identified 32 different haplotypes among 118 wild P. leucopus at a Connecticut field site. These findings help to further establish P. leucopus as a model organism for studies of emerging infectious diseases, ecology, and in other disciplines.

Molecular prevalence and ecoregion distribution of select tick-borne pathogens in Texas dogs.

Tick-borne diseases (TBD), caused by borrelial, rickettsial and babesial pathogens, are common across the United States and can cause severe clinical disease in susceptible hosts, such as domestic dogs. However, there are limited TBD molecular epidemiological reports for dogs in Texas, and none for the non-Lyme borrelial pathogen responsible for causing tick-borne relapsing fever (TBRF). Therefore, data to support the prevalence of TBRF in the canine population is inadequate. This study aimed to characterize the molecular prevalence of 11 causative agents responsible for three TBD groups within domestic dogs with an emphasis on pathogen distribution within Texas ecoregions. A total representative number of 1,171 whole-blood samples were collected opportunistically from two Texas veterinary diagnostic laboratories. A layerplex real-time PCR assay was utilized to screen the dog samples for all 11 pathogens simultaneously. The overall molecular infection prevalence of disease was 0.68% borrelial, 1.8% rickettsial and 0.43% babesial pathogens, for a TBD total of 2.73% across Texas. Higher molecular prevalence was observed when analysed by ecoregion distinction, including 5.78% rickettsial infections by Ehrlichia canis and Anaplasma platys in the Rolling Plains ecoregion, and an average of 1.1% Borrelia turicatae and 1.0% Babesia gibsoni across detected ecoregions. To our knowledge, our findings indicate the first molecular detection of A. platys in Texas, and the first report of coinfections with E. canis and A. platys in dogs of Texas. The zoonotic concerns associated with TBDs, in conjunction with dogs' implication as an effective sentinel for human disease, highlight the importance of characterizing and monitoring regions associated with active infections in dogs. Surveillance data obtained from this study may aid public health agencies in updating maps depicting high-risk areas of disease and developing preventative measures for the affected areas.

Pathogen communities of songbird-derived ticks in Europe's low countries.

BACKGROUND: Birds play a major role in the maintenance of enzootic cycles of pathogens transmitted by ticks. Due to their mobility, they affect the spatial distribution and abundance of both ticks and pathogens. In the present study, we aim to identify members of a pathogen community [Borrelia burgdorferi (s.l.), B. miyamotoi, 'Ca. Neoehrlichia mikurensis', Anaplasma phagocytophilum and Rickettsia helvetica] in songbird-derived ticks from 11 locations in the Netherlands and Belgium (2012-2014). RESULTS: Overall, 375 infested songbird individuals were captured, belonging to 35 species. Thrushes (Turdus iliacus, T. merula and T. philomelos) were trapped most often and had the highest mean infestation intensity for both Ixodes ricinus and I. frontalis. Of the 671 bird-derived ticks, 51% contained DNA of at least one pathogenic agent and 13% showed co-infections with two or more pathogens. Borrelia burgdorferi (s.l.) DNA was found in 34% of the ticks of which majority belong to so-called avian Borrelia species (distribution in Borrelia-infected ticks: 47% B. garinii, 34% B. valaisiana, 3% B. turdi), but also the mammal-associated B. afzelii (16%) was detected. The occurrence of B. miyamotoi was low (1%). Prevalence of R. helvetica in ticks was high (22%), while A. phagocytophilum and 'Ca. N. mikurensis' prevalences were 5% and 4%, respectively. The occurrence of B. burgdorferi (s.l.) was positively correlated with the occurrence of 'Ca. N. mikurensis', reflecting variation in susceptibility among birds and/or suggesting transmission facilitation due to interactions between pathogens. CONCLUSIONS: Our findings highlight the contribution of European songbirds to co-infections in tick individuals and consequently to the exposure of humans to multiple pathogens during a tick bite. Although poorly studied, exposure to and possibly also infection with multiple tick-borne pathogens in humans seems to be the rule rather than the exception.

A Retrospective Cohort Study of Tick Paralysis in British Columbia.

BACKGROUND: Tick paralysis is a frequently overlooked severe disease characterized by bilateral ascending flaccid paralysis caused by a neurotoxin produced by feeding ticks. We aimed to characterize suspected tick paralysis cases documented at the BC Centre for Disease Control (BCCDC) in British Columbia (BC) from 1993 to 2016 and reviewed prevention, diagnosis, and treatment considerations. METHODS: Demographic, geographic, and clinical data from test requisition forms for ticks submitted to the BCCDC Public Health Laboratory (PHL) from patients across BC between 1993 and 2016 for suspected human and animal tick paralysis were reviewed. Descriptive statistics were generated to characterize tick paralysis cases in BC, including tick species implicated, seasonality of disease, and regional differences. RESULTS: From 1993 to 2016, there were 56 cases of suspected tick paralysis with at least one tick specimen submitted for testing at the BCCDC PHL. Humans and animals were involved in 43% and 57% of cases, respectively. The majority of cases involved a Dermacentor andersoni tick (48 cases or 86%) and occurred between the months of April and June (49 cases or 88%). Among known locations of tick acquisition, the Interior region of BC was disproportionately affected, with 25 cases (69%) of tick bites occurring in that area. CONCLUSIONS: Tick paralysis is a rare condition in BC. The region of highest risk is the Interior, particularly during the spring and summer months. Increasing awareness of tick paralysis among healthcare workers and the general public is paramount to preventing morbidity and mortality from this rare disease.

Assessment of using recombinant Ixodes ricinus AV422 saliva protein for confirmation of tick bites in hunting dogs as naturally infested hosts.

Due to the recorded spreading of ticks in past years, a higher incidence of tick-borne diseases (TBDs) can be expected in the future in endemic areas, but can also pose an emerging public health concern in areas where they have not yet been recognized. Assessment of the exposure of vulnerable hosts to ticks would be a very helpful tool for TBD epidemiological studies, as well as for their proper managing. To confirm previous tick bites, the method of choice is detection of antibodies in host serum as markers developed against injected tick saliva proteins during feeding. We recently showed that the recombinant form of Ixodes ricinus AV422 saliva protein (rIrAV422) can serve for detection of markers in experimentally infested rats. Here we examine whether it can be used in the same manner in naturally exposed hosts. We chose hunting dogs as good sentinel animals. The study group consisted of 15 dogs that varied in breed, age, sex, previous tick infestation history and repellent treatment. Western blot analysis with rIrAV422 as an antigen confirmed the presence of tick bite markers in all analysed dogs. For some of the dogs, their previous tick infestation history was unclear, which emphasizes the usefulness of rIrAV422 for revealing it. Since hunting dogs are naturally infested with different ticks, the potential of rIrAV422 in assessment of general exposure to ticks is highlighted. Use of rIrAV422 can also be helpful in veterinary practice and research as a tool for validation of the efficiency of tick repellent products.

Clinical presentation, convalescence, and relapse of rocky mountain spotted fever in dogs experimentally infected via tick bite.

Rocky Mountain spotted fever (RMSF) is a tick-borne disease caused by R. rickettsii in North and South America. Domestic dogs are susceptible to infection and canine RMSF can be fatal without appropriate treatment. Although clinical signs of R. rickettsii infection in dogs have been described, published reports usually include descriptions of either advanced clinical cases or experimental infections caused by needle-inoculation of cultured pathogen rather than by tick bite. The natural progression of a tick-borne R. rickettsii infection has not been studied in sufficient detail. Here, we provide a detailed description of clinical, hematological, molecular, and serological dynamics of RMSF in domestic dogs from the day of experimental exposure to infected ticks through recovery. Presented data indicate that neither the height/duration of fever nor detection of rickettsial DNA in dogs' blood by PCR are good indicators for clinical prognosis. Only the apex and subsequent subsidence of neutrophilia seem to mark the beginning of recovery and allow predicting a favorable outcome in Rickettsia-infected dogs, even despite the continuing persistence of mucosal petechiae and skin rash. On the other hand the appropriate (doxycycline) antibiotic therapy of sufficient duration is crucial in prevention of RMSF relapses in dogs.