A compartment and metapopulation model of Rocky Mountain spotted fever in southwestern United States and northern Mexico

Rocky Mountain spotted fever (RMSF) is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century. Along the US south-western border and across northern Mexico, the brown dog tick, Rhipicephalus sanguineus, is responsible for spreading the disease between dogs and humans. The widespread nature of the disease and the ongoing epidemics contrast with historically sporadic patterns of the disease. Because dogs are amplifying hosts for the Rickettsia rickettsii bacteria, transmission dynamics between dogs and ticks are critical for understanding the epidemic. In this paper, we developed a compartment metapopulation model and used it to explore the dynamics and drivers of RMSF in dogs and brown dog ticks in a theoretical region in western North America. We discovered that there is an extended lag-as much as two years-between introduction of the pathogen to a naïve population and epidemic-level transmission, suggesting that infected ticks could disseminate extensively before disease is detected. A single large city-size population of dogs was sufficient to maintain the disease over a decade and serve as a source for disease in surrounding smaller towns. This model is a novel tool that can be used to identify high risk areas and key intervention points for epidemic RMSF spread by brown dog ticks.

Rickettsioses in Colombia during the 20th century: A historical review

Rickettsioses are vector-borne zoonotic diseases whose etiological agents are bacteria of the genera Rickettsia and Orientia. In Colombia, literature published on rickettsioses during the 20th century is limited and disperse; to date, there are no detailed publications that compile the affected regions or the involved Rickettsia species in each outbreak. Since early works of Luis Patiño-Camargo, the study of rickettsioses gained major importance with the subsequent description of significant outbreaks in some departments of the country. During the 1940s, many articles were published reporting outbreaks probably caused by Rickettsia rickettsii, Rickettsia typhi, and Rickettsia prowazekii, as well as studies on their diagnosis, vaccination, and prophylaxis. One of the most notorious works was published by Patiño-Camargo where he named the R. rickettsii rickettsiosis as "Tobia fever". However, in the subsequent decades, these entities entered a prolonged period of neglected research and surveillance, and just gained importance until the 21st century, when new fatal cases began to be reported in the country; thus, many questions remained unanswered during this overlooked period. The present work reviewed online databases, repositories, and libraries to compile literature related to rickettsioses in Colombia published during the 20th century. Gathered data show that typhus group rickettsioses (including infections by R. typhi and R. prowazekii) were broadly distributed in departments from the Andean and Caribbean regions, and that spotted fever group rickettsioses cases (including infections by R. rickettsii) were registered in other locations different from Tobia (Cundinamarca), like Atlántico, Bolivar, and Santander departments. These findings contribute to the knowledge of these diseases, their historical distribution, public health burden, and set new horizons for rickettsioses research in different Colombian locations.

Clinical manifestations of Rickettsia rickettsii in a familial outbreak in Panama

We report an isolated outbreak of Rickettsia rickettsii in the Ngäbe-Buglé indigenous region, located 750 m (tropical wet) above sea level, in a jungle and mountainous area of Western Panama. Seven members of a family were infected simultaneously, resulting in four deaths. Family outbreaks have been previously described and are responsible for 4-8% of the cases described [1-4]. The simultaneous onset of symptoms in the affected population group is extremely unusual [1,5], but it should not dissuade the clinician from considering the possibility of Rickettsia rickettsii infection.

Peculiarities of Q fever and human cases reported so far in the Czech Republic

INTRODUCTION

Q fever is a zoonosis with a worldwide occurrence. Coxiella burnetii infection is most commonly transmitted by inhalation of air containing contaminated dust in cow, sheep and goat farming areas. The other modes of transmission are alimentary route (ingestion) and through sucking ticks. We set ourselves the goal of presenting a descriptive analysis of cases of Q fever in the Czech Republic (CZ) and former Czechoslovakia and draw attention to this often-overlooked issue.

METHODS

Summary of available information about Q fever was processed, and a narrative search of published cases of Q fever in the CZ and former Czechoslovakia, in Czech, Slovak and English, without time restrictions was performed. Furthermore, a descriptive analysis of Q fever cases reported to the Czech infectious diseases reporting system in 1982-2021 was done. After analysis, the available information system data were supplemented with data from a search of published scientific literature and weekly reports on the current epidemiological situation of the public health protection authorities of the CZ.

RESULTS

The disease has been reported in former Czechoslovakia and then in CZ since 1952. In 1952-1954, six outbreaks were reported with a total of 150 cases, mostly in connection with work with cattle. In 1980, a large-scale outbreak of Q fever affected 526 employees of the cotton production plant at Staré Město near Uherské Hradiště. Otherwise, units to dozens of cases were reported. From 1993 to 2021, 27 cases of the disease were detected in the CZ, of which 22 (81.5%) occurred in men. The age range was 0-60 years (mean 31, median 30 years). Seasonality by reporting month was highest in January and September.

CONCLUSION

There has been a decline in human cases of Q fever in the European Union (EU) in recent years, and only few cases of the disease occur in the CZ. Still, due to potential severity of the disease, the current climate change with the consequent increase in the spread of ticks as vectors of Coxiella, and animal movements associated with the global market, it is important to consider Q fever in the differential diagnosis. As part of the prevention, it is necessary to ensure compliance with basic hygiene rules, especially in at-risk occupations, and to consume only pasteurized dairy products. Vaccination of humans is not available in EU countries, although vaccination of livestock is possible.

Gastrointestinal and hepatic symptoms of tickborne diseases

While investigating patients with gastrointestinal (GI) and/or hepatic symptoms, tickborne diseases are only rarely considered to be the cause. However, the Czech Republic is an endemic region for several of tickborne diseases and, therefore, they should be a part of differential diagnosis of GI symptoms of unknown origin. This article describes GI and hepatic symptoms of several tickborne diseases - Lyme disease, ehrlichiosis, Rocky mountain spotted fever, tularemia, Colorado tick fever, tickborne relapsing fever, Q fever and babesiosis. GI and hepatic symptoms are quite common in Lyme disease patients. The prognosis is generally favourable with antibiotics treatment, however, serious courses have been described. Lyme disease should be a part of differential diagnosis of liver tests elevation and GI symptoms in patients from endemic regions regardless erythema migrans presence. Ehrlichiosis should be a part of differential diagnosis of acute febrile illness with GI symptoms especially in the presence of leukopenia/thrombocytopenia and/or liver tests elevation. Tularemia should be considered as a rare etiology of cholestatic hepatopathy and a history of a tick bite. In general, the importance of careful patient interviewing, including the history of a tick bite, can be highlighted also as a part of investigation of patients with seemingly unrelated GI and/or hepatic symptoms.

The Rickettsioses: A Practical Update

Rickettsia are small, obligately intracellular, gram-negative bacilli. They are distributed among a variety of hematophagous arthropod vectors and cause illness throughout the world. Rickettsioses present as an acute undifferentiated febrile illness and are often accompanied by headache, myalgias, and malaise. Cutaneous manifestations include rash and eschar, which both occur at varying incidence depending on the infecting species. Serology is the mainstay of diagnosis, and the indirect immunofluorescence assay is the test of choice. Reactive antibodies are seldom present during early illness, so testing should be performed on both acute-phase and convalescent-phase sera. Doxycycline is the treatment of choice.

[Fiebre manchada de montañas rocosas: experiencia en 5 años de vigilancia activa en un hospital pediátrico de segundo nivel en el noreste de México]

Introducción

La fiebre manchada de las montañas rocosas (FMMR) es causada por Rickettsia rickettsii. En Coahuila, la región de la Comarca Lagunera se considera una zona endémica. No se han reportado casos en la zona sur del estado, específicamente en la ciudad de Saltillo.

Métodos

Estudio prospectivo, reporte de casos. Se incluyeron los casos de niños atendidos en el Hospital del Niño Dr. Federico Gómez Santos en la ciudad de Saltillo, Coah., del mes de septiembre de 2012 a septiembre 2017 con diagnóstico confirmado clínicamente y por reacción en cadena de la polimerasa (PCR) de FMMR. Se presentan los antecedentes epidemiológicos, las características clínicas y evolución de los pacientes.

Resultados

Se confirmaron 14 pacientes. La relación masculino:femenino fue de 1.8:1, la edad promedio de los pacientes fue de 7.6 años (18 meses a 13 años). El 42.8% de los pacientes refirió el contacto con perros y el 57.1% afirmó tener contacto con garrapatas. En todos los casos hubo fiebre y exantema purpúrico; alrededor del 70% manifestaron mialgias y artralgias; el 28% tuvo sangrado del tubo digestivo, y el 11% alteraciones neurológicas graves. El 64.2% de los casos recibió tratamiento adecuado con doxiciclina. Fallecieron 8 pacientes, con una tasa de letalidad de 57.1%.

Conclusiones

La zona sur de Coahuila debe considerarse una zona endémica para FMMR. El retraso en el diagnóstico y tratamiento favorecen una mayor letalidad.

Background

Rocky Mountain Spotted Fever (RMSF) is caused by Rickettsia rickettsii. In Coahuila, Comarca Lagunera is considered an endemic zone; no cases have been reported in the southern zone of the state, specifically in the city of ­Saltillo.

Methods

Prospective study, cases report. Children evaluated in the Hospital del Niño Dr. Federico Gómez Santos from September 2012 to September 2017, with clinically and laboratory (by polymerase chain reaction, PCR) confirmed diagnosis of FMMR were included. The epidemiological antecedents, clinical characteristics and patient’s evolution are presented.

Results

14 patients were confirmed. The male: female ratio was 1.8: 1, the average age of the patients was 7.6 years (18 months to 13 years). 42.8% reported contact with dogs and 57.1% confirmed contact with ticks. In all cases, there was fever and purpuric rash; around 70% manifested myalgias and arthralgias; 28% presented digestive tract bleeding and 11% had severe neurological alterations. 64.2% of the cases received adequate treatment with doxycycline. Eight patients died with a case fatality rate of 57.1%.

Conclusions

The southern zone of Coahuila should be considered an endemic area for FMMR. The delay in diagnosis and treatment favor a greater lethality.

Long term neurologic sequelae in a Mexican rocky mountain spotted fever case

During the second half of the twentieth century, neurologic sequelae associated with central nervous system impairment caused by Rickettsia rickettsii were studied widely and exclusively in the United States. We present the case of a Mexican pediatric patient with neurologic sequelae 10 years after an acute infection by R. rickettsii.

Experimental infection of horses with Rickettsia rickettsii

Background

Rickettsia rickettsii is vectored by ticks, and some vertebrate hosts can be sources of infection to ticks during bacteremic periods. In Brazil, the main vector for R. rickettsii is the tick Amblyomma sculptum, a member of the A. cajennense complex. Horses, in turn, are one of the major hosts for A. sculptum. In this study, horses experimentally infected with R. rickettsii were assessed for clinical changes and their capability to transmit the infection to A. sculptum ticks.

Methods

Four horses were infected with R. rickettsii through either intraperitoneal injection or infestation with R. rickettsii-infected A. sculptum ticks. Simultaneously, the animals were infested with non-infected A. sculptum ticks. The horses were monitored for 30 days by clinical examination, hematological and biochemical tests, real-time PCR of blood for the detection of Rickettsia, and inoculation of blood in guinea pigs. IgG antibody titers were followed until the horses have shown seronegativity or until the end of the experiment. Uninfected ticks that fed on horses were subjected to real-time PCR and/or were fed on susceptible rabbits.

Results

The horses showed no clinical, hematological or blood biochemical alterations, and bacteremia was not detected by real-time PCR or by inoculation of horse blood into guinea pigs. Anti-R. rickettsii antibodies were detected in horses from 10 days to 2 years after infection. Uninfected ticks, after feeding on infected horses, showed 2.1 % positivity in real-time PCR, but failed to transmit the infection to rabbits at a next feeding stage.

Conclusions

Rickettsia rickettsii-infected horses did not manifest illness and are not competent amplifier hosts of R. rickettsii for A. sculptum ticks.