Urban ecology of hosts and vectors of Rickettsia in a rickettsiosis-endemic city of the Yucatan peninsula, Mexico

Sewer-associated rodents in countries with lower human development, a time-bomb for zoonoses?

Sewer-associated rodents inhabiting urban and peri-urban areas constitute a potential infection source for many zoonotic pathogens at a global scale. However, there is a lack of scientific information about the implications of these micromammals in regions with fragile sanitary services, low economic resources and weak educational systems. Consequently, this study aimed to review the scientific knowledge about rodent-borne zoonoses in sewer-related environments from countries with lower Human Development Index (HDI). Our results revealed a low number of publications (n = 13) evaluating the epidemiology of sewer-associated rodents in countries with lower HDI, which were distributed across Central/South America (69.2 %; 9/13), Africa (23.1 %; 3/13) and Asia (7.7 %; 1/13). The most evaluated rodents were Rattus norvegicus -brown rat- (present in 10/13 articles), followed by Rattus rattus -black rat- (6/13) and Mus musculus -house mouse- (5/13). Fourteen zoonotic pathogens were assessed, specifically bacteria (n = 6 publications) and parasites (n = 7), with the highest prevalence described for Bartonella spp. (85.0 %), Calodium hepaticum (83.8 %), Rickettsia spp. (75.0 %), Leptospira spp. (68.0 %) and Hymenolepis nana (60.0 %). Most reviewed publications described the use of molecular methods and direct examination of samples to identify the pathogens studied (46.2 %; 6/13 each), followed by the MALDI-TOF technique (15.4 %; 2/13). The four clusters building the semantic network reinforced the pivotal role of sewer-associated rodents as reservoirs of both vector-borne pathogens and directly transmitted zoonoses. Our findings evidence a severe gap of knowledge in lower-resource areas about the role of sewer-associated rodents in the epidemiology of zoonotic diseases, which could impact on the sanitary system of not only the evaluated countries, but also in other developed and non-developed regions worldwide.

The Relationship Between the Spatial Occurrence of Leptospira Exposed Animals and the Characteristics of the Peridomiciles They Inhabit in a Locality of Southeastern Mexico

The occurrence of Leptospira in mammals is an indicator for assessing potential health risks, particularly in tropical regions. Understanding their hosts' habitat characteristics and spatial occurrence is essential to surveil them. This study aimed to determine the characteristics of the peridomiciles associated with the spatial occurrence of Leptospira hosts. We inventoried the characteristics of the peridomiciles. Blood serum was gathered from dogs, opossums, and rodents for a microagglutination essay to detect exposure to several serogroups of Leptospira. A generalized linear model with binomial distribution helped estimate risk ratios and 95% confidence intervals between a seropositive animal's occurrence and the peridomiciles' characteristics. For estimates with the occurrence of one or more seropositive animals, a multinomial model was fitted. The seroprevalence in rodents was 81.8%; in opossums 31.2%; and 56.5% for dogs. The most frequent serogroup in dogs and rodents was Canicola. In opossums, the seroreaction was against Tarassovi, Ballum, Sejroe, and Cynopteri. The results showed that the peridomicile area (m2), the geographic polygon, and the accumulation of plastic containers (PET) were characteristics related to the occurrence of seropositive animals. The results revealed that the peridomicile's characteristics and spatial distribution in the locality help explain the occurrence of Leptospira hosts.

An unusual identification of Rickettsia parkeri in synanthropic rodents and domiciliated dogs of a rural community from Yucatán, Mexico

Rickettsia parkeri belongs to the spotted fever group (SFG) of the Rickettsia genus. This bacterium causes mild rickettsiosis in humans and is mainly transmitted by Amblyomma ticks. Its medical importance is emerging in the Americas, including Mexico. Synanthropic rodents and domiciled dogs participate as accidental hosts in epidemiological cycles of Rickettsia of the SFG. The aim is to report the presence of R. parkeri in synanthropic rodents and domiciled dogs from a rural community of Yucatán, Mexico. Rodents were captured, and plasma samples were taken from dogs in 48 households from Ucú, Yucatán, Mexico. A spleen sample (rodents) and plasma (dogs) were used in the propagation of Rickettsia on Vero cells. These infected cells were used in the extraction of genomic DNA. Rickettsia DNA was identified using a semi-nested PCR (snPCR); some products were sent for sequencing. The recovered sequences were analysed with bioinformatics programs, and a phylogenetic tree was built to determine the Rickettsia species. One hundred animals were sampled: 36 synanthropic rodents and 64 dogs. The snPCR evidenced the presence of Rickettsia DNA in 10 rodents (10/36, 27.8%) and 18 dogs (18/64, 28.1%), which represents a global frequency of 28% (28/100) in this study. The bioinformatics analysis yielded homology to R. parkeri and was demonstrated in the phylogenetic tree. The first evidence of the presence of R. parkeri in synanthropic rodents (Mus musculus) from Mexico is presented; likewise, the participation of domestic dogs in the transmission cycle of this bacterium with potential importance in public health is confirmed.

Confirmation of the presence of Rickettsia felis infecting Ornithodoros puertoricensis in Mexico

Soft ticks are neglected competent vectors of a wide range of pathogenic microorganisms, among which bacteria of the genera Rickettsia and Borrelia stand out. In Mexico, previous studies have shown the presence of a member of the Ornithodoros talaje complex in the Virginia opossum (Didelphis virginiana Didelphimorphia: Didelphidae Kerr) from southeastern Mexico. However, its specific identification has not been achieved. Two D. virginiana were treated in a private clinic during the period of April-May 2022. Tick larvae were manually removed, DNA extraction was performed, and some genes from various bacterial and parasitic pathogens were amplified and sequenced. A total of 96 larvae were recovered, which were morphologically identified as Ornithodoros puertoricensis (Ixodida: Argasidae Fox); the 16 S sequences showed a similarity of 96.79%-99.51% with sequences of O. puertoricensis from Panama and Colombia. The presence of Rickettsia felis (Rickettsiales: Rickettsiaceae Bouyer et al.) was detected in 15 specimens from one host. The soft tick O. puertoricensis is recorded for the first time as an ectoparasite of the Virginia opossum in America and represents the second report for this soft tick in Mexico since 1963. This represents the most northern record of this tick species in its geographic distribution and brings a new soft tick-Rickettsia association.

Antibody Prevalence and Risk Factors Associated with Rickettsia spp. in a Pediatric Cohort: SFGR Remains Underdiagnosed and Underreported in El Salvador

Spotted fever group rickettsioses (SFGR) are caused by a group of tick-borne pathogens that are increasing in incidence globally. These diseases are typically underreported and undiagnosed in low- and middle-income countries, and thus, have been classified as neglected bacterial pathogens. Countries with high poverty, low human development index score, and limited health infrastructure—like El Salvador in Central America—lack necessary surveillance for SFGR and other tick-borne pathogens. This paucity of baseline SFGR infection prevalence leaves vulnerable populations at risk of misdiagnosis. Further, tick-borne disease burdens in El Salvador are severely limited. To lay the foundation for tick-borne disease epidemiology in El Salvador, our team conducted two different enzyme-linked immunosorbent assays (ELISA) on banked human sera samples from a cohort of approximately 1000 pediatric participants from a high-risk vector-borne disease population. Eleven percent of all tested banked pediatric sera were positive for at least one ELISA assay at the time of enrollment: 10.7% were positive for only IgM antibodies (acute SFGR infection), and 2.5% were positive for IgG antibodies (a past SFGR infection). Older, male, children enrolled during the wet season, with a household history of infectious disease and higher maternal education level had higher odds of SFGR antibodies. Additionally, children from households with domestic poultry birds and previous knowledge of other vector-borne diseases had significantly reduced odds of SFGR antibodies. The large percentage of acute SFGR infections indicates that it continues to remain an underreported and undiagnosed issue in El Salvador and the Central American region. Much is still unknown regarding the complexity of the tick, animal host, and human host ecology transmission cycle of SFGR in El Salvador.

Epidemiological Study of the Occurrence of Typhus Group Rickettsia Natural Infection in Domiciliated Dogs from a Rural Community in South-Eastern Mexico

Simple Summary

Rickettsioses are relevant emergent and reemergent zoonoses in the Americas, including Mexico. Murine typhus caused by typhus group (TG) Rickettsia is prevalent in humans and their companion animals, such as dogs. This study found that 23.9% of the dogs (34/142) were infected by TG Rickettsia in Maxcanú, Yucatan (southeastern Mexico). Statistical analyses showed that reduced outdoor activities, age, sex and previous antiparasitic treatment are associated factors with less risk of TG Rickettsia infection in the sampled dogs. Monitoring and controlling these factors could help to restrict the enzootic transmission risk and prevent the potential zoonotic transmission.

Abstract

The aim is to describe the Typhus group (TG) Rickettsia infection in dogs and to identify factors associated with this infection. We collected blood samples and gathered exposure and clinical data of 142 dogs from a rural community of Yucatan. The Rickettsia group was determined by semi-nested PCR. Generalized linear models with binomial error distribution were used to model the associated factors from the dog sample for risk ratio (RR) estimation. Thirty-four dogs (23.9%) showed molecular evidence of TG Rickettsia DNA. The multivariate model showed that mixed-breed dogs (RR = 0.06) and dogs that had received antiparasitic treatment (RR = 0.049) had a lower risk of getting infected, taking as reference the purebred group and the non-treated dogs, respectively. Looking at variable interactions, adult dogs without outdoor activities had a lower infection risk than puppies (RR = 0.26). Among dogs with antiparasitic treatment, females had a higher infection risk than male dogs (RR = 26.2). The results showed enzootic TG Rickettsia circulation in dogs of a rural community. The factors outdoor activities, age and previous antiparasitic treatment, as well as the clinical variables signs of hemorrhages and epistaxis, were associated with a less chance of natural infection in the studied dogs. Prevention and control of the enzootic transmission risk of TG Rickettsia should help to reduce the potential zoonotic transmission of this pathogen.