Rat Flea Research Articles

Genetic differentiation of the oriental rat flea, Xenopsylla cheopis, from two sympatric host species

BackgroundThe oriental rat flea (Xenopsylla cheopis), which infests several mammals, primarily rats (Rattus spp.), is the most notorious vector of human plague. In this study, we measured the genetic differentiation among populations of fleas from the Asian house rat (Rattus tanezumi) and the brown rat (R. norvegicus) using microsatellite markers in order to investigate the extent of host-switching in this parasite.ResultsWe developed 11 polymorphic microsatellite loci for our study, nine of which showed high potential for inbreeding. AMOVA showed that the majority (84.07%, P < 0.001) of the variation was derived from within populations, followed by variation among groups (14.96%, P < 0.001); in contrast, variation within groups of populations was nearly absent (0.97%, P > 0.05). Analyses of the pairwise fixation index revealed that most of the ten allopatric population pairs but none of the five sympatric population pairs were significantly differentiated. Moreover, based on genetic structure clustering analysis, there was obvious differentiation between allopatric populations but not between sympatric population pairs.ConclusionsThese results indicate the presence of frequent migrations of the oriental rat flea between the sympatric Asian house rat and brown rat, causing a high rate of gene flow and limited genetic differentiation. We suggest that there is no clear boundary limiting the migration of oriental rat fleas between the two hosts, and thus both rat species should be monitored equally for the purposes of plague prevention and control.

The 2017 plague outbreak in Madagascar: Data descriptions and epidemic modelling

From August to November 2017, Madagascar endured an outbreak of plague. A total of 2417 cases of plague were confirmed, causing a death toll of 209. Public health intervention efforts were introduced and successfully stopped the epidemic at the end of November. The plague, however, is endemic in the region and occurs annually, posing the risk of future outbreaks. To understand the plague transmission, we collected real-time data from official reports, described the outbreak's characteristics, and estimated transmission parameters using statistical and mathematical models. The pneumonic plague epidemic curve exhibited multiple peaks, coinciding with sporadic introductions of new bubonic cases. Optimal climate conditions for rat flea to flourish were observed during the epidemic. Estimate of the plague basic reproduction number during the large wave of the epidemic was high, ranging from 5 to 7 depending on model assumptions. The incubation and infection periods for bubonic and pneumonic plague were 4.3 and 3.4 days and 3.8 and 2.9 days, respectively. Parameter estimation suggested that even with a small fraction of the population exposed to infected rat fleas (1/10,000) and a small probability of transition from a bubonic case to a secondary pneumonic case (3%), the high human-to-human transmission rate can still generate a large outbreak. Controlling rodent and fleas can prevent new index cases, but managing human-to-human transmission is key to prevent large-scale outbreaks.

Acquisition of Bartonella elizabethae by Experimentally Exposed Oriental Rat Fleas (Xenopsylla cheopis; Siphonaptera, Pulicidae) and Excretion of Bartonella DNA in Flea Feces.

Few studies have been able to provide experimental evidence of the ability of fleas to maintain rodent-associated Bartonella infections and excrete these bacteria. These data are important for understanding the transmission cycles and prevalence of these bacteria in hosts and vectors. We used an artificial feeding approach to expose groups of the oriental rat flea (Xenopsylla cheopis Rothschild; Siphonaptera, Pulicidae) to rat blood inoculated with varying concentrations of Bartonella elizabethae Daly (Bartonellaceae: Rhizobiales). Flea populations were maintained by membrane feeding on pathogen-free bloodmeals for up to 13 d post infection. Individual fleas and pools of flea feces were tested for the presence of Bartonella DNA using molecular methods (quantitative and conventional polymerase chain reaction [PCR]). The threshold number of Bartonellae required in the infectious bloodmeal for fleas to be detected as positive was 106 colony-forming units per milliliter (CFU/ml). Individual fleas were capable of harboring infections for at least 13 d post infection and continuously excreted Bartonella DNA in their feces over the same period. This experiment demonstrated that X. cheopis are capable of acquiring and excreting B. elizabethae over several days. These results will guide future work to model and understand the role of X. cheopis in the natural transmission cycle of rodent-borne Bartonella species. Future experiments using this artificial feeding approach will be useful for examining the horizontal transmission of B. elizabethae or other rodent-associated Bartonella species to naïve hosts and for determining the viability of excreted bacteria.

High mitochondrial sequence divergence in synanthropic flea species (Insecta: Siphonaptera) from Europe and the Mediterranean

BackgroundAdult fleas are haematophagous ectoparasites of warm-blooded vertebrates, particularly mammals. Among them, the cat flea (Ctenocephalides felis) and the human flea (Pulex irritans) have high veterinary-medical significance, owing to their cosmopolitan distribution and role in the transmission of important vector-borne pathogens. While the taxonomy of Ct. felis has been investigated on a morphological basis during the past decades, its molecular-phylogenetic analyses have been only recently conducted. This study expands the knowledge on Ct. felis from hitherto less studied geographical regions, and includes representatives from additional flea families, less investigated with molecular approaches.MethodsFleas were collected in four countries of the Mediterranean Basin (Croatia, Italy, Malta and Israel), as well as in Hungary, from domestic and wild carnivores, rodents and humans. The DNA extracts of representative fleas (n = 148), belonging to ten species of eight genera, were used for PCR amplification of part of their cytochrome c oxidase subunits 1, 2 (cox1, cox2) and 18S rRNA genes, followed by sequencing and phylogenetic analyses.ResultsThe majority (65.6%) of Ct. felis felis cox2 sequences showed 99.4–100% similarity to each other (haplogroup A), whereas those from Malta and Israel had 98.1–98.7% sequence similarity (haplogroup B), and a third sequence from Israel (haplotype C) had as low as 96.3% sequence similarity in comparison with a reference sequence from group “A”. Except for the shape of the head, no consistent morphological differences (e.g. in chaetotaxy) were found between haplogroups “A” and “C”. Haplotypes of Ct. canis were genetically more homogenous, with 99.6–100% sequence similarity to each other. However, when P. irritans collected from humans was compared to those from three species of wild carnivores, these only had 96.6% cox2 similarity. The mouse flea, Leptopsylla segnis and the northern rat flea, Nosopsyllus fasciatus were both shown to have haplotypes with low intraspecific cox2 similarities (96.2 and 94.4%, respectively). Taken together, differences between mitochondrial lineages within four flea species exceeded that observed between two Chaetopsylla spp. (which had 97.3% cox2 similarity). The topologies of cox1 and cox2 phylogenetic trees were in line with relevant sequence comparisons. Conversely, 18S rRNA gene analyses only resolved differences above the species level.ConclusionsCtenocephalides felis felis, P. irritans, L. segnis and N. fasciatus were shown to have such a high level of mitochondrial gene heterogeneity, that the uniformity of these flea taxa should be reconsidered. Although the present results are limited (especially in the case of L. segnis and N. fasciatus), there appears to be no geographical or host restriction, which could explain the divergence of these genetic lineages.

Evidence of Rickettsia typhi in rat fleas of various habitat and the potential transmission of murine typhus in banjarnegara, Central Java, Indonesia

Murine typhus is a zoonotic infectious disease caused by Rickettsia typhi, whose transmission is carried out by rat fleas. The climatic and ecologic conditions in Banjarnegara is favorable for maintaining reservoirs and vectors of murine typhus. There has been no report about the occurrence of R. typhi in rat fleas. Therefore, we investigated the role of fleas as possible vector of murine typhus in Banjarnegara. During September to Nopember 2017, flea were collected from rats trapping of various habitat in Banjarnegara. Fleas preserved in 70% ethanol were eventually prepared onto slides for identification. Fleas of the same species were pooled by species of small mammal and habitat and then preserved in sodium chloride store at-20°C until evaluated for the presence of Rickettsia typhi by polymerase chain reaction. Two flea species were identified: Xenopsylla cheopis and Stivalius cognatus. Stivalius cognatus was collected from R. exulans and R. tiomanicus. Rickettsia spp. was detected in X. cheopis (45/88) and S. cognatus (3/11). The highest minimum infection rate of R. typhi was seen in X. cheopis infesting R. tanezumi in Kutabanjarnegara village (103.8). The presence of R. typhi in X. cheopis at residential area of Banjarnegara needs serious attention, as a form of awareness of disease transmission, especially murine typhus.

\u201cFluidic diode\u201d for passive unidirectional liquid transport bioinspired by the spermathecae of fleas

We present a device for passive unidirectional liquid transport. The capillary channels used are bioinspired by the shape of the spermathecae (receptaculum seminis) of rabbit fleas (Spilopsyllus cuniculi) and rat fleas (Xenopsylla cheopis). The spermatheca is an organ of female fleas that stores sperm until suitable conditions to lay eggs are found. We translated and multiplied the natural form and function of a spermatheca to create a continuous capillary system from which we designed our microfluidic device based directly on the model from nature. Applying the Young-Laplace equation, we derived a theoretical description of local liquid transport, which enables model-guided design. We arranged the bioinspired capillaries in parallel and engraved them in poly(methyl methacrylate) (PMMA) plates by CO2 laser ablation. The fabricated structures transport soapy water passively (i.e., without external energy input) in the forward direction at velocities of about 1 mm·s−1 while halting the liquid fronts completely in the backward direction. The bioinspired capillary channels are capable of unidirectional liquid transport against gravity. Distance and velocity measurements prove the feasibility of the concept. Unidirectional passive liquid transport might be advantageous in technical surfaces for liquid management, for instance, in biomedical microfluidics, lab-on-chip, lubrication, electronics cooling and in micro-analysis devices.

Insects as Biological Weapons

This study was conducted at University of Gujrat during 2017 to 2018 as a term paper for Master of Philosophy. The data regarding use of Insects as Biological Weapons was reviewed and compiled as a review paper from various published articles of international reputed journals annual/environmental reports of recognized organization and e-books. Use of entomological weapons is a wide field of research. Insects were used as biological weapons from ancient times and this concept is very old. Different insects can be used for this purpose by different ways. Insects can be used as biological weapons against crops, animals and human beings. Insects may be used as direct pests against crop or they may be used as vectors to spread diseases in animals and human beings. In both cases their effects are devastating. House Flies, Oriental Rat Flea, Colorado potato beetle, Ticks, screw worm larvae are the examples of some insects which can be used as biological weapons. Use of biological weapons in war against humans is however illegal.

Plague risk in vulnerable community: assessment of Xenopsylla cheopis susceptibility to insecticides in Malagasy prisons

BackgroundPrisons in Madagascar are at high risk of plague outbreak. Occurrence of plague epidemic in prisons can cause significant episode of urban plague through the movement of potentially infected humans, rodents and fleas. Rodent and flea controls are essential in plague prevention, by reducing human contact with plague reservoirs and vectors. Insecticide treatment is the key step available for the control of rat fleas which transmit the disease from infected rodents to human. The implementation of an adapted flea control strategy should rely on the insecticide susceptibility status of the targeted population. For the purpose of plague prevention campaign in prisons, we conducted insecticide resistance survey on Xenopsylla cheopis, the rat flea.MethodsFleas were collected on rats caught in six prisons of Madagascar. They were exposed to insecticide treated filter papers and mortality was recorded following World Health Organization protocol.ResultsThe fleas collected in the prisons had different resistance patterns, while a high level of resistance to insecticides tested was described in the Antanimora prison, located in the heart of Antananarivo, the capital of Madagascar.ConclusionsThis finding is alarming in the context of public health, knowing that the effectiveness of flea control could be jeopardized by insecticide resistance. In order to establish more accurate rat fleas control in prisons, the main recommendations are based on continuous monitoring insecticide susceptibility of flea, insecticide rotation, and the development of a new method for flea control.

Model-based analysis of an outbreak of bubonic plague in Cairo in 1801.

Bubonic plague has caused three deadly pandemics in human history: from the mid-sixth to mid-eighth century, from the mid-fourteenth to the mid-eighteenth century and from the end of the nineteenth until the mid-twentieth century. Between the second and the third pandemics, plague was causing sporadic outbreaks in only a few countries in the Middle East, including Egypt. Little is known about this historical phase of plague, even though it represents the temporal, geographical and phylogenetic transition between the second and third pandemics. Here we analysed in detail an outbreak of plague that took place in Cairo in 1801, and for which epidemiological data are uniquely available thanks to the presence of medical officers accompanying the Napoleonic expedition into Egypt at that time. We propose a new stochastic model describing how bubonic plague outbreaks unfold in both rat and human populations, and perform Bayesian inference under this model using a particle Markov chain Monte Carlo. Rat carcasses were estimated to be infectious for approximately 4 days after death, which is in good agreement with local observations on the survival of infectious rat fleas. The estimated transmission rate between rats implies a basic reproduction number R0 of approximately 3, causing the collapse of the rat population in approximately 100 days. Simultaneously, the force of infection exerted by each infected rat carcass onto the human population increases progressively by more than an order of magnitude. We also considered human-to-human transmission via pneumonic plague or human specific vectors, but found this route to account for only a small fraction of cases and to be significantly below the threshold required to sustain an outbreak.

PCR-based identification of Trypanosoma lewisi and Trypanosoma musculi using maxicircle kinetoplast DNA

Trypanosoma lewisi, transmitted by rat fleas, is a widespread pathogen specific to rats with records of human infection cases. Its closely related species with global distribution, Trypanosoma musculi, is transmitted between mice by ingestion of infected fleas. These trypanosomes are of similar morphology, making it difficult to distinguish them by microscopy. In this study, we have developed a rapid, sensitive and reliable PCR method for the diagnosis of T. lewisi and T. musculi. The T. lewisi-specific amplicons were not produced by other Trypanosoma, such as T. musculi, T. brucei complex or T. cruzi, neither by an outgroup of Leishmania amazonensis. The detection limits of the three pairs of T. lewisi-specific primers were 50ng, 1ng and 10ng of total DNA, respectively. The primers designed for T. musculi primers showed specifically that amplicon strictly in T. musculi and their detection limits were 10ng and 1ng of total DNA. To simplify the detection process, we managed to apply our method directly on tail blood samples without complicated DNA purification. In conclusion, PCR with our primers could be a highly sensitive, specific protocol to detect and distinguish T. lewisi and T. musculi from other trypanosomes.

Bubonic Panic: When Plague Invaded America by G. Jarrow

Jarrow, Gail. Bubonic Panic: When Plague Invaded America. Calkins Creek, 2015.If public health seems like it would be one of those topics that would send you to sleep, then Bubonic Plague: When Plague Invaded America by Gail Jarrow will change your mind. This is the final book in her trilogy about Deadly Diseases for middle grades and higher.Jarrow is fairly succinct in presenting the history, transmission, and trajectory of various waves of plague around the world. She briefly charts its first appearance in 541 in Turkey, then vividly describes the second wave that started in 1346 and at its most virulent was named the Black Death, killing millions in Europe and parts of Asia and North Africa. The majority of the book focuses on the third wave, when it reached North America.The third pandemic began in the mid-1800s when China became ground zero for this next wave, which spread to Hong Kong by 1894. Hong Kong was a busy port town and trade and travel on steamships allowed for rapid dispersion of the disease. Researchers from a number of countries sought feverishly to identify the source of the epidemic and learn how it was spread. By the late 1890s two of them had proven it was rat fleas. Unfortunately almost nobody believed them, which became problematic when in 1900 San Francisco saw its first deaths in Chinatown.Jarrow provides a fascinating look at the political and social climate of this period in relation to the attitudes of Americans towards Chinese immigrants and the impact quarantining San Francisco’s Chinatown would have on businesses reliant on trade and tourism. It became a complicated and fraught tug-o-war between politicians, businessmen, doctors and public health officials, fighting about whether to recognize and publicize the deaths and quarantine when the evidence seemed inconclusive as to their cause. Even after proof was offered action was surprisingly slow to follow and the disease was able to spread, although the number of deaths was comparatively low, being in the low hundreds.This well researched book also includes information about contemporary cases in the United States, ongoing research and treatments for all three strains of plague. There are extensive source notes and bibliography, a glossary, timeline, index and an author’s note explaining her keen interest in public health and the importance it had in the past,and will have when the next global pandemic hits. Also included are numerous photographs (some a little gruesome), newspaper clippings, cartoons, posters and illustrations to engage readers’ interest.This will pair perfectly with a middle grade novel, Chasing Secrets by Gennifer Choldenko, 2015 that gives a fictional account of the outbreak in San Francisco.This is a strong finish to a fascinating series that combines history, social issues, scientific research, technological developments and culture in America, showing long term implications for today’s government policies towards health.Highly Recommended: 4 out of 4 starsReviewer: Tammy FlandersTammy is the Reference Coordinator in the Doucette Library of Teaching Resources at the University of Calgary. She also reviews juvenile resources with an eye to classroom use in her blog, Apples with Many Seeds.

The transmission of the Black Death to western Europe: a critical review of the existing evidence

In 1347 the Black Death was introduced from the north-eastern coast of the Black Sea and the Sea of Asov towards southern and western Europe, where it then spread dramatically. A report by the Italian chronicler Gabriel de Mussis of the siege of Caffa (1345–47) is often credited as describing an early deployment of a “biological weapon”, thus triggering the “Black Death” in western Europe. He reports that Mongol troops threw plague victims into the city with catapults, thus contaminating the inhabitants. However, re-evaluation of historical, biological and epidemiological data indicates that the spread of the disease was probably an inevitable consequence of the intense trade relations along the coasts of the Black Sea and the Mediterranean. Therefore, the alleged catapulting of infected corpses would rather have been a marginal contribution to the diffusion of the disease (if it took place at all). The infection was subsequently spread by refugee ships via ports at Constantinople and along the Mediterranean trading routes and harbours towards Genoa, Marseille and Venice, thus initiating the Plague in Europe. The further propagation of the disease inland is still a matter of controversial discussions. However, epidemiological data indicate that the most essential animal vector for further distribution of the plague in central and northern Europe was probably the human louse (Pediculus humanis), instead of the oriental (or tropical) rat flea (Xenopsylla cheopis).

Direct evidence of Rickettsia typhi infection in Rhipicephalus sanguineus ticks and their canine hosts.

Murine typhus is a rickettsiosis caused by Rickettsia typhi, whose transmission is carried out by rat fleas in urban settlements as classically known, but it also has been related to cat fleas in a sub-urban alternative cycle that has been suggested by recent reports. These studies remarks that in addition to rats, other animals like cats, opossums and dogs could be implied in the transmission of Rickettsia typhi as infected fleas obtained from serologically positive animals have been detected in samples from endemic areas. In Mexico, the higher number of murine typhus cases have been detected in the Yucatan peninsula, which includes a great southeastern region of Mexico that shows ecologic characteristics similar to the sub-urban alternative cycle recently described in Texas and California at the United States. To find out which are the particular ecologic characteristics of murine typhus transmission in this region, we analyzed blood and Rhipicephalus sanguineus ticks obtained from domestic dogs by molecular approaches, demonstrating that both samples were infected by Rickettsia typhi. Following this, we obtained isolates that were analyzed by genetic sequencing to corroborate this infection in 100% of the analyzed samples. This evidence suggests for the first time that ticks and dogs could be actively participating in the transmission of murine typhus, in a role that requires further studies for its precise description.

Flea outbreak at United Nations base in South Sudan: A public health challenge

Background: A large number Indian troops are deployed in International Peacekeeping Missions Worldwide and are exposed to emerging and re-emerging vectors and diseases in unfamiliar terrain. This article describes the experience of a flea outbreak among Indian UN Peacekeepers in a remote part of South Sudan. Methods: Health visits to the area confirmed presence of dog fleas. Flea bites disrupted daily routine of the unit and many troopers reported to medical facilities with severe dermatitis. Death of a field rat in the immediate vicinity along with detection of rat fleas was cause for worry as Plague and other flea-borne diseases are known to occur in the country in sylvatic form. Result: Conventional vector control measures had limited impact and unconventional measures had to be devised due to limited capacity in the inaccessible area. Severity of the problem, potential to cause flea-borne diseases and unavailability of conventional insecticides prompted the author to use Aviation Turbine Fuel (ATF) for area spray in the UN base. Conclusion: Healthcare providers in fast-evolving operational situations such as Peacekeeping Missions need to maintain high index of suspicion and often adopt innovative methods to ensure effective public health cover to troops.

EFFICACY OF THREE INSECTICIDES ON RAT FLEA (XENOPSYLLA CHEOPIS) INFESTING RODENTS IN GIZA GOVERNORATE, EGYPT.

The extensive use of insecticides in public health and agriculture sectors is the main reason for development of resistance in fleas associated in domestic rodents. The present work was planned to investigate the insecticidal efficacy of Lambda-cyhalothrin, Chlorpyrifos and Fenitrothion against rat flea (Xenopsylla cheopis) infesting rodent species in Giza Governorate, Egypt. The lethal concentration Lc₅₀ and Lc₉₀ of population percent were obtained from the established regression log concentrate-response lines. Data indicated that the values of lethal concentration (Lc₅₀) were 0.293, 1.725 & 2.328% for Lambda-cyhalothrin, chlorpyrifos and Fenitrothion, respectively. The values of lethal concentration (Lc₉₀) were 0.467, 2.839 & 5.197% for Lambda-cyhalothrin, chlorpyrifos and Fenitrothion, respectively.

Surveillance of Trypanosoma Spp of Rodents and Studies in Their Transmission Probability by Fleas in Some Rural Egyptian Areas

A new public health problem arises from animal trypanosomes that afflict human by a disease called atypical human trypanosomiasis. Although humans have an innate protection against most Trypanosoma species, nineteen cases of atypical human trypanosomiasis caused by the animal trypanosome as T. b. brucei, T. vivax, T. congolense, T. evansi and T. lewisi have been recorded. Some of theserecorded cases were transient, six required trypanocidal treatments however two patients died. Rodent trypanosome, T. lewisi is transmitted via ingestion of fleas or their feces containing the infective stage, the metacyclic trypomastigote. Because of the high densities of various species of rodents and their distribution all over the country especially in rural areas, the present work aimed to evaluate the trypanosomiasis among rodents collected from November to March 2016 and study transmission probability by their fleas in some rural areas in Abu Alnomros Center, Giza. The overall trypanosomiasis prevalence among the different rodent species was (21 rats) 24.7%. All the infected rats belonged to Rattus r. spp where the prevalence of infection with Trypanosoma lewisi among that species was very high 51.2% while none of rats belonged to Rattus norvegicus were infected. That may be attributed to the solid immunity gained by the R. norvegicus where most of the collected norvegicus were aged and weighed more than 200 grams. There was an inverse significant correlation between the densities of parasites and the weights of the losts. The rat which recorded the highest parasite density (60,000 parasites/microliter) was a female Rattus r. captured indoor (inside house). As to sex of Rattus rattus spp no significant difference was found between males and females in trypanosomiasis. Also there was no significant correlation between the densities of parasites and the number of white blood cells among Rattus rattus spp. All positive rats were collected indoors (from houses) and all the rats which were captured from outdoors (farms) were negative for T. lewisi. The difference between infections with trypanosomiasis among rats inhabited the houses and that found in farms was highly significant. Only two species of fleas were found on rats, Xenopsylla cheopis and Leptopsylla segnis. The oriental fleas, X cheopis, were found mainly on R. norvegicus where 57.5% of R. norvegicus were positive for X cheopis while only one rat was positive for L. segnis. On other hand the rat fleas, L. segnis, were found mainly on Rattus rattus spp where 39% of these rats were positive for L. segnis. The present work revealed a significant correlation between the infection with T. lewisi, and the presence of L. segnis on the rats however that correlation regarding X. cheopis was not significant.

Plague-Carrying Fleas Resist Insecticides

Despite decades of work trying to control plague, the illness is still a major health concern in Madagascar. A 2014 outbreak in that country infected more than 335 people at its peak and claimed at least 79 lives, according to the World Health Organization. Plague is primarily transmitted to people from rats via the Oriental rat flea Xenopsylla cheopis. Efforts to keep the disease in check focus on controlling the flea population with insecticides. But a study by Adélaïde Miarinjara and Sébastien Boyer, of the Pasteur Institute of Madagascar, reveals that of 12 standard insecticides, six—including the most commonly used insecticide deltamethrin—are ineffective against local fleas (PLOS Neglected Trop. Dis. 2016, DOI: 10.1371/journal.pntd.0004414). Miarinjara and Boyer studied eight flea populations from around the island and found that only one insecticide—dieldrin—was 100% effective on all populations. Dieldrin is an organochlorine compound that’s toxic to mammals and known to accumulate in the

Feeding Behavior Modulates Biofilm-Mediated Transmission of Yersinia pestis by the Cat Flea, Ctenocephalides felis.

BackgroundThe cat flea, Ctenocephalides felis, is prevalent worldwide, will parasitize animal reservoirs of plague, and is associated with human habitations in known plague foci. Despite its pervasiveness, limited information is available about the cat flea’s competence as a vector for Yersinia pestis. It is generally considered to be a poor vector, based on studies examining early-phase transmission during the first week after infection, but transmission potential by the biofilm-dependent proventricular-blocking mechanism has never been systematically evaluated. In this study, we assessed the vector competence of cat fleas by both mechanisms. Because the feeding behavior of cat fleas differs markedly from important rat flea vectors, we also examined the influence of feeding behavior on transmission dynamics.Methodology/Principal FindingsGroups of cat fleas were infected with Y. pestis and subsequently provided access to sterile blood meals twice-weekly, 5 times per week, or daily for 4 weeks and monitored for infection, the development of proventricular biofilm and blockage, mortality, and the ability to transmit. In cat fleas allowed prolonged, daily access to blood meals, mimicking their natural feeding behavior, Y. pestis did not efficiently colonize the digestive tract and could only be transmitted during the first week after infection. In contrast, cat fleas that were fed intermittently, mimicking the feeding behavior of the efficient vector Xenopsylla cheopis, could become blocked and regularly transmitted Y. pestis for 3–4 weeks by the biofilm-mediated mechanism, but early-phase transmission was not detected.ConclusionsThe normal feeding behavior of C. felis, more than an intrinsic resistance to infection or blockage by Y. pestis, limits its vector competence. Rapid turnover of midgut contents results in bacterial clearance and disruption of biofilm accumulation in the proventriculus. Anatomical features of the cat flea foregut may also restrict transmission by both early-phase and proventricular biofilm-dependent mechanisms.

Detection of Rickettsia Species in Fleas Collected from Cats in Regions Endemic and Nonendemic for Flea-Borne Rickettsioses in California.

Rickettsia typhi, transmitted by rat fleas, causes most human flea-borne rickettsioses worldwide. Another rickettsia, Rickettsia felis, found in cat fleas, Ctenocephalides felis, has also been implicated as a potential human pathogen. In the continental United States, human cases of flea-borne rickettsioses are reported primarily from the southern regions of Texas and California where the cat flea is considered the principal vector. In California, more than 90% of locally acquired human cases are reported from suburban communities within Los Angeles and Orange counties despite the almost ubiquitous presence of cat fleas and their hosts throughout the state. The objective of this study is to assess the presence and infection rate of Rickettsia species in cat fleas from selected endemic and nonendemic regions of California. Cat fleas were collected from cats in Los Angeles County (endemic region) and Sacramento and Contra Costa counties (nonendemic region). Sequencing of 17 amplicons confirmed the presence of R. felis in both the endemic and non-endemic regions with a calculated maximum likelihood estimation of 131 and 234 per 1000 fleas, respectively. R. typhi was not detected in any flea pools. Two R. felis-like genotypes were also detected in fleas from Los Angeles County; Genotype 1 was detected in 1 flea pool and Genotype 2 was found in 10 flea pools. Genotype 1 was also detected in a single flea pool from Sacramento County. Results from this study show that R. felis is widespread in cat flea populations in both flea-borne rickettsioses endemic and nonendemic regions of California, suggesting that a high prevalence of this bacterium in cat fleas does not predispose to increased risk of human infection. Further studies are needed to elucidate the role of R. felis and the two R. felis-like organisms as etiologic agents of human flea-borne rickettsioses in California.

Orange County Vector Control and the County’s Feral Cat TNR Program: Ne’er the Twain Shall Meet?

In 2006, flea-borne rickettsiosis (flea-borne typhus), a zoonotic disease caused by either Rickettsia typhi or R. felis and transmitted primarily by two flea species, the Oriental rat flea and the cat flea, re-emerged as an important vector-borne disease in Orange County, California. The Orange County Mosquito and Vector Control District (OC Vector Control) has investigated 142 human cases of flea-borne rickettsiosis. Results of these investigations have established a link with Rickettsia-infected cat fleas, opossums, feral cats, and disease transmission to humans; no cases have been associated with rats and their fleas. Since initiation of a Trap-Neuter-Return (TNR) Program by Orange County (OC) Animal Care in 2009, OC Vector Control has been working with OC Animal Care to minimize the potential public health risks associated with the TNR Program. Interagency discussions have led OC Animal Care to prohibit the release of TNR cats at locations with a high risk for zoonotic disease transmission to humans, such as schools, parks, and health care facilities, and also to disclose the release sites to OC Vector Control. OC Animal Care has not agreed to OC Vector Control’s request for a zoonotic disease review of its TNR Program, nor has it provided a procedural manual to verify the verbal agreements reached by the two agencies. In agreement with OC Vector Control’s concerns, an investigation in 2015 by the Orange County Grand Jury of OC Animal Care’s TNR Program recognized the Program’s potential to increase zoonotic disease transmission to the public and other wildlife. We discuss the conflicting views arising from two governmental agencies, which perceive the zoonotic diseases risk associated with a TNR program at significantly different thresholds of concern.