Poor vector competence of the human flea, Pulex irritans, to transmit Yersinia pestis.

BACKGROUND: The human flea, Pulex irritans, is widespread globally and has a long association with humans, one of its principal hosts. Its role in plague transmission is still under discussion, although its high prevalence in plague-endemic regions and the presence of infected fleas of this species during plague outbreaks has led to proposals that it has been a significant vector in human-to-human transmission in some historical and present-day epidemiologic situations. However, based on a limited number of studies, P. irritans is considered to be a poor vector and receives very little attention from public health policymakers. In this study we examined the vector competence of P. irritans collected from foxes and owls in the western United States, using a standard protocol and artificial infection system. METHODS: Wild-caught fleas were maintained in the laboratory and infected by allowing them to feed on human or rat blood containing 2 × 108 to 1 × 109 Y. pestis/ml. The fleas were then monitored periodically for infection rate and bacterial load, mortality, feeding rate, bacterial biofilm formation in the foregut (proventricular blockage), and ability to transmit Y. pestis after their single infectious blood meal. RESULTS: P. irritans were susceptible to infection, with more than 30% maintaining high bacterial loads for up to 20 days. Transmission during this time was infrequent and inefficient, however. Consistent with previous studies, a low level of early-phase transmission (3 days after the infectious blood meal) was detected in some trials. Transmission at later time points was also sporadic, and the incidence of proventricular blockage, required for this mode of transmission, was low in fleas infected using rat blood and never occurred in fleas infected using human blood. The highest level of blockage and transmission was seen in fleas infected using rat blood and allowed to feed intermittently rather than daily, indicating that host blood and feeding frequency influence vector competence. CONCLUSIONS: Our results affirm the reputation of P. irritans as a feeble vector compared to rodent flea species examined similarly, and its vector competence may be lower when infected by feeding on bacteremic human blood.

Metagenomic analysis of human-biting cat fleas in urban northeastern United States of America reveals an emerging zoonotic pathogen.

An infestation of cat fleas in a research center led to the detection of two genotypes of Ctenocephalides felis biting humans in New Jersey, USA. The rarer flea genotype had an 83% incidence of Rickettsia asembonensis, a recently described bacterium closely related to R. felis, a known human pathogen. A metagenomics analysis developed in under a week recovered the entire R. asembonensis genome at high coverage and matched it to identical or almost identical (> 99% similarity) strains reported worldwide. Our study exposes the potential of cat fleas as vectors of human pathogens in crowded northeastern U.S, cities and suburbs where free-ranging cats are abundant. Furthermore, it demonstrates the power of metagenomics to glean large amounts of comparative data regarding both emerging vectors and their pathogens.

Domestic dogs are mammalian reservoirs for the emerging zoonosis flea-borne spotted fever, caused by Rickettsia felis.

Rickettsia felis is an obligate intracellular bacterium that is being increasingly recognized as an etiological agent of human rickettsial disease globally. The agent is transmitted through the bite of an infected vector, the cat flea, Ctenocephalides felis, however there is to date, no consensus on the pathogen's vertebrate reservoir, required for the maintenance of this agent in nature. This study for the first time, demonstrates the role of the domestic dog (Canis familiaris) as a vertebrate reservoir of R. felis. The ability of dogs to sustain prolonged periods of rickettsemia, ability to remain asymptomatically infected with normal haematological parameters and ability to act as biological vehicles for the horizontal transmission of R. felis between infected and uninfected fleas provides indication of their status as a mammalian reservoir of this emerging zoonosis.

Exposure of client-owned cats to zoonotic vector-borne pathogens: Clinic-pathological alterations and infection risk analysis.

Zoonotic Vector-Borne Diseases (VBDs) represent a relevant health issue for pets and humans. Italy is a major epidemiological hub for feline VBDs, because of suitable conditions for vector biology and disease transmission patterns. The present study investigated the exposure to major zoonotic arthropod-borne pathogens of cats in Italy, along with the evaluation of clinic-pathological features and a risk factor analysis. Out of 167 examined cats, 52 (31.1%) were seropositive for at least one vector-borne pathogen, being positivity for Bartonella henselae the most recorded (18%). Also, various cats seroreacted for Rickettsia felis (10.8%) and Rickettisa typhi (4.2%), Leishmania infantum (3%), Anaplasma phagocytophilum (2.4%) and Ehrlichia canis (2.4%). Forty-six cats were tested also for antibodies against D. immitis and two (4.3%) scored positive. The statistical analysis showed a positive association between flea infestation and seropositivity to B. henselae, other than an association between the administration of monthly ectoparasiticide treatments and seronegativity for Rickettsia spp.; seropositive cats were older than negative animals and the lifestyle (i.e. indoor vs outdoor) was not correlated with exposure to vector-borne pathogens. The majority of seropositive cats appeared clinically healthy or showed aspecific clinical signs. Around 80% of seropositive cats had one or more biochemical and/or complete blood count abnormalities. The present data confirm the endemicity of zoonotic feline VBDs in Italy and indicate that awareness on arthropod infections and transmitted pathogens should be kept high and possible implemented, towards the protection of animal and human health with adequate surveillance plans.

Analysis of 3800-year-old Yersinia pestis genomes suggests Bronze Age origin for bubonic plague.

The origin of Yersinia pestis and the early stages of its evolution are fundamental subjects of investigation given its high virulence and mortality that resulted from past pandemics. Although the earliest evidence of Y. pestis infections in humans has been identified in Late Neolithic/Bronze Age Eurasia (LNBA 5000-3500y BP), these strains lack key genetic components required for flea adaptation, thus making their mode of transmission and disease presentation in humans unclear. Here, we reconstruct ancient Y. pestis genomes from individuals associated with the Late Bronze Age period (~3800 BP) in the Samara region of modern-day Russia. We show clear distinctions between our new strains and the LNBA lineage, and suggest that the full ability for flea-mediated transmission causing bubonic plague evolved more than 1000 years earlier than previously suggested. Finally, we propose that several Y. pestis lineages were established during the Bronze Age, some of which persist to the present day.

Cat fleas (Ctenocephalides felis) carrying Rickettsia felis and Bartonella species in Hong Kong.

Fleas are commonly recorded on stray as well as domestic dogs and cats in Hong Kong. Fleas can be a major cause of pruritus in dogs and cats and also vectors of potentially zoonotic bacteria in the genera Rickettsia and Bartonella. Morphological examination of 174 fleas from dogs and cats living in Hong Kong revealed only cat fleas (Ctenocephalides felis). Cytochrome c oxidase subunit 1 gene (cox1) genotyping of 20 randomly selected specimens, revealed three cox1 haplotypes (HK-h1 to HK-h3). The most common haplotype was HK-h1 with 17 specimens (17/20, 85%). HK-h1 was identical to cox1 sequences of fleas in Thailand and Fiji. HK-h1 and HK-h2 form a distinct cat flea cox1 clade previously recognized as the Clade 3. HK-h3 forms a new Clade 6. A multiplex Bartonella and Rickettsia real-time PCR of DNA from 20 C. felis found Bartonella and Rickettsia DNA in three (15%) and ten (50%) C. felis, respectively. DNA sequencing confirmed the presence of R. felis, B. clarridgeiae and Bartonella henselae. This is the first reported study of that kind in Hong Kong, and further work is required to expand the survey of companion animals in the geographical region. The sampling of fleas on domestic cats and dogs in Hong Kong revealed them to be exclusively infested by the cat flea and to be harbouring pathogens of zoonotic potential.

Modelling the current distribution and predicted spread of the flea species Ctenocephalides felis infesting outdoor dogs in Spain.

BACKGROUND: The cat flea, Ctenocephalides felis, is the most prevalent flea species detected on dogs and cats in Europe and other world regions. The status of flea infestation today is an evident public health concern because of their cosmopolitan distribution and the flea-borne diseases transmission. This study determines the spatial distribution of the cat flea C. felis infesting dogs in Spain. Using geospatial tools, models were constructed based on entomological data collected from dogs during the period 2013-2015. Bioclimatic zones, covering broad climate and vegetation ranges, were surveyed in relation to their size. RESULTS: The models builded were obtained by negative binomial regression of several environmental variables to show impacts on C. felis infestation prevalence: land cover, bioclimatic zone, mean summer and autumn temperature, mean summer rainfall, distance to urban settlement and normalized difference vegetation index. In the face of climate change, we also simulated the future distributions of C. felis for the global climate model (GCM) "GFDL-CM3" and for the representative concentration pathway RCP45, which predicts their spread in the country. CONCLUSIONS: Predictive models for current climate conditions indicated the widespread distribution of C. felis throughout Spain, mainly across the central northernmost zone of the mainland. Under predicted conditions of climate change, the risk of spread was slightly greater, especially in the north and central peninsula, than for the current situation. The data provided will be useful for local veterinarians to design effective strategies against flea infestation and the pathogens transmitted by these arthropods.

Swabbing Prairie Dog Burrows for Fleas That Transmit Yersinia pestis: Influences on Efficiency.

Scientists and health-care professionals sometimes use a swabbing technique to collect fleas from rodent burrows, and later test the fleas for Yersinia pestis, the causative agent of plague. Detection of Y. pestis is enhanced when large pools of fleas are available. The following study investigated factors that might affect the rate at which fleas are collected from burrows in colonies of black-tailed prairie dogs (Cynomys ludovicianus). Data were collected from 13 colonies in New Mexico during 0600-1000 hours, June-August 2010-2011. Fleas were scarce on swabs inserted into burrows that were not actively used by prairie dogs; fleas are presumably suppressed in burrows that are void of hosts and might have begun to collapse due to a lack of maintenance. Fleas were scarce on swabs inserted into burrows with little sunlight entering the tunnel; many species of fleas use changes in light intensity to locate objects, but if light is limited, it might be difficult to locate a swab. Fleas were scarce on swabs inserted to shallow depths underground, especially during hot mornings, and during the hottest portions of mornings; when conditions are hot above ground, ectothermic fleas might migrate into the deep components of burrows, or become less willing to jump onto hosts, making it difficult to collect the fleas with swabs. If the swabbing technique is used to survey for Y. pestis on colonies of black-tailed prairie dogs, investigators might use the results of this study to modify their methods and increase the number of fleas collected.

[ON SOME DEBATABLE PROBLEMS OF THE NATURAL NIDALITY OF PLAGUE].

The communication substantiates the opinion that the theory of natural nidality of plague; which is based on the fundamental recognition that fleas play a leading role in the transmission and accumulation of the plague pathogen, cannot be disproved or substantially changed on the alternative weakly reasoned assumptions and hypotheses. All its "bottlenecks" are quite understandable when considering the long-term volumetric materials that have been gathered directly in nature and generalized in multiple publications. Plague is an obligate transmissive infection; its, agent is a highly specialized parasite that is completely associated in its vital activity with the only group of the blood-sucking insects--fleas and that is transmitted through periodic colonization of warm-blooded animals for a short time. All other types of plague microbe persistence in nature are either occasional or minor and do not play any significant role in pathogen persistence in the natural foci of this disease. There are no strong grounds for seriously considering the attempts to revise the main points of the theory of natural nidality of plague, which are widely held in current academic publications.

[IMPACT OF CASPIAN SEA LEVEL FLUCTUATIONS ON THE EPIZOOTIC ACTIVITY OF THE CASPIAN SANDY NATURAL PLAGUE FOCUS].

There is evidence that in 1923-2014 the sharp aggravations of the epizootic situation of plague in the area of its Caspian sandy natural focus after long interepizootic periods are in time with the ups of the Caspian Sea in the extrema of 11-year solar cycles. There were cases of multiple manifestations of plague in the same areas in the epizootic cycles of 1946-1954, 1979-1996, 2001, and 2013-2014. The paper considers the possible role of amebae of the genus Acanthamoeba and nematodes, the representatives of the orders Rhabditida and Tylenchida in the microfocal pattern of plague manifestations.

[PLAGUE IN MANCHURIA (1910-1911) AND EBOLA VIRUS DISEASE IN WEST AFRICA (2014-2015): COMMON PREREQUISITES FOR THE DEVELOPMENT OF EPIDEMICS].

The paper gives the results of a comparative analysis of the prerequisites for the emergence and spread of epidemics of particularly dangerous infections, by using plague in Manchuria (1910-1911) and Ebola virus disease in West Africa (2014-2015) as examples. Analysis of literature and archival data and online information could reveal a number of common factors and conditions, which substantially contributed to the epidemics. Organization of anti-epidemic (preventive) measures in cases of the threatening epidemic spread, of particularly dangerous diseases must be based on the minimization, of the influence of the specific factors and conditions, which facilitate disease transmission in a given area in a given time.

[A NATURAL PLAGUE FOCUS. IN GORNYI ALTAI: FORMATION, DEVELOPMENT, AND FUNCTIONING].

The paper gives the results of analyzing the data of long-term studies of the natural focal pattern of plague in the Gornyi Altai natural focus. It describes a wide range of biological processes occurring in the focus and shows the most important patterns of its functioning as a complex multilevel ecological system. The key features of the formation of the focus have been revealed. The plague focus in South-Western Altai has formed relatively, recently, about half a century ago, then it has intensively developed and its enzootic area and the activity of epizootic manifestations have considerably increased. This process is due to the space-time transformations of the basic ecological and population characteristics of Pallas' pika (Ochotoma pallasi), the principal vector of the pathogen of plague and fleas parasitizing the mammal, which is in turn related to the aridization of mountain steppes in South-Western Altai.

[The involvement of some flea species in the epizootic process in the Gorno-Altai natural plague focus: spatial and temporary characteristics].

The relative number of plague pathogen strains isolated from some flea species in different Gorno-Altai natural plague foci substantially varies; this indicator also varies with time. These patterns are due to the difference in the structure of multispecies communities of ectoparasites in these areas and their long-term transformation. As of now, the three species Paradoxopsyllus scorodumovi, Ctenophyllus hirticrus, and Amphalius runatus are widely involved in pathogen transmission in all three foci. These ectoparasites should be referred to as main plague vectors. In each focus, they are joined by other flea species, such as Rhadinopsylla dahurica and Amphipsylla primaris in the Ulandryk focus, Frontopsylla hetera, R. dahurica, Paradoxopsyllus kalabukhovi, and Paramonopsyllus scalodae in the Tarkhatin focus, and P. scalonae and P. kalabukhovi in the Kurai focus, which should be classified as an additional vector.

Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa.

Populations of large wildlife are declining on local and global scales. The impacts of this pulse of size-selective defaunation include cascading changes to smaller animals, particularly rodents, and alteration of many ecosystem processes and services, potentially involving changes to prevalence and transmission of zoonotic disease. Understanding linkages between biodiversity loss and zoonotic disease is important for both public health and nature conservation programs, and has been a source of much recent scientific debate. In the case of rodent-borne zoonoses, there is strong conceptual support, but limited empirical evidence, for the hypothesis that defaunation, the loss of large wildlife, increases zoonotic disease risk by directly or indirectly releasing controls on rodent density. We tested this hypothesis by experimentally excluding large wildlife from a savanna ecosystem in East Africa, and examining changes in prevalence and abundance of Bartonella spp. infection in rodents and their flea vectors. We found no effect of wildlife removal on per capita prevalence of Bartonella infection in either rodents or fleas. However, because rodent and, consequently, flea abundance doubled following experimental defaunation, the density of infected hosts and infected fleas was roughly twofold higher in sites where large wildlife was absent. Thus, defaunation represents an elevated risk in Bartonella transmission to humans (bartonellosis). Our results (i) provide experimental evidence of large wildlife defaunation increasing landscape-level disease prevalence, (ii) highlight the importance of susceptible host regulation pathways and host/vector density responses in biodiversity-disease relationships, and (iii) suggest that rodent-borne disease responses to large wildlife loss may represent an important context where this relationship is largely negative.

Direct transmission of the cat flea (Ctenocephalides felis) between cats exhibiting social behaviour.

A study design was created to assess the potential for fleas to infest cats directly from other cats. In the first experiment, six cats were infested with 100 fleas each and then immediately put in contact with six flea-free cats for 24 h. After removal of all fleas the study was repeated and the contact between cats lasted 48 h. The total numbers of fleas recovered out of the 600 fleas deposited on the 6 donor cats after each infestation were 499 and 486 at 24 h and 48 h respectively. At 1 h post-contact, five fleas were found on the receiver cats, with three cats having one flea and one cat, two fleas. The number of fleas recovered on receiver cats increased towards the end of the study. At 24 h, 20% of the fleas were found on the receiver cats, and at 48 h, 23%. In a second experiment, the six flea-free cats were put in contact with the six donor cats which were each infested by 100 fleas 48 h before. Fewer fleas were found on the receiver cats (n = 15), representing 3.8% of all fleas recovered (n = 403). All the observed fleas had fed. The fleas collected on receiving cats comprised 10 males and 5 females, and 4 of the 5 females were engorged and contained eggs. The fleas collected on donor cats comprised 153 males and 235 females, they were all fed and all females contained eggs. This experiment demonstrated that gravid female fleas have a tendency to become permanently but not exclusively parasitic. Nevertheless, a few can change their cat host in as little as 1 h, which may play a role in the rapid introduction of a new flea population into a cat environment.

[Zoonoses from ticks and fleas in dogs and cats]. / Zoönosen van teken- en vlooien bij honden en katten.

Fleas and ticks may transmit zoonotic diseases. This is an overview of tick- and flea-borne zoonoses where dogs and cats are involved in the epidemiology.

[Flea and tick control in dogs and cats]. / Bestrijding van vlooien en teken bij hond en kat.

Fleas and ticks may cause skin problems in dogs and cats and transmit (zoonotic) diseases. This is an overview about the present situation of the ectoparasites control.

Identification of Rickettsia africae and Wolbachia sp. in Ceratophyllus garei fleas from Passerine birds migrated from Africa.

The aim of the study was to reveal new aspects of the role of flea vector taken from migratory birds by screening of specimens with molecular biological methods. A field study was done in fishponds in Slovakia. Actually, 47 fleas were collected from reed warblers (Acrocephalus scirpaceus) and their nests. DNA was extracted and analyzed for representatives of the orders Rickettsiales. A rickettsia that shares 99.7% of identity by gltA gene with Rickettsia africae was identified in Ceratophyllus garei collected from A. scirpaceus. Moreover, two Wolbachia sp. were also detected in fleas. This is the first record of R. africae and Wolbachia sp. identified so far in Central Europe in fleas collected from migratory bird returning from Africa. This molecular study extends the geographic range and vector spectrum of arthropod-borne agents.