Vectors and Hosts of Rickettsia felis in Europe

Vectors and Hosts of Rickettsia felis in Europe: Comparison

Please note this is a comparison between Version 2 by Lindsay Dong and Version 1 by George Valiakos.

Rickettsia felis in an obligate intracellular Gram negative bacterium and the causative agent of flea-borne spotted fever (FBSF). Rickettsia felis requires a vertebrate and invertebrate host to survive and reproduce. The cat flea (Ctenocephalides felis) is considered as the primary vector and the reservoir host of this pathogen.

Rickettsia felis
rickettsiosis
zoonosis

1. Introduction

Rickettsia felis requires a vertebrate and invertebrate host to survive and reproduce. The cat flea (Ctenocephalides felis) is considered as the primary vector and the reservoir host of this pathogen [2,5]. Rickettsia felis has been also identified in various flea species and there is a growing evidence of detection in other arthropods: ticks, mites, lice and mosquitoes. Similarly, the host range of R. felis is increasing; reports on infected humans, domestic and wild animals are coming from all over the world. However, the competency of the different arthropods and hosts as vectors and reservoirs, respectively, is yet to be demonstrated [5].

Rickettsia felis follows the distribution of its vector; it occurs on all continents except Antarctica [6]. The first human case was reported in Texas in 1994 [7] and the first autochthonous human case was reported in Europe in 2002 [8], suggesting that this pathogen was not restricted to USA and it had the potential for global distribution. The lack of specific diagnostics and the similarity of FBSF with the disease caused by R. typhi [Flea-borne (murine) typhus] or with other vector-borne diseases, potentially leads to the under-diagnosis of the disease caused by R. felis. Thus, the true number of R. felis cases may be under-estimated. Under-reporting may also be enhanced by the self-limiting nature of the disease [5].

Although originally considered a sporadic disease, febrile illness has recently been regularly associated with R. felis in sub-Saharan Africa; the monthly incidence of R. felis infection in humans was found to reach approximately 17% during spring [9,10]. The recent identification of R. felis in the literature, and the increasing number of human cases from different regions in parallel to the fast-growing reports of the worldwide detection of R. felis in different arthropod and host species, justify its designation as an emerging pathogen [5,11,12].

2. Vectors and Hosts of R. felis in Europe

2.1. Vectors

During 2017–2022, a total of 11 European countries reported the occurrence of R. felis in several vector species (Figure 1). The vectors found to be infected included flea, tick and mite species; the dominant flea and tick species were C. felis and I. ricinus, respectively. The baseline characteristics of the studies on vectors which were included in Table 1.

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Figure 1. Map showing the European countries (in green) that reported the occurrence of R. felis during 2017–2022 in hosts and vectors (https://www.mapchart.net/europe.html, accessed on 12 November 2022).

Table 1.

The reported occurrence of

R. felis

in different vectors in Europe (2017–2022).

Countries	Study Period	Vectors	Prevalence in Vector	Vector Hosts	Reference

Countries	Study Period	Host	Prevalence in Host	Reference
Austria	2016	C. felis	Not defined (1/105)	Cats	[	14	]
Germany	2008	Human	2.7% (15/559) *	[	34	]
France	2014–2017	I. ricinus	0.1% (1/998)	Environment	[	25	]
Germany	2010–2014	Wild mammals (	A. amphibious	,	A. flavicollis	,	A. sylvaticus	)	Not defined	[	39	]	France	2017	I. ricinus	7% **	Environment	[	26	]
Germany	2012–2014	Small mammals (	A. flavicollis	)	Not defined	[	Greece	2013	C. felis	13% (3/23)	Cats	[	16	]
27	]
Greece	2013	Human	3.5% (8/223) *	[	16	]	Greece	2016–2017	C. felis	,	C. canis	,	P. irritans	14% (14/100) *	Dogs and Cats	[	17	]
Italy	2010–2016	Cats	8.04% (23/286) *	[	36	]	Italy	2013	Rh. turanicus	2.9% (1/34) *	Sheep
Italy	2018–2021	[	Cats	28	]
17.89% (17/95) *	[	37	]	Italy	2014–2016	I. hexagonus	Not defined	Hedgehog and fox
Malta	2017	[	Cats	29	]
0%	[	20	]	Lithuania	2013–2014	H. microti	,	L. agilis	,	Ct. agyrtes	,	H. talpae	Not defined	Rodents	[	18	]
Poland	2014	Small mammals (	A. flavicollis	)	Not defined	[	40	]	Malta	2017	C. felis	39.47% (15/38)	Cats
Serbia	2019	[	Human	19	]
3% (1/30)	[	31	]	Malta	2017	C. felis	96.42% (54/56) *	Serbia	2020	Human	Not defined (1/85)Cats	[	32	][	20	]
Romania	2018	I. ricinus	Not defined (1/222)	Rodents, birds, hedgehogs	[	30	]
Slovakia	Serbia	2019	I. ricinus	3% (1/31)	Humans	[	31	]
Serbia	2020	Ticks	4.3%	Humans	[	32	]
Slovakia	2012–2014	N. fasciatus	,	Ct. assimilis	Not defined	Rodents	[	22	]
Slovakia	2014–2016	Ct. solutus	Not defined	Small mammals (	A. agrarius	)	[	21	]
Spain	2011–2018	C. felis	28.3% (15/53)	Dogs	[	15	]
		A. erinacei	33.3% (6/18)	Hedgehogs
		Ct. b. boisseauorum	1.6% (1/60)	Rodents (	A. terrestris	)
Spain	2015–2017	I. ricinus	0.46% (1/219)	Environment	[	33	]
Spain	2019–2020	C. felis	29.6% (38/128)	Dogs and Cats	[	23	]
UK	2018	C. felis	,	C. canis	5.7% (27/470) *	Dogs and Cats	[	24	]

* pooled samples. ** refers to tissue samples.

2.2. Hosts

During 2017–2022, a total of nine European countries reported the occurrence of R. felis in different hosts (Figure 1). The hosts found to be infected by R. felis by molecular methods or exposed to R. felis by serology were humans, cats and small mammals. The baseline characteristics of the studies on hosts which were included in Table 2.

Table 2.

The occurrence of

R. felis

in different hosts in Europe (2017–2022).

2014–2015
Small mammals

(
A. flavicollis
)
1.1% (3/27)
[	41	]
Sweden	2015	Human	Not defined *	[	35	]
Turkey	2017–2021	Cats	26.3% (44/167)	[	38	]

* Serological methods (IFA/MIF).

European countries reported the detection of R. felis in several arthropod and host species: fleas, ticks and mites, and cats, small mammals and humans, respectively. Several studies provided the first evidence of R. felis detection in some countries, vectors or animal species, such as in Ct. agyrtes and H. talpae fleas and H. microti and L. agilis mites in Lithuania [18], fleas from cats in Malta [19], Ct. b. boisseauorum fleas in Spain [15], Rh. turanicus in Italy [28], cats in Turkey [38] and A. flavicollis in Slovakia [41]. In the studies conducted, R. felis positive fleas, ticks and mites were removed from different hosts: cats, dogs, hedgehogs, foxes, sheep, rodents, birds, small mammals (A. agrarius, A. agrarius) and humans, as well as from the environment (flagging) [17].

Among the flea species examined, C. felis, C. canis, P. irritans, Ct. agyrtes, H. talpae, Ct. solutus, N. fasciatus, Ct. assimilis, A. erinacei and Ct. b. boisseauorum were found to be infected with R. felis—with some of them being the first ever recordings [14,16,17,18,19,22,23,33,41]. Other flea species that have been found to be infected in previous studies include C. orientis, Anomiopsyllus nudata, Ctenophthalmus sp., X. cheopis, X. brasilliensis, Tunga penetrans, Ceratophyllus gallinae, Spilospsyllus cuniculi and Echidnophaga gallinacean [12,42,43]. Although numerous flea species have been found to be infected by R. felis, the cat flea is deemed as the primary vector of R. felis. Furthermore, the pathogen has been identified in the mid-gut, ovaries and salivary glands of C. felis suggesting that infection is disseminated within the arthropod [44]. Moreover, R. felis is transmitted transovarially and transstadially in cat fleas and vertical transmission of R. felis persists in C. felis for at least 12 generations without the aid of an R. felis-infected bloodmeal [45,46]. Several host species, including cats, dogs, opossums, raccoons, rodents, and humans, were either seropositive or PCR positive for R. felis DNA. However, until now, a definitive host with appropriate clinical signs and bacteremia has not been identified [6,11,47]. The vertebrate hosts which were found to be R. felis infected or exposed during investigations in the last five years in Europe are cats (0–26.3%) [36,37,38], small mammals (1.1%) [41] and humans (2.7–3.5%) [16,31]. Free-roaming animals as well as the wild animals are of increased importance as they do not receive routine veterinary care as domestic cats and dogs do. Especially under certain circumstances that bring wildlife, free-roaming cats, and domestic animals in close proximity (e.g., when food is left outdoors), the potential for exchanging fleas and other ectoparasites increases [58]. Rickettsia felis is an emerging arthropod-borne pathogen which has been detected in a wide range of vectors and hosts worldwide. However, the role of the multiple arthropods that harbor the pathogen is still unclear; extensive field research, including of hosts and vectors close to the residences of R. felis human cases, would provide an insight into the components involved in the transmission chain. Clinicians should be aware of the epidemiology of the disease caused by R. felis and include it in the differential diagnosis of febrile disease with or without the presence of a rash. Additionally, clinicians should be well-informed about the possible arthropod species that could harbor R. felis and include information on exposure to these vectors during data collection of the clinical case history. As for pets, veterinarians should keep training pet owners on the need for effective year-round arthropod control, especially for fleas, on their pets and in the environment.