Molecular Survey of Rickettsia spp.,Anaplasma spp.,Ehrlichia spp.,Bartonella spp.,and Borrelia spp. in Fleas and Lice in Ethiopia

Introduction

Mosquito-borne diseases such as dengue, Zika, chikungunya, and yellow fever are widely recognized as important entities in tropical and subtropical areas. However, there are numerous nonmosquito vector-borne pathogens that are less frequently studied but cause diseases such as rickettsiosis, anaplasmosis, ehrlichiosis, bartonellosis, and borreliosis, febrile entities that are prevalent in low-resource countries (Oguntomole et al. 2018).

In tropical and subtropical low-income settings, there is a high prevalence of parasites such as ticks, fleas, and lice, which can transmit these diseases to humans (Oguntomole et al. 2018). Different studies have analyzed the prevalence of pathogens in such insects, with a plurality focusing on ticks as the main arthropod responsible for transmitting the microorganisms (Mediannikov et al. 2010). Fewer studies have focused on fleas or lice (Foongladda et al. 2011, Leulmi et al. 2014).

To fill this gap, we designed a study to assess the prevalence of Rickettsia spp., Anaplasma spp., Ehrlichia spp., Bartonella spp., and Borrelia spp. in fleas and lice in a rural area of southeast Ethiopia. These arthropods are potentially transmitters of pathogenic microorganisms to humans.

Materials and Methods

Results

Nifty-one fleas and 30 lice were studied. Of 91 fleas, 50 (54.9%) were identified as Ctenocephalides felis, 37 (40.1%) as Pulex irritans, and 4 (4.4%) as Ctenocephalides canis.

Pathogens were present in 79 of 91 fleas (86.8%). The distribution of pathogen by species of fleas is shown in Table 1. The main pathogens by genus were Rickettsia spp. (n = 43; 47.3%) and Anaplasma spp. (n = 40; 44.0%), followed by Ehrlichia spp. (n = 1; 1.1%) and Bartonella spp. (n = 1; 1.1%). Most of the Rickettsia spp. were Rickettsia felis (n = 41), and only two were Rickettsia monacensis. All isolated Anaplasma spp. were Anaplasma platys. C. felis and P. irritans showed a similar prevalence of Rickettsia spp. (48.0% and 43.2%). However, P. irritans was more frequently infected with Anaplasma spp. (67.7%), with C. felis showing a lower prevalence (30.7%) (p < 0.001). Fourteen cases (15.4%) showed coinfection with two pathogens (Table 2), usually A. platys and R. felis (n = 12; 13.4%).

Of the 30 lice identified, 16 (53.3%) were Pediculus humanus capitis and 14 (46.7%) Pediculus humanus humanus. Pathogens were present in 7 (23.3%) cases: 4 (16.7%) Bartonella quintana, 2 (6.7%) Ehrlichia muris, and 1 (3.3%) Borrelia recurrentis. The distribution of pathogens in lice is shown in Table 3.

Discussion

In this study in a rural area of Ethiopia, there was a notably high prevalence of pathogenic microorganisms (∼85%) in fleas, especially R. felis and A. platys. These results are consistent with other molecular surveys of fleas, which have reported a pathogen prevalence of around 80% (Lappin 2018).

With regard to the epidemiology of the fleas identified for our study, the presence of C. felis and P. irritans stand out the most, followed by C. canis; we did not observe any specimens of Xenopsylla cheopis (oriental rat flea). The epidemiology of the fleas depends on the setting where the specimens are collected. Thus, in a setting of dogs and wolves, the main fleas identified are X. cheopis and C. canis (Torina et al. 2013). This indicates the differences in distribution according to the geographical area studied.

The main pathogens identified in fleas were Rickettsia spp., especially R. felis (∼46%). The prevalence of R. felis in parasites is variable and has been reported in 100% of the population of dog fleas in South Africa (Kolo et al. 2016), 67% of the dog and cat fleas in Bangkok (Foongladda et al. 2011), about 19% of the cat fleas in Australia (Barrs et al. 2010), ∼11% of the dogs in Cambodia (Inpankaew et al. 2016), and just 5% in samples collected from farm animals in Iran (Ghavami et al. 2018).

First identified in 1992, R. felis is emerging as a pathogen from among the traditional Rickettsia microorganisms (Yazid Abdad et al. 2011). It is the cause of flea-borne spotted fever in humans, and in Africa, it is responsible for numerous febrile processes (Legendre et al. 2017). The high prevalence of R. felis in C. felis and P. irritans should alert the medical community to this pathogen's potential role in acute undifferentiated febrile illnesses in low-resource tropical and subtropical zones, where there is an increased risk of human infection.

Rickettsia typhi is a flea-borne pathogen, causing acute undifferentiated febrile diseases throughout the world (Blanton et al. 2017). As a member of the typhus group, it is also the agent of murine (or endemic) typhus (Pieracci et al. 2017). We did not observe any cases of R. typhi in the fleas or lice included in our analyses; however, this pathogen is transmitted from rat to humans by the X. cheopis, which we did not find in our study.

We did identify R. monacensis in two fleas (C. felis). This microorganism is transmitted by ticks and is responsible for febrile episodes with exanthema or Mediterranean spotted fever (Portillo et al. 2015). The isolation of this pathogen in fleas is somewhat novel, but this could be a potential vector for human infection (Kim et al. 2017).

The species of Anaplasma identified in all of our samples was A. platys, with no evidence of other species such as Anaplasma centrale, Anaplasma bovis, Anaplasma ovis, Anaplasma marginale, or Anaplasma phagocytophilum (Torina et al. 2013). Other studies have reported a predominance of A. phagocytophilum (Lappin 2018) or A. ovis (Torina et al. 2013). The prevalence of A. platys (∼40%) found in our study is well above that observed elsewhere, where it stands only at about 3% (Foongladda et al. 2011).

A. platys is responsible for cyclic thrombocytopenia in dogs (Harrus et al. 1997), and it has been isolated in dogs and cats (Lima et al. 2010). It has also been suspected as having a role in febrile episodes of veterinarians exposed to cat and dog fleas (Maggi et al. 2013). Transmission of Bartonella spp. (Bartonella henselae and Bartonella clarridgeiae) by fleas is well documented (Lappin 2018). The prevalence of Bartonella spp. in our study was marginal (∼1%); the sole case was B. clarridgeiae. Another series observed that up to 20–28% of the fleas were vectors for species of the Bartonella genus (Barrs et al. 2010, Foongladda et al. 2011).

Ehrlichia spp. was an infrequent pathogen in our study, found in only one flea specimen, as an E. muris-like agent. Other series have found Ehrlichia spp.—specifically E. canis—in up to 20% of the fleas in dogs in Cambodia (Inpankaew et al. 2016). Species in this genus have also been identified in up to 3% of ticks (Murphy et al. 2017). Other genera that are close to Ehrlichia have also been found in fleas and ticks, for example, Neoehrlichia mikurensis (Oguntomole et al. 2018).

All of these pathogens have been identified in fleas, which may act as vectors for transmitting these pathogens to other animals and potentially to humans. Some of the pathogens identified in this study have not been identified as responsible for febrile episodes, but advances in molecular techniques could change that, allowing researchers to identify these pathogens as the cause of febrile episodes in humans (Kim et al. 2017).

In this study, one in four lice tested positive for a pathogen, with similar results among human body lice and human head lice. Recent studies have shown that these pathogens can be present on the head itself (Amanzougaghene et al. 2017, Ulutasdemir et al. 2018).

In agreement with other reports (Ulutasdemir et al. 2018), the main pathogen we found in lice was Bartonella spp. There are several Bartonella species, including B. quintana, Bartonella elizabethae, and B. henselae. In our case, B. quintana was identified in about 16% of the lice (∼19% of human head lice and 7% of human body lice). This species is the main Bartonella species identified from the body lice collected in homeless people in Colombia (Faccini-Martínez et al. 2017), and it has also been identified in head lice (Boutellis et al. 2012), as in our study. The cause of trench fever, bacillary angiomatosis, endocarditis, chronic bacteremia, and chronic lymphadenopathy, it appears in conditions of overcrowding, marginalization, and poverty (Boutellis et al. 2012).

In one sample, we identified an E. muris-like agent. This microorganism has been identified in different species of ticks (Rhipicephalus microplus, Ixodidae spp., etc.) (Lynn et al. 2015), but our literature review in PubMed did not uncover any cases in fleas.

There was one case of B. recurrentis in a flea. It is well known that body lice are vectors for louse-borne relapsing fever in areas of Ethiopia; our group described one such epidemic outbreak in the Gambo region in 2003 (Ramos et al. 2004). The findings of the present study suggest that this pathogen continues to be marginally present in the country.

Rickettsia prowazekii, which is responsible for epidemic louse-borne typhus (Ulutasdemir et al. 2018), was not identified in any of our samples.

Limitations of this study include its small sample size of fleas and lice as well as the convenience sampling method used to collect specimens. However, it does give a valuable picture of the pathogen prevalence in fleas and lice in a rural setting of Ethiopia. We did not analyze other pathogens such as Candidatus Mycoplasma haematoparvum, which can also be transmitted by these arthropods. Although some research from Africa has been published (Boutellis et al. 2012, Kolo et al. 2016), there is still a need for studies with a larger scope that allow an approach to everyday practice with regard to pathogen prevalence in fleas and lice in rural areas of Africa, to understand the real potential for transmission to humans.

In conclusion, there was a high prevalence of pathogens among the fleas collected from the hospital setting and the rural village, and these pathogens could be responsible for infections in humans. The lice were also vectors for microorganisms causing fever in humans. However, it is not possible to confirm that these vectors could transmit some of these pathogens because perhaps they are there just secondary to blood meal. Efforts should be made to improve hygiene in rural areas to control these vectors, and in turn limit the reach of pathogens that can cause infections in humans.