Serologic Survey for Rickettsiosis in Bats from São Paulo City,Brazil

Introduction

B ats are recognized carriers of zoonoses, such as rabies and histoplasmosis. Among 1198 bat species described in the world, 167 are found in Brazil (Reis et al. 2007). Bats live in almost every part of the world, and insectivorous bats comprise about 70% of the chiropteran species (Bredt et al. 1996). Environmental alterations caused by urban expansion and the availability of food and shelters have made São Paulo city attractive for bats, particularly insectivorous bats that are attracted by the insect population, abundant in the urban areas (Rydell and Racey 1995). These facts associated with a lack of predators have contributed to migration and adaptation of several bat species to human dwellings (Kunz 1982), increasing the probability of contact with people and domestic animals.

The genus Rickettsia has recently been classified into four groups of bacteria: the spotted fever group (SFG), the transitional group, the typhus group, and the ancestral group (AG) (Gillespie et al. 2007). In Brazil, at least seven Rickettsia species have been reported, namely, the SFG R. rickettsii, R. parkeri, R. amblyommii, and R. rhipicephali, all associated with ticks; the transitional group R. felis, and the typhus group R. typhi, both associated with fleas; and the AG R. bellii, associated with ticks (Labruna 2009). R. rickettsii is a recognized human and canine pathogen causing Rocky Mountain spotted fever (RMSF) (Dumler and Walker 2005, Labruna et al. 2009). R. parkeri was also shown to be pathogenic for humans in the United States and possibly in Uruguay (Paddock 2005), but human infection in Brazil remains unreported (Labruna 2009). R. felis and R. typhi are also pathogenic for humans, causing disease less severe than RMSF (Parola et al. 2005a). The remaining Rickettsia species in Brazil have never been associated with human disease, although R. amblyommii was recently incriminated as the etiological agent of human febrile illness in the United States (Apperson et al. 2008).

Ticks that have been recognized as vectors of rickettsioses to humans or animals are within the Ixodidae family, composed of the hard ticks (Parola et al. 2005b). These ticks are common parasites of a number of vertebrate species, but seldom found feeding on bats (Guglielmone et al. 2003, Barros-Battesti et al. 2006). On the other hand, the Argasidae tick family, composed of the soft ticks, bears at least 10 species that feed primarily on bats in Brazil (Barros-Battesti et al. 2006). Some of these ticks (Carios spp.) are important human-biting species that feed on humans inside their homes. In this case, the tick population is maintained by bats living in the roof of human dwellings (Carvalho 1942). During the last few years, one of the authors (M.B.L.) received several complaints of human bites by bat ticks inside homes in suburban areas of the states of São Paulo and Minas Gerais. The ticks were identified as Carios sp. and were associated with bats living in the roof of the human dwellings.

Soft ticks have been poorly studied regarding tick-borne rickettsiosis, reflected by only a few reports of natural infection by rickettsiae in soft ticks in a few countries (Rehacek et al. 1977, Philip et al. 1983, Hoogstraal 1985, Loftis et al. 2005, Cutler et al. 2006). However, under laboratory conditions, soft ticks were excellent competent vectors and reservoirs of R. rickettsii (Davis 1943). Rickettsioses in bats have also been poorly investigated. To our knowledge, there has been only a single study that investigated natural rickettsial infection in bats (Reeves et al. 2006), in which sera from 56 Eptesicus fuscus (insectivorous bat) from Georgia were tested against R. conorii and R. rickettsii antigens. Only one (1.8%) bat was shown to be seropositive, with a serologic titer of 256 for both antigens. Earlier studies showed that under experimental conditions bats are susceptible to R. rickettsii (Steinhaus 1947, Tamsitt and Valdivieso 1970). In addition, the bat species Histiotus velatus (Vespertilionidae) and Carollia perspicillata (reported as Hemiderma perspicillatum; Phyllostomidae) were reported to be reservoirs of RMSF (Magalhães 1944); however, we are not aware of any specific data that support these statements.

Considering the real risks of human infestations by bat ticks, bats should be good sentinels for the presence of Rickettsia-infecting bat-associated ticks. Thus, the goal of our study was to perform a serological analysis for rickettsial infection in chiropterans captured between 2006 and 2008 in the city of São Paulo, Brazil.

Materials and Methods

Results

From 451 bats, serum samples of 358 bats were tested against the five rickettsial antigens, resulting in 9.5%, 9.5%, 7.8%, 1.1%, and 0% seropositivity for R. rickettsii, R. parkeri, R. amblyommii, R. rhipicephali, and R. bellii, respectively. Due to availability of antigens, another 93 serum samples were tested against only R. rickettsii, resulting in 5.4% positivity. Overall, 8.6% (39/451), 9.5% (34/358), 7.8% (28/358), 1.1% (4/358), and 0% (0/358) serum samples were reactive to R. rickettsii, R. parkeri, R. amblyommii, R. rhipicephali, and R. bellii, respectively. Endpoint titers for rickettsial antigens according to bat species are presented in Table 1. Frequency of seropositive bats according to bat species and families are shown in Table 2. From 20 bat species of 3 different families, 46 animals were shown to be reactive to at least one rickettsial antigen. Seropositivity per bat species ranged from 0% to 33.3%.

Discussion

IFA is currently the gold-standard test for serologic diagnosis of rickettsial infection in humans and animals (Brown et al. 1983, Raoult et al. 1986, La Scola and Raoult 1997). In the present study, we applied this serologic test to perform an indirect diagnosis of rickettsial infection in bats of São Paulo city. For this purpose, we used antigens of four SFG species and one AG species that have been isolated from Brazilian ticks. Seropositivity for SFG rickettsial antigens in the absence of reactivity against R. bellii (AG species) suggests that bats from São Paulo city can be infected by SFG rickettsiae. Since SFG species share numerous outer membrane and related proteins, serum cross reaction for two or more SFG species is expected (La Scola and Raoult 1997), as observed in the present study, in which most of the serologically positive sera reacted to two or more rickettsial antigens. For this reason, it was not possible to determine the SFG species that infected the bats.

The bat family Molossidae, the most numerous in the present study, and the family Vespertilionidae include insectivorous bats (Nowak 2003). These two families comprised 9 out of the 11 bat species with reagent sera. In São Paulo city, these bats live in groups of hundreds, or even larger groups, roosting body contact in closed spaces, mainly in the roof of buildings. Possibly, these shelters could be favorable for establishment of Argasidae ticks. Bats of the Phyllostomidae family have a remarkable variety of food habits, but the ones found to be seropositive in the present study are frugivorous (Nowak 2003). These bats roost in small groups in trees, where Argasidae ticks could also be established. Thus, it is possible that Argasidae ticks serve as vectors of SFG rickettsia to bat species in São Paulo city, although this statement deserves further investigation. Alternatively, other ectoparasites commonly found on bats, such as flies (Nycteribiidae, Streblidae), bugs (Polyctenidae), fleas (Ischnopsyllidae), or mites (Spinturnicidae, Macronyssidae, Trombiculidae) (Seneviratne et al. 2009), could be vectors of rickettsiae to bats.

Continued degradation and fragmentation of the natural habitat of bats has forced increased overlap of bats, domestic animals, and human coexistence, and this has created opportunities for bat-borne zoonotic diseases to emerge. The role of bats as carriers of Rickettsia is unknown. Regarding bat ticks (Argasidae), nothing is known about their association with Rickettsia under natural conditions in Brazil, and scarce information is available in other parts of the world. In contrast to a previous rickettsial serosurvey in bats in one site of the United States (Reeves et al. 2006), the present study showed that a significant number of bats living in the São Paulo city metropolitan area have been in contact with SFG rickettsiae. Further studies are needed to investigate the possible role of bat ticks as vectors of rickettsioses, especially in the urban areas where higher bat and human densities exist.