CADORE, G.C.

HILGER, R.B.

LABRUNA, M.B.

OGRZEWALSKA, M.

PACHECO, R.C.

SANGIONI, L.A.

TONIM, R.

VOGEL, F.F.S.

L.A. Sangioni

F.F.S. Vogel

G.C. Cadore

R.B. Hilger

R. Tonim

R.C. Pacheco

M. Ogrzewalska

M.B. Labruna

Directory of Open Access Journals

Rickettsial infection in Cerro Largo, State of Rio Grande do Sul, Brazil

Universidade de São Paulo

Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Infecção rickettsial em Cerro Largo, Rio Grande do Sul

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Biblioteca Digital da Produção Intelectual da Universidade de São Paulo (BDPI/USP)

Arq. Bras. Med. Vet. Zootec., v.63, n.2, p.511-514, 2011 
 
Communication 
 
[Comunicação] 
 
Rickettsial infection in Cerro Largo, State of Rio Grande do Sul, Brazil 
 
[Infecção rickettsial em Cerro Largo, Rio Grande do Sul] 
 
L.A. Sangioni1, F.F.S. Vogel1, G.C. Cadore1, R.B. Hilger2, R. Tonim2, R.C. Pacheco3,  
M. Ogrzewalska4,  M.B. Labruna4 
 
1Universidade Federal de Santa Maria – Santa Maria, RS 
2Secretaria da Saúde – Cerro Largo, RS 
3Universidade Federal do Mato Grosso – Cuiabá, MT 
4Universidade de São Paulo – São Paulo, SP 
 
Bacteria of the genus Rickettsia are obligate 
intracellular organisms primarily associated with 
invertebrate hosts, such as ticks, mites, fleas, 
lice, leeches, and insects. A few Rickettsia 
species are capable of infecting vertebrates 
including humans, to whom they are vectored 
mostly by ticks (Weinert et al., 2009). In 2005, 
there was the first reported case of spotted fever 
group (SFG) rickettsiosis in Rio Grande do Sul, 
in a patient from Cerro Largo municipality who 
developed headache, arthralgia, generalized body 
aches, nasal secretion, and fever 20 days after a 
tick bite on his back. Since only one serum 
sample was collected from this patient (during 
the acute phase), which reacted positively (titer 
>64) against R. rickettsii antigens by indirect 
immunofluorescence assay (IFA), this case was 
regarded as probable. In 2007, there was the first 
laboratory-confirmed case of SFG rickettsiosis in 
Rio Grande do Sul, in another patient from the 
same area, who developed general symptoms 
similar to the first case, with no fatality. The case 
was serologically confirmed by IFA on paired 
serum samples using R. rickettsii antigens; acute 
serum was non-reactive whereas convalescent 
serum gave a titer of 128 (unpublished data from 
the Brazilian Ministry of Health). Based on these 
cases, an epidemiological study that evaluated 
rickettsial infection in domestic animals 
(considered to be sentinels for rickettsiosis) and 
asymptomatic humans was performed in the rural 
area of Cero Largo, where the two cases of SFG 
rickettsiosis had occurred.   
 
                                                          
Recebido em 3 de dezembro de 2010 
 
Aceito em 21 de dezembro de 2010 
E mail: sangioni@smail.ufsm.br 
The municipality of Cerro Largo has a 
population of 12,000 inhabitants and its economy 
is based on services, commerce, industry, and 
agropecuary (soy, wheat, corn, swine and dairy 
cattle). There are many small, family-employed 
farms. Often, these small properties raise horses 
and dogs in areas near native forests and 
ecological reserves. On the outskirts of the town, 
the horse and cart are common ways of 
transportation for many of the residents, who 
keep horses and dogs in natural fields that are 
infested with ticks.  
 
In March 2007, blood samples were collected 
from 31 horses, 27 dogs, and 27 humans living in 
rural properties on the outskirts of Cerro Largo. 
Animal blood samples were collected by the 
jugular vein in order to obtain sera samples by 
centrifugation, which were stored at – 20°C until 
processed by serological analysis. All serum 
samples were individually processed by IFA 
using crude antigens of the following Rickettsia 
species that have been isolated from ticks in 
Brazil: R. rickettsii (strain Taiaçu) and R. parkeri 
(strain At24). If a serum reacted at the 1/64 
dilution to any of these two antigens, its IgG titer 
was titrated from 1/64 to the endpoint dilution 
against both, and also against the following 
Rickettsia species: R. amblyommii (strain Ac37), 
R. rhipicephali (strain HJ5), and R. bellii (strain 
Mogi). Antigen preparation and IFA reactions 
were performed as previously described (Horta et 
al., 2004; Labruna et al., 2007). Serum showing 
for a Rickettsia species titer at least 4-fold higher 
than that observed for any other Rickettsia  
 
 
 
Sangioni et al. 
512  Arq. Bras. Med. Vet. Zootec., v.63, n.2, p.511-514, 2011 
species was considered homologous to the first 
Rickettsia species or to a very closely related 
species, as previously determined (Horta et al., 
2004; Labruna et al., 2007; Piranda et al., 2008; 
Saito et al. 2008).  
  
This study was approved by the Ethics 
Committee at the Universidade Federal de Santa 
Maria and is in a accordance with the CNS 
Resolution 196/96 (CEP 23081.008609/2007-
54/CAAE: 0091.0.243.000-07). 
 
A total of 16 (51.6%) horses, six (22.3%) dogs, 
and eight (29.6%) humans were shown to contain 
reactive antibodies (titer ≥64) to R. rickettsii and 
R. parkeri. These sera showed endpoint titers 
varying from 64 to 2,048 to at least one of the 
five rickettsial antigens tested by titration  
(Tables 1-3). No serum showed higher titer to a 
Rickettsia species other than those elicited to R. 
parkeri or/and R. rickettsii. No serum showed 
endpoint titer to R. rickettsii 4-fold higher than 
that to R. parkeri. Two canine sera (Table 2) 
showed titers to R. parkeri at least 4-fold higher 
than those to any of the other four antigens. The 
antibody titers in these two dogs were considered 
to have been stimulated by R. parkeri or a very 
closely related species. This result is in 
accordance with a recent epidemiological study 
performed in another part of the State of Rio 
Grande do Sul (Saito et al., 2008), in which at 
least 100 dogs showed serological evidence of 
infection by R. parkeri or a very close-related 
genotype, as indicated by titers anti-R. parkeri at 
least 4-fold higher than those against the same 
other four Rickettsia species tested in the present 
study. 
 
Table 1. Endpoint antibody titers by indirect immunofluorescence assay (IFA) to five Rickettsia species in 
horses from the rural area of Cerro Largo, State of Rio Grande do Sul, Brazil 
Horse R. parkeri R. rickettsii R. amblyommii R. bellii R. rhipicephali 
E2 128 256 128 128 128 
E3 128  256 64 nr nr 
E4 64  128 64 nr nr 
E5 64 128 nr 64 nr 
E7 64 64 nr 64 nr 
E9 64 128 64 nr 128 
E13 256 512 512 64 512 
E15 64 256 128 128 nr 
E17 64 128  128 nr 64 
E20 64 128 64 128 128 
E21 128 256 64 64 128 
E22 64 128 64 64 nr 
E23 128 128 nr nr nr 
E26 64 128 128 64 nr 
E27 64 128 128 64 nr 
E31 128 128 128 128 128 
nr: non-reactive serum at the 1/64 dilution. 
 
 
Table 2. Endpoint antibody titers by indirect immunofluorescence assay (IFA) to five Rickettsia species in 
dogs from the rural area of Cerro Largo, State of Rio Grande do Sul, Brazil 
Dog R. parkeri R. rickettsii R. amblyommii R. bellii R. rhipicephali 
C1 512 256 256 nr 128 
C2 1,024 256 256 nr 128 
C3 128 64 nr nr nr 
C4 64 64 nr nr nr 
C5 1,024 256  128 nr 256 
C19 1,024 512 128 nr 64 
nr: non-reactive serum at the 1/64 dilution. 
 
Rickettsial infection... 
Arq. Bras. Med. Vet. Zootec., v.63, n.2, p.511-514, 2011 513 
Table 3. Endpoint antibody titers by indirect immunofluorescence assay (IFA) to five Rickettsia species in 
humans from the rural area of Cerro Largo, State of Rio Grande do Sul, Brazil 
Humans R. parkeri R. rickettsii R. amblyommii R. bellii R. rhipicephali 
H4 64 64 nr nr nr 
H5 128 128 nr nr nr 
H12 64 64 nr nr 64 
H14 64 64 nr nr nr 
H15 64 64 nr 64 nr 
H18 1,024 2,048 256 512 512 
H19 256 512 128 256 256 
H20 128 128 nr nr nr 
nr: non-reactive serum at the 1/64 dilution. 
 
None of the serologically positive humans of the 
present study recalled recent febrile illness 
compatible with classic spotted fever (fever, 
headache, and rash), and also, none of them 
reported to have taken antibiotics to treat a 
possible rickettsiosis. However, rickettsiosis can 
manifest with a multiplicity of general symptoms 
(Parola et al., 2005), making it difficult to recall 
previous clinical rickettsiosis with certainty. 
These facts also indicate that the SFG agent 
infecting humans in Rio Grande do Sul is 
potentially not lethal, in contrast to Southeastern 
Brazil, where R. rickettsii is highly pathogenic 
with high fatality rates in untreated cases.  
 
The serological results indicated that horses, 
dogs, and humans have been in contact with SFG 
rickettsiae in Cerro Largo municipality. Results 
from at least two dogs indicated that R. parkeri 
or a close-related genotype is circulating in the 
region, a condition also observed in other 
municipalities in the State of Rio Grande do Sul 
(Saito et al., 2008). R. parkeri and its closest 
known species (R. africae and R. sibirica) are 
recognized human pathogens in other countries 
where they induce a milder spotted fever with no 
lethality reported to date (Parola et al., 2005). 
These facts suggest that a different rickettsial 
agent, possibly related to R. parkeri, is the 
etiological agent of spotted fever in Southern 
Brazil (States of Rio Grande do Sul and Santa 
Catarina). Further studies are needed to isolate 
the rickettsial agent in order to determine its 
definitive taxonomic identification.   
 
From 2006 to 2007, 20 ticks that were found 
attached or walking on humans in the rural area 
of Cerro Largo were collected by the local 
population and sent to the Laboratório Central do 
RS (LACEN), where they were all identified as 
adults of Amblyomma ovale (unpublished data), 
indicating that this species is the main human-
biting tick in Cerro Largo. A. ovale is the main 
vector of Rickettsia sp. strain in Southeastern 
Brazil (Sabatini et al., 2010). Also, 17 of these 
ticks were tested by polymerase chain reaction 
targeting SFG rickettsial DNA, which was not 
found in any individual tick (unpublished data). 
Since these ticks represented only a small 
sample, further studies should encompass a 
larger sample of A. ovale, a potential vector of 
spotted fever in Southern Brazil.  
 
Keywords: Rickettsia, Brazilian spotted fever, 
sorology, Rio Grande do Sul 
 
RESUMO 
 
O presente estudo teve por objetivo avaliar, por imunofluorescência indireta, infecções ricketsiais em 
animais e humanos assintomáticos da área rural de Cerro Largo, RS. Dezesseis (51.6%) equinos, seis 
(22.3%) cães e oito (29.6%) humanos mostraram anticorpos reagentes (título ≥64) para  Ricksettia 
rickettsii e para Ricksettia parkeri. Os estudos sorológicos indicaram que equinos, cães e humanos 
entraram em contato com rickettsias do grupo da febre maculosa nesse município. Dois cães mostraram 
títulos de R. parkeri no mínimo quatro vezes maior que os demais agentes ricketsiais testados e sugerindo 
que R. parkeri ou um genótipo próximo está circulando na região.  
 
Palavras-chave: Rickettsia, febre maculosa, sorologia, Rio Grande do Sul 
 
Sangioni et al. 
514  Arq. Bras. Med. Vet. Zootec., v.63, n.2, p.511-514, 2011 
ACKNOWLEDGMENTS 
 
We are grateful to Secretaria de Saúde de Cerro 
Largo for logistic support and valuable help 
during field works. Thanks to Renata D'Avila 
Couto (Brazilian Ministry of Health) for 
providing information about laboratory-
confirmed cases of BSF in Rio Grande do Sul. 
This work was financially supported by the 
Universidade Federal de Santa Maria (FIPE) and 
Universidade de São Paulo. 
 
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Sangioni,L.A.

Vogel,F.F.S.

Cadore,G.C.

Hilger,R.B.

Tonim,R.

Pacheco,R.C.

Ogrzewalska,M.

Labruna,M.B.

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Infecção rickettsial em Cerro Largo, Rio Grande do Sul

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