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Neotrop. Helminthol., 7(1), 2013
2013 Asociación Peruana de Helmintología e Invertebrados Afines (APHIA)
ISSN: 2218-6425 impreso / ISSN: 1995-1043 on line
NOTA CIENTÍFICA/ RESEARCH NOTE
MIGRATION ROUTES OF TOXOCARA CANIS AND TOXOCARA CATI IN TISSUES OF
EXPERIMENTALLY INFECTED RATTUS NORVEGICUS
RUTAS DE MIGRACIÓN DE TOXOCARA CANIS Y TOCARA CATI EN LOS TEJIDOS DE
RATTUS NORVEGICUS INFECTADOS EXPERIMENTALMENTE
Suggested citation: Lescano, SZ, Santos,SV, Queiroz, ML, Castro, JM & Chieffi, PP. 2013. Migration routes of Toxocara canis
and Toxocara cati in tissues of experimentally infected Rattus norvegicus. Neotropical Helminthology, vol. 7, N°1, jan-jun, pp.
149 - 153.
1 2
Instituto de Medicina Tropical de São Paulo (LIM 06), Brazil SUVIS-MG/PMSP, São Paulo, Brazil
3Faculdade de Ciências Médicas da Santa Casa de São Paulo, Brazil. suzeles@hotmail.com
1 1,3 1 2 1,3
Susana Zevallos Lescano , Sérgio Vieira Santos , Maísa Leite Queiroz , João Manoel Castro & Pedro Paulo Chieffi
Abstract
Toxocariasis is currently considered an important zoonosis in many countries and is usually attributed
to larvae of Toxocara canis Werner, 1782 but less frequently, T. cat. This study attempts to compare the
migration routes followed by T. canis and Toxocara cati (Schrank, 1788) in Rattus norvegicus
Berkenhout, 1769 and to determine the percentage of larvae recovered in each organ of experimentally
infected rats. Twenty-one 8-week-old, male specimens of R. norvegicus (Wistar) were inoculated
orally with 500 embryonated eggs of T. canis, while another 21 rats of the same species were
inoculated orally with 300 embryonated eggs of T. cati. On postinfection days 3, 5, 8, 10, 15, 30 and 60,
three rats from each group were sacrificed and larval recovery was performed from various organs and
the carcass following digestion with 0.5% HCl method. Comparisons of the percentage of recovered
larvae revealed that T. cati larvae migrated in greater quantities, as early as day 3 postinfection, to the
lungs (23.77%, compared to 0.34% for T. canis), while migration of T. cati larvae to the carcass was
observed from day 3 up to day 60 postinoculation. This experiment verified that the larvae of these two
species follow distinct migration routes and have different recovery rates.
Keywords: larval recovery - migration routes - Rattus norvegicus - Toxocara canis - Toxocara cati.
Resumen
La toxocariasis es actualmente considerada una importante zoonosis en muchos países y es
generalmente atribuida a larvas de Toxocara canis (Werner, 1782, entretanto, a pesar de ser menos
frecuente, T. cati (Schrank, 1788) puede causar enfermedad. El objetivo de este estudio fue comparar
las rutas de migración seguidas por T. canis y T. cati en Rattus norvegicus (Berkenhout, 1769) y
determinar el porcentaje de larvas obtenidas en cada órgano de las ratas infectadas experimentalmente.
Veintiún especímenes machos de R. norvegicus (Wistar), con ocho semanas de edad fueron
inoculados oralmente con 500 huevos larvados de T. canis, en cuanto que otras 21 ratas de la misma
especie fueron inoculadas oralmente con 300 huevos embrionados de T. cati. En los días 3, 5, 8, 10, 15,
30 y 60 pos-infección, tres ratas de cada grupo fueron sacrificadas y la recuperación de larvas fue
realizada en varios órganos y la musculatura después de la digestión con el método de HCl a 0,5%. La
comparación de los porcentajes de larvas recuperadas reveló que las larvas de T. cati migraron para los
pulmones en mayor cantidad, luego en el tercer día pos-infección (23,77%, y solamente 0,34% en el
caso de T. canis) al paso que la migración de larvas de T. cati para la musculatura fue observada desde
el día 3 hasta el día 60 pos-inoculación. Con este experimento se verificó que las larvas de estas dos
especies siguen rutas de migración distintas y tienen tasas de recuperación diferentes.
Palabras clave: recuperación de larvas - rutas de migración - Rattus norvegicus - Toxocara canis - Toxocara cati.
150
Toxocara canis and Toxocara cati in tissues of Rattus Lescano et al.
Toxocara canis (Werner, 1782) and Toxocara
cati (Schrank, 1788) are common intestinal
nematodes of dogs and cats, respectively. Since
diagnosis of human infection by embryonated
eggs of Toxocara became available by relative
safety inmunological methods, toxocariasis has
been considered a public health problem in
many countries. This zoonosis is usually
attributed to the migrating larvae of T. canis;
however, less frequently, T. cati is the cause of
disease (Fisher, 2003).
Rodents are reservoirs for Toxocara spp., act as
indicators of environmental contamination,
particularly in urban areas, and are a source of
infection in dogs and cats, the definitive hosts of
T. canis and T. cati, respectively (Cardillo et al.,
2009). Together with other rodent species,
Rattus norvegicus (Berkenhout, 1769) has been
highlighted as a common paratenic host for
Toxocara spp. (Chieffi et al., 1981) and previous
studies have described the distribution of larvae
of T. canis and T. cati in its tissues and organs
following experimental infection (Lescano et
al., 2004, Santos et al., 2009); however, there are
no reports comparing the larval migration of
these species in the organs of this rodent.
Our objectives were to evaluate the role of R.
norvegicus as a paratenic host of T. canis and T.
cati, compare the migration routes followed by
these two ascarids and determine the percentage
of larvae recovered in each organ of R.
norvegicus up to 60 days following
experimental infection.
Toxocara canis and T. cati females were
dissected in Petri dishes containing acidified
water (pH 3), their uteruses were removed and
cut open to release the eggs. The eggs recovered
were then concentrated by centrifugation at
1500 rpm for 5 min. The pellet containing the
eggs was transferred to Erlenmeyer flasks
containing approximately 200 ml of 2%
formalin each, sealed with a hydrophobic cotton
INTRODUCTION lid. The flasks were incubated at 28°C for
approximately 30 days, with daily manual
agitation to ensure oxygenation of the eggs and
promote the development of third stage larvae.
Twenty-one 8-week-old, male R. norvegicus
Wistar rats were orally infected by stomach tube,
with approximately 500 embryonated eggs of T.
canis each. Another 21 8-week-old, male rats of
the same species were orally infected with
approximately 300 embryonated eggs of T. cati.
Animals were provided by the Centro de
Bioterismo da Faculdade de Medicina da
Universidade de São Paulo, were group-housed
and water and pellet commercial food were
supplied ad libitum the cages being cleaned at
regular periods.
The rats were divided into seven groups
euthanized on different postinfection days
(PIDs), i.e. on PIDs 3, 5, 8, 10, 15, 30 and 60. The
euthanized rats were processed for larvae
recovery from the liver, brain, lungs, kidneys
and carcass, using the method of digestion with
0.5% HCl for 24 h at 37°C. The resulting liquid
was centrifuged for 2 min at 1500 RPM and all
the sediment was examined under a microscope
to count the larvae (Xi & Jin, 1998).
The experimental protocol was approved by the
Research Ethics Committee of the São Paulo
Institute of Tropical Medicine (protocol CPE-
IMT010/06).
Statistical analysis were performed using One
Way Anova test , followed by the Kruskal-Wallis
test using Prisma program, 5.0 version. Only
probability values of p< 0,001 were considered
statistically significant.
Table 1 presents the results obtained following
larval recovery from the various organs of the
infected rats. T. cati larvae migrated in greater
quantities to the muscles and were detected from
PID 3 (22.4% compared with 0% for T. canis).
Both species of the ascarid were recovered from
MATERIALS AND METHODS
RESULTS
Neotrop. Helminthol., 7(1), 2013
the viscera as early as PID 3 (42.9% for T. canis
and 32.7% for T. cati) and marked reduction of
larvae in these organs was observed on PID 60.
Fig. 1 represents the larval recovery in different
tissues and organs and significant difference is
only observed in the number of larvae in carcass
of the two groups of rodents, with T. cati larvae
being the most abundant (p<0,001).
In this study, we analyzed and compared the
migration patterns of T. canis and T. cati larvae in
R. norvegicus in the visceral and myotropic-
neurotropic phases. Tests using different
experimental models have described infection in
animals showing varying results, in some cases,
different from those obtained in our experiment.
Studies concerning the migration of T. canis
larvae in NIH mice (Abo-Shehada & Herbert,
1984) determined that the visceral phase peaked
on PIDs 2 and 3 in the liver and lungs,
respectively, whereas the myotropic-
neurotropic phase peaked on PID 7. Cardillo et
al. (2009) observed that migration of T. cati
larvae in BALB/c mice showed a peak for the
visceral phase on PID 2, while the peak for the
myotropic-neurotropic phase occurred on PID
28.
Table 1. Mean number / percentage of T. canis and T. cati larvae recovered from tissues and organs of Rattus
norvegicus – comparison of the migration routes from the two nematoda species.
Figure 1. Larvae recovered in diverse organs of R. norvegicus infected with T. canis or T. cati embryonated
ova.(*comparison of T. canis and T. cati larvae recovered in carcass of rats).
Carcass Viscera* Brain DPI T. canis T. cati T. canis
T. cati
T. canis T. cati
3 0.0 67.2 (22.4%)
128.7 (42.9%)
98.1 (32.7%)
0.0 0.0
5 69.1 (23.2%)
153.9 (51.3%)
131.7 (43.9%)
114.9 (38.3%)
3.6 (1.2%) 3.3 (1.1%)
8 31.2 (10.5%)
115.2 (38.4%)
28.5 (9.5%)
18.6 (6.2%)
5.1 (1.7%) 0.6 (0.2%)
10
31.8 (10.6%)
54.6 (18.2%)
13.2 (4.4%)
12.3 (4.1%)
3.9 (1.3%) 0.9 (0.3%)
15 55.8 (18.6%) 236.4 (78.8%) 25.8 (8.6%) 43.8 (14.6%) 13.5 (4.5%) 1.5 (0.5%)
30 19.2 (6.4%) 176.4 (58.8%) 7.2 (2.4%) 16.5 (5.5%) 5.7 (1.9%) 3.3 (1.1%)
60 21.6 (7.2%) 240.3 (80.1%) 12.3 (4.1%) 46.2 (15.4%) 11.7 (3.9%) 0.0
DISCUSSION
* Liver, lungs and kidneys
151
Toxocara canis and Toxocara cati in tissues of Rattus Lescano et al.
Hamilton et al. (2006) compared the migration
of larval T. canis in seven strains of mice,
including BALB/c and NIH. In these two strains,
the greatest recovery of larvae in the lungs
occurred on PID 7 and was greater in BALB/c
mice. In contrast, liver parasite burden was very
similar in both strains on PIDs 7, 35 and 42.
Larval recovery in the muscles was less frequent
than that recovered in the viscera; however,
BALB/c mice showed increased larva load in the
carcass on PID 42, with a higher frequency of
larva recovery in the brain compared with other
organs.
In chickens, Taira et al. (2003) studied the
migrating larvae of T. canis from PIDs 1 to 6 and
observed that the majority of the larvae were
recovered in the lungs (PID 3) and in the liver
(PID 6). Larvae were also detected in the brain
and muscle on PID 6, but to a lesser extent
compared with other organs. Experimental
infection of chickens with T. cati was conducted
by Taira et al. in (2011), who observed the initial
establishment of infection in the liver and lungs
between PIDs 1 and 3; later, the larvae migrated
to the muscles, where almost 99% of them were
recovered between PIDs 29 and 176. The
migration pattern of larval T. canis in pigs was
studied by Helwigh et al. (1999) and showed a
similar pattern to that verified in mice (Abo-
Shehada & Herbert, 1984).
The presence of larvae in the brain, detected on
PID 15, was more frequent in rats infected by T.
canis (4.5% for T. canis and 0.5% for T. cati).
Havasiová-Reiterová et al. (1995) infected
C57BL6/J mice with 500 or 1000 eggs of T. cati
and T. canis, and detected higher numbers of T.
canis larvae in the brains of these rodents too.
There are few studies on larval migration of
Toxocara spp. in rats (Strube et al., 2013); in this
report the migration routes of the larvae of two
species of Toxocara (T. canis and T. cati) during
the experimental infection of rats was compared.
Some notable differences were observed: the
migration of T. cati larvae to the CNS was less
pronounced and occurred between PID 5 (1.1%)
and PID 30 (1.1%), while T. canis larvae were
recovered in this organ between PID 5 (1.2%)
and PID 60 (3.9%), with peak recovery
occurring on PID 15 (4.5%). In the carcass, the
largest count of T. cati larvae was obtained as
early as PID 3 (22.4%), and persisted to a
remarkable extent (80.1%) by the end of the
experimental period, whereas T. canis larvae
diminished progressively in the carcass from
PID 15 up to the end of the experiment (7.2%).
Analysis of our results indicates that R.
norvegicus can be considered a suitable
experimental paratenic host for T. canis and T.
cati, maintaining the living larvae of these
roundworms in different tissues and organs at
least up to 60 days postinfection. Moreover, our
findings showed that the larvae of both species
have distinct migration routes and different
recovery rates. These rodents continue to pose a
risk to public health because they are reservoirs
for Toxocara spp. and can infect dogs and cats,
the definitive hosts, thus maintaining the cycle
of these ascarids in nature.
This study compares T. canis and T. cati larval
migration in R. norvegicus however; these data
must be carefully considered when other species
of rodents or paratenic hosts are studied, since
there are some differences in parasite behavior in
diverse species.
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Received March 12, 2013.
Accepted April 11, 2013.
Correspondence to author/ Autor para
correspondencia:
Susana Zevallos Lescano
Instituto de Medicina Tropical de São Paulo. Av.
o
Enéas de Carvalho Aguiar N 500 – 2º andar
CEP 05403 000 – São Paulo – SP – Brazil. Tel:
+55 11 3061-7063; fax +55 11 3064-5132.
E-mail / Correo electrónico:
suzeles@hotmail.com
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