Print version ISSN 0036-4665
Rev. Inst. Med. trop. S. Paulo vol.52 no.5 São Paulo Sept./Oct. 2010
Susceptibilidade e morbidade entre camundongos Swiss machos e fêmeas infectados com Angiostrongylus costaricensis
Márcia B. MentzI; Eliane DallegraveI; Carlos Graeff-TeixeiraII
IInstituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
IIGrupo de Parasitologia Biomédica da Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, RS, Brazil
The gender of vertebrate hosts may affect the outcome of parasitic infections. An experimental murine infection with Angiostrongylus costaricensis was followed with determinations of body weight, fecal larval elimination, number and length of adult worms, number of macroscopic intestinal lesions, and mortality. Groups of male and female Swiss mice were infected with 10 3rd-stage A. costaricensis larvae per animal. The results indicate there are no significant differences related to gender of the host, except for higher length of worms developed in male mice.
Keywords: Metastrongyloidea; Angiostrongylus costaricensis; Gender; Sex; Murine.
O sexo dos hospedeiros vertebrados pode influenciar no resultado de infecções parasitárias. A infecção experimental de camundongos com Angiostrongylus costaricensis foi acompanhada com observação do peso corporal, eliminação de larvas nas fezes, número e comprimento dos vermes adultos, número de lesões macroscópicas nos intestinos e mortalidade. Grupos de camundongos Swiss machos e fêmeas foram infectados cada um com 10 larvas de terceiro estágio de A. costaricensis. Os resultados indicam que não há diferenças significativas relacionados ao sexo dos hospedeiros, exceto pelo maior comprimento dos vermes nos hospedeiros machos.
Angiostrongylus costaricensis Morera and Céspedes, 1971 is the etiologic agent of human abdominal angiostrongyliasis. This nematode lives inside the ileo-colic branches of the mesenteric artery of wild rodents, and its larvae develop in terrestrial mollusks9. The naturally infected rodent hosts are primarily wild species found in Central America and southern Brazil: Tylomys watsoni, Lyomis salvini, L. adspersus, Proechimys semispinosus, Peromyscus nudipes, Zygodontomys microtinus, Oryzomys albigularis, O. caliginosus, O. fulvescens, O. nigripes, and O. ratticeps3,10,14. The cotton rat, Sigmodon hispidus, is the most important definitive host and occurs both in the wild and in peridomiciliar areas10. All experimental A. costaricensis studies reported thus far have used male mice, Mus musculus, and none have assessed whether gender is a determining factor for susceptibility or morbidity. The aim of the present study was to compare the course of A. costaricensis infection in male and female Swiss mice.
MATERIAL AND METHODS
Infective third-stage A. costaricensis larvae (L3), Santa Rosa strain, were inoculated orally through a metal cannula into six week-old mice. The larvae were obtained from experimentally infected Phyllocaulis soleiformis slugs. The mollusks were digested in a 0.03% pepsin (Sigma P-7125) solution in 0.7% HCl for two hours at 37 ºC. Two groups of seven male (M) and female (F) mice were inoculated with 10 L3 per animal. Infection was confirmed at 21 days post infection (dpi) by isolation of first stage larvae (L1) from feces, using the Baermann-Moraes method, followed by daily L1 quantification until 35 dpi. Body weight was registered at the beginning and end of the experiment, and was expressed as relative body weight (variation of the final weight, taking the initial weight as 100%). All surviving mice were sacrificed by CO2 inhalation at 35 dpi and examined for the presence, number, location, and size of adult worms and macroscopic intestinal lesions. During the experiment, animals were housed in polystyrene boxes and maintained under laboratory conditions with food and tap water ad libitum. Animal handling was performed in accordance with the recommendations from the "Colégio Brasileiro de Experimentação Animal" (COBEA) and approved by the local Ethics Committee.
RESULTS AND DISCUSSION
There was a significant difference (p < 0.05; ANOVA of Repeated Measure, Bonferroni) in body mass gain, with groups M and F having losses of 6.0% and 14.5%. Variance analysis revealed that relative body weight was equally affected in both sexes (p = 0.0050). Gender did not influence the number of larvae released, since average daily larvae outputs were 5.0 and 5.3. Male mice survival was 43% (3/7) while 57% (4/7) of the female animals were alive at the end of the observations (p > 0.05). Variance analysis did not show differences in the proportion of macroscopic intestinal lesions (p = 0.567). There was also no significant difference (p > 0.05, chi-square) in the proportion of male/female worms recovered from their intra-arterial location, 9:9 and 7:6 for M and F groups. Worms recovered from M group (n = 18) were larger than those from F group (n = 13), 2.3 cm ± 0.21(mean ± standard deviation) as compared to 2.1 cm ± 0.22 (p < 0.05, variance analysis).
Although natural infection of M. musculus with A. costaricensis has never been documented8,13,14, experimental investigation of the immunology and biology of parasitism in abdominal angiostrongyliasis have been carried out in several strains of mice: C57BL6, BALB/c, DBA/2, and C3H/He4. Ishii et al.5 infected inbred strains of rats (DA, JAR-2, LOU/M, NIG-III, WBN/Kob, and Wm) and two species of wild rodents, Rattus norvegicus and R. rattus, in order to study infection susceptibility and resistance. Later, Ishii & Nishimura6 described mortality, worm burden, hematocrit, and the magnitude of splenomegaly in the experimental infection of SM/J and A/J mice. However, there are scarce reports addressing gender differences in murine models of angiostrongyliasis, as has been done with other infectious agents, like Paracoccidioides brasiliensis7. It is well recognized that inbred strains of mice may differ in their susceptibility to infection by certain parasitic helminths1,2,15. Variability in recovery of parasites from different individuals of the same host strain, or from animals of different strains, has led to the suggestion that genetic background may affect susceptibility or resistance to infection4,11. Helminth infections are usually more severe in male than in female vertebrate hosts12. The hypothesis of a facilitating effect of host gender on worm development was supported by the results of a meta-analysis showing higher worm growth rates in male hosts12, which is also supported by the present data.
Overall, the results now reported do not indicate that gender significantly influences the susceptibility and morbidity in the murine experimental model for studies on abdominal angiostrongyliasis.
Financial support by "Conselho Nacional de Desenvolvimento Científico e Tecnológico do Brasil" (CNPq 477260/2007-1) and "Coordenação de Aperfeiçoamento de Pessoal de Nível Superior do Brasil (CAPES)". C. Graeff-Teixeira is the recipient of a CNPq PQ 1D fellowship and grant (300456/2007-7).
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Prof. Dr. Carlos Graeff-Teixeira
Av. Ipiranga 6690 HSL 2º andar, Sala 20
90690 900 Porto Alegre, RS, Brazil
Fax 55 51 3320 3312
Received: 9 June 2010
Accepted: 9 August 2010