Litomosoides sigmodontis: a simple method to infect mice with L3 larvae obtained from the pleural space of recently infected jirds (Meriones unguiculatus)

Abstract

Litomosoides sigmodontis is a filarial nematode that is used as a mouse model for human filarial infections. The life cycle of L. sigmodontis comprises rodents as definitive hosts and tropical rat mites as alternate hosts. Here, we describe a method of infecting mice with third stage larvae (L3) extracted from the pleural space of recently infected jirds (Meriones unguiculatus). This method enables infection of mice with a known number of L3 larvae without the time-consuming dissection of L3 larvae from mites and results in higher worm recovery and patency rates than conventional methods. Additionally, this method allows for geographical separation of the facility maintaining the L. sigmodontis life cycle from the institution at which mice are infected.

Figure 1

Laboratory life cycle of Litomosoides sigmodontis: Generally, L. sigmodontis is maintained in either its natural host, the cotton rat Sigmodon hispidus, or in jirds, Meriones unguiculatus, as surrogate hosts. Infection is initiated by introduction of infective-stage L3s into the mammalian hosts by either direct injection or through the bite of infected tropical mites (Ornithonyssus bacoti), the natural vector. After inoculation, larvae migrate via the lymphatic system to the pleural cavity by d2-6 post-infection (p.i.), where subsequent development takes place. Larvae molt to L4 stage larvae between d8-12 p.i., become adults by d25-30p.i., and are able to produce microfilariae which circulate in the blood by d50p.i.

Fig. 2

Number of worms recovered 6 weeks after infection of BALB/c mice with 40 L3 larvae obtained from the pleural cavity from 4-day, 5-day, or 6-day infected jirds. Significant differences between groups were analyzed by the Kruskal-Wallis test, followed by Dunn's post-hoc multiple comparisons (*p<0.05).

Fig. 3

A) Number of worms and B) microfilariae recovered 6, 8 or 10 weeks after infection of BALB/c mice with 40 L3 larvae obtained from the pleural cavity from 4-day infected jirds.