# Transient Intraperitoneal Residence of Dirofilaria immitis Larvae in the Mongolian Gerbil (Meriones unguiculatus)

## TL;DR

This study explores why Dirofilaria immitis larvae fail to establish in Mongolian gerbils, finding a strong immune response after the third larval molt.

## Contribution

The study identifies a specific larval stage where host immunity blocks D. immitis establishment in nonpermissive hosts.

## Key findings

- Dirofilaria immitis larvae showed transient peritoneal residence peaking at 3 days post infection.
- No viable D. immitis larvae were recovered by 36 days, unlike permissive Brugia malayi.
- Macrophages were identified as a key component of the immune response against D. immitis larvae.

## Abstract

Understanding the determinants of host specificity in Dirofilaria immitis can be advanced through the use of the nonpermissive Mongolian gerbil (jird) model. We hypothesized that host immunity dictates D. immitis establishment following the third larval molt. Jirds were infected intraperitoneally with 100 Brugia malayi (permissive control) or D. immitis third-stage larvae (L3). Necropsies occurred at 1, 3, 10, and 36 days post infection (dpi) to quantify larvae via peritoneal lavage. Initial recovery at 1 dpi showed 37.4% for B. malayi but only 0.4% for D. immitis (p < 0.0001). Dirofilaria immitis recovery increased to 23.6% by 3 dpi, suggesting a period of transient tissue residence during the third molt. Recovery for both species decreased by 10 dpi. Brugia malayi reached the immature adult stage (15.2%) by 36 dpi, whereas no viable D. immitis were recovered (p < 0.0001). These findings suggest that D. immitis larvae encounter a robust cellular response, primarily macrophages, shortly after the third molt. Identifying the specific larval stage at which establishment fails provides critical insight into the mechanisms governing filarial host specificity.