During 1995, 16 species of arthropods and 2 species of filarioids, totaling 1 287 specimens were collected from 64 wild rodents captured in the Hudson Natural Reserve, Buenos Aires, Argentina. Infestation parameters and indexes were analyzed. Host specific richness was S = 6, diversity H = 1.48, and relative density RDI = 40%. High values of parasite species richness and diversity were found on
Oligoryzomys delticola
(S = 9; H = 1.40),
Oxymycterus rufus
(S = 9; H = 1.37), and
Oligoryzomys flavescens
(S = 9; H = 1.28), followed by
Scapteromys aquaticus
(S = 6; H = 0.17), and
Akodon azarae
(S = 4; H = 1.20).
Deltamys kempi
was infested only by
Androlaelaps rotundus
.
O. delticola and
O. flavescens showed the highest similarity index (O = 74.19%), followed by
O. flavescens with
S. aquaticus, as a result of historical processes and shared microhabitats. Considering arthropods-filarioids associations, significant affinity was observed in Litomosoides bonaerensis with
Hoplopleura travassosi
,
Laelaps paulistanensis
, and
Gigantolaelaps wolffsohni
.