Fig 1.
Map of trapping sites in east Hawai‘i Island.
Refer to Table 1 for details of all site locations.
Table 1.
List of trapping locations for rats (Rattus. exulans and Rattus rattus) sampled for rat lungworm (Angiostrongylus cantonensis) on east Hawai‘i Island (see Fig 1 for site map).
Values for infected rats indicate individuals observed positive for live adult worms only. Agencies involved in trapping include USDA-APHIS National Wildlife Research Center (NWRC) and the Hawai‘i Department of Health (HDOH) Vector Control Branch.
Fig 2.
Observed prevalence of adult and third stage (L3) larvae of rat lungworms (A. cantonensis) in the lungs of two species of wild rats (R. exulans and R. rattus) on east Hawai‘i Island.
Columns within groups with different letters differ (P < 0.05).
Table 2.
Mean body mass (g) and confidence intervals for observed presence/absence of adult rat lungworms (Angiostrongylus cantonensis), third stage (L3) larvae, encysted adult worms, and granular lung lobes in wild rats (Rattus spp.) on east Hawai‘i Island.
All p-values reported are from comparisons of body mass between positive and negative individuals within each group using unpaired, two-tailed t-tests.
Fig 3.
Images of multiple stages of Angiostrongylus cantonensis in situ.
a. Embryonated A. cantonensis eggs in the lung tissue of a rat (40X). b. A. cantonensis eggs that were located in the uterus of a female worm (40X). c. A. cantonensis L1 larvae in lung visualized by tissue squash (10X). d. A. cantonensis L1 larvae observed in rat feces (10x). e. Small black worms, later determined to be L3 A. cantonensis larvae observed in the rat’s lungs. f. The transition between the esophagus and intestine are clearly defined in A. cantonensis L3 larvae.
Fig 4.
Evidence of infection included presence of decaying encysted adults, granular lung lobes, live adult worms in the pulmonary artery and detection of worms in the brain.
a. Decaying, encysted adult Angiostrongylus cantonensis worms, apparently indicative of a previous infection, were observed in the rat’s lungs. b. Granular upper right lobe of lung. c. Adult A. cantonensis visible in the intact pulmonary artery. d. Adult A. cantonensis emerging from the pulmonary artery of a rat. Males are smaller and females are larger with helical-striped appearance. (See S1 Video). e. Superior view of Rattus exulans brain at a magnification of 6.6X. During dissection, A. cantonensis were commonly found at locations indicated by arrows. The dark spot seen on the surface of the right hemisphere is believed to be a hemorrhage. Hemorrhages were often times an indicator of worm location during dissections. f. Measurement of A. cantonensis L5 from the brain measuring approximately 10 mm. The exsiccated nature of the worm is due to light intensity of the microscope.
Table 3.
Summary of AICc (Akaike’s Information Criterion corrected for small sample size) model selection of rat lungworm (Angiostrongylus cantonensis) infection in rats (Rattus spp.) sampled on east Hawai‘i Island for five independent generalized linear model (GLM) analyses (A-E).
(A) Prevalence of adult worms, (B) intensity of adult worms, (C) prevalence of encysted worms, (D) prevalence of third stage larvae in the lungs, (E) prevalence of granular lung lobes. Model factors include host characteristics (body mass, species, and sex) and sampling location (site); numbers preceding models indicate model rank within each analysis; k = number of parameters in the models.
Fig 5.
Observed prevalence of adult rat lungworms (Angiostrongylus cantonensis) for multiple body mass categories in two species of wild rats (Rattus exulans and R. rattus) on east Hawai‘i Island.
Results displayed are from rat individuals used in the GLM analysis only (n = 405; see Table 2). Columns with different letters differ (P < 0.05). The star indicates significance could not be determined due to low sample size.