Combined effects of heavy metals and parasite infections on the haematological and biochemical profiles of wild rats from Awotan Municipal Dumpsite in Ibadan City

Abstract

The combined effects of heavy metals and parasitic infections on wild rats from Awotan municipal dumpsite in Ibadan city southwest Nigeria were determined. A total of thirty rats were captured from the dumpsite and five rats from a control site using live traps. Rats were identified, weighed and body length measured to determine body condition index. Blood samples were collected from the rats using the cardiac puncture method. Rats were euthanized and dissected to extract various organs (kidney, liver and intestine). Intestinal helminths were extracted, identified and preserved. Blood parasites were identified using Giemsa staining technique of thick and thin films while intestinal helminths recovered were preserved and identified to species level. Organs, intestinal helminths and blood samples were digested and concentrated for heavy metals (Fe, Cu, Cr, Cd, and Pb) using Atomic Absorption Spectrophotometry (AAS). Cortisol level was determined using ELISA technique. All statistical significance was at probability value p < 0.05. Three species of rats were captured, Rattus rattus, Rattus novergicus and Cricetomys gambianus. The mean ± sd of the body condition index of the rats from dumpsite and control groups were 1.82±0.17 and 1.59± 0.38 respectively. There were significant differences in the mean values of eosinophils, platelets and white blood cell counts of rats from the two study sites. Overall parasite prevalence in dumpsite and control were 76.6% and 20% respectively. The overall prevalence of parasite  species from dumpsite was in the order Hymenolepis diminuta (26.6%) >Monoliformis monoliformis (20%) >Plasmodium spp (20%) >Trypanosoma spp (10%). The mean concentration (mg/kg) of heavy metals in kidney, liver, intestine and blood of wild rats from both dumpsite and control decreased in the order Fe> Cr> Cu> Cd> Pb. Cortisol level was higher in infected rats from dumpsite (351±58.83ng/ml) than in uninfected rats from dumpsite (237.22± 44.46ng/ml), indicating exposure to immune stressors. A higher prevalence of parasitic infection, heavy metal pollution and the elevated cortisol concentrations in infected rats showed that the animals’ health and well-being are compromised.