Geology topics

V.O. Ezenwa

Publications and source records attributed to V.O. Ezenwa.

5 recordsLinked to original sources

USGS2007

Land cover variation and West Nile virus prevalence: Patterns, processes, and implications for disease control

Identifying links between environmental variables and infectious disease risk is essential to understanding how human-induced environmental changes will effect the dynamics of human and wildlife diseases. Although land cover change has often been tied to spatial variation in disease occurrence, the underlying factors driving the correlations are often unknown, limiting the applicability of these results for disease prevention and control. In this study, we described associations between land cover composition and West Nile virus (WNV) infection prevalence, and investigated three potential processes accounting for observed patterns: (1) variation in vector density; (2) variation in amplification host abundance; and (3) variation in host community composition. Interestingly, we found that WNV infection rates among Culex mosquitoes declined with increasing wetland cover, but wetland area was not significantly associated with either vector density or amplification host abundance. By contrast, wetland area was strongly correlated with host community composition, and model comparisons suggested that this factor accounted, at least partially, for the observed effect of wetland area on WNV infection risk. Our results suggest that preserving large wetland areas, and by extension, intact wetland bird communities, may represent a valuable ecosystem-based approach for controlling WNV outbreaks. ?? Mary Ann Liebert, Inc.

Vector-Borne and Zoonotic Diseases↗

USGS2004

Selective defecation and selective foraging: Antiparasite behavior in wild ungulates?

Selective defecation and selective foraging are two potential antiparasite behaviors used by grazing ungulates to reduce infection by fecal-oral transmitted parasites. While there is some evidence that domestic species use these strategies, less is known about the occurrence and efficacy of these behaviors in wild ungulates. In this study, I examined whether wild antelope use selective defecation and selective foraging strategies to reduce exposure to gastrointestinal nematode parasites. By quantifying parasite levels in the environment in relation to the defecation patterns of three species, dik-dik (Madoqua kirkii), Grant's gazelle (Gazella granti), and impala (Aepyceros melampus), I found that nematode larval concentrations in pasture were higher in the vicinity of clusters of feces (dung middens) compared to single fecal pellet groups or dung-free areas. In addition, experimental feeding trials in free-ranging dik-dik showed that individuals selectively avoided feeding near concentrations of feces. Given that increased parasite contamination was found in the immediate vicinity of fecal clusters, fecal avoidance could help reduce host consumption of parasites and may therefore be an effective antiparasite behavior for certain species. On the other hand, while the concentration of parasite larvae in the vicinity of middens coupled with host avoidance of these areas during grazing could reduce host contact with parasites, results showing a positive correlation between the number of middens in a habitat and larval abundance at control sites suggest that dung middens might increase and not decrease overall host exposure to parasites. If this is the case, dung midden formation may not be a viable antiparasite strategy.

Ethology↗

USGS2004

Parasite infection rates of impala (Aepyceros melampus) in fenced game reserves in relation to reserve characteristics

Under certain conditions reserves can pose a threat to wildlife conservation by increasing the transmission of parasites and pathogens. In this study, I investigated associations between reserve characteristics including area, density and species richness and parasite infection rates in impala (Aepyceros melampus). Using coprological methods to measure gastrointestinal parasitism rates of impala inhabiting five fully or partially fenced game reserves in central Kenya, I found that bovid species richness was correlated with parasite taxa richness across reserves, and that prevalence rates of multi-host strongyle nematodes were higher in reserves with more species. In addition, reserve size was also implicated as a potential predictor of infection risk. Overall, these results suggest that wildlife inhabiting highly diverse and small reserves may suffer from higher than normal rates of infection. Given the potential debilitating effects increases in parasitism can have on wildlife, these results underscore the importance of considering parasite transmission dynamics in the management of small, fenced protected areas. ?? 2003 Elsevier Ltd. All rights reserved.

Biological Conservation↗

USGS2004

Interactions among host diet, nutritional status and gastrointestinal parasite infection in wild bovids

In this study, I explored the interactions among host diet, nutritional status and gastrointestinal parasitism in wild bovids by examining temporal patterns of nematode faecal egg shedding in species with different diet types during a drought and non-drought year. Study species included three grass and roughage feeders (buffalo, hartebeest, waterbuck), four mixed or intermediate feeders (eland, Grant's gazelle, impala, Thomson's gazelle) and two concentrate selectors (dik-dik, klipspringer). Six out of the nine focal species had higher mean faecal egg counts in the drought year compared to the normal year, and over the course of the dry year, monthly faecal egg counts were correlated with drought intensity in four species with low-quality diets, but no such relationship was found for species with high-quality diets. Comparisons of dietary crude protein and faecal egg count in impala showed that during the dry season, individuals with high faecal egg counts (???1550 eggs/g of faeces) had significantly lower crude protein levels than individuals with low (0-500 eggs/g) or moderate (550-1500 eggs/g) egg counts. These results suggest that under drought conditions, species unable to maintain adequate nutrition, mainly low-quality feeders, are less able to cope with gastrointestinal parasite infections. In particular, during dry periods, reduced protein intake seems to be associated with declining resilience and resistance to infection. ?? 2003 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

International Journal for Parasitology↗

USGS2004

Host social behavior and parasitic infection: A multifactorial approach

I examined associations between several components of host social organization, including group size and gregariousness, group stability, territoriality and social class, and gastrointestinal parasite load in African bovids. At an intraspecific level, group size was positively correlated with parasite prevalence, but only when the parasite was relatively host specific and only among host species living in stable groups. Social class was also an important predictor of infection rates. Among gazelles, territorial males had higher parasite intensities than did either bachelor males or females and juveniles, suggesting that highly territorial individuals may be either more exposed or more susceptible to parasites. Associations among territoriality, grouping, and parasitism were also found across taxa. Territorial host genera were more likely to be infected with strongyle nematodes than were nonterritorial hosts, and gregarious hosts were more infected than were solitary hosts. Analyses also revealed that gregariousness and territoriality had an interactive effect on individual parasite richness, whereby hosts with both traits harbored significantly more parasite groups than did hosts with only one or neither trait. Overall, study results indicate that multiple features of host social behavior influence infection risk and suggest that synergism between traits also has important effects on host parasite load.

Behavioral Ecology↗