David P. Cowan

THE NORWAY RAT AS A RESERVOIR HOST OF CRYPTOSPORIDIUM PARVUM

The potential of Norway rats (Rattus norvegicus) to spread the parasite Cryptosporidium parvum was investigated by examining parasite prevalence in relation to the structure and movements of three permanent rat populations living on farmland in Warwickshire (UK) from October 1994 to March 1997. One population lived among a group of farm buildings housing cattle, while the other two had no contact with livestock, one living around a pond and its outflowing stream and the other on a rubbish tip. Overall, parasite occurrence was 24% (n = 438), but it varied according to body weight (age) with 40% of juveniles (≤100 g) infected decreasing to 12% for adults >400 g, suggesting that actively breeding populations are potentially more likely to spread the parasite than non-breeding populations. There was no difference in prevalence between the three populations. The parasite was detected in more males (29%) than females (19%). Seasonally, on the livestock farm, prevalence was significantly lower in autumn (10%), but varied little (31–36%) from winter to summer. In contrast, on the arable farm, prevalence peaked in summer (50%) with a trough in winter (6%). Infection in rats appeared to last <67 days. Rats living on the livestock farm had home ranges largely confined to the cattle sheds, thereby maintaining a potential source of infection for livestock if rodent control was not part of a decontamination program. Equally, rats living around the pond on the arable farm provided a source of oocysts to contaminate the pond water, as well as being able to carry the parasite to nearby farm buildings or even to neighboring farms.

Tapering Bias Inherent in Minimum Number Alive (MNA) Population Indices

Abstract Minimum number alive (MNA) is commonly used to assess population size with capture-mark-recapture data. However, MNA uses information from prior and subsequent capture sessions to assess the population at each point in a longitudinal study. Therefore, it is subject to negative bias that is greatest at the beginning and end of the study and least in the middle. Stochastic simulations performed with constant population size and capture rate showed that MNA peaked at the middle of the study. The tapering bias was greatest when survival rate between capture sessions was high. If indices (rather than statistical estimators) are used to assess population size, then the number of individuals captured should be chosen in preference to MNA.

Strength and persistence of conditioned taste aversion in rats: evaluation of 11 potential compounds

Abstract Conditioned taste aversion (CTA) occurs when animals associate the taste of a food with illness and subsequently avoid that food. CTA can be experimentally induced by adding an undetectable, illness-inducing chemical to food. The use of CTA has been suggested as a humane, non-lethal method for vertebrate pest control. The present study tested the ability of the following 11 chemicals to generate CTA in laboratory rats Rattus norvegicus after a single oral administration: thiabendazole, levamisole hydrochloride, xylazine, copper sulphate, caffeine, ipecacuanha, nicotine, aspirin, fluoxetine hydrochloride, clotrimazole and nifedipine. Thiabendazole, levamisole, fluoxetine, and clotrimazole induced strong, long-lasting CTA. No extinction of the aversion was observed over 14 weekly food presentations after an initial administration of thiabendazole. An attenuation of the aversion was noted for rats dosed with levamisole and fluoxetine, although the average food consumption of these groups remained significantly lower than that of controls. Persistence of CTA was negatively related to pre-conditioning food consumption by individual rats.

Conditioned taste aversion can reduce egg predation by rats

Predation on eggs affects the population dynamics of many bird species throughout the world. We investigated whether Conditioned Taste Aversion (CTA) can be used to decrease predation on bird eggs by rats. Conditioned taste aversion occurs when an animal associates the taste of a particular food with illness and subsequently avoids consuming that food. On Day 1 of the experiment (conditioning test), laboratory rats (Rottus norvegicus) were presented with either chicken (Callus gallus) or quail (Coturnix coturnix) eggs and 30 minutes later administered with the CTA-inducing agent thiabendazole. In 8 post-conditioning tests over the following 3 weeks, rats were offered either the same egg type they received on conditioning day or a different egg type. Results showed that conditioning induced a strong aversion to eggs. Across all post-conditioning tests, treated rats took 2.7 times longer than control rats to start eating an egg. In the same period, treated rats spent 39% less time than control rats eating eggs and ate 34% fewer eggs than control rats. Thiabendazole was equally effective in inducing CTA to chicken and quail eggs, and the aversion transferred to different egg types.

Long-lasting Systemic Bait Markers for Eurasian Badgers

This study was carried out to assess whether Rhodamine B, ethyl-iophenoxic acid (EtIPA), and propyl-iophenoxic acid (PrIPA) can be used as long-lasting systemic bait markers for free-living badgers (Meles meles). Between June and November 2003, these chemicals were incorporated into bait distributed around badger setts. Serum, hair, and whiskers from individually marked badgers were collected in the following 4 to 24 wk. Rhodamine B was detectable as fluorescent bands up to 24 wk after ingestion of the bait. Individual badgers were found positive for EtIPA and PrIPA up to 20 wk and 18 wk after exposure, respectively. This study indicates that Rhodamine B, PrIPA, and EtIPA could be used as long-lasting markers for badgers.

Effects of bait type and deployment strategy on uptake by free-living badgers

Baits are increasingly used in wildlife management to deliver orally administered vaccines and contraceptives. The efficacy and cost-effectiveness of vaccination or fertility-control campaigns can be substantially affected by bait uptake rates. This study assessed whether bait type and deployment strategy affected bait uptake by free-living badgers (Meles meles L.). Six social groups of badgers were presented with three bait types (meat, fruit, cereals) and two deployment strategies (dispersed single baits versus aggregated multiple baits at fixed baiting stations) for six weeks. In each social group, the type of bait and deployment strategy were rotated every week so that by the end of the test every group had experienced all combinations. On three days, biomarkers (ethyl iophenoxic acid, propyl iophenoxic acid and rhodamine B) were added to the baits to determine the proportion of badgers ingesting these baits. The results indicated that both bait type and deployment strategy affected the proportion of baits eaten by badgers and the number of badgers gaining access to baits. Meat and fruit baits were taken significantly more frequently than cereals, and dispersed meat baits had the highest rates of disappearance. Biomarker levels suggested that the proportion of badgers that gained access to all baits was substantially lower when baits were aggregated, although small sample sizes prevented statistical assessment of this effect. The results suggest that dispersed single baits are likely to be consumed in greater proportions by a higher number of individual badgers than multiple baits at fixed stations.

Levamisole can induce conditioned taste aversion in foxes

Conditioned Taste Aversion (CTA) develops when animals associate the taste of a particular food with illness and subsequently avoid consuming that food. We evaluated the potential of two chemicals, thiabendazole and levamisole hydrochloride, to induce CTA to meat in captive foxes (Vulpes vulpes). Foxes were presented for 45 min with thiabendazole or levamisole-treated meat (treatment group) or with untreated meat (control group). In subsequent tests, carried out at 3-week intervals, we tested whether foxes had established an aversion to untreated meat. One or two doses of thiabendazole induced CTA to the test meat in 3 out of 4 foxes. All foxes that had consumed a single portion of levamisole-treated meat avoided eating untreated test meat for the following five to seven post-treatment tests. The potential of using levamisole-induced CTA as a non-lethal method of manipulating the behaviour of predators is discussed.

Feeding of grey squirrels (Sciurus carolinensis) with the contraceptive agent DiazaCon™: effect on cholesterol, hematology, and blood chemistry

Grey squirrels (Sciurus carolinensis) are an invasive species in Britain and Italy. They have replaced native red squirrels (Sciurus vulgaris) throughout most of Britain, and cause damage to trees. Currently, lethal control is used to manage grey squirrel populations in Britain, but nonlethal methods might be more acceptable to the public. One such method is contraception with 20,25-diazacholesterol dihydrochloride (DiazaCon™). DiazaCon™ inhibits the conversion of desmosterol to cholesterol, resulting in increasing desmosterol concentrations and decreasing cholesterol concentrations. Because cholesterol is needed for the synthesis of steroid reproductive hormones, such as progesterone and testosterone, inhibition of cholesterol synthesis indirectly inhibits reproduction. Desmosterol is used as a marker of efficacy in laboratory studies with species that do not reproduce readily in captivity. Grey squirrels were gavaged with a DiazaCon™ solution for 2 days, and then fed DiazaCon™-coated peanuts for an additional 8 days at target doses of 50 and 100 mg DiazaCon™ per kg body weight. There was a significant difference in cholesterol concentrations in the treatment groups compared to the control group. Cholesterol was reduced by ≥ 40% for 2 months in both treatment groups. There were no differences among groups with respect to blood chemistry and hematology parameters, and mean values are reported. The mean overall dose of DiazaCon™ received was 29.0 ± 1.6 and 55.3 ± 4.3 mg/kg in the low (50 mg/kg) and high dose (100 mg/kg) groups, respectively. DiazaCon™ might provide an effective, acceptable alternative to lethal control.

Taste-aversion conditioning of house mice (Mus domesticus) using the non-lethal repellent, cinnamamide

Abstract The potential of cinnamamide, a non-lethal repellent, to induce a conditioned taste aversion in house mice ( Mus domesticus ) was investigated. Mice were presented with saccharin solution, then assigned to one of four groups, each of six individuals, receiving lithium chloride, cinnamamide or blank carrier by oral intubation. The fourth group were handled but not intubated. Animals treated with cinnamamide developed a strong and persistent aversion to saccharin which showed no evidence of attenuation during the 64-day trial. In contrast, the aversive response of the animals in the other treatment groups was either variable (LiCl and Blank groups) or absent (Handling group). Our results demonstrate that cinnamamide can induce a powerful conditioned aversion, a property that could be used to reduce problems posed by pest species without resorting to lethal control methods.

Potential compounds for inducing conditioned taste aversion in ferrets

Abstract Conditioned taste aversion (CTA) develops when an animal associates the taste of a particular food with illness and subsequently avoids consuming that food. We evaluated the potential of two compounds, levamisole hydrochloride and antimony potassium tartrate (APT) to induce CTA to meat in captive ferrets (Mustela furo). On conditioning day, one group of ferrets was presented with meat treated with a compound and another group of ferrets was presented with untreated meat. In post‐conditioning tests we established whether ferrets had acquired an aversion to untreated meat. Ferrets could detect levamisole and formed an aversion to this compound. APT induced an aversion to meat in treated ferrets, which ate less meat than controls. We suggest that APT is a promising agent to induce CTA in ferrets, while levamisole can act as a feeding repellent. The ability of levamisole to induce CTA should be tested once the flavour of this compound is masked.