Manfred E. Rau

Effects of Eubothrium salvelini (Cestoda) on the behaviour of Cyclops vernalis (Copepoda) and its susceptibility to fish predators

To facilitate the completion of their life-cycle, many helminth parasites have evolved the ability to manipulate the behaviour of their intermediate host in order to make it more likely to be eaten by the parasites definitive host. Here, we determined whether the cestode Eubothrium salvelini modifies the behaviour of its intermediate host, the copepod Cyclops vernalis , and makes it more susceptible to predation by brook trout, Salvelinus fontinalis , the parasites final host. Following the experimental infection of copepods, the spontaneous activity of infected and control subjects was quantified weekly. In addition, we regularly quantified predation by individual brook trout fry on known numbers of infected and control copepods. At approximately the time when the cestode larvae became infective to fish (2–3 weeks following infection), the infected copepods started to swim more actively than uninfected controls. Also at that time, infected individuals became more likely to be captured by fish than uninfected ones. Copepod size and intensity of infection had no significant effect on their behaviour or their risk of being eaten by fish. Thus cestode- induced changes in copepod swimming activity can lead to infected copepods becoming highly vulnerable to fish predators, and may have resulted from selection on the parasite to increase its transmission success

Occurrence of the leucine-to-phenylalanine knockdown resistance (kdr) mutation in Anopheles arabiensis populations in Tanzania, detected by a simplified high-throughput SSOP-ELISA method

BackgroundMolecular markers of insecticide resistance can provide sensitive indicators of resistance development in malaria vector populations. Monitoring of insecticide resistance in vector populations is an important component of current malaria control programmes. Knockdown resistance (kdr) confers resistance to the pyrethroid class of insecticides with cross-resistance to DDT through single nucleotide polymorphisms (SNPs) in the voltage-gated sodium channel gene.MethodsTo enable detection of kdr mutations at low frequency a method was developed that uses polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA)-based technology, allowing rapid, reliable and cost-effective testing of large numbers of individual mosquitoes. This was used to assay mosquitoes from sites in lower Moshi, Tanzania.ResultsSequence-specific oligonucleotide probes (SSOP) were used for simultaneous detection of both East and West African kdr mutations with high specificity and sensitivity. Application of the SSOP-ELISA method to 1,620 field-collected Anopheles arabiensis from Tanzania identified the West African leucine-phenylalanine kdr mutation in two heterozygous individuals, indicating the potential for resistance development that requires close monitoring.ConclusionThe presence of the West African kdr mutation at low frequency in this East African population of An. arabiensis has implications for the spread of the kdr gene across the African continent.

Parasite-induced susceptibility to predation in diplostomiasis

Guppies ( Lebistes reticulatis ) exposed to doses as low as 25 cercariae of Diplostomum spathaceum for 30 min were consistently and significantly more susceptible to predation by brook trout ( Salvelinus fontinalis ) than uninfected controls. The increase in susceptibility to predation was correlated with a marked decrease in the activity of infected fish.

Establishment and maintenance of behavioural dominance in male mice infected with Trichinella spiralis

Trichinella spiralis infections influenced the establishment and maintenance of behavioural dominance among outbred male mice. Infected animals assumed a subordinate status when challenged by normal or more lightly infected conspecifics both in an unfamiliar test arena and in their established home cages. These effects were demonstrable during the acute and the chronic phases of infection. The significance of this phenomenon to the survival of the mouse host and the transmission of the parasite is discussed.

Infection of brook trout fry, Salvelinus fontinalis, by ectoparasitic copepods: the role of host behaviour and initial parasite load

Abstract Ectoparasitic copepods tend to aggregate on their fish hosts, with few fish harbouring many parasites and most fish harbouring few or none. In laboratory experiments, it was determined whether individual differences in behaviour among uninfected hosts, and parasite-induced behavioural changes in infected hosts, act to generate aggregated distributions of the copepod Salmincola edwardsii on brook trout fry. Fish were individually exposed to parasites twice, first to numbers ranging from 0 to 80 copepods, to produce variability in initial parasite load, and then to 40 copepods. Fish behaviour was significantly affected by the presence of copepods in the surrounding water in both exposures. However, there was no clear relationship between copepod density and host behaviour. Among uninfected fish exposed to copepods for the first time, the number of copepods acquired by a fish was inversely related to the time it spent motionless. Prior infection increased the probability that a fish would acquire further copepods during a subsequent exposure. This may be due to copepod-induced behavioural changes, since the time spent motionless by fish decreased as the number of copepods harboured increased. This suggests that behavioural differences among uninfected hosts, and greater risks of acquiring further parasites through behavioural changes in infected hosts, could lead to few fish harbouring most parasites in natural populations.

Efficacy of pyrethroid-treated nets against malaria vectors and nuisance-biting mosquitoes in Tanzania in areas with long-term insecticide-treated net use

Objective  To measure pyrethroid susceptibility in populations of malaria vectors and nuisance‐biting mosquitoes in Tanzania and to test the biological efficacy of current insecticide formulations used for net treatment.

Plagiorchis elegans : emergence, longevity and infectivity of cercariae, and host behavioural modifications during cercarial emergence

We investigated changes in the behaviour of Stagnicola elodes associated with the emergence of Plagiorchis elegans cercariae. Within 15 min of the reduction in light intensity, which triggered the onset of cercarial emergence, infected snails moved to the top of the water column and remained there for 2-3 h. Seventy-nine percent of all cercariae that emerged from the snail did so during this period. Uninfected snails showed no such behavioural changes following the change in light intensity. Cercariae were released in a dense cloud around the snail at the water surface and dispersed passively. Within 3-4 h more than 80% of all cercariae had settled in the bottom 5 cm of the water column. The infectivity of cercariae increased from less than 20% upon emergence from the snail to greater than 75% 4-6 h post-emergence, and then declined steadily to below 5% by 24 h post-emergence. Cercarial longevity was greater than 30 h and exceeded the period of infectivity. This may be related to steadily falling endogenous glycogen levels. A delay in attaining maximum infectivity may represent an adaptive mechanism allowing time for cercarial dissemination, thus reducing superinfection, and subsequent parasite-associated mortality, of second intermediate hosts.

The open-field behaviour of mice infected with Trichinella pseudospiralis

The behaviour of mice exposed to graded doses of Trichinella pseudospiralis larvae was monitored in an open-field situation. Ambulatory activity declined briefly during the acute phase of the infection (day 11) but regained pre-infection levels 1 week later. Animals receiving heavy doses of T. pseudospiralis exhibited a mild increase in the level of ambulatory activity during the chronic phase of the infection. The infections did not affect the level of exploratory activity. The effects of the T. pseudospiralis infections on the behaviour of the mouse host were much less pronounced than those induced by T. spiralis. It is suggested that these differences may be associated with the small size of T. pseudospiralis and the lack of capsule formation.

Entomological Evaluation of Malaria Vectors at Different Altitudes in Hai District, Northeastern Tanzania

Abstract Entomological monitoring in four villages situated along an altitude transect in the Hai District of Northeastern Tanzania identified Anopheles arabiensis Patton as the principal vector of malaria and detected seasonal changes in vector behavior. Over a 13-mo sampling period, 10,557 mosquitoes were collected with CDC light traps, pyrethrum spray catches, and pit traps of which 5,969 (56.5%) were An. arabiensis, 762 (7.2%) were Anopheles funestus Giles s.l., 3,578 (33.9%) were culicines, and 248 (2.3%) were nonvector anophelines. Vector densities declined rapidly with increasing altitude, demonstrating a 50% decrease in annual human biting rate for every 86-m rise in altitude. Light traps were found to be more efficient than spray catches for the collection of An. arabiensis. This observation was attributed to increased exophily of this species, most notably in the wet season, and is supported by seasonal changes in the human blood index and fed/gravid ratio. These results indicate that spray catches may underestimate the abundance of exophilic vectors such as An. arabiensis and that entomological monitoring may require more than one collection method, especially at low vector densities. The annual entomological inoculation rate (EIR) decreased sharply with increasing altitude, with large variation around the estimate at low vector densities. Increased transmission because of unpredictable short rains at low altitudes and spatial clustering of infective mosquitoes may contribute to elevated EIR estimates.

Loss of behavioural dominance in male mice infected with Trichinella spiralis

Trichinella spiralis infections may lead to the loss of behavioural dominance among male mice. Reversals of dominance order first appear at the time when newborn larvae are released into the circulation of the host. The duration of dominance reversals bears no relationship to the number of muscle larvae harboured.