APPLIED TOPOGRAPHIC-ANATOMICAL STUDIES OF EAST AFRICAN GAME RUMINANTS

The topographic relationships of the so-called “vital centres” like the spinal chord brain, heart and major blood vessels of East African game ruminants are discussed, using the impala and the buffalo as type animals for a series of diagrams. Anatomical conditions in relation to the effect of shots in the various body regions are demonstrated with the aim of reducing irresponsible and painful wounding of game animals. Investigations and diagrams are based upon material from 59 animals of 18 species; of these, 47 animals were formalin-fixed and dissected in a natural standing position.     

Hosts and parasites as aliens

Over the past decades, various free-living animals (hosts) and their parasites have invaded recipient areas in which they had not previously occurred, thus gaining the status of aliens or exotics. In general this happened to a low extent for hundreds of years. With variable frequency, invasions have been followed by the dispersal and establishment of non-indigenous species, whether host or parasite. In the literature thus far, colonizations by both hosts and parasites have not been treated and reviewed together, although both are usually interwoven in various ways. As to those factors permitting invasive success and colonization strength, various hypotheses have been put forward depending on the scientific background of respective authors and on the conspicuousness of certain invasions. Researchers who have tried to analyse characteristic developmental patterns, the speed of dispersal or the degree of genetic divergence in populations of alien species have come to different conclusions. Among parasitologists, the applied aspects of parasite invasions, such as the negative effects on economically important hosts, have long been at the centre of interest. In this contribution, invasions by hosts as well as parasites are considered comparatively, revealing many similarities and a few differences. Two helminths, the liver fluke, Fasciola hepatica, of cattle and sheep and the swimbladder nematode, Anguillicola crassus, of eels are shown to be useful as model parasites for the study of animal invasions and environmental global change. Introductions of F. hepatica have been associated with imports of cattle or other grazing animals. In various target areas, susceptible lymnaeid snails serving as intermediate hosts were either naturally present and/or were introduced from the donor continent of the parasite (Europe) and/or from other regions which were not within the original range of the parasite, partly reflecting progressive stages of a global biota change. In several introduced areas, F. hepatica co-occurs with native or exotic populations of the congeneric F. gigantica, with thus far unknown implications. Over the fluke's extended range, in addition to domestic stock animals, wild native or naturalized mammals can also serve as final hosts. Indigenous and displaced populations of F. hepatica, however, have not yet been studied comparatively from an evolutionary perspective. A. crassus, from the Far East, has invaded three continents, without the previous naturalization of its natural host Anguilla japonica, by switching to the respective indigenous eel species. Local entomostrac crustaceans serve as susceptible intermediate hosts. The novel final hosts turned out to be naive in respect to the introduced nematode with far reaching consequences for the parasite's morphology (size), abundance and pathogenicity. Comparative infection experiments with Japanese and European eels yielded many differences in the hosts' immune defence, mirroring coevolution versus an abrupt host switch associated with the introduction of the helminth. In other associations of native hosts and invasive parasites, the elevated pathogenicity of the parasite seems to result from other deficiencies such as a lack of anti-parasitic behaviour of the na?ve host compared to the donor host which displays distinct behavioural patterns, keeping the abundance of the parasite low. From the small amount of available literature, it can be concluded that the adaptation of certain populations of the novel host to the alien parasite takes several decades to a century or more. Summarizing all we know about hosts and parasites as aliens, tentative patterns and principles can be figured out, but individual case studies teach us that generalizations should be avoided.     

Patterns of host-parasite interactions between the nematode Heligmosomum mixtum (Schulz, 1952) and the bank vole (Clethrionomys glareolus Schreber, 1780)

Some aspects of the host-parasite interaction of the nematode Heligmosomum mixtum and the bank vole have been studied. The dependence of infestation on the host sex, age and weight, the seasonal and annual abundance dynamics are investigated. It has been found that the bank vole is the main host of H. mixtum; the distribution of H. mixtum abundances in the host population is described by a negative binomial distribution model. The greatest infestation is characteristic for mature bank voles; males are infected more heavily than females. Infestation with the nematode increases alongside with the host weight. Seasonal dynamics of the nematode abundance in a bank vole population appears as a curve with a maximum in January and a minimum in August; the infestation curve for 1-month-old animals captured from June through October has two peaks (in July and October), with a minimum in June. The number of parasites in the ecosystem over a long-term period changed synchronously with the host abundance. The synchronism in the host-parasite system dynamics is possible when the parasite has a short life span, and does not influence the host abundance.     

Ectoparasites and age-dependent survival in a desert rodent

Host age is one of the key factors in host–parasite relationships as it possibly affects infestation levels, parasite-induced mortality of a host, and parasite distribution among host individuals. We tested two alternative hypotheses about infestation pattern and survival under parasitism in relation to host age. The first hypothesis assumes that parasites are recruited faster than they die and, thus, suggests that adult hosts will show higher infestation levels than juveniles because the former have more time to accumulate parasites. The second hypothesis assumes that parasites die faster than they are recruited and, thus, suggests that adults will show lower infestation levels because of acquired immune response and/or the mortality of heavily infested juveniles and, thus, selection for less infested adults. As the negative effects of parasites on host are often intensity-dependent, we expected that the age-related differences in infestation may be translated to lower or higher survival under parasitism of adults, in the cases of the first and the second hypotheses, respectively. We manipulated ectoparasite numbers using insecticide and assessed the infestation pattern in adult and juvenile gerbils (Gerbillus andersoni) in the Negev Desert. We found only a partial support for age-dependent parasitism. No age-related differences in infestation and distribution among host individuals were found after adjusting the ectoparasite numbers to the host’s surface area. However, age-related differences in survival under parasitism were revealed. The survival probability of parasitized juveniles decreased in about 48% compared to unparasitized hosts while the survival probability of adults was not affected by ectoparasites. Our results suggest that the effect of host age on host–parasite dynamics may not explicitly be determined by age-dependent differences in ectoparasite recruitment or mortality processes but may also be affected by other host-related and parasite-related traits.     

Studies on the helminth parasites of the Long-tailed field mouse, Apodemus sylvaticus sylvaticus from Wales

The incidence and degree of infestation of the Long-tailed field mouse, Apodemus sylvaticus with helminth parasites have been studied from a rough grassland and woodland area, Aberystwyth and from Skomer Island in Wales. With few exceptions, adult mice were more heavily infested than juveniles.
In Aberystwyth, where the composition of the helminth fauna was found to be more varied than that from the island of Skomer, three species of helminths, one digenean and two nematodes, showed evidence of seasonal variation in the degree of infestation of mice. The factors affecting this fluctuation in parasite numbers throughout the year are discussed.
It is suggested the distribution of helminths in the mouse population may be represented by a negative binomial, indicating that the infective eggs, larvae or intermediate hosts of the respective helminths were aggregated in their distribution in the selected areas of study.     

Parasitic Nematode Abundance Aggregation as a Mechanism of the Adaptive Response of the Host Plant to Temperature Variations

The mathematical model of host–parasite relations suggested previously by the authors was applied to analyze the formation of the aggregated distribution of parasites in the case of the host plant–parasitic nematode system. For nearly the same conditions and empirical infection levels, nematode abundances in the host population followed the gamma distribution. Exposure to temperature stresses modifies the resistance of the plant population to infection. Experiments with prolonged chilling of potato plants prior to nematode infestation revealed no statistically reliable increase in the share of resistant plants compared to the control, although the mean and the range of variation of the infection rate, as well as the aggregation of the parasite distribution, decreased. Short-term chilling of the plants prior to infestation led to a reliable decrease in the mean abundance of parasites and to the lowest aggregation of the parasitic nematode in the host plant population. The results of this study showed that this temperature stress caused potatoes to develop a reliably high and uniform resistance to the nematode.     

The role of host traits, season and group size on parasite burdens in a cooperative mammal

The distribution of parasites among hosts is often characterised by a high degree of heterogeneity with a small number of hosts harbouring the majority of parasites. Such patterns of aggregation have been linked to variation in host exposure and susceptibility as well as parasite traits and environmental factors. Host exposure and susceptibility may differ with sexes, reproductive effort and group size. Furthermore, environmental factors may affect both the host and parasite directly and contribute to temporal heterogeneities in parasite loads. We investigated the contributions of host and parasite traits as well as season on parasite loads in highveld mole-rats (Cryptomys hottentotus pretoriae). This cooperative breeder exhibits a reproductive division of labour and animals live in colonies of varying sizes that procreate seasonally. Mole-rats were parasitised by lice, mites, cestodes and nematodes with mites (Androlaelaps sp.) and cestodes (Mathevotaenia sp.) being the dominant ecto- and endoparasites, respectively. Sex and reproductive status contributed little to the observed parasite prevalence and abundances possibly as a result of the shared burrow system. Clear seasonal patterns of parasite prevalence and abundance emerged with peaks in summer for mites and in winter for cestodes. Group size correlated negatively with mite abundance while it had no effect on cestode burdens and group membership affected infestation with both parasites. We propose that the mode of transmission as well as social factors constrain parasite propagation generating parasite patterns deviating from those commonly predicted.     

Effects of food abundance, age, and flea infestation on the body condition and immunological variables of a rodent host, and their consequences for flea survival

Temporal variation in body condition and immunological variables of animals that harbor parasites may explain patterns of variation in infestation, as well as parasite impact on the host. We emulated such variability in Sundevall's jirds by manipulating food availability and flea infestation in juveniles and adults and examining how these changes affect survival of fleas on their hosts. Body condition of food-restricted jirds deteriorated, but there was no change in their immunological variables. Adult jirds were in better body condition and had higher immunocompetence than juveniles, however there were no significant effects of flea infestation on any of the variables examined. The main effects of flea infestation were a decrease in the response to phytohaemagglutinin injection, and an increase in the negative effects of food restriction on body mass. Flea survival was higher on juveniles, but fleas did not respond to temporal variability in body condition and immunocompetence of the jirds. We concluded that changes in body condition and immune responses due to growth or variability in food abundance are more important than changes caused by the fleas themselves. Flea infestation is more detrimental to jirds when they are not able to compensate for mass loss through increased food consumption.     

Studies on the host parasite relationship between the parasitic prosobranch Thyca crystallina and the asteroid starfish Linckia laevigata

A study of the Blue starfish Linckia laevigata in the Banda Islands, Moluccas, Indonesia, revealed 62% infestation by the molluscan prosobranch parasite Thyca crystallina. Infestation rate varies directly with the degree of water movement. A marked difference in settlement pattern according to parasite size is observed. The smallest limpets tend to settle on the upper surface of the distal parts of the arms and are randomly oriented. The largest parasites are found on the oral arm surface on the right hand side of the ambulacral groove and facing the starfish mouth. All of the attached parasites were female. Most of the large females had a dwarf male, one tenth the length, attached, under the mantle, at the anterior end. Amongst the small limpets, less than half had made a proboscis hole in the host integument and none had made an attachment disc lesion; of the large parasites 90% had the proboscis embedded in the host and 80% left an attachment disc lesion on the host. Small parasites can move very slowly over the host surface. Larger limpets are probably permanently attached. A detached parasite of any size is probably unable to reattach. There is evidence of an extended parasite breeding period and repetitive settlement on the hosts, which could cause the observed overdispersion without invoking a mature female parasite pheromone.     

Are parasite intensity and related costs of the milichiid fly Carnus hemapterus related to host sociality?

Ectoparasites have often been shown to have detrimental effects on their host. Not much is known, however, about determinants of infestation, e.g. the question of which factors affect distribution and occurrence of parasites on different host species (degree of host specificity) and their infestation rates. In this study we examine possible effects of host determinants on parasite intensity of Carnus hemapterus (Carnidae), an ectoparasitic fly on nestling birds, in the European bee-eater (Merops apiaster), which is a common host of C. hemapterus. Our results show that European bee-eaters seem to be one of the most heavily infested host species of C. hemapterus. We found that brood size, nestling age, and colony size are the most important determinants of infestation by C. hemapterus. This parasite seems to prefer medium-sized bee-eater chicks and to select them according to their condition. Our results further suggest a negative effect of C. hemapterus on chick development.     

Sex-biased parasitism is not universal: evidence from rodent–flea associations from three biomes

The distribution of parasites among individual hosts is characterised by high variability that is believed to be a result of variations in host traits. To find general patterns of host traits affecting parasite abundance, we studied flea infestation of nine rodent species from three different biomes (temperate zone of central Europe, desert of Middle East and tropics of East Africa). We tested for independent and interactive effects of host sex and body mass on the number of fleas harboured by an individual host while accounting for spatial clustering of host and parasite sampling and temporal variation. We found no consistent patterns of the effect of host sex and body mass on flea abundance either among species within a biome or among biomes. We found evidence for sex-biased flea infestation in just five host species (Apodemus agrarius, Myodes glareolus, Microtus arvalis, Gerbillus andersoni, Mastomys natalensis). In six rodent species, we found an effect of body mass on flea abundance (all species mentioned above and Meriones crassus). This effect was positive in five species and negative in one species (Microtus arvalis). In M. glareolus, G. andersoni, M. natalensis, and M. arvalis, the relationship between body mass and flea abundance was mediated by host sex. This was manifested in steeper change in flea abundance with increasing body mass in male than female individuals (M. glareolus, G. andersoni, M. natalensis), whereas the opposite pattern was found in M. arvalis. Our findings suggest that sex and body mass are common determinants of parasite infestation in mammalian hosts, but neither of them follows universal rules. This implies that the effect of host individual characteristics on mechanisms responsible for flea acquisition may be manifested differently in different host species.     

Relative fitness of a generalist parasite on two alternative hosts: a cross‐infestation experiment to test host specialization of the hen flea Ceratophyllus gallinae (Schrank)

Host range is a key element of a parasite's ecology and evolution and can vary greatly depending on spatial scale. Generalist parasites frequently show local population structure in relation to alternative sympatric hosts (i.e. host races) and may thus be specialists at local scales. Here, we investigated local population specialization of a common avian nest‐based parasite, the hen flea Ceratophyllus gallinae (Schrank), exploiting two abundant host species that share the same breeding sites, the great tit Parus major (Linnaeus) and the collared flycatcher Ficedula albicollis (Temminck). We performed a cross‐infestation experiment of fleas between the two host species in two distinct study areas during a single breeding season and recorded the reproductive success of both hosts and parasites. In the following year, hosts were monitored again to assess the long‐term impact of cross‐infestation. Our results partly support the local specialization hypothesis: in great tit nests, tit fleas caused higher damage to their hosts than flycatcher fleas, and in collared flycatcher nests, flycatcher fleas had a faster larval development rates than tit fleas. However, these results were significant in only one of the two studied areas, suggesting that the location and history of the host population can modulate the specialization process. Caution is therefore called for when interpreting single location studies. More generally, our results emphasize the need to explicitly account for host diversity in order to understand the population ecology and evolutionary trajectory of generalist parasites.     

Reaction of the mussel Mytilus galloprovincialis (Bivalvia) to Eugymnanthea inquilina (Cnidaria) and Urastoma cyprinae (Turbellaria) concurrent infestation

In total 480 individuals of Mytilus galloprovincialis were sampled monthly from October 2009 to September 2010, at the shellfish farm in the Mali Ston Bay, south Adriatic Sea (Croatia) in order to assess the extent of pathology imposed by two parasites, Eugymnanthea inquilina (Cnidaria) and Urastoma cyprinae (Turbellaria). Although a deteriorating impact on host reproduction or condition index was lacking, we evidenced ultrastructural and functional alteration in host cells at the attachment site. Ultrastructural changes included hemocytic encapsulation of the turbellarian and cell desquamation in medusoid infestation. Caspase positive reaction inferred by immunohistochemistry (IHC) was triggered in cases of turbellarian infestation, in contrast with hydroids, suggesting that the former exhibits more complex host-parasite interaction, reflected in the persistent attempts of the parasite to survive bivalve reaction. We have evidenced that both organisms trigger specific host reaction that although not costly in terms of host reproductive cycle or growth, results in mild tissue destruction and hemocyte activation. A lower degree of tissue reaction was observed in cases of hydroid infestation, compared to turbellarian.     

Infestation of the jack mackerel, Trachurus declivis (Jenyns), with the cymothoid isopod, Ceratothoa imbricatus (Fabricus), in south eastern Australian waters

The tongue biter, Ceratothoa imbricatus , a cymothoid isopod, commonly found on a number of Australian inshore temperate fish species, was recorded in the pelagic jack mackerel, Trachurus declivis , in 26 of 43 trawls. The infestation rate was low (1·76%) in the 26 trawls where the association was noted. It is suggested that infestation occurs at an early age and that subsequent growth by the isopod is mediated by the host. Estimates of the growth parameters indicate that the isopods are long lived, and can remain for at least nine years on the host fish. Protandrous hermaphroditism, common in the Cymothoidae, is found in C. imbricatus with females attaining a large size in the bucco-pharyngeal cavity while the male, with suppressed growth, is restricted to the branchial arches.
Although cymothoid isopods are commonly described as parasites, observable damage on the jack mackerel was restricted to the tissues at the points of attachment of the isopods. The effect of the isopod on the jack mackerel may not be as debilitating as might be expected and it is argued that the relationship may best be described as commensalism.     

The microsporidian Encephalitozoon

Encephalitozoon cuniculi is an attractive model system for amitochondriate intracellular eukaryotic parasites. It is characterized by a very small genome (below 3 Mbp) and a unique invasion apparatus. Furthermore, as an infectious agent, it is important in human and veterinary medicine. The compactness of its genome involves the reduction of rDNA sequences as well as of some protein-coding genes and intergenic regions. Its highly differentiated apparatus to penetrate the host cell, an extrusome-like polar tube, is composed of novel proteins and may permit various pathways of infestation. Completion of the systematic E. cuniculi sequencing project should provide an important reference system for the comparative genomics of amitochondriate and mitochondriate parasites. Further analysis of orphan genes should help to identify factors that are responsible for its intracellular parasitic way of life.     

Influence of parasitic infection on food intake

The results of controlled experiments have demonstrated unequivocally that host food intake is often altered during the course of infections with eukaryotic parasites. Generally, host food intake is reduced depending on either the infective dose given to the host or the number of established parasites present. The onset in the reduction of host food intake varies according to the species of parasite involved and may be related to a particular developmental stage or event during the course of the host-parasite relationship. Some of the many sensory, neural, and hormonal factors that are now considered to modulate food intake in healthy animals are known to be affected during certain host-parasite relationships, and it is tentatively suggested that these physiological perturbations may initiate the observed changes in host food intake. Not unexpectedly, human appetite for food and food intake have been reported to become depressed during parasitic infections.     

LIVEWEIGHTS AND BODY MEASUREMENTS OF SERENGETI GAME ANIMALS

More than 300 game animals shot in the Grumeti Controlled Area, Tanzania during research into game utilisation were weighed and measured. The results are presented and compared with other available data. Considerable variation is apparent between animals of the same species from different areas.
The techniques of linear measurement are fully described in an attempt to standardise measurements for comparative purposes.     

Intestinal parasites infestation and anemia in primary school children in Gaza Governorates--Palestine

A comparative study was carried out to identify the prevalence of anemia, nutritional indices and intestinal parasitic infestation in primary school children. The target population included 209 pupils aged 6-11 years, attending schools in two areas, Rimal area (urban) and Jabalia village (rural), in Gaza Governorates. Prevalence of intestinal parasites was high in Jabalia village (more than 53%) in comparison to Rimal area (33%). The main intestinal parasites were Entamoeba histolytica, Giardia intestinalis and Ascaris lumbricoides. Polyparasitism frequency is higher especially in rural area. In both areas anemia showed a high prevalence in children due to malnutrition and intestinal parasitic diseases. There was no association between intestinal parasitic infestation and children growth, but there was association between anemia and intestinal parasitic infestation in children, particularly in rural area. The correlation between anemia and mixed infestation reaches a highly significant level.     

Host and habitat specialization of avian malaria in Africa

Studies of both vertebrates and invertebrates have suggested that specialists, as compared to generalists, are likely to suffer more serious declines in response to environmental change. Less is known about the effects of environmental conditions on specialist versus generalist parasites. Here, we study the evolutionary strategies of malaria parasites (Plasmodium spp.) among different bird host communities. We determined the parasite diversity and prevalence of avian malaria in three bird communities in the lowland forests in Cameroon, highland forests in East Africa and fynbos in South Africa. We calculated the host specificity index of parasites to examine the range of hosts parasitized as a function of the habitat and investigated the phylogenetic relationships of parasites. First, using phylogenetic and ancestral reconstruction analyses, we found an evolutionary tendency for generalist malaria parasites to become specialists. The transition rate at which generalists become specialists was nearly four times as great as the rate at which specialists become generalists. We also found more specialist parasites and greater parasite diversity in African lowland rainforests as compared to the more climatically variable habitats of the fynbos and the highland forests. Thus, with environmental changes, we anticipate a change in the distribution of both specialist and generalist parasites with potential impacts on bird communities.