Origin of the epidermis in parasitic platyhelminths

The epidermis of members of the major parasitic taxon Neodermata is distinctive among flatworms, being a syncytial, insunk, non-ciliated epidermis that develops through a wholesale replacement of larval epidermis at metamorphosis when the larva attacks a host. How it arose in evolution from what must have been a turbellarian-like ancestor is not immediately evident. While many turbellarian flatworms have also adopted a symbiotic way of life, the literature on ultrastructure of epidermis in these symbionts shows quite a variety of morphologies, many not so different from that of their free-living relatives. Various turbellarians do have syncytial or insunk epidermises or reduction of epidermal ciliation as is characteristic of the Neodermata, but co-occurrence in a single turbellarian of all features common to neodermatans has not been reported. Urastoma cyprinae, for example, which is ectosymbiotic on bivalves, has a ciliated cellular epidermis that is little different from what is known of epidermises of its free-living relatives. The endoparasitic Anoplodium hymanae, from the coelom of sea cucumbers, also bears a ciliated cellular epidermis, as is typical of many other rhabdocoels, but it shows marked phagocytic activity as well as incorporation of endosymbiotic bacteria. The closest similarity to neodermatan epidermis is that of the turbellarian Genostoma kozloffi, an ectosymbiont of the crustacean Nebalia: covering the bulk of the body is a non-ciliated syncytium with multiple branching connections to insunk nucleated portions, much as in epidermis of adult neodermatans and, on its ventral surface, is a field of ciliated cellular insunk epidermis resembling the epidermis of some larval neodermatans. Developmental clues to the origin of the neodermatan epidermis can be seen in turbellarian embryos. Before hatching, embryos of proseriate and triclad embryos go through 3 generations of epidermis, each replacing the next; 2 generations of epidermis are reported in the literature on rhabdocoel embryos. This process of replacement parallels the epidermal replacement that larval neodermatans undergo at metamorphosis. Ultrastructural study of developing acoel, polyclad and macrostomid embryos shows that they, too, have epidermal replacement and growth through immigration of deeper-lying cells, comparable to the processes seen in higher flatworms. Succession of distinct generations of epidermis in such animals as the proseriates, triclads and rhabdocoels is probably an adaptation to development of ectolecithal eggs, providing the means for the embryo to use yolk that resides in vitellocytes, outside its blastomeres. We propose that the Neodermata has taken advantage of this developmental mechanism, producing successive generations of epidermal cells even in its larval stages, to counter the defenses of hosts.     

Duodenal volvulus in free-living green turtles from coastal United Arab Emirates

Post-mortem examinations performed during May and August of 1997 on three free-living green turtles (Chelonia mydas) in the United Arab Emirates revealed that all had stomachs full of fresh seagrass (approximately 99% of the total ingesta) and presented with a duodenal volvulus involving a length of approximately 100 cm. Duodeni appeared empty and necrotic with diffuse purple-black mucosa. No apparent signs of obstruction by foreign objects, acute endoparasitism, or other disorders were observed. In all cases, duodenal volvulus was diagnosed, the cause of which may have been dietary in origin. The rise in water temperature, with an associated rise in the temperature of seagrass, thus enhancing the over-fermentation of ingesta with the subsequent liberation of excessive amounts of gas was the probable cause of volvulus formation. Ingestion of foreign bodies and physical movement also are discussed as causes of digestive disorders. It is recommended that handlers should avoid 360 degrees rotation when overturning turtles onto their carapaces.     

Contributions of microbes in vertebrate gastrointestinal tract to production and conservation of nutrients

The vertebrate gastrointestinal tract is populated by bacteria and, in some species, protozoa and fungi that can convert dietary and endogenous substrates into absorbable nutrients. Because of a neutral pH and longer digesta retention time, the largest bacterial populations are found in the hindgut or large intestine of mammals, birds, reptiles, and adult amphibians and in the foregut of a few mammals and at least one species of bird. Bacteria ferment carbohydrates into short-chain fatty acids (SCFA), convert dietary and endogenous nitrogenous compounds into ammonia and microbial protein, and synthesize B vitamins. Absorption of SCFA provides energy for the gut epithelial cells and plays an important role in the absorption of Na and water. Ammonia absorption aids in the conservation of nitrogen and water. A larger gut capacity and longer digesta retention time provide herbivores with additional SCFA for maintenance energy and foregut-fermenting and copoprophagic hindgut-fermenting species with access to microbially synthesized protein and B vitamins. Protozoa and fungi also contribute nutrients to the host. This review discusses the contributions of gut microorganisms common to all vertebrates, the numerous digestive strategies that allow herbivores to maximize these contributions, and the effects of low-fiber diets and discontinuous feeding schedules on these microbial digestive processes.     

An experimental model for studies on the effects of food and digestive secretions on the digestive-absorptive capacity of rat small intestine

At an average of 32 days after a modified Roux-en-y repositioning of rat small intestine, the mucosal mass, mucosal composition, in vivo absorption of galactose and the activity of maltase, sucrase and alkaline phosphatase were measured. In the gut segment with digestive secretions but without food (A) the only change was a decrease of sucrase activity which occurred most probably at the cellular level. In the gut segment with food and gastric juice and a reflux of digestive secretions (B) complex changes took place. An increase in mucosal mass was not accompanied by an increase in galactose absorption. There was a high increase of sucrase activity, a moderate increase of maltase activity and a tendency of the alkaline phosphatase activity to decrease. The changes (increase in mucosal mass and total enzyme activity, but no changes in activity at the cellular level) in the segment exposed to both digestive secretions and food (C) were compatible with a more proximal promotion of a distal gut segment.     

Pathogenesis of enteric diseases

The pathogenesis of digestive disease in poultry involves the cellular events and reactions that result in a deviation from normal structure and function. To a degree, the differentiation of disease and normal in commercial poultry also involves an economic perspective. Factors external to the digestive tract may mimic digestive disease, including reductions in the density of various nutrients and feed refusal. Antinutritional factors, such as certain storage polysaccharides and proteins, are inaccessible to endogenous enzymes and are either indigestible or act as blockers of the digestion of other nutrients. Changes in digestive secretions that result in either excess or deficiency also influence digestive structure and function. Infectious agents and toxins that cause degeneration and necrosis are especially injurious because a series of critical repair events must occur in order to regain function. The consequences range from lethal injury of the host animal to diminished performance. The digestive tract has a large component of lymphoid tissue and impairment of the immune system influences the course of protozoan, bacterial and viral enteric diseases.     

Pathophysiology of infection with Ostertagia ostertagi in cattle

Infection with the abomasal nematode, Ostertagia ostertagi, is an important cause of impaired productivity in young cattle in temperate parts of the world. Such losses have been associated with marked changes in feed intake, gastrointestinal function, protein, energy and mineral metabolism, and in body composition. The reduction in feed intake is an important factor in the pathogenesis of infection and may account for a large part of the difference in weight gain between ad libitum fed control and infected calves. Despite the obvious importance of inappetance, only recently has an association been made between reduced intake, altered gut motility and elevated levels of certain gastrointestinal hormones, such as gastrin. It has been suggested that the elevated gastrin levels accompanying abomasal parasitism may impair reticulo-ruminal motility and slow down abomasal emptying, leading to a stasis of ingesta and a reduction in feed intake. The rise in blood gastrin levels may also be partly responsible for the marked hyperplasia of the fundic mucosa seen in abomasal infections. Pronounced changes in protein metabolism have also been associated with Ostertagia infection. Radioisotopic studies have demonstrated increased losses of albumin into the gastrointestinal tract which are accompanied by an increase in the rate of synthesis in the liver. Dietary protein breakdown in the abomasum is also likely to be impaired, although there is evidence of a compensatory increase in protein digestion in the lower gut of parasitised calves. Increased losses of albumin are not always accompanied by increases in faecal nitrogen, suggesting that albumin is broken down and recycled as ammonia. Radioisotopic studies in animals with intestinal nematode infections have demonstrated a marked reduction in muscle protein synthesis and an increase in protein synthesis in gastrointestinal tissue. Such changes in the balance of protein synthesis are likely to be brought about by alterations in the balance of certain metabolic hormones. Marked changes in energy metabolism also accompany Ostertagia infection. Parasitised calves exhibit a marked increase in non-esterified fatty acid levels, resulting from the mobilisation of adipose tissue, and a reduction in digestive efficiency of energy, probably associated with the increase in cycling of protein through the gastrointestinal tract and the compensatory increases in protein synthesis. Mineral metabolism may also be affected although relatively little work has been conducted in cattle. Changes in body composition reflect a reduction in deposition of muscle protein and fat, and an increase in bone content and water retention.     

Ecology of flea groups of the species conformis (Siphonaptera: Pulicidae: Xenopsylla) of the fauna of Russia and adjacent countries (review)

Within the boundaries of the former USSR, the northern part of the conformis group distribution is located. It spreads over the arid regions of the Trans-Cacucasus, Pricaspijckaja lowland, Kazakhstan and Middle Asia. In this area 10 species and subspecies occur. They are mainly parasites of gerbillins. Unlike many other Siphonaptera the conformis fleas, when in the host's home, do not concentrate in the nest but inhabit the passages of burrow and food chambers throughout the year. On this reason the preimaginal development and existence of the adults take place not at the temperature of the habitable nest, which is heated by the host body, but at the temperature of the soil at a depth of burrow. The temperature threshold for preimaginal development of conformis fleas is reported to be 10-12 degrees. Temperature below the threshold is fatal for all immature instars. On the contrary the imago can survive at freezing temperature. The annual cycle of the conformis fleas is characterized by the presence of adults throughout the year. They breed in the warmer season and overwinter in the state of reproductive diapause. In this state the fleas are able to attack the host and to feed but do not deposit eggs. In the north deserts the reproduction begins at the early April and terminates at the early September. Southern, the reproductive period is longer. Furthermore, the complete interruption of the reproduction in the autumn-winter time may be absent as it was observed in X. gerbilli gerbilli and X. hirtipes in the south of the Middle Asia. On the other hand it is noted that in southern deserts the rate of oviposition falls in the most hot time. The number of generation per year in the conformis fleas varies from 2-3 in north deserts to 6-7 in south ones. The flea populations peak in late autumn when the insects cease to bread. The high abundance is maintained until springtime. After the diapause is ceased and the fleas begin breeding their abundance declines. In the late spring and early summer the emergence of adults begins and the populations increase. In a mild of summer the second fall takes place and then the fall is replaced by the autumnal peak. On their main hosts the conformis fleas prevail over all other species of Siphonaptera especially for warmer time when their quota among other fleas does not descend as a rule below 90% but more oftently it approaches to 100%. The fleas of this group and especially species parasitizing Rhombomys opimus are remarkable for the high level of their abundance. In the northern deserts in the periods of the most high abundance (late autumn, winter and early spring) the number of fleas per burrow occupied by family of Rh. opimus exceeds usually 1000 specimens and sometimes it can reach several thousands. In the southern deserts the abundance of the fleas is lower but the period of their active parasitizing is longer. In the species parasitizing Rh. opimus it is shown that in a complex burrow only some part of fleas has the possibility to feed regularly. In the spring and summer the percentage of fleas daily attacking the host varied from 17 to 86% and from 10 to 150 ectoparasites feed daily on one animal depending on the quantity of fleas and of hosts in the burrow. The number of attacking fleas is regulated by behaviour of the hosts, which change the used parts of burrow when the fleas are crowded there.     

Immunohistochemical and ultrastructural analyses of in situ activation of hepatic stellate cells around Propionibacterium acnes-induced granulomas in the rat liver

During their autumn migratory phase, thrush nightingales (Luscinia luscinia) previously starved for 2 d were allowed to refuel under three different ambient temperature conditions (-7 degrees, 7 degrees, and 22 degrees C). During the refueling period, as well as during the preceding control and starvation periods, food intake, body mass, and feces production were monitored. In addition, daily energy expenditure was measured during the refueling period. The compilation of the energy balance during the refueling period revealed an energy density of the deposited tissue of 33.6 kJ g-1. Assuming that the deposited tissue consists of fat and protein exclusively, with energy densities of 39.6 and 5.5 kJ g-1 wet mass, respectively, we estimated the deposited tissue to consist of 82% fat and 18% wet protein (6% dry protein and 12% water). Nitrogen balances during control, starvation, and refueling phases and during a period of prolonged and complete starvation indicated that 5% of the nutrient stores consisted of dry protein. Our results support recent findings that nutrient stores for migration often contain protein in addition to fat and consequently are 15%-25% less energy rich than pure fat stores. These proteins might be stored as muscle or other functional tissue and may be required to support the extra mass of the stores and/or reflect an incapacity of the metabolic machinery to catabolize far exclusively. Fuel deposition rate was positively related with ambient temperature, whereas food intake rate was unaffected by temperature. These results indicate that the rate of fuel deposition is limited by a ceiling in food intake rate; when this ceiling is reached, fuel deposition rate is negatively affected by daily energy expenditure rate. To a certain extent, the ceiling in food intake rate varies depending on feeding conditions over the previous days. These variations in food intake capacity probably reflect the building and breakdown of gut tissues and/or gut enzyme systems and might be insensible and not evolutionary adaptive. Significant energetic costs, however, are probably associated with the maintenance of gut tissues. It is therefore feasible that changes in digestive capacity are regulated and are directed at energy economization.     

Vector-host-parasite inter-relationships in leishmaniasis. IV. Electrophoretic studies on proteins of four vertebrate bloods with and without Leishmania infantum or L. major

Fifty five protein bands with relative mobilities of 8,954 to 245,471 kilo Daltons (kD) were electrophoretically separated from 12 feeding media of blood from 4 natural vertebrate hosts of Phlebotomus langeroni. The feeding media included human, dog (Canis familiaris), rat (Rattus rattus) and turkey (Melagris gallopava) bloods without or with Leishmania infantum or L. major promastigotes. Protein bands were identical among the feeding media of one host's blood but varied in number (24-28 bands) and relative mobilities among the various hosts' blood. Some protein fractions were common among the various hosts blood, others were only present in two or three hosts' blood and some were restricted to one host blood and were unique for each host. This study provides data which may help in understanding why blood from different natural hosts may variably influence the life cycle of Leishmania parasite in the sand fly gut.     

Cutaneous leishmaniasis in Egypt (review and comment)

Leishmania is primarily characterized by existing in two stages in its life cycle, each occurs in a distinct host. The amastigote stage found in the cytoplasm of the reticulo- endothelial cells, monocytes and other phagocytic cells of the vertebrate host. The promastigote stage found in the gut of its insect vector. The leishmaniasis comprise several diseases of wide diversity of manifestations caused by different species of the genus Leishmania. Because of the virtual morphological identity of the organisms throughout the genus, they are classified according to the clinical conditions which they produce in man, under three main headings: (1) Cutaneous leishmaniasis (CL.), (2) Mucocutaneous leishmaniasis (MCL.), (3) Visceral leishmaniasis (VL). Generally speaking, leishmaniasis is an example of a zoonosis that reaches man through an insect vector. The great majority of the Leishmania species are maintained by mammalian reservoir hosts in natural foci of infection. Rodents, dogs, wild cats, jackals, foxes, sloths, hyraxes and other carnivores are the animal reservoirs which maintain the infection in nature. The insect vectors are over 50 species of the genus Phlebotomus in the Old World and genus Lutzomyia in the New World.     

Novel taste facilitation of the association of visual cues with toxicosis in rats.

Conducted 3 experiments with 118 male Long-Evans rats to examine the conditions under which rats rapidly learn to avoid ingesting visually distinctive food objects associated with toxicosis. It was found that the presence of a novel taste associated with a visually distinctive food object facilitated acquisition of visual-cue/toxicosis associations. Further experiments failed to support either higher order conditioning or sensory preconditioning models of this phenomenon. Results are discussed in terms of species differences in the conditions under which attention is directed to visual cues associated with ingesta. The implications of these findings for the existence of visual aposematisms (warning colors) in naturally occurring toxic species are also examined. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biology of Isospora spp. from humans, nonhuman primates, and domestic animals

Coccidial parasites of the genus Isospora cause intestinal disease in several mammalian host species. These protozoal parasites have asexual and sexual stages within intestinal cells of their hosts and produce an environmentally resistant cyst stage, the oocyst. Infections are acquired by the ingestion of infective (sporulated) oocysts in contaminated food or water. Some species of mammalian Isospora have evolved the ability to use paratenic (transport) hosts. In these cases, infections can be acquired by ingestion of an infected paratenic host. Human intestinal isosporiasis is caused by Isospora belli. Symptoms of I. belli infection in immunocompetent patients include diarrhea, steatorrhea, headache, fever, malaise, abdominal pain, vomiting, dehydration, and weight loss, blood is not usually present in the feces. The disease is often chronic, with parasites present in the feces or biopsy specimens for several months to years. Recurrences are common, Symptoms are more severe in AIDS patients, with the diarrhea being more watery. Extraintestinal stages of I. belli have been observed in AIDS patients but not immunocompetent patients. Treatment of I. belli infection with trimethoprim-sulfamethoxazole usually results in a rapid clinical response. Maintenance treatment with trimethoprim-sulfamethoxazole is needed because relapses often occur once treatment is stopped.     

Isolation of an amoeba naturally harboring a distinctive Legionella species

There are numerous in vitro studies documenting the multiplication of Legionella species in free-living amoebae and other protozoa. It is believed that protozoa serve as host cells for the intracellular replication of certain Legionella species in a variety of environmental settings. This study describes the isolation and characterization of a bacterium initially observed within an amoeba taken from a soil sample. In the laboratory, the bacterium multiplied within and was highly pathogenic for Acanthamoeba polyphaga. Extracellular multiplication was observed on buffered charcoal yeast extract agar but not on a variety of conventional laboratory media. A 16S rRNA gene analysis placed the bacterium within the genus Legionella. Serological studies indicate that it is distinct from previously described species of the genus. This report also describes methods that should prove useful for the isolation and characterization of additional Legionella-like bacteria from free-living amoebae. In addition, the characterization of bacterial pathogens of amoebae has significant implications for understanding the ecology and identification of other unrecognized bacterial pathogens.     

Apparent absorption efficiency and gut morphometry of wood mice, Apodemus sylvaticus, from two distinct populations with different diets

Interpopulation variation in the diet of the wood mouse, Apodemus sylvaticus, is well documented. In this study, we examined the gut morphology and apparent absorption efficiencies of two populations of wood mice whose diet in the field was known to differ. One population inhabited sand dunes, where food availability was relatively low and the diet was dominated by invertebrates. The other population lived in deciduous woodland, with greater food availability and a diet consisting primarily of seeds. Wood mice from the woodland had longer small intestines and total digestive tract lengths than mice from the sand dunes. However, these differences had no effect on the apparent absorption efficiencies of dry mass or energy when the mice were fed mealworms, wheat grain, or All-Bran diets (apparent energy absorption efficiencies of 88%, 89%, and 65%, respectively). The population differences in gut morphometry may be linked to different resource availabilities at the two field sites.     

A tumor profile in Down syndrome

For most groups of biological control agents the relationship between laboratory (physiological) host range and the host range in the field (ecological host range) has not been explored empirically. The objective of our study was to investigate this relationship using the North America gypsy moth, Lymantria dispar, as a model nontarget host for microsporidia from native North American Lepidoptera. The gypsy moth, L. dispar, a native of Europe, has been established in North America for nearly 130 years and presumably exposed to many species of microsporidia from sympatric native Lepidoptera. Nevertheless, microsporidia have never been observed in North American populations of L. dispar. We conducted traditional laboratory feeding experiments using microsporidia from 20 lepidopteran host species and 1 coleopteran host species against L. dispar. Microsporidia from 18 native hosts infected L. dispar larvae. Although some of the infections were not typical of infections in the indigenous natural hosts, mature spores were produced in most of these infections. Horizontal transmission experiments, based on exposure of uninfected L. dispar larvae to infected L. dispar larvae, demonstrated that the microsporidia were far more host specific than the direct feeding experiments suggested. Of the three microsporidian biotypes that were horizontally transmitted between the nontarget L. dispar larvae, all were transmitted at very low levels. The results of our experiments provide additional evidence that the ecological host specificity of terrestrial microsporidia is much narrower than the physiological host specificity. Our studies establish the validity of using nonindigenous insect species with long-term data sets on natural enemies associated with them as a tool for testing hypotheses about host specificity.     

Apoptosis of neutrophils

Cercarial behavior patterns were examined in 4 species of frog lung flukes (Haematoloechus spp.). Cercariae of Haematoloechus complexus, Haematoloechus medioplexus, Haematoloechus longiplexus, and Haematoloechus varioplexus were exposed to 3 species of experimental arthropods and an inanimate control. The number of cercariae attached to an experimental host at 5 min postexposure was recorded. Haematoloechus longiplexus and H. complexus cercariae attached to experimental hosts at higher rates than cercariae of H. medioplexus and H. varioplexus. Cercariae of H. longiplexus attached to experimental hosts in approximately the same numbers as H. complexus, but H. longiplexus penetrated only damselfly naiads, and only at the base of the zygopteran caudal gills. Cercariae of H. complexus, a second intermediate host generalist, were able to penetrate and enter several arthropod species at the intersegmental membranes. Haematoloechus medioplexus and H. varioplexus are restricted to development in dragonfly naiads and cercariae rarely attached to and never penetrated experimental hosts. These behavioral patterns dictate the range of hosts suitable for metacercarial development of H. complexus, H. longiplexus, H. medioplexus, and H. varioplexus. The evolution of disparate patterns of behavior among the cercariae of these 4 congeners has directly affected subsequent patterns of transmission to the definitive host.     

Chromosome region 8p11-p21: refined mapping and molecular alterations in breast cancer

This review illustrates the use of experimental approaches combined with microscopy to study the biology of monogenean parasites. Studies of feeding, development, reproduction, and systematics have been based on gyrodactylids, flatworms infecting teleost fishes. In a contrasting system involving an amphibian host in a desert environment, analysis of adaptations to extreme conditions has focused on Pseudodiplorchis americanus. The unusual reproductive strategies, particularly the interactions between mother and offspring, are highlighted for both monogeneans. Species of Gyrodactylus are viviparous, maintaining up to three generations of embryos simultaneously in utero, and many of their reproductive specializations are related to progenesis. Embryo nutrition takes place via a metabolically-active syncytial uterine lining that has close association with the parental gut. Microscopy has also proved an essential adjunct to molecular studies of speciation and host specificity. P. americanus is ovoviviparous and the adaptations for embryo maintenance are unique. The primary keratin-type eggshell is replaced by a flexible secondary elastin capsule produced by the uterus; parental nutrients are transferred through cytoplasmic connections to the developing embryo. TEM has demonstrated unique adaptations of P. americanus to its micro-environments, including secretion of tegumental vesicles that provide protection from digestive enzymes during migration through the host gut. This paper highlights the potential of monogeneans for studies of fundamental biological principles.     

Lower begging responsiveness of host versus parasitic brown-headed cowbird (Molothrus ater) nestlings is related to species identity but not to early social experience.

The survival of young brood parasites depends critically on their many adaptations to exploit hosts. Parasitic survival is particularly related to competitive superiority for foster parental care whenever host young are not destroyed in parasitized nests. Brown-headed cowbirds (Molothrus ater) are generalist obligate parasites whose early social environments are unpredictable regarding host species and numbers of nestmates. Young avian brood parasites typically beg more intensively and loudly than foster siblings, but an untested prediction is that young parasites are also more likely to respond by begging to a wider variety of stimulus types. Avian vocalizations were used in a playback experiment to stimulate begging behavior in cowbird hosts. Compared with age-matched cowbird nestlings, hosts begged less frequently to acoustic stimuli, and lower begging responsiveness was irrespective of whether hosts had been reared in parasitized nests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parasites, immunology of hosts, and host sexual selection

Parasite-mediated sexual selection is reviewed with special emphasis on the bird literature. Choosy females may benefit from choosing parasite-free mates if such males provide better parental care, do not transmit contagious parasites, or provide resistance genes to offspring. There is evidence in support of each of these mechanisms. The immunocompetence handicap hypothesis posits that secondary sexual characters reliably reveal the ability of males to resist parasites due to the immunosuppressive effects of testosterone and other biochemicals. Several aspects of these negative feedback mechanisms are supported by laboratory studies, but evidence from free-living animals is almost completely absent. Corticosterone rather than testosterone may potentially mediate the immunocompetence handicap mechanism. A simple version of the immunocompetence handicap is developed suggesting that body condition of male hosts is a sufficient mediator of the handicap mechanism of reliable sexual signaling. Sexual selection appears to be more intense in sexually dichromatic bird species, and comparative studies using pairwise comparisons of closely related taxa reveal that sexually dichromatic bird species have larger spleens, larger bursa of Fabricius, and higher concentrations of leukocytes than monochromatic species. Parasite-mediated sexual selection is proposed to affect parasite biology by increasing (1) the variance-to-mean ratio in parasite abundance, (2) variance in the intensity of natural selection affecting hosts, and (3) speciation rates among parasites exploiting hosts subject to intense sexual selection as compared to those subject to less intense selection.     

Amebic meningoencephalitis caused by Balamuthia mandrillaris: case report and review

Balamuthia mandrillaris, formerly referred to as a leptomyxid ameba, is a free-living ameba that has recently been identified as a cause of meningoencephalitis. Previously, only two genera, Naegleria and Acanthamoeba, were recognized as causes of central nervous system (CNS) infections in humans. In contrast to Naegleria, Balamuthia causes a subacute-to-chronic infection of the CNS. Distinct from Acanthamoeba, which appears to favor the immunocompromised host, Balamuthia is capable of infecting both healthy and immunosuppressed hosts. Retrospective analyses as well as an accumulation of newly identified cases have demonstrated that this ameba is an increasingly important pathogen to recognize. We report the isolation, histopathologic features, and confirmation by indirect immunofluorescence of B. mandrillaris in a case of fatal amebic meningoencephalitis.