Studies on the specificity of killing of intracellular pathogens by macrophages.

To determine whether macrophages can discriminate in an immunologically specific manner between the intracellular pathogens which they inhibit or kill, unelicited peritoneal macrophages from mice infected with either of two related but antigenically dissimilar protozoa were challenged with these protozoa in vitro. Experimental conditions were varied in an attempt to establish a state in vivo in which macrophage specificity might be demonstrated. No differences could be discerned between the ability of macrophages from three different strains of mice infected with the protozoa to kill Besnoitia and Toxoplasma. The effect of macrophages on Toxoplasma as compared with Besnoitia did not evolve or vary during development, expression, or decline of an immune response, i.e., with varying times after infection of mice as well as with varying times after treatment of mice with irradiated Toxoplasma. The route of infection could not be shown to confer specificity on macrophages, as subcutaneous and intraperitoneal inoculation of Toxoplasma did not lead to differential ability of macrophages to inhibit or kill the protozoa. The different strains of protozoa used for infection of mice did not affect the ability of peritoneal macrophages from Besnoitia- and Toxoplasma-infected mice to inhibit multiplication of or kill Besnoitia and Toxoplasma comparably in vitro. Peritoneal macrophages of mice treated with Corynebacterium parvum kill both organisms efficiently. These macrophages were employed to determine whether stimulation of macrophages by treatment of mice with a substance unrelated to the protozoa would produce activated macrophages. Uninfected mice and mice infected with either Besnoitia or Toxoplasma were challenged with varying doses of the protozoa in parallel with examination of macrophages from the same groups of mice in vitro to determine whether the presence of stimulated macrophages in the peritoneal cavity was necessary for protection against Toxoplasma and Besnoitia, and if so if their presence was sufficient for protection. Only mice with activated peritoneal macrophages were protected. However, protection was greater when the primary infection was with the same organisms used for challenge at a time when macrophages inhibited or killed both protozoa efficiently in vitro. The possible role of other effector cells, subpopulations of macrophages of different functional abilities in various sites, and antibody or other lymphocyte products acting in concert with macrophages as factors which may explain the differences observed between in vivo protection and in vitro capacity to inhibit or kill the protozoa are discussed.     

Exploiting amoeboid and non-vertebrate animal model systems to study the virulence of human pathogenic fungi

Experiments with insects, protozoa, nematodes, and slime molds have recently come to the forefront in the study of host-fungal interactions. Many of the virulence factors required for pathogenicity in mammals are also important for fungal survival during interactions with non-vertebrate hosts, suggesting that fungal virulence may have evolved, and been maintained, as a countermeasure to environmental predation by amoebae and nematodes and other small non-vertebrates that feed on microorganisms. Host innate immune responses are also broadly conserved across many phyla. The study of the interaction between invertebrate model hosts and pathogenic fungi therefore provides insights into the mechanisms underlying pathogen virulence and host immunity, and complements the use of mammalian models by enabling whole-animal high throughput infection assays. This review aims to assist researchers in identifying appropriate invertebrate systems for the study of particular aspects of fungal pathogenesis.     

Ultrastructure of the cyst wall of Sarcocystis spp. from some rodents in Malaysia.

The cyst wall of Sarcocystis cysts from the skeletal muscles and subcutaneous tissues of 4 species of rats and 1 species of bandicoot in Malaysia was examined under the electron microscope. Three types of sarcosysts with morphologically distinct cyst walls were found in these rodents. These morphologically distinct types of sarcocysts occurred as single or mixed infections in their various rodent hosts, suggesting that these rodents are important, though non-specific, intermediate hosts in the life cycle of at least 3 species of Sarcocystis. The final hosts of these Sarcocystis species are unknown.     

Biologie comparée des interactions entre les macrophages et Trypanosoma cruzi,Leishmania spp. et Toxoplasma gondii

Macrophages have a central role in the immune system by eliminating a lot of pathogens. Nevertheless, they are often infected by pathogenic microorganisms in particular parasitic protozoa. They thus play the role of host cell by harbouring the intracellular survival and multiplication of these pathogens. Various mechanisms (receptors/ligands interactions, enzymes…) are involved in recognition and adhesion steps. When suitably activated, they become effector cells and they can control infection at least partially through the production of reactive oxygen derivatives. But parasitic protozoa can escape these defence mechanisms. In addition, macrophages are also antigen presenting cells and they are inductor cells of the immune response. Once again, parasitic protozoa interfere with these functions and induce chronic infections. Biology of Trypanosoma cruzi, Leishmania spp. and Toxoplasma gondii will be briefly reviewed to illustrate these various aspects of cellular parasitism.     

Trypanosoma musculi and Trichinella spirails: Concomitant infections and selection for resistance genotypes in mice

Trypanosoma musculi infections were given to mice of different strains before, at the same time, and after an infection with 400 Trichinella spiralis. Examined parameters of the host response to T. spiralis were worm rejection, antifecundity responses, development of immunological memory, and muscle larvae burden. After dual infection, each mouse strain showed characteristic effects on resistance to T. spiralis. This was due to a dynamic interaction between the genes controlling rejection of T. spiralis and those influencing T. musculi growth. C3H mice develop high trypanosome parasitemias. This impairs worm expulsion and the development of memory to T. spiralis when Trypanosoma infections take place on the same day or 7 days before. The C57B1/6 mouse develops low parasitemias and T. musculi infections on the same day, or 7 days before T. spiralis, delaying worm rejection only slightly despite the overall weak capacity of B6 mice to expel worms. NFR-strain mice are strong responders to T. spiralis and also develop low parasitemias. Trypanosome infections on the same day, or after T. spiralis, produce a delay in worm rejection; the former is comparable to C3H mice. However, NFR mice alone showed enhanced rejection of worm when T. musculi infections preceded T. spiralis by 7 days. An unusual feature of C3H mice was that T. musculi infections 7 days before T. spiralis increased antifecundity responses at the same time that worm expulsion was inhibited. Trypanosome infections can therefore modulate distinct antihelminth immune responses in different directions simultaneously. The different outcomes of dual infections compared with single infections provides another selective mechanism by which genetic polymorphisms can be established and maintained in the vertebrate host.     

Bovine sarcocystosis: Sarcocystis species,diagnosis, prevalence,economic and public health considerations,and association of Sarcocystis species with eosinophilic myositis in cattle

Infections by Sarcocystis in cattle are ubiquitous worldwide. There is considerable debate concerning the identity of Sarcocystis spp. in cattle. Proper diagnosis of Sarcocystis spp. is important to assess their economic and public health importance. Currently there are seven named species: Sarcocystis hirsuta, Sarcocystis cruzi, Sarcocystis hominis, Sarcocystis bovifelis, arcocystis heydorni, Sarcocystis bovini and Sarcocystis rommeli. Additionally, there are unnamed Sarcocystis spp. Two species, S. hominis and S. heydorni, are zoonotic. One out of seven species (S. hirsuta, contracted from cats) forms macroscopic cysts which can be visible during carcass inspection. Current molecular characterization is based on DNA extracted from sarcocysts from naturally infected cattle because DNA was not characterized from tissues of experimentally infected cattle or feces of experimentally infected definitive hosts. Sarcocystis cruzi (transmitted via canids) is recognized as the most pathogenic species and it causes abortion, low milk yield, poor body growth, and outbreaks of clinical sarcocystosis and death. Additionally, Sarcocystis infections have been linked to an inflammatory condition of striated muscles termed bovine eosinophilic myositis (BEM). Cattle affected by BEM appear clinically normal. Diagnosis of BEM at slaughter occurs when inspecting the carcass surface, or once the carcass has been divided into prime cuts or quarters. Sex and breed have no apparent influence on prevalence of BEM. The condition evidently occurs with equal frequency in steers, cows, and heifers. Virtually all striated muscles can be affected including skeletal muscles, the muscles of the eye, larynx, and the heart. In the USA, regulations require condemnation of BEM-affected parts, or (in severe cases) the entire carcass. These aesthetic considerations result in economic losses. Cattle experimentally infected with Sarcocystis did not have BEM at slaughter. Here, we review the status of Sarcocystis spp. and BEM in cattle including prevalence, lesions, epidemiology, and association of BEM with different species of Sarcocystis.     

Pythons,parasites, and pests: anthropogenic impacts on Sarcocystis (Sarcocystidae) transmission in a multi‐host system

Parasites are essential components of ecosystems and can be instrumental in maintaining host diversity and populations; however, their role in trophic interactions has often been overlooked. Three apicomplexan parasite species of Sarcocystis (S. singaporensis, S. zamani, and S. villivillosi) use the reticulated python as their definitive hosts and several species within the Rattus genus as intermediate hosts, and they form a system useful for studying interactions between host–parasite and predator–prey relationships, as well as anthropogenic impacts on parasite transmission. Based on predictions from a 1998 survey, which detected an inverse relationship between urban development and Sarcocystis infection in Rattus, we tested the hypothesis that Sarcocystis transmission in Singapore will decrease over time due to anthropogenic activities. Despite a large proportion of the reticulated python diet consisting of Rattus species at all sizes of pythons, Sarcocystis infection rates decreased from 1998 to 2010. Pythons found in industrial areas had lower Sarcocystis infection rates, particularly in the western industrial area of Singapore Island. Average python size also decreased, with implications that we predict may disrupt host–parasite relationships. Anthropogenic activities such as habitat modification, fragmentation, and systematic removal and translocation of pythons have negative impacts on Sarcocystis transmission in Singapore, which in turn may augment pest rat populations. Trends observed may ultimately have negative impacts on human health and biodiversity in the region.     

Predation risk, host immune response, and parasitism

Predation risk may affect the allocation priorities of limitingresources by potential prey. Investment in immune function shouldreceive reduced priority, when hosts are exposed to predatorsbecause of the costs of immune function. We tested this hypothesisby randomly exposing adult house sparrows, Passer domesticus,to either a cat, Felis catus, or a rabbit, Oryctolagus cuniculus,for 6 h while assessing their ability to raise a T-cell–mediatedimmune response to a challenge with phytohemagglutinin. Sparrowsexposed to a cat had a significant reduction of, on average,18% and 36% in T-cell response in two different experimentscompared with sparrows that were exposed to a rabbit. In a fieldexperiment with a barn owl, Tyto alba, or a rock dove, Columbalivia, placed next to a nest-box during laying, we found a meanreduction in T-cell–mediated immune response of 20%. Inmales, the reduction in cell-mediated immune response owingto cat exposure increased with increasing size of the badge,which is a secondary sexual character, but only during the breedingseason. In a third experiment, house sparrows were either exposedto a barn own, T. alba, or a rock dove, C. livia, and developmentof malarial infections was recorded during the following 6 weeks.Individual sparrows exposed to a predator had a higher prevalenceand intensity of Haemoproteus malarial infection than did controlindividuals. Therefore, exposure to predators reduced theirability of hosts to cope with parasitism mediated through effectson immune function.     

The effect of Plasmodium berghei and Trypanosoma brucei infections on the immune expulsion of the nematode Trichuris muris from mice

The effects of concurrent P. berghei or T. brucei infections on the immune expulsion of primary and challenge infections of T. muris from CFLP strain mice have been examined. CFLP mice usually expel the nematode 18–21 days after a primary infection and within 4–6 days after a challenge infection. Both acute malaria and trypanosome infections initiated at the same time as the T. muris infection suppressed worm expulsion; when the protozoal infections were started 7 days after the T. muris infection worm expulsion was suppressed in a proportion of the mice. Acute trypanosome and malaria infections delayed the expulsion of a challenge infection from immune mice, but in the case of P. berghei the delay was short-lived.     

Histomorphological changes in the reproductive condition of parasitized marine planktonic copepods

Changes in the internal morphology of parasitized copepods sampledin the Gulf of Naples from 1986 to 1988 were investigated usingboth light and transmission electron microscopy. The most commonand devastating form of infection was due to the parasitic dinoflagellateSyndinium, which induced gross modifications in the internaland external morphology of the host population. The parasitereduced fecundity and longevity of infected individuals, whichmainly included juvenile and female populations of the copepodParacalanus parvus. Infection rates for this species were ashigh as 12% for. juveniles and 13% for adult females for theperiod investigated. Infection by the parasitic dinoflagellateBlastodinium induced less negative effects on the reproductivebiology of their hosts. This pathogen did not lead to sexualcastration and oogonal development appeared normal. Other formsof infestation were rare and included infections due to protozoa,fungi and bacteria. ^*Died tragically at sea during a cruise on December 15, 1988     

Trichinella spiralis: antifecundity and antinewborn larvae immunity in swine

The development of antifecundity and antinewborn larvae immunity in swine infected with Trichinella spiralis was investigated. In primary infections, adult female worm fecundity dropped sharply after 3 weeks, although adults could be recovered from the small intestine for at least 7 weeks after infection. In challenge infections of pigs infected previously, adult female worm fecundity was depressed up to 51% and the adults were expelled within 3 weeks. Since immune pigs are almost completely resistant to the secondary establishment of muscle larvae, this suggested the existence of immune effector mechanisms also acting on the newborn larvae. This was supported by observations, using an indirect fluorescent antibody assay, that pig antibody bound to the surface of the newborn larvae. Passive transfer of immune pig serum resulted in a large reduction in muscle larvae burden in both infected pig and rat recipients. Adult female worm fecundity in such immune serum recipients was reduced only by 20% and worm survival in the intestine was unaffected. These results indicate that immunity to the newborn larvae, in addition to antifecundity effects, are responsible for the high levels of acquired resistance to T. spiralis in swine.     

SIV infection in natural hosts: resolution of immune activation during the acute-to-chronic transition phase

SIV-infected natural hosts do not progress to clinical AIDS yet display high viral replication and an acute immunologic response similar to pathogenic SIV/HIV infections. During chronic SIV infection, natural hosts suppress their immune activation, whereas pathogenic hosts display a highly activated immune state. Here, we review natural host SIV infections with an emphasis on specific immune cells and their contribution to the transition from the acute-to-chronic phases of infection.     

The Infection of Trifolium subterraneum Root Hairs by Rhizobium trifolii

Both host cultivar and Rhizobium strain influence the numberof infected root hairs of Trifolium subl-errctneum, seedlings;Yarloop had fewer infections than Cranmore, Mount Barker, orTallarook and Rhizobium trifolii strain 5 infected fewer hairsthan strain TA1. Hybrid lines bred for sparse or abundant nodulationhad similar numbers of infected hairs, but. as in the cultivars,these always greatly exceeded the number of nodules formed.More infection threads aborted early during growth in the roothairs of Cranmore than in other hosts and early abortion wasmore common with strain 5 than strain TA1 In all hosts and with both Rhizobium strains, infection beganon day 3 and was initially restricted to one or two zones alongthe root with later infections extending these zones or initiatingnew ones. The exponential rate of infection (least for Yarloop)slows sharply when nodules appear. Early nodules and lateral roots formed at different places indifferent hosts, and in most cultivars and hybrid lines nodulesand laterals occurred in mutually exclusive zones. Primordiaarising above the first nodule failed to develop.     

Using model systems to unravel host–Pseudomonas aeruginosa interactions

Using model systems in infection biology has led to the discoveries of many pathogen-encoded virulence factors and critical host immune factors to fight pathogenic infections. Studies of the remarkable Pseudomonas aeruginosa bacterium that infects and causes disease in hosts as divergent as humans and plants afford unique opportunities to shed new light on virulence strategies and host defence mechanisms. One of the rationales for using model systems as a discovery tool to characterise bacterial factors driving human infection outcomes is that many P. aeruginosa virulence factors are required for pathogenesis in diverse different hosts. On the other side, many host signalling components, such as the evolutionarily conserved mitogen-activated protein kinases, are involved in immune signalling in a diverse range of hosts. Some model organisms that have less complex immune systems also allow dissection of the direct impacts of innate immunity on host defence without the interference of adaptive immunity. In this review, we start with discussing the occurrence of P. aeruginosa in the environment and the ability of this bacterium to cause disease in various hosts as a natural opportunistic pathogen. We then summarise the use of some model systems to study host defence and P. aeruginosa virulence.     

Interactions of antimicrobial peptides with Leishmania and trypanosomes and their functional role in host parasitism

Antimicrobial peptides (AMPs) are multifunctional components of the innate systems of both insect and mammalian hosts of the pathogenic trypanosomatids Leishmania and Trypanosoma species. Structurally diverse AMPs from a wide range of organisms have in vitro activity against these parasites acting mainly to disrupt surface-membranes. In some cases AMPs also localize intracellularly to affect calcium levels, mitochondrial function and induce autophagy, necrosis and apoptosis. In this review we discuss the work done in the area of AMP interactions with trypanosomatid protozoa, propose potential targets of AMP activity at the cellular level and discuss how AMPs might influence parasite growth and differentiation in their hosts to determine the outcome of natural infection.     

A Legacy of Low-Impact Logging does not Elevate Prevalence of Potentially Pathogenic Protozoa in Free-Ranging Gorillas and Chimpanzees in the Republic of Congo: Logging and Parasitism in African Apes

Many studies have examined the long-term effects of selective logging on the abundance and diversity of free-ranging primates. Logging is known to reduce the abundance of some primate species through associated hunting and the loss of food trees for frugivores; however, the potential role of pathogens in such primate population declines is largely unexplored. Selective logging results in a suite of alterations in host ecology and forest structure that may alter pathogen dynamics in resident wildlife populations. In addition, environmental pollution with human fecal material may present a risk for wildlife infections with zoonotic protozoa, such as Cryptosporidium and Giardia. To better understand this interplay, we compared patterns of infection with these potentially pathogenic protozoa in sympatric western lowland gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes troglodytes) in the undisturbed Goualougo Triangle of Nouabalé-Ndoki National Park and the adjacent previously logged Kabo Concession in northern Republic of Congo. No Cryptosporidium infections were detected in any of the apes examined and prevalence of infection with Giardia was low (3.73% overall) and did not differ between logged and undisturbed forest for chimpanzees or gorillas. These results provide a baseline for prevalence of these protozoa in forest-dwelling African apes and suggest that low-intensity logging may not result in long-term elevated prevalence of potentially pathogenic protozoa.     

Recolonizing gray wolves increase parasite infection risk in their prey

The recent recolonization of Central Europe by the European gray wolf (Canis lupus) provides an opportunity to study the dynamics of parasite transmission for cases when a definitive host returns after a phase of local extinction. We investigated whether a newly established wolf population increased the prevalence of those parasites in ungulate intermediate hosts representing wolf prey, whether some parasite species are particularly well adapted to wolves, and the potential basis for such adaptations. We recorded Sarcocystis species richness in wolves and Sarcocystis prevalence in ungulates harvested in study sites with and without permanent wolf presence in Germany using microscopy and DNA metabarcoding. Sarcocystis prevalence in red deer (Cervus elaphus) was significantly higher in wolf areas (79.7%) than in control areas (26.3%) but not in roe deer (Capreolus capreolus) (97.2% vs. 90.4%) or wild boar (Sus scrofa) (82.8% vs. 64.9%). Of 11 Sarcocystis species, Sarcocystis taeniata and Sarcocystis grueneri occurred more often in wolves than expected from the Sarcocystis infection patterns of ungulate prey. Both Sarcocystis species showed a higher increase in prevalence in ungulates in wolf areas than other Sarcocystis species, suggesting that they are particularly well adapted to wolves, and are examples of “wolf specialists”. Sarcocystis species richness in wolves was significantly higher in pups than in adults. “Wolf specialists” persisted during wolf maturation. The results of this study demonstrate that (1) predator–prey interactions influence parasite prevalence, if both predator and prey are part of the parasite life cycle, (2) mesopredators do not necessarily replace the apex predator in parasite transmission dynamics for particular parasites of which the apex predator is the definitive host, even if meso‐ and apex predators were from the same taxonomic family (here: Canidae, e.g., red foxes Vulpes vulpes), and (3) age‐dependent immune maturation contributes to the control of protozoan infection in wolves.     

Effects of parasites on marine mammals

This report examines the broad range of organisms which can parasitize marine mammals, and identifies those which we feel have the greatest impact on individuals and populations.Many parasites colonize and damage the integument in some way. Only the sucking lice of seals are associated with debilitating disease. In addition, at least one species, E. horridus can serve as intermediate host of the seal heartworm, D. spirocauda.Of the few protozoa, the one deserving most attention is Sarcocystis sp. Its ubiquitous distribution challenges our understanding of coccidian life cycles as currently perceived.Acanthocephalans and cestodes are rarely associated with clinically significant illness. It is intriguing that cetaceans and pinnipeds serve as mammalian intermediate hosts for larval tetraphyllidians destined to mature in elasmobranchs.Digeneans occupy the gastrointestinal tract and severely damage liver and pancreas of cetaceans. Nasitrema sp. infects cranial sinuses of small odontocetes, and enters the brain, thereby leading to stranding and death in selected populations.Nematodes represent the broadest group of parasites. Pseudaliids often infect the respiratory system, causing sufficient damage to affect survival. There is no evidence that Stenums sp., a pseudaliid inhabiting the cranial sinuses of some whales and dolphins, plays any role in mass strandings, as has been popularly suggested. Filarioids are highly pathogenic in pinnipeds and are probably responsible for significant mortality, especially in young animals. Anisakine nematodes in the stomach are of little consequence to the host. The role of marine mammals in transmitting the parasites to commercially exploited fish stocks is a public health issue. The only other parasite which represents a threat to humans is Trichinella spiralis, which is widespread in Arctic mammals.The Crassicaudinae are the largest nematodes in cetaceans. Evidence is accumulating that the damage they cause in cranial bone, mammary tissue and the urinary tract may influence productivity and survival among certain groups.Most of our understanding of the parasites of marine mammals derives from studies on specimens which come ashore. The information is fragmentary, and suffers from our inability to follow the progress of infection and the overall condition of the parasitized animal. Yet we might conclude that the parasitism we see is as advanced as can be tolerated by the host. Weak animals retreat from the protection of the herd, become vulnerable to predators, and probably cannot survive in an environment which places heavy demands on thermoregulation, respiration and mobility.