It seems inevitable that chemotherapy will continue, at least in the near-term, to be a significant factor in the control of infectious diseases. The effectiveness of new drugs has invariably been reduced by the emergence of drug resistance. Efforts to thwart resistance should continue, but there are also other areas that might profitably be re-examined. They include (1) methods of new-drug discovery; (2) selection of parasite life-cycle targets; (3) epidemiological determinants of effectiveness in large-scale control programs; and (4) the economic, managerial, psychological, and political ramifications of drug discovery and drug utilization.

Baylisascaris procyonis is a nematode whose definitive host is the raccoon (Procyon lotor). Adult parasites are not particularly pathogenic to raccoons; however, larvae in intermediate hosts can cause visceral, ocular, and neural larva migrans. Humans serve as dead-end hosts, and pathological responses are similar to those found in infected intermediate hosts. Infected raccoons expose intermediate hosts through their feces, which can contain millions of B. procyonis eggs. Our objective was to determine how the quantity and viability of B. procyonis eggs in soil changed over time within different soil texture, moisture, and sun exposure. To examine egg survival and movement through soil we placed 100 B. procyonis eggs on 100 squares in 48 boxes representing a full factorial treatment of soil texture, moisture, and sun level. We monitored egg percolation and survival for 2 yr, removing (at 0, 1, 3, 6, 12, 18, and 24 mo) 5 squares from each box and counting the number of viable eggs at each depth in the soil column. Dry soils were mainly impermeable; even after 2 yr, >60% of B. procyonis eggs remained on the surface of all soil textures. Wet soils were more permeable than dry soils, but even in wet sandy soils where the greatest egg movement occurred, it required 1 yr before 60% of eggs transitioned from the soil surface to the next soil depth. For all soil textures, moistures, sun exposures, and depths, >92% of B. procyonis eggs remained viable after 2 yr in the southern Texas environment. Therefore, high exposure risk exists for potential hosts because B. procyonis eggs remain viable on or near the soil surface for at least 2 yr.

Host specificity of parasites is a basic principle in parasitology; however, it is not easily measured. Previously, host specificity was calculated as the number of species that a parasite infected, but this is not an accurate description of host usage because some species are capable of being infected but do not contribute to the completion of the life cycle. Instead, measures of host specificity should take into consideration interactions between a parasite and a potential host species as well as interactions between current and subsequent hosts in the life cycle. The objectives of this study were to track the development of 2 trematode species, Halipegus eccentricus and Halipegus occidualis, in 3 phylogenetically and ecologically distinct microcrustacean second intermediate hosts, and then evaluate the extent to which each of these hosts contributed to transmission of each Halipegus species to the next odonate host in the life cycle. All 3 microcrustacean species exposed became infected with both species of Halipegus. The patterns of growth of H. eccentricus and H. occidualis were similar, but there were consistent differences in the rates of growth among the microcrustacean species in both Halipegus species. Regardless of host species infected, all individuals of both species were considered to be developmentally infective to the next host in the life cycle by 19 days postexposure (DPE) when they lost their excretory bladder. Worms of varying sizes were capable of surviving without this structure, suggesting that there is not a strong relationship between the rate of growth of the metacercariae and the development of their osmoregulatory system. Although Halipegus species were capable of living without an excretory bladder at 19 DPE, there were differences in their size and rates at which the 3 microcrustaceans contributed to transmission of the parasites to subsequent odonate hosts. Collectively, under controlled laboratory conditions, there was an approximate 2-fold difference in the average percentage of worms that established in odonates from the ostracod, Cypridopsis sp., than from the harpacticoid copepod, Phyllognathopus sp., and the difference was nearly 3-fold between Cypridopsis sp. and the cyclopoid copepod, Thermocyclops sp. Therefore, despite all 3 microcrustacean species becoming infected, not all species were equally suited for transmission and completion of the life cycle. Differences among the 3 microcrustacean species in cercaria ingestion, metacercarial growth and development, and odonate predation rates on infected microcrustacean species were important factors in determining transmission of the 2 Halipegus species to odonate hosts.

California has more reported human raccoon roundworm cases than any other state due to large and overlapping human and raccoon populations. Infection by this parasite, Baylisascaris procyonis, is relatively benign in raccoons but can cause severe pathology in other species. Disease risk is driven by environmental egg contamination which increases with raccoon density, worm intensity, and worm prevalence. To improve knowledge about risk to humans and other species, 189 raccoons from southern California were examined to investigate how host age and season affect worm abundance, demography, and fecundity. Adult worms were present in animals as young as 10 wk and 100% of 4-mo-old raccoons were infected. Although 80% of sampled raccoons hosted adult B. procyonis, prevalence and abundance were lower in older animals. There were more worms in juvenile than in adult raccoons, resulting in a convex age-intensity profile. Coupled with raccoon demography, this drove fall peaks in parasite abundance and egg production. Eggs per-gram feces averaged 4,606 ± 661 (SE), and this output increased with worm intensity, with no evidence that crowding reduced parasite size or fecundity. High parasite egg outputs from hosts in this California raccoon population increase human exposure risk, and this risk could be reduced by management strategies that target heavily infected juvenile raccoons.

This study tests the hypothesis that in chronic Toxoplasma gondii infection communication among immune cells promotes neuroinflammation through cytokine networks and potentiate cognitive impairments in BALB/c mice with Alzheimer's disease (AD). The animal model of Toxoplasma infection was established by the intraperitoneal inoculation of 20–25 tissue cysts from the Tehran strain of T. gondii. We injected amyloid-beta 1–42 peptide (Aβ_1–42, 1 and 2 μl) into the hippocampus of BALB/c mice to establish an animal model of AD. The behavioral experiments such as spatial learning and memory were performed using the Morris water maze test. The mRNA levels of TNF-α, IL-1β, IFN-γ, and inducible nitric oxide synthase (iNOS) were examined by real-time PCR. We found that T. gondii infection caused AD-like symptoms and impaired learning and memory functions of the infected BALB/c mice. We also found that in Toxoplasma infection Aβ_1–42 (1 μl) group, T. gondii infection could potentiate AD in infected mice receiving subdoses of Aβ_1–42 (1 μl) and caused considerable impairment in learning and memory functions similar to AD group. Comparison of the results demonstrated that mRNA levels of IL-1β, TNF-α, IFN-γ, and iNOS significantly (P < 0.001) increased in T. gondii Aβ_1–42 (1 μl) in comparison with the other tested groups. The obtained results showed that chronic T. gondii infection communication among immune cells promotes neuroinflammation through cytokine networks and induces pathological progression of AD in the mice brain, whereas the presence of neuroanatomical Toxoplasma tissue cysts in the brain could also affect the behavioral functions in T. gondii–infected mice.

Hemosporidians are a diverse group of blood parasites that infect terrestrial vertebrates worldwide, but there is variability in parasite prevalence and parasitemia with infections ranging from virtually inconsequential to lethal. In this study, we determined prevalence and parasitemia of avian hemosporidians in the Tufted Titmouse (Baeolophus bicolor; n = 81). Plasmodium and Parahaemoproteus were detected and quantified from blood samples using microscopy, polymerase chain reaction (PCR), and quantitative PCR. Thirteen mitochondrial cytochrome b lineages of hemosporidian parasites were found, including generalist and specialist lineages, and the data indicate that prevalence is 69.1% (Plasmodium 89.3%; Parahaemoproteus 7.1%; double infection 3.6%). However, parasitemia was low in all infected birds. Seasonally, parasite prevalence varied significantly, although prevalence and parasitemia were not associated with host sex, age, or health. Observations of infection in this naturally infected bird provide details on host susceptibility that are applicable to the understanding of hemosporidian parasites in other avian hosts.

This study provides a parasitological analysis of the elasmobranch species caught in the northern and central Adriatic Sea. Sixty-two marine leeches were recorded on 747 individuals of Raja clavata Linnaeus, 1758 (thornback ray), Myliobatis aquila Linnaeus, 1758 (common eagle ray), and Torpedo marmorata Risso, 1810 (marbled torpedo ray) caught in 56 hauls over a 5 yr period. All leeches were identified as Pontobdella muricata, which is a typical ectoparasite of benthic elasmobranchs. The prevalence of infection ranged from 7.11% on R. clavata to 12.00% on M. aquila. The intensity of infection, the preferential sites of attachment to the host, and the periodicity of infection were evaluated.

The grass shrimp (Palaemonetes pugio) is a staple prey species in the diet of many ecologically and economically important species such as blue crab and striped bass and is commonly infected with a trematode parasite, Microphallus turgidus. To complete its life cycle, M. turgidus must be consumed as a metacercaria by a bird or mammal definitive host. Previous research has found that infected grass shrimp behave more conspicuously than uninfected shrimp around predators, which include mummichogs (Fundulus heteroclitus). In addition, grass shrimp are more likely to avoid predation when they have access to coarse woody debris (CWD). Aquaria experiments revealed that uninfected shrimp significantly reduce the amount of time spent swimming in the presence of a fish predator, whereas infected shrimp did not exhibit this predation avoidance behavior. Uninfected shrimp also increased predator avoidance behavior (“backthrusts”) in the absence of CWD, whereas infected shrimp did not. These findings suggest that M. turgidus does not influence grass shrimp usage of CWD, but it alters shrimp swimming and backthrust behavior, thereby rendering infected shrimp more susceptible to predation. The implications of increased predation by a fish (nonhost or possible paratenic host) versus by a bird or mammal (definitive host) for parasite transmission are discussed.

This paper presents the first report of parasites from the genus Renicola sp. in the kidneys of Magellanic penguins. The histological analysis revealed inflammatory infiltrate (eonsinophils, lymphocytes, and plasmocytes), together with fibroplasia and compression of the adjacent ducts.

The redclaw crayfish, Cherax quadricarinatus (Decapoda: Parastacidae), is native to Australia but has been introduced to South Africa as a warm-water aquaculture species. In a South African natural waterbody, examined crayfish had high-intensity infections of 3 temnocephalan species on their body surfaces and within the branchial chambers. Temnocephalans were characterized using light and scanning electron microscopy and identified as Craspedella pedum, Diceratocephala boschmai, and Didymorchis sp. This is the first report of the introduction of Australian temnocephalans, C. pedum and Didymorchis sp., to Africa and expands the known distribution of these species beyond their presumptive native range. The present study also documents a naturalized population of C. quadricarinatus from a natural water body in South Africa, comprising a new geographical locality record.