Trichinella spiralis in an agricultural ecosystem: transmission in the rat population

Four hundred forty-three Norway rats (Rattus norvegicus) were examined to determine their role in the transmission and maintenance of Trichinella spiralis on a pig farm. Rats, classified by sex and weight, were examined for trichinellosis by peptic digestion of muscle samples. Over a 25-mo period, 188 (42.4%) rats were found to be infected with T. spiralis. The mean intensity of infection was 293.2 larvae per gram (LPG) of muscle; 65 (34.6%) infected rats had intensities of infection greater than 100 LPG. Even in the absence of a known source of infected meat (garbage containing meat scraps or dead animals), the rat population maintained the infection, probably through cannibalism. Population reduction was an effective method for reducing the prevalence of infection within the rat population. Therefore, to reduce the likelihood of transmission of T. spiralis between rats and swine, it is essential that rat populations in a farmyard environment be controlled.     

Prevalence of Trichinella spp. in black bears, grizzly bears, and wolves in the Dehcho Region, Northwest Territories, Canada, including the first report of T. nativa in a grizzly bear from Canada

Samples of muscle from 120 black bears (Ursus americanus), 11 grizzly bears (Ursus arctos), and 27 wolves (Canis lupus) collected in the Dehcho Region of the Northwest Territories from 2001 to 2010 were examined for the presence of Trichinella spp. larvae using a pepsin-HCl digestion assay. Trichinella spp. larvae were found in eight of 11 (73%) grizzly bears, 14 of 27 (52%) wolves, and seven of 120 (5.8%) black bears. The average age of positive grizzly bears, black bears, and wolves was 13.5, 9.9, and approximately 4 yr, respectively. Larvae from 11 wolves, six black bears, and seven grizzly bears were genotyped. Six wolves were infected with T. nativa and five with Trichinella T6, four black bears were infected with T. nativa and two with Trichinella T6, and all seven grizzly bears were infected with Trichinella T6 and one of them had a coinfection with T. nativa. This is the first report of T. nativa in a grizzly bear from Canada. Bears have been linked to trichinellosis outbreaks in humans in Canada, and black bears are a subsistence food source for residents of the Dehcho region. In order to assess food safety risk it is important to monitor the prevalence of Trichinella spp. in both species of bear and their cohabiting mammalian food sources.     

The effect of Trichinella spiralis on muscular activity of experimentally infected mice

Nematodes of genus Trichinella are wide-spread zoonotic parasites, able to infect a large variety of vertebrates. Animal hosts are usually regarded as asymptomatic carriers. However, there is little data regarding the functional consequences that T. spiralis infection renders on muscle cells. The aim of the present study was to assess the effect of T. spiralis on the effort capacity of experimentally infected mice. Overall, 60 mice, divided into three groups were used: M (uninfected), L200 and L1000, infected with 200 or 1000 larvae/mouse respectively. The mice were periodically weighed and their effort capacity was evaluated (days 0, 7, 15, 35 and 60). From each group, two randomly selected mice were euthanized after evaluation carcasses were artificially digested in order to establish the number of larvae per gram (LPG). On day 0, there were no significant differences among groups. Starting with day 7, the effort capacity of infected groups decreased, with significant differences between group M and the infected groups. From day 15, the differences between the infected groups also became significant. The LPG gradually increased and the differences between groups were always significant. A strong correlation between the LPG and decreased effort capacity was noted. The present study demonstrates the reduction of muscular capacity in mice experimentally infected with Trichinella spiralis, in correlation with the infective dose, providing new insights in this parasite's transmission strategy.     

Density-related variation in vertical transmission of a virus in the African armyworm

Larvae of the African armyworm, Spodoptera exempta, are darker and more resistant to baculovirus infection when reared in groups (gregarious form) compared to being reared singly (solitary form). Lepidoptera that survive virus challenge as larvae could potentially retain a sublethal virus infection which is then transmitted vertically to the next generation. Here we examine whether gregarious and solitary forms of the armyworm differ in the costs of surviving virus infection and in their capacity to transmit an active baculovirus infection to their offspring. Pupae of larvae reared gregariously that survived virus challenge weighed significantly less than uninfected individuals, but this was not so for those reared solitarily. This did not, however, translate into differences in fecundity, at least under laboratory conditions. As found in previous studies, pre-oviposition period was shorter for solitary than gregarious insects, and it was also shorter for females that had been challenged with virus as larvae. Both the prevalence of egg batches containing larvae that died from nucleopolyhedrovirus (NPV) infection and the proportion of infected larvae within each egg batch were significantly increased (approximately doubled) when parental moths were previously challenged with the virus during their larval state. This demonstrates that horizontal transmission in one generation can elevate vertical transmission to the next generation. Moreover, prevalence of overt infection in the offspring generation was two to three times greater when parental moths were reared solitarily as larvae than when reared gregariously. Disease prevalence and proportional infection were both independent of the sex of the infected parent and whether or not the egg batch was surface-sterilized to remove potential contaminants. This suggests that the eggs are infected internally (transovarial) rather than externally (transovum). These results help to shed light on the observed temporal pattern of virus epizootics in eastern Africa.     

Epidemiology of sheep infection by Oestrus ovis in Algeria

313 sheep were examined in 1996 to assess the importance and seasonal evolution of Oestrus ovis infection in the Algerian region of El-Tarf. Prevalence was found to be 67.4%. The larval burden was 18 larvae by infected sheep. The prevalence was higher in older sheep than in lambs; intensity was similar. The different larval stages were found all along the year in sheep with prevalence ranging from 33.1 to 80.5% for L1, 9.7 to 43.9% for L2 and 8.4 to 23.0% for L3. The sheep were the least infected in winter (prevalence from 35.7 to 44% and intensity seven to ten larvae per sheep). The highest infection was found during the warm season (spring to autumn, prevalence from 62 to 90% and intensity ranging from 15 to 25). This larval evolution profile suggested the existence of one long cycle (November-April) and possibly two shorts cycles (May-October). This epidemiological pattern is similar to that in Morocco but was slightly different from the situation in Tunisia where the winter cycle was apparently of lesser importance.     

Costs of cannibalism in the presence of an iridovirus pathogen of Spodoptera frugiperda

Abstract.  1. The costs of cannibalism were examined in larvae of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in the presence of conspecifics infected by a lethal invertebrate iridescent virus (IIV). The hypothesis of a positive correlation between insect density and the likelihood of disease transmission by cannibalism was examined in laboratory microcosms and a field experiment.
2. Transmission was negligible following peroral infection of early instars with purified virus suspensions or following coprophagy of virus-contaminated faeces excreted by infected insects. In contrast, 92% of the insects that predated infected conspecifics acquired the infection and died prior to adult emergence in the laboratory. Diseased larvae were more likely to be victims of cannibalism than healthy larvae.
3. The prevalence of cannibalism was density dependent in laboratory microcosms with a low density (10 healthy insects + one infected insect) or high density (30 healthy insects + one infected insect) of insects, and field experiments performed on maize plants infested with one or four healthy insects + one infected insect.
4. Cannibalism in the presence of virus-infected conspecifics was highly costly to S. frugiperda ; in all cases, insect survival was reduced by between ≈ 50% (laboratory) and ≈ 30% (field) in the presence of the pathogen. Contrary to expectations, the prevalence of disease was not sensitive to density because cannibalism resulted in self-thinning. As infected individuals are consumed and disappear from the population, the prevalence of disease will be determined by the timescale over which transmission can be achieved, and the rate at which individuals that have acquired an infection become themselves infectious to conspecific predators.     

Biotic and abiotic parameters associated with an epizootic of Coelomomyces punctatus in a larval population of the mosquito Anopheles quadrimaculatus.

Biotic and abiotic parameters associated with an epizootic of the fungus Coelomomyces punctatus in larval populations of the mosquito Anopheles quadrimaculatus were investigated for three mosquito breeding seasons (1986-1988) in two adjacent farm ponds in North Carolina. In the first pond, the prevalence of infected larvae averaged 42% (range 0-85%) for collections made weekly from May 1 to November 20, 1986, but larvae did not occur in this pond in 1987. Infection rates in the adjacent pond, sampled during the mosquito breeding seasons of 1987 and 1988, declined from 10.9% (range 0-27.5%) in 1987 to 2.5% (range 0-14.2%) in 1988. Correlation analyses between the number of female copepods and fungal infection rates in sentinel mosquitoes were significant (P < 0.01) for Acanthocyclops robustus but insignificant for eight other species. Infections obtained in sentinel larvae placed in the ponds for 3 hr intervals indicated that C. punctatus infected larvae around sundown. Infection rates for field-collected larvae increased with the stage of larval development. However, experiments with sentinel larvae showed that early instars were more susceptible to infection than later instars, suggesting that the higher infection rates in late instars resulted from individual larvae being infected by two or more zygotes during larval development. Standard multiple regression analyses, used to determine the relationship between seasonal infection rates and water chemistry, weather variables, and the abundance of early and late instar larvae, showed that the abundance of late instars was the only independent variable common to linear models. The models only accounted for 20 and 9% of the variation in larval infection rates for 1987 and 1988, respectively. These results indicate that of the parameters examined, the seasonal abundance of the copepod, A. robustus, was the most important factor (or variable) correlated with the prevalence of mosquito infection.     

Importance of the wild boar in the epidemiology of wild trichinellosis in Piedmont and Liguria

Muscle samples from 1,508 wild boars (Sus scrofa) harvested in Piedmont and Liguria between 1987 and 1990 were examined for larvae of Trichinella sp. by trichinelloscopy and peptic digestion. No wild boar was infected, though trichinellosis was present in foxes (Vulpes vulpes) from the same areas (14 positives out of 608) with the highest prevalence in the mountain range (25.0%). Infection was also not found in 40 stone martens, 5 badgers and 3 stoats. Five vulpine isolates were identified as belonging to T3 zymodeme. These results show that free-ranging wild boars, although being a source of trichinellosis infection for man in Italy (9.2% of the 584 cases diagnosed since 1961), have no significance in maintaining the sylvatic cycle of this parasite in the study area. The data agree with the low infectivity of Italian strains of fox origin for swine seen in the experimental infections carried out so far.     

Serological response of cats to experimental Besnoitia darlingi and Besnoitia neotomofelis infections and prevalence of antibodies to these parasites in cats from Virginia and Pennsylvania

Besnoitia darlingi and Besnoitia neotomofelis are cyst-forming tissue apicomplexan parasites that use domestic cats (Felis domesticus) as definitive hosts and opossums (Didelphis virginiana ) and Southern Plains woodrats (Neotoma micropus) as intermediate hosts, respectively. Nothing is known about the prevalence of B. darlingi or B. neotomofelis in cats from the United States. Besnoitia darlingi infections have been reported in naturally infected opossums from many states in the United States, and B. neotomofelis infections have been reported from Southern Plains woodrats from Texas, but naturally infected cats have not been identified. The present study examined the IgG antibody response of cats to experimental infection (B. darlingi n = 1 cat; B. neotomofelis n = 3 cats). Samples from these cats were used to develop an indirect immunofluorescent antibody test (IFAT), which was then used to examine seroprevalence of IgG antibodies to tachyzoites of B. darlingi and B. neotomofelis in a population of domestic cats from Virginia (N = 232 cats) and Pennsylvania (N = 209). The serum from cats inoculated with B. darlingi or B. neotomofelis cross-reacted with each other's tachyzoites. The titers to heterologous tachyzoites were 1 to 3 dilutions lower than to homologous tachyzoites. Sera from B. darlingi- or B. neotomofelis-infected cats did not react with tachyzoites of Toxoplasma gondii or Neospora caninum or merozoites of Sarcocystis neurona using the IFAT. Antibodies to B. darlingi were found in 14% and 2% of cats from Virginia and Pennsylvania, respectively. Antibodies to B. neotomofelis were found in 5% and 4% of cats from Virginia and Pennsylvania, respectively. Nine cats from Virginia and 1 cat from Pennsylvania were positive for both.     

Sylvatic trichinellosis in southwestern Spain

The epidemiology of Trichinella spp. in their main sylvatic hosts, wild boar (Sus scrofa ferus and red fox (Vulpes vulpes), in Extremadura (southwestern Spain) was studied. We examined 88 Trichinella spp.-positive wild boar muscle-tissue samples from a total of 29,333 killed animals, referred to the Veterinary Parasitology Department (University of Extremadura, Spain) by the Extremadura Veterinary Service. Additionally, 227 red foxes killed during the hunting season and thus not subject to veterinary controls were examined for trichinellosis. Trichinella spp. larvae were found in six (3%) of the red foxes. All samples were examined using direct diagnostic techniques, including trichinoscopy and artificial digestion. The mean intensity of infection was 74.8 larvae/g (LPG) of muscle tissue in wild boars, compared to 30.6 LPG in foxes. Trichinella spiralis (sensu stricto) predominated over T. britovi in wild boars. Random amplified polymorphic DNA (RAPD) and alloenzyme typing showed that 74% of infected wild boars had only T. spiralis, 21% had only T. britovi, and 5% showed mixed infections. In contrast, 33% of infected foxes were infected only with T. spiralis, while 67% had T. britovi, suggesting a clear predominance of the latter in foxes. We suspect the existence of a paranthropic or sylvatic cycle in large areas of this region; given the ease of transfer between sylvatic and domestic or semi-domestic animals, this implies a high epidemiological risk.     

Quantifying horizontal transmission of Nosema lymantriae, a microsporidian pathogen of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in field cage studies

Nosema lymantriae is a microsporidian pathogen of the gypsy moth, Lymantria dispar that has been documented to be at least partially responsible for the collapse of L. dispar outbreak populations in Europe. To quantify horizontal transmission of this pathogen under field conditions we performed caged-tree experiments that varied (1) the density of the pathogen through the introduction of laboratory-infected larvae, and (2) the total time that susceptible (test) larvae were exposed to these infected larvae. The time frame of the experiments extended from the early phase of colonization of the target tissues by the microsporidium to the onset of pathogen-induced mortality or pupation of test larvae. Upon termination of each experiment, the prevalence of infection in test larvae was evaluated. In the experiments performed over a range of pathogen densities, infection of test larvae increased with increasing density of inoculated larvae, from 14.2 ± 3.5% at density of 10 inoculated per 100 larvae to 36.7 ± 5.7% at 30 inoculated per 100 larvae. At higher densities, percent infection in test larvae appeared to level off (35.7 ± 5.5% at 50 inoculated per 100 larvae). When larval exposure to the pathogen was varied, transmission of N. lymantriae did not occur within the first 15 d post-inoculation (dpi) (11 d post-exposure of test larvae to inoculated larvae). We found the first infected test larvae in samples taken 20 dpi (16 d post-exposure). Transmission increased over time; in the cages sampled 25 dpi (21 d post-exposure), Nosema prevalence in test larvae ranged from 20.6% to 39.2%.     

Vertical transmission of Nosema fumiferanae (Microsporidia: Nosematidae) and consequences for distribution, post-diapause emergence and dispersal of second-instar larvae of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

We examined vertical transmission of Nosema fumiferanae in the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), and how it affects overwintering distribution and survival and spring emergence and dispersal of second-instar larvae in outbreak populations. Females containing 5.0 x 10(5) spores or more consistently produced 100% infected progeny. Transmission efficiency was still 50% at burdens as low as 0.2 x 10(5) spores per moth. Infection intensity in offspring increased with maternal spore load but became highly variable above 25 x 10(5) spores per female. Nosema multiplied in second instars for at least 1 month after they entered dormancy, regardless of temperature (2 degrees C versus 21 degrees C). Infection did not affect the distribution of overwintering larvae in a white spruce canopy. Dormancy survival between late-summer and the following spring was lower in families from infected females and was negatively correlated with larval infection intensity. Infection delayed larval emergence from hibernacula in the spring and resulted in delayed dispersal of emerged larvae, at least when parasite prevalence and infection intensities were high. Infected larvae were less successful in establishing feeding sites after dispersal. Our results underscore the potential of Nosema infection to negatively affect processes early in the budworm life cycle.     

Larval Mortality Factors of <Emphasis Type="Italic">Spodoptera Littoralis</Emphasis> in the Azores

Mortality among larval developmental stages of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), was determined by weekly sampling on weeds in a pasture on São Miguel Island (Azores, Portugal), from August to December, over a 3-year period (1999–2001). In all the years surveyed, larvae of S. littoralis usually appeared in pastures after the third week of August, with higher abundances in September and the beginning of October. Three different factors causing larval mortality were identified: one fungal pathogen, Furia virescens (Thaxter) Humber (Zygomycetes: Entomophthoraceae), two nucleopolyhedroviruses and one larval parasitoid, Meteorus communis (Cresson) (Hymenoptera: Braconidae). The percentages of dead larvae infected by virus or fungus were significantly higher than the other causes of mortality, regardless of the year. Furthermore, the percentage of larvae that died due to virus contamination was generally higher than the percentage of larvae infected by fungus. Significant correlations between the environmental factors and the percentage of larvae infected by virus or by fungus, were only observed during 2001. In 2001, the prevalence of fungal infection was negatively correlated with that of viral infection although prevalences of these two agents were positively correlated in both 1999 and 2000. These results show that virus and fungus are potential biological control agents for S. littoralis in Azores.     

Amplification of tick-borne encephalitis virus infection during co-feeding of ticks

Abstract. Following engorgement of Rhipicephalus appendiculatus larvae on guinea-pigs infected with tick-borne encephalitis (TBE) virus, none of the engorged larvae or emergent nymphs contained detectable infectious virus. However, one of twelve pools, each containing three of the unfed nymphs, was positive when screened by polymerase chain reaction (PCR), indicating a low prevalence of TBE virus infection in the unfed nymphs. After engorgement of the nymphs on four uninfected guinea-pigs, 19/24 (79%) fed nymphs from one guinea-pig and 4/25 (16%) fed nymphs from a second guinea-pig were infected; all the ticks examined from the other two guinea-pigs were uninfected. The results suggest that TBE virus was transmitted from a low proportion of infected nymphs (infected as larvae) to uninfected nymphs as they fed together on an uninfected guinea-pig. Such amplification of the initial infection, at the population level, could play an important role in maintaining TBE virus infections in nature, particularly if there is a low level of vertical transmission from one tick generation to the next.     

Larvae of Contracaecum sp. among inshore fish species of southwestern Australia

Larval nematode infections were investigated in 236 fish from 17 estuarine and near-shore species in southwestern Australia. Larvae of the genus Contracaecum were found in 4 species of fish (Acanthopagrus butcheri, Sillaginodes punctata, Mugil cephalus and Aldrichetta forsteri). The prevalence and intensity of infection was highest in the 2 species of mullet: 81% infected and 9.8 +/- 1.5 larvae fish(-1) for M. cephalus; 100% and 12.7 +/- 3.7 larvae fish(-1) for A. forsteri. There was no evidence of post-mortem migration of worms from the visceral organs to the musculature of the fish.     

Fecal counts of lungworm larvae and reproductive effort in bighorn sheep, Ovis canadensis

Because parasite resistance and reproduction require metabolic resources, life-history models predict a tradeoff between current reproduction and parasite load. These tradeoffs have been widely studied in birds, but few studies have been conducted on mammals. We monitored lungworm ( Protostrongylus spp.) larvae counts in bighorn sheep ( Ovis canadensis ) over four years to examine how individual differences in fecal output of lungworm larvae (LPG) by yearlings and adults were affected by season, sex, body mass, age and reproductive effort. We also compared lamb mass at six months and LPG. Overall, we found that LPG varies seasonally, peaking in females prior to lambing and in males during the rut. Age had no effect on LPG for either sex. During autumn, we found no effect of age or mass on LPG for sheep one year and older. Lamb body size or sex did not affect LPG. Females that weaned a lamb had higher counts than females that did not produce a lamb or females whose lamb died during summer. For rams, social rank and testosterone levels were not related to LPG but LPG increased with time spent searching for estrous ewes during the rut. Our results suggest a tradeoff between parasite resistance and reproductive effort in bighorn sheep of both sexes.     

The role of volunteer potatoes in the spread of potato virus YN in ware crops of cv. Record

Surveys were made for the presence of potato virus Y (PVY) in the planted seed and harvested tubers in ware potato crops of cv. Record grown at three sites in England in 1994 (survey 1) and seven sites in 1995 (survey 2). PVY was not found in samples of planted seed, but high levels of infection were found in many, but not all, harvested crops. However, plants of volunteer potatoes (VP) (i.e. plants arising from tubers or true seed derived from previous crops and surviving in the soil) were frequently found to be infected. Infection in tubers harvested from crops in the first survey ranged from 2–52%. In 1995, VP were collected from two of the three English sites where potato crops had been grown the previous season and also from a site in Scotland where PVY infection in an experimental crop of cv. Record had been monitored in 1994. The percentages of infected VP ranged from 2–54%. PVY^N was the predominant strain found in sampled VP, with only two plants (out of 300 infected) containing PVY^O. In the second survey, VP were assessed within the 1995 ware crops and were found at four sites, at which they comprised between 4–8% of emerged potato plants. Between 31–93% of VP were infected. Again, PVY^N was the predominant strain with one plant containing PVY^O and another PVY^C (out of 189 infected). A sample of harvested tubers from each site was also tested for PVY. At those sites which had many infected VP, the harvested crop contained a large percentage of infected tubers, ranging from 60–97%. Two sites which had not previously been used for cropping potatoes had no VP and a very low incidence of PVY infection in the harvested tubers (1% and 2%). However, although no VP were found at one site, 31% of harvested tubers were infected, suggesting that alternative inoculum sources may be important.     

Prevalence and abundance of Ixodes pacificus immatures (Acari: Ixodidae) infesting western fence lizards (Sceloporus occidentalis) in northern California: temporal trends and environmental correlates.

The prevalence and abundance of immature Ixodes pacificus ticks on western fence lizards (Sceloporus occidentalis) were examined in relation to time of year, host attributes (i.e., age, gender, and presence or absence of blood parasites), and 5 environmental characteristics, including topographic exposure and ground cover substrate, over a 2-year period in northern California. Lizards were infested with subadult ticks from early March until late July or early August, with peak median numbers of larvae and nymphs recorded in late April and early May of both years. Peak larval and nymphal abundances differed between years. The overall ratio of larvae to nymphs on adult male lizards was low, ranging from 0.80 in 1999 to 2.41 in 2000. Such intensive feeding of nymphs versus larvae on these lizards, which are reservoir-incompetent for Borrelia burgdorferi spirochetes, may explain previous observations of decreasing spirochetal infection prevalence from the nymphal to adult stage in northwestern California. Adult male lizards were more likely to be infested with nymphs and harbored greater abundances of larvae and nymphs than adult females. Lizards uninfected with blood parasites had more nymphs than infected lizards. The measured environmental characteristics could explain only a small percentage of the total variation observed in larval prevalence (22%) and in larval and nymphal abundance (12 and 3%, respectively).     

Aspiculuris tetraptera in wild Mus musculus. Age resistance and acquired immunity.

Wild house mice, naturally infected with Aspiculuris tetraptera were segregated according to their weight into six age groups. The prevalence of infection and the mean worm burden of these mice were studied in the different age groups. The overall prevalence of infection was high (57% or more) in all the groups except the youngest. Mice acquired larvae soon after weaning; the highest larval burdens were reached in juvenile mice and the highest mature worm burdens, a group later, in mature mice. Older mice had fewer larvae and fewer mature worms. The mature worm burdens decreased but relatively slower than the larval burdens. It is suggested that eigher innate or acquired resistance could account for these observations.