Seasonal Fluctuations In Prevalence Research Articles

Seasonal Patterns in the Frequency of Candidatus Liberibacter Asiaticus in Populations of Diaphorina citri (Hemiptera: Psyllidae) in Florida.

Candidatus Liberibacter asiaticus (CLas) is one of the putative causal agents of huanglongbing, which is a serious disease in citrus production. The pathogen is transmitted by Diaphorina citri Kuwayama (Hemiptera: Psyllidae). As an observational study, six groves in central Florida and one grove at the southern tip of Florida were sampled monthly from January 2008 through February 2012 (50 months). The collected psyllids were sorted by sex and abdominal color. Disease prevalence in adults peaked in November, with a minor peak in February. Gray/brown females had the highest prevalence, and blue/green individuals of either sex had the lowest prevalence. CLas prevalence in blue/green females was highly correlated with the prevalence in other sexes and colors. Thus, the underlying causes for seasonal fluctuations in prevalence operated in a similar fashion for all psyllids. The pattern was caused by larger nymphs displacing smaller ones from the optimal feeding sites and immunological robustness in different sex-color morphotypes. Alternative hypotheses were also considered. Improving our understanding of biological interactions and how to sample them will improve management decisions. We agree with other authors that psyllid management is critical year-round.

Seasonal fluctuation of beak and feather disease virus (BFDV) infection in wild Crimson Rosellas (Platycercus elegans)

Understanding patterns of pathogen emergence can help identify mechanisms involved in transmission dynamics. Beak and feather disease virus (BFDV) poses a major threat world-wide to wild and captive parrots. Yet data from wild birds on seasonal fluctuations in prevalence and infection intensity, and thereby the potential high-risk times for virus transmission, have been lacking. We screened wild Crimson Rosellas (Platycercus elegans) for BFDV in blood and cloacal swabs. Prevalence in blood samples and cloacal swabs, as well as viral load varied with Julian date and in blood, were highest after the breeding season. Breeding birds had lower viral load and lower BFDV prevalence in blood than non-breeding birds (10.1% prevalence in breeding vs. 43.2% in non-breeding birds). BFDV prevalence was much higher in younger (<3 years) than older (≥3 years) birds for both blood samples (42.9% vs. 4.5%) and cloacal swabs (56.4% vs. 12.3%). BFDV status in blood and cloacal samples was not correlated within individuals. We show that, at least in P. elegans, BFDV infection seems to occur year-round, with seasonal changes in prevalence and load found in our samples. Our analyses suggest that the seasonal changes were associated primarily with the breeding season. We also discuss age and sex as important predictors of BFDV infection.

Occurrence of microsporidians Glugea hertwigi and Pleistophora ladogensis, in smelt Osmerus eperlanus from two German rivers, North Sea coast.

Monthly samples of smelt Osmerus eperlanus (Linnaeus, 1758) were collected from July 1985 to May 1986, in the river Elbe (Germany), and examined for infections with microsporidians. Two microsporidians were found: Glugea hertwigi Weissenberg, 1911, infecting the digestive tract and Pleistophora ladogenis Voronin, 1978, infecting the skeletal musculature. G. hertwigi infection led to the formation of xenomas, whereas P. ladogensis was characterized by diffuse infections, with the production of macroscopic visible thread-like or oval-shaped infection foci. Development of G. hertwigi in the host cells showed characteristics typical of the genus Glugea. The ultrastructural development of P. ladogensis showed features typical of the genus Pleistophora, without evidence of the production of 2 types of spores. Host reaction consisted of inflammatory tissue surrounding some of the infection foci as well as phagocytosis of spores. G. hertwigi was only found in juvenile smelt (<10 cm in length), whereas P. ladogensis infected smelts from 6 to 26 cm in length. Prevalence increased with fish length to a maximum value of 9.6%. Seasonal fluctuations in prevalence of infection were also found, with the lowest value in the winter months (2.5% in January 1986) and the highest in summer (11.8% in July 1985). The differences in prevalence of infection with fish length and date of sampling were significant. Additionally, samples of smelt caught in April 1986 from the rivers Eider and Ems revealed infections with P. ladogensis in the first river system only.

Seasonal variability of prevalence and occurrence of multiple infections shape the population structure of Crithidia bombi, an intestinal parasite of bumblebees (Bombus spp.)

Ergonomic growth phases of annual social insect societies strongly influence horizontally transmitted parasites. Herein, we focused on the impact of temporal changes in host demography on the population structure of a horizontally transmitted parasite. Seasonal fluctuations in prevalence and the occurrence of multiple infections of the gut parasite Crithidia bombi were analyzed in repeatedly sampled populations of two common bumblebee (Bombus spp.) species. Prevalence of C. bombi was greatest in the middle of the foraging season and coincided with the maximal occurrence of multiple infections. Both decline later in the season. The genetic structure of the parasite population also showed strong seasonal fluctuations with a drastic decline in effective population size and an increase in linkage disequilibrium when infection rates were highest. These effects are mainly attributable to significant changes in parasite allele frequencies leading to selection of specific alleles and increasing the frequency of homozygote genotypes in the middle of the season. Within host, competition between parasite genotypes might explain the observed pattern leading to selection of these alleles, and thus a boost of homozygote genotypes in the middle of the season. Toward the end of the season, selection appears to relax and we observed a recovery in linkage equilibrium, as well as an increase in effective population size. This might be explained by genetic exchange in these trypanosomes in natural populations.

Dynamics of a novel pathogen in an avian host: Mycoplasmal conjunctivitis in house finches

In early 1994, a novel strain of Mycoplasma gallisepticum (MG)—a poultry pathogen with a world-wide distribution—emerged in wild house finches and within 3 years had reached epidemic proportions across their eastern North American range. The ensuing epizootic resulted in a rapid decline of the host population coupled with considerable seasonal fluctuations in prevalence. To understand the dynamics of this disease system, a multi-disciplinary team composed of biologists, veterinarians, microbiologists and mathematical modelers set forth to determine factors driving and influenced by this host–pathogen system. On a broad geographic scale, volunteer observers (“citizen scientists”) collected and reported data used for calculating both host abundance and disease prevalence. The scale at which this monitoring initiative was conducted is unprecedented and it has been an invaluable source of data for researchers at the Cornell Laboratory of Ornithology to track the spread and magnitude of disease both spatially and temporally. At a finer scale, localized and intensive field studies provided data used to quantify the effects of disease on host demographic parameters via capture–mark–recapture modeling, effects of host behavior on disease and vice-versa, and the biological and genetic profiles of birds with known phenotypic characteristics. To balance the field-based component of the study, experiments were conducted with finches held in captivity to describe and quantify the effects of experimental infections on hosts in both individual and social settings. The confluence of these various elements of the investigation provided the foundation for construction of a general compartmentalized epidemiological model of the dynamics of the house finch–MG system. This paper serves several purposes including (i) a basic review of the pathogen, host, and epidemic cycle; (ii) an explanation of our research strategy; (iii) a basic review of results from the diverse multi-disciplinary approaches employed; and (iv) pertinent questions relevant to this and other wildlife disease studies that require further investigation.

Seasonal dynamics of mycoplasmal conjunctivitis in eastern North American house finches

SummaryMycoplasma gallisepticumis an emerging eye disease that spread rapidly among wild house finches (Carpodacus mexicanus) in the eastern United States following initial reports of infected birds in 1994. The hallmark signs of infection have allowed systematic monitoring of disease at both local and continent‐wide scales for more than 7 years since the onset of the epidemic.Using data collected by a network of citizen science volunteers, we examined both long‐term trends and seasonal dynamics of mycoplasmal conjunctivitis in three different climatic regions in eastern North America over a 77‐month period (November 1994–March 2001).Time‐series prevalence data from all three regions suggest that following establishment, marked seasonal fluctuations in prevalence each year were characterized by autumn–winter epidemics (in October and February) and consistent summer declines (with prevalence falling close to zero from May to July).The maximum peak, annual rates of increase and timing of epidemics varied among three geographical locations that were delineated by minimum winter temperatures. Annual autumn prevalence in the South increased more rapidly, and maximum prevalence was nearly three times greater in the South than in the colder North and Central regions.Longer‐term trends showed evidence for multiyear fluctuations in prevalence that were characterized by greater amplitude in the southern region.Finally, monthly estimates of house finch flock sizes derived from a similar citizen science data set showed that winter flock sizes were associated positively with average monthly prevalence in the northern and central regions, although regional differences in flock sizes did not correspond to regional differences in maximum prevalence.This study represents the first evidence of multiyear fluctuations, regional differences and highly predictable annual outbreaks of this recently emerged wildlife pathogen. Several factors associated with house finch life history and behaviour are likely to contribute to temporal and spatial variation in prevalence, including annual changes in host reproduction, social behaviour and environmental effects on host stress or immunocompetence.

Seasonal abundances of Prosomicrocotyla gotoi (Monogenea) and Opecoelus sphaericus (Digenea) from greenlings Hexagrammos otakii in a southern coastal area in Korea

Seasonal fluctuations in prevalence and abundance of Prosomicrocotyla gotoi (Monogenea) and Opecoelus sphaericus (Digenea) infecting greenlings Hexagrammos otakii were investigated in a southern coastal area of Korea from June 1998 to October 1999. P. gotoi was found on the gills of 70 (34.5%) greenlings; 1 to 14 parasites per fish. Prevalence values of P. gotoi ranged from 0% (May 1999) to 61.9% (September 1998). Abundance of P. gotoi sharply increased to a peak in late fall (November), then it declined gradually to May in 1999. O. sphaericus occurred in the intestines of 42 (20.7%) greenlings and ranged from one to eight trematodes per fish. Prevalence values of O. sphaericus ranged from 0% (May, June and July 1999) to 71.4% (October 1998). Abundance of O. sphaericus peaked in October 1998, then remained at a low level. Weak positive correlations were observed between intensities of each parasite species and host body length. The period of peak abundances of both P. gotoi and O. sphaericus infections were well corresponded to the spawning season of greenlings.

Life history of the nematode Rhabdochona hellichi, a parasite of the barbel in the Jihlava River, Czech Republic

From April 1992 until June 1993, the seasonal dynamics of Rhabdochona hellichi (Srámek, 1901) in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 93% and intensity of infection 1-1384 [mean 78] nematodes per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values associated with the parasite's seasonal cycle of maturation. Prevalence was very high (usually 100%) during most months of the year, while lowest values were recorded in August and October. The highest values of mean intensity occurred in April. Both prevalence and mean intensity values increased with the body length of the hosts. The parasite exhibited a distinct annual cycle of maturation with egg-producing females present only from June until August, whereas larvae occurred in barbel mostly from September until April of the next year. Trichopteran (caddis-fly) larvae of the genus Hydropsyche (H. angustipennis and H. pellucidula) were found as natural intermediate hosts of R. hellichi (prevalence 4%, intensity 1-10 nematode larvae). The strictly seasonal maturation of this nematode may be associated with the temperature regime in the locality and seasonal cycles of maturation of its intermediate hosts.

Seasonal occurrence and maturation of Neoechinorhynchus rutili (Acanthocephala) in barbel, Barbus barbus (Pisces), of the Jihlava River, Czech Republic.

From April 1992 until June 1993, the seasonal occurrence and maturation of the acanthocephalan Neoechinorhynchus rutili in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 84% and intensity of infection 1-533 [mean 25] acanthocephalars per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values: prevalence attained 100% in February and March, whereas its lowest value was recorded in July; the lowest values of mean intensity occurred in July-August. Both prevalence and mean intensity values distinctly increased with the body length of hosts. The parasite exhibited a distinct annual maturation cycle when egg-producing females were present mainly in the spring and summer (May-July) and, at a lesser extent, also from December to April of the next year. The seasonal maturation of N. rutili appears to be induced principally by the temperature regimen in the locality. N. rutili cystacanths were recovered from larval Sialis lutaria (Megaloptera) (prevalence 6%).

Occurrence of Contracaecum clavatum Rudolphi in angler-fish ( Lophius piscatorius L.) from the North Irish Sea

Infestation of angler-fish Lophius piscatorius L. with the nematode Contracaecum clavatum Rudolphi was investigated. Of 1621 angler-fish examined from the north Irish Sea, 45.4% harboured Contracaecum, the stomach being the most frequent site of infection. Seasonal fluctuations in prevalence and abundance of Contracaecum were observed, infestation peaking during the winter period, coinciding with maximum feeding activity and dominance of known transport hosts in the diet. Infestation initially increased with age of host, 2- and 3-year-old Lophius being most heavily infected. A decline among older fish is probably related to termination of infection rather than parasite-induced mortality. This is supported by a shift in diet among older angler-fish away from prey which harbour Contracaecum infections.