Distribution patterns of Opisthorchis viverrini within a human community

Parasitology ◽  
1991 ◽  
Vol 103 (1) ◽  
pp. 97-101 ◽  
Author(s):  
M. R. Haswell-Elkins ◽  
D. B. Elkins ◽  
Paiboon Sithithaworn ◽  
Phattara Treesarawat ◽  
Sasithorn Kaewkes
Keyword(s):  
Worm Burden ◽  
Distribution Patterns ◽  
Opisthorchis Viverrini ◽  
Parasite Control ◽  
Intensity Of Infection ◽  
Community Based ◽  
Human Community ◽  
Control Programmes ◽  
Over Dispersion ◽  
Antibody Levels

This paper describes patterns of infection with Opisthorchis viverrini within a human community assessed by egg count, parasite-specific antibody levels and worm burden determined by expulsion chemotherapy. All three measurements increased significantly with age, reaching a plateau in young adults. There were no significant sex-associated differences in the prevalence or intensity of infection, antibody levels, or in the frequency of heavy worm burdens. A striking 81·5% of the total Opisthorchis population and 74% of the total egg output were expelled by the most heavily infected 10% of the humans sampled. This extreme over-dispersion, together with recent findings that hepatobiliary disease frequently accompanies heavy infections, argues that the priority for community-based parasite control programmes should be to maximize treatment and health promotion efforts toward heavily infected individuals.

Opisthorchis viverrini: relationships between egg counts, worms recovered and antibody levels within an endemic community in Northeast Thailand

Parasitology ◽  
1991 ◽  
Vol 102 (2) ◽  
pp. 283-288 ◽  
Author(s):  
D. B. Elkins ◽  
P. Sithithaworn ◽  
M. Haswell-Elkins ◽  
S. Kaewkes ◽  
P. Awacharagan ◽  
...  
Keyword(s):  
Relative Intensity ◽  
Worm Burden ◽  
Egg Production ◽  
Epidemiological Studies ◽  
Opisthorchis Viverrini ◽  
Northeast Thailand ◽  
Intensity Of Infection ◽  
Antibody Levels ◽  
Serum Igg Levels ◽  
Total Worm Burden

SUMMARYThree techniques for estimating the intensity of Opisthorchis viverrini infection in individuals from a Northeast That community are compared. Egg counts were determined using a quantitative formalin/ethyl acetate technique, worm burdens were estimated by expulsion chemotherapy and antibody levels were measured by ELISA. Log-transformed worm and egg counts were closely correlated (r = 0·80), suggesting that both measurements provide good assessments of relative intensity of infection. However, no Opisthorchis worms were recovered from 34 people with high egg counts; probably due to problems with the expulsion technique in some individuals. Examination of egg production per fluke indicated that each fluke contributed an average of 180 eggs per gram (epg) of faeces and fecundity was negatively associated with total worm burden. Serum IgG levels correlated significantly with Opisthorchis egg count (r = 0·61) at two independent assessments. Although significant associations were observed between antibody levels and echinostome infection, analysis suggested that these reflected independent associations between these two variables and Opisthorchis infection and age. We conclude that all three measurements are useful for epidemiological studies.

Distribution of Ascaris suum in experimentally and naturally infected pigs and comparison with Ascaris lumbricoides infections in humans

Parasitology ◽  
1998 ◽  
Vol 117 (6) ◽  
pp. 589-596 ◽  
Author(s):  
J. BOES ◽  
G. F. MEDLEY ◽  
L. ERIKSEN ◽  
A. ROEPSTORFF ◽  
P. NANSEN
Keyword(s):  
Worm Burden ◽  
Ascaris Suum ◽  
Natural Infection ◽  
Distribution Patterns ◽  
Human Populations ◽  
Suitable Model ◽  
Post Mortem ◽  
Intensity Of Infection ◽  
Low Intensity ◽  
Low Prevalence

This paper describes the distribution of Ascaris suum in experimentally and naturally infected pigs, and offers a comparison with A. lumbricoides infections in humans. In the first study, worms were recovered post-mortem from a group of 38 pigs that had been trickle inoculated with 10000 infective A. suum eggs twice weekly for 12 weeks. In the second study, worms were collected from a group of 49 pigs that had been kept on a pasture contaminated with infective A. suum eggs for 10 weeks, after which they received treatment with an anthelmintic; they then were turned out on the same pasture for a second 10-week period before slaughter. The worm burdens of the naturally infected pigs were recorded both at treatment and post-mortem. Mean worm counts were similar at all occasions but the prevalence of infection was higher in the trickle infected and naturally reinfected pigs. Furthermore, the prevalence in naturally infected pigs increased significantly over the study period. Worm burden distributions in all groups were heavily overdispersed, but the distribution patterns differed significantly between groups: lower exposure (initial natural infection) gave a low prevalence and an almost uniform distribution of worm burdens among infected hosts. Continued or higher exposure (trickle and natural reinfection) resulted in increased prevalence and a reduction in the proportion of hosts with increasing worm load. A positive correlation was found between initial and reinfection worm burdens in the naturally infected pig population, suggesting that individual pigs are predisposed to a high or low intensity of infection. The prevalence and intensity as well as the distribution observed for A. suum infection in pigs were comparable to those reported for A. lumbricoides in endemic areas, and there is evidence for predisposition to A. suum in pigs, with an estimated correlation coefficient similar to that found in humans. It is concluded that A. suum infections in pigs are a suitable model to study the population dynamics of A. lumbricoides in human populations.

scholarly journals The development and validation of an age-structured model for the evaluation of disease control strategies for intestinal helminths

Parasitology ◽  
1994 ◽  
Vol 109 (3) ◽  
pp. 389-396 ◽  
Author(s):  
M. S. Chan ◽  
H. L. Guyatt ◽  
D. A. P. Bundy ◽  
G. F. Medley
Keyword(s):  
Helminth Infection ◽  
Control Strategies ◽  
Intestinal Helminth ◽  
Intestinal Helminths ◽  
Parasite Control ◽  
Age Related ◽  
Control Programmes ◽  
Age Structured ◽  
Development And Validation ◽  
Age Structured Model

SummaryEpidemiological modelling can be a useful tool for the evaluation of parasite control strategies. An age-structured epidemiological model of intestinal helminth dynamics is developed. This model includes the explicit representation of changing worm distributions between hosts as a result of treatment, and estimates the morbidity due to heavy infections. The model is used to evaluate the effectiveness of different programmes of age-targeted community chemotherapy in reducing the amount of morbidity due to helminth infection. The magnitude of age-related heterogeneities is found to be very important in determining the results of age-targeted treatment programmes. The model was verified using field data from control programmes for Ascaris lumbricoides and Trichuris trichiura, and was found to provide accurate predictions of prevalence and mean intensities of infection during and following different control regimes.

The regulation ofOstertagia ostertagipopulations in calves: density-dependent control of fecundity

Parasitology ◽  
1987 ◽  
Vol 95 (2) ◽  
pp. 373-388 ◽  
Author(s):  
G. Smith ◽  
B. T. Grenfell ◽  
R. M. Anderson
Keyword(s):  
Worm Burden ◽  
Egg Production ◽  
Inverse Function ◽  
Single Infection ◽  
Intensity Of Infection ◽  
Density Dependent ◽  
Helminth Infections ◽  
Model Predictions ◽  
Initial Peak ◽  
Infection Experiments

SUMMARYThe decline in faecal egg counts, characteristic of calves which have been experimentally infected withOstertagia ostertagi, is analysed using a mathematical model in which parasite fecundity is assumed to be an inverse function of both the duration and intensity of infection. The model incorporates a description of the frequency distribution of mature parasites between hosts (which is less over-dispersed than is usual for many other helminth infections). The model provides a good overall description of the decline in faecal egg production observed during trickle and single infection experiments. The main discrepancy between a comparison of the model predictions and the results of the most detailed available series of trickle infection experiments occurs at the initial peak of egg production. The magnitude of this difference appears to be related to the worm burden at the peak of egg production. The possible mechanisms underlying density-dependent regulation of the fecundity ofO. ostertagiaare discussed.

The evaluation of potential global morbidity attributable to intestinal nematode infections

Parasitology ◽  
1994 ◽  
Vol 109 (3) ◽  
pp. 373-387 ◽  
Author(s):  
M. S. Chan ◽  
G. F. Medley ◽  
D. Jamison ◽  
D. A. P. Bundy
Keyword(s):  
Spatial Heterogeneity ◽  
Ascaris Lumbricoides ◽  
Worm Burden ◽  
Disease Burden ◽  
Trichuris Trichiura ◽  
Intensity Of Infection ◽  
Intestinal Nematode ◽  
Prevalence Estimates ◽  
Global Disease Burden

SummaryThis paper presents a method of estimating the potential global morbidity due to human intestinal nematode infections (Ascaris lumbricoides, Trichuris trichiura and hookworms), based on the observed prevalence of infection. The method relies on the observed relationships between prevalence and intensity of infection, and between worm burden and potential morbidity. This approach is shown to be sensitive to the precision of the original prevalence estimates and, in particular, to the degree of spatial heterogeneity in levels of infection. The estimates presented here indicate that several tens of millions of children are likely to suffer developmental consequences from infection, and suggest that the global disease burden of geohelminthiasis may be significantly greater than was supposed.

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