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PubMed1996

Onchocerca fasciata: histochemical demonstration of succinate and NADH dehydrogenase.

The activities of selected enzymes of the respiratory chain system in Onchocerca fasciata (Filarioidea: Onchocercidae) have been investigated histochemically. Thus, the localization and distributions of NADH dehydrogenase (EC 1.6.99.3), succinate dehydrogenase (SDH) (EC 1.3.99.1) and cytochrome oxidase (EC 1.9.3.1) were investigated in various tissues of the adult female worm by employing MTT, Nitro BT (dehydrogenases) and DAB (cytochrome oxidase). Different tissues varied considerably in their enzymatic activities. The hypodermis and reproductive tissues showed strong and identical localization of NADH and SDH dehydrogenase activities reflecting high metabolic rates. Little or no dehydrogenase activities were observed in the intestine and cuticle. In contrast to the two dehyrogenases, no activity was observed for cytochrome oxidase in any of the tissues in adult or embryonic stages of the worm. The significance of these results with respect to the energy metabolism of the worm is discussed. It is suggested that O. fasciata lacks a classical, mammalian-type respiratory pathway and that oxidative phosphorylation is of no importance as an energy generating pathway in this essentially anaerobic parasite.

Animals↗
PubMed1993

Viability of Onchocerca volvulus in vitro.

The use of a selective schedule of tests to identify a viable population of isolated adult Onchocerca volvulus (Nematoda: Filarioidea) has been investigated in a large worm population. The study was initiated to develop methodology appropriate to test new candidate macrofilaricides for their in vitro activity against O. volvulus. After removal from the host the viability of isolated intact parasites was estimated by assessing the motility indices of male worms, and the colorimetric quantification of the reduction of the bioreducible tetrazolium reagent XTT and lactate output by female worms. Additionally the motility of whole females and the movement of inner organs of female worms were scored quantitatively. These response parameters were used to sort the adult worms into viability groups at the start of the in vitro culture. The adult worms were then observed for 6 days and viability was assessed regularly during the culture period. At the end of the culture period, the reduction of the water-insoluble tetrazolium reagent MTT was used to determine the formazan formed by the entire male and female worms. The response parameters used at the start of the culture proved to be highly predictive for detecting viable and non-viable adult worms. In the group of worms selected as 'viable' around 70% kept their motility and metabolic activity at a high level until the end of the culture compared to the initial level. In contrast, none of the female worms and only 13% of the male worms categorized as 'poorly viable' demonstrated a motility index or metabolic level at the end of the culture period that was comparable to that of the worms in the 'viable' groups. For female worms the lactate output correlated significantly with weight whereas no correlation was seen between MTT reduction and weight.

Animals↗
PubMed1993

Filariasis: nutritional interactions in human and animal hosts.

Vector-borne nematodes of the Order Filarioidea produce chronic, debilitating human infections which are usually nonfatal but are associated with a high degree of severe morbidity. Weight loss often accompanies infection and is probably a consequence of the increased energy cost associated with filarial fever, lymphangitis and lymphadenitis. In onchocerciasis, weight loss is associated with heavy worm loads as assessed by abundant nodules and large numbers of skin microfilariae. Experimental infections using rodent filariae have confirmed these observations and have also shown that low protein diets render hosts more susceptible to infection; nevertheless, parasite growth and embryogenesis is retarded in stunted female worms from protein deficient animals. In the absence of appropriate evidence, studies of experimental filariasis suggest that human protein-energy malnutrition may delay the development of stage-specific acquired immunity with a corresponding prolongation of patency. Epidemiological and experimental evidence shows that filarial nematodes acquire certain nutrients directly from their hosts. Of major importance in this respect is vitamin A which is taken up preferentially by human and rodent filariae; in humans, symptoms of hypovitaminosis A often accompany infection and could be an aggravating factor in onchocerciasis. Filariae also appear to require other specific nutrients such as iodine, thiamine and pyridoxine; dietary levels of these nutrients affect the host-parasite relationships in filariasis and pyridoxine seems to be of particular importance in this respect. Filarial parasites obviously compete with their hosts for available nutrients and, in the real world, human filariasis is often associated with a deterioration in the plane of nutrition of infected individuals.

Adult↗
PubMed2001

The New World filarial genus Molinema Freitas & Lent, 1939 (Nematoda: Onchocercidae), with a description of four new species parasitic in the Echimyidae (Rodentia).

Four new species of Molinema (Filarioidea: Onchocercidae), parasites of echimyid rodents in South America, are described: M. algardneri n. sp. from Proechimys amphichoricus, M. barbarae n. sp. from P. cayennensis, both in Venezuela (Rio Negro and Cerro La Neblina, respectively), M. peruviensis n. sp. from P. steerei in Peru (lower Urubamba), and M. nattereri n. sp. (= Filaria diacantha Molin, 1858 pro parte) from Echimys ? didelphoides (= Loncheres rufa) in Brazil (Matto Grosso). They differ from each other and from the previously described species in the following characters: flat or concave head, cephalic ratio (distance between cephalic papillae in median view/lateral view), size and shape of the buccal capsule, length of the oesophagus, cuticular ornamentation of the female body, length of the ovijector, thick or slim female tail, area rugosa, long or short filament in the left spicule, heel in the right spicule, respective position of postcloacal papilla pairs 5 and 6, shape of the caudal lappets, terminal point present or absent, and the microfilariae. Molinema, which belongs to the worldwide Dipetalonema line, is distributed in two of the ten families of the Caviomorpha (South American Hystrichognathi have extended their distribution in South America since the early Oligocene). Nine species are parasitic in the Echimyidae (suborder Caviida); they have a short oesophagus and a complete or reduced set of precloacal papillae (four or three pairs). Two species are parasitic in the Erethizontidae (Erethizontida) and might be more primitive in having a well-developed oesophagus. However, the type-species M. diacantha, of which a female specimen was studied, has a large buccal capsule and has evolved concave head, while M. arbuta has a reduced buccal capsule and primitive flat head. This last species is a parasite of a Nearctic porcupine and probably represents a small line of Molinema which migrated to the north with its hosts when communications were established between the two American continents 3 mya (Pleistocene). M. sprenti, the unique parasite of the Castoridae in North America, is considered to be derived from this group by capture.

Animals↗
PubMed2002

Impact of untreated bednets on prevalence of Wuchereria bancrofti transmitted by Anopheles farauti in Papua New Guinea.

Despite the growing evidence that insecticide-treated mosquito nets reduce malaria morbidity and mortality in a variety of epidemiological conditions, their value against lymphatic filariasis infection and disease is yet to be established. The impact of untreated bednets on the prevalence of Wuchereria bancrofti (Cobbold) (Nematoda: Filarioidea) infection and disease was investigated on Bagabag island in Papua New Guinea, where both malaria and filariasis are transmitted by the same vector mosquitoes of the Anopheles punctulatus Dönitz group (Diptera: Culicidae). Community-wide surveys were conducted recording demographic characteristics including bednet usage. Physical examinations for hydrocoele and lymphoedema were performed and blood samples assessed for filarial and malaria parasites. Mosquitoes were sampled using the all-night landing catch method and individually dissected to determine W. bancrofti infection and infective rates. Bednet usage among residents was 61% and the mean age of users (25.6 years) was similar to non-users (22.5 years). Anopheles farauti Laveran was the only species were found to contain filarial larvae: 2.7% infected (all stages), 0.5% infective (L3). The overall W. bancrofti microfilaraemia and antigenaemia rates were 28.5% and 53.1%, respectively. Bednet users had lower prevalence of W. bancrofti microfilaraemia, antigenaemia and hydrocoele rates than non-users. In comparison, untreated bednets had no effect on the prevalence and intensity of Plasmodium falciparum and P. vivax infections. The impact of bednet usage on rates of microfilaraemia and antigenaemia remained significant even when confounding factors such as age, location and sex were taken into account, suggesting that untreated bednets protect against W. bancrofti infection.

Adult↗
PubMed2002

Transmission dynamics of lymphatic filariasis: density-dependence in the uptake of Wuchereria bancrofti microfilariae by vector mosquitoes.

Gaining a better understanding of parasite infection dynamics in the vector mosquito (Diptera: Culicidae) population is central to improving knowledge regarding the transmission, persistence and hence control of lymphatic filariasis. Here, we use data on mosquito feeding experiments collated from the published literature to examine the available evidence regarding the functional form of the first component of this parasite-vector relationship for Wuchereria bancrofti (Filarioidea: Onchocercidae) causing Bancroftian filariasis, i.e. the rate of microfilariae (mf) uptake from the blood of infected humans by the feeding mosquito vector. Using a simple logarithmic regression model for describing the observed relationships between the mean numbers of mf ingested per mosquito and parasite load in humans in each study, and a linear mixed-effects meta-analytical framework for synthesizing the observed regressions across studies, we show here for the first time clear evidence for the existence of density-dependence in this process for all the three major filariasis transmitting mosquito vectors. An important finding of this study is that this regulation of mf uptake also varies significantly between the vector genera, being weakest in Culex, comparatively stronger in Aedes and most severe and occurring at significantly lower human mf loads in Anopheles mosquitoes. The analysis of the corresponding mf uptake prevalence data has further highlighted how density-dependence in mf uptake may influence the observed distributions of mf in vector populations. These results show that whereas strong regulation of mf uptake, especially when it leads to saturation in uptake at low human parasite intensities, can lead to static distributions of mf per mosquito with host parasite intensity, a weaker regulation of mf ingestion can give rise to changes in both mean mf loads and in the frequency distribution of parasites/mosquito with increasing human parasite intensity. These findings highlight the importance of considering local vector infection dynamics when attempting to predict the impacts of community-based filariasis control. They also emphasize the value of developing and applying robust meta-analytic methods for estimating functional relationships regarding parasitic infection from population ecological data.

Animals↗
PubMed2002

Isoenzyme variation in Aedes aegypti correlated with Dirofilaria immitis infectability.

From the Vero Beach strain of the mosquito Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae), substrains were selected for susceptibility (SS) and refractoriness (RR) to the dog heartworm Dirofilaria immitis (Leidy) (Filarioidea: Onchocercidae). These two lines and their reciprocal F1 hybrids were analysed for genetic variation at 14 enzyme loci, using polyacrylamide gel electrophoresis. Six of the enzyme loci showed variation (sample size 48 alleles/locus/line). Three of these were monomorphic in the refractory line but polymorphic in the susceptible, i.e. aconitase hydratase (Acoh), isocitrate dehydrogenase-1 (Idh-1) and phosphoglucomutase (Pgm). The other three loci, glucose-6-phosphate isomerase (Gpi), hexokinase-1 (Hk-1) and isocitrate dehydrogenase-2 (Idh-2), were polymorphic in both SS and RR lines and their hybrids. At two loci (Hk-1, Pgm) three alleles were detected, whereas the other polymorphic loci had only two alleles. For Hk-1, the most frequent allele was Hk-1(80) (0.563) in refractory and Hk-1(100) in the susceptible (0.521) and F1 hybrids. For Pgm the most frequent alleles were Pgm125 in the susceptible line (0.646) and Pgm100 in the F1 hybrids (0.563 and 0.604) and refractory line (1.000). The mean observed heterozygosity (Ho), the mean Hardy-Weinberg expected heterozygosity (He) and the mean number of alleles per locus in the refractory line were lower, but not significantly so, than in the susceptible line and their reciprocal F1 hybrids; the proportion of polymorphic loci was significantly lower in the refractory than in the susceptible line and their F1 hybrids. Within both lines all polymorphisms were in Hardy-Weinberg equilibrium, whereas significant departures from predicted frequencies were observed in SS x RR hybrids at four polymorphic loci (Acoh, Gpi, Hk-1, Pgm) and at three polymorphic loci (Acoh, Hk-1, Pgm) in RR x SS hybrids. The average Nei's and modified Rogers' genetic distances between the lines were 0.024 and 0.139, respectively. These electrophoretic data show that the refractory line (putatively lacking fi allele) can be distinguished from the susceptible line (fi/fi) and their hybrids (heterozygous fi) by isozyme marker frequencies, but it remains to be seen whether this difference is causal or chance linkage. In any case, this model system of Ae. aegypti/D. immitis provides opportunities to better understand and manipulate the molecular biology of filariasis transmission.

Aedes↗
PubMed1991

[Human dirofilariasis in Italy].

Since 1971, at the Laboratory of Parasitology, Faculty of Veterinary Medicine, University of Bologna, 30 cases of human dirofilariasis were observed out of the 101 cases reported in Italy. The causative agent was identified in nearly all the cases as Dirofilaria repens (Nematoda, Filarioidea) a parasite relatively common in the dog in Italy. 23 cases were localized in the subcutaneous tissue, 4 in the submucosa and 3 in the lungs. In the majority of the cases the diagnosis had been misinterpreted, the lesions being first seen as malignant or benign tumours or foreign-body granuloma. The parasite was histologically recognized. In 3 cases the parasite could be extracted intact from the nodule. The authors believe that human dirofilariasis is more frequent than reported by the relevant scientific literature in that many cases are likely to recover spontaneously while others would remain undetected.

Dirofilariasis↗
PubMed2006

Transmission dynamics of lymphatic filariasis: vector-specific density dependence in the development of Wuchereria bancrofti infective larvae in mosquitoes.

The principles of meta-analysis developed in a previous study were extended to investigate the process of Wuchereria bancrofti (Cobbold) (Filarioidea: Onchocercidae) infection in mosquito (Diptera: Culicidae) hosts, focusing specifically on the functional forms and strength of density dependence in the development of ingested microfilariae (mf) to infective (third instar) larvae (L3). Mathematical models describing observed mf-L3 functional responses for each of the major three parasite-transmitting vector genera, Aedes, Culex and Anopheles mosquitoes, were fitted to paired mf-L3 data collated from all available studies in the published literature. Model parameters were estimated and compared by deriving and applying a data synthetic framework, based on applying a non-linear weighted regression model for fitting mathematical models to multistudy data. The results confirm previous findings of the existence of significant between-genera differences in the mf-L3 development relationship, particularly with regard to the occurrence of limitation in Culex mosquitoes and facilitation in Aedes and Anopheles mosquitoes. New and unexpected findings regarding L3 development from ingested mf were discovered as follows: (1) for Culex, overcompensation in L3 development at higher intensities of mf (or a peaked mf-L3 functional response) was detected; (2) for Aedes mosquitoes, facilitation (with an apparent asymptotic constraint on L3 development at high mf densities) was shown to be the major process governing L3 development, and (3) for Anopheles, a stronger facilitation type of response with no apparent saturation in L3 development appears to govern L3 output from ingested mf. These results yield major new insights regarding filarial vector infection dynamics and their potential impacts on parasite control, and demonstrate the efficacy of employing a data synthetic approach to reveal and estimate parasitic infection processes in host populations.

Aedes↗
PubMed1982

Nondevelopment of Wuchereria bancrofti in nude (congenitally athymic) mice.

Infective larvae of Wuchereria bancrofti (Nematoda: Filarioidea) were harvested from Aedes aegypti mosquitoes fed in vitro on microfilaremic blood of Haitian volunteers. Larvae were inoculated either into the subcutaneous tissue (SC) or peritoneal cavity (IP) of congenitally athymic (nude) mice, C3H/HeN (nu/nu). Initially 15 male and two female mice received larval doses from 38-180, and necropsy was done between 11 and 75 days post-inoculation. No worms were found at necropsy. Four additional male mice given 75 larvae each were also injected daily with 0.3 ml of normal human serum, but again no worms were recovered at necropsy on days 13 through 17. Given the severe nature of the nude immunodeficiency, it seems unlikely that the total failure of W. bancrofti to develop in nude mice results from a T cell-dependent immune response. Perhaps either non-immune mechanisms actively destroy larvae or the mouse lacks a factor(s) essential for parasite development, but not found in human serum. In any case, the thymic independence of resistance to W. bancrofti is clearly unlike that shown to the related filaria, Brugia pahangi.

Animals↗
PubMed1984

Morphogenesis of larval Onchocerca volvulus in the Panamanian black fly, Simulium quadrivittatum.

Simulium quadrivittatum Loew (Diptera: Simuliidae), a man-biting black fly, was shown, for the first time, to be capable of supporting development of Onchocerca volvulus Leuckart (Nematoda: Filarioidea) from microfilariae to third-stage (infective) larvae. The black flies were collected in Chiriqui Province, Panama and transported alive to Guatemala, where they were allowed to feed on a human subject infected with O. volvulus. Samples of these flies were dissected over an 11-day period to assess morphogenesis of the parasite. Vigorously motile microfilariae were recovered from the mid-gut during the first 24 hours postfeeding; second-stage larvae were found in the thoracic musculature on day 4; and fully developed third-stage larvae were obtained from the cephalic capsule by day 10. This rate of larval development is similar to that observed in Guatemalan S. ochraceum. Onchocerciasis is not known to occur in Panama. The results of the present study direct attention to a potential public health hazard there and possibly elsewhere in Central America.

Animals↗
PubMed2000

Human dirofilariasis due to Dirofilaria (Nochtiella) repens: an update of world literature from 1995 to 2000.

Following on from their review of 1995 (Pampiglione et al.), the authors present an update of human cases of dirofilariasis due to Dirofilaria (Nochtiella) repens (Nematoda, Filarioidea, Onchocercidae) reported in the world literature. Cases of the parasitosis published from 1995 to 2000 are reported country by country. The essential data are presented in tabular form and the clinical, parasitological, histopathological, epidemiological features are analysed. 372 new cases spread over 25 countries are thus added to the list published in 1995. The countries most affected are Italy, Sri Lanka, some republics of the ex-Soviet Union. The age of the patients varied from 4 months to 100 years, the majority being in their 40s. There was virtually no difference in incidence between sexes. The parasite appeared most frequently in the upper half of the body, particularly in the head and ocular region and also in the upper limbs. Cases of visceral involvement are also reported. Of the various forms of human dirofilariasis, that due to D. (N.) repens is confirmed to be the most important as regards not only the number of subjects affected and the wide geographical distribution but also the variety of organs involved, notably the lungs, the male genitals and the female breast, invariably leading to a wrong diagnosis of malignant tumour. In man, the zoonosis may be described as emerging: whereas until the middle of the last century only a few dozen cases were reported, in the last 50 years the number has gradually increased to reach the present 782.

Adolescent↗
PubMed2002

Human dirofilariasis in Italy: a new case in the spermatic cord.

A new case of human dirofilariasis associated with Dirofilaria (Nochtiella) repens (Nematoda, Filarioidea, Onchocercidae) located in the spermatic cord is reported in a 71-year-old man from the province of Campobasso (Central Italy). When clinical signs pointed to a testicular tumor, a monolateral orchifuniculectomy was performed. According to the scientific literature, this case appears to be exceptional in its location, being only the eighth such case recorded in the world until now. The nematode, as well as the presence of vectors suitable for its transmission, had already been observed both in dogs and in humans (3 subcutaneous cases) in the same geographical area.

Aged↗
PubMed1992

Hydrolytic activity of an onchocercoma.

The onchocercoma or nodule produced by the nematode Onchocerca volvulus (Filarioidea) in the skin of patients suffering from onchocerciasis has not been examined by histochemical techniques. In this work we have used histochemical techniques to evaluate 5 hydrolytic enzymes, namely phosphatases, esterases and beta-glucuronidase. The results show increased enzymatic activity at the sites of major metabolic activity and within reactive cells including macrophages (mc) and giant cells (gc) of the onchocercoma.

Animals↗
PubMed1984

In vitro cultivation of Dipetalonema viteae third-stage larvae: effect of the gas phase.

The effect of the gas phase on the in vitro growth and development of Dipetalonema viteae (Nematoda: Filarioidea) third-stage larvae obtained from the tick vector and 3 day infections of jirds was examined. Measurements of the oxygen (pO2) and carbon dioxide (pCO2) tensions and the pH in the medium were made for each gas phase. In cultures gassed with 5% carbon dioxide in nitrogen the pO2 was between 32 and 50 mm Hg, the pCO2 ranged from 25 to 40 mm Hg and the pH was between 7.2 and 7.4. This gas phase resulted in the best growth and development of third-stage larvae to the fourth-stage. Survival and development of larvae were decreased in cultures with oxygen tensions less than 20 mm Hg and greater than 50 mm Hg.

Animals↗
PubMed1983

Effect of immune reconstitution on resistance to Brugia pahangi in congenitally athymic nude mice.

The dichotomy of resistance to Brugia pahangi (Nematoda: Filarioidea) between nonsusceptible, euthymic C3H/HeN mice, heterozygotic for the "nu" gene (+/nu), and susceptible, congenitally-athymic "nude" (nu/nu) C3H/HeN mice, suggests that resistance is thymus-dependent. To test this hypothesis, the effect of syngeneic neonatal thymus grafts and neonatal thymus cell suspensions on recovery of worms at day 40 PI, and responses to Concanavalin A (Con A) were examined in reconstituted nudes. Nude recipients of a thymus graft 7 or 14 wk before subcutaneous inoculation with 50 infective larvae (L3) yielded no worms and responded strongly to Con A. Serum from these mice reacted in two lines of identity with serum from similarly-infected heterozygotes by double radial immunodiffusion against an adult worm saline extract. Nude recipients of a thymus 2 days or 3 wk before inoculation harbored an average of three or two worms, respectively. Intravenous injection of nude recipients with 10(7) or 10(8) neonatal thymus cells seven weeks before inoculation was less effective in conferring resistance to B. pahangi and responsiveness to Con A. Complete resistance to B. pahangi could be adoptively transferred to nude mice by 10(8) spleen cells obtained from infection-primed heterozygotes and injected intravenously on the day of larval inoculation. The same numbers of worms were significantly reduced. less effective when injected 3 wk before inoculation, although numbers of worms were significantly reduced. Passive transfer of primed heterozygote serum, containing high titers of antibodies to adult worm and larval antigens, failed to protect nude recipients against a larval inoculum in the absence of cellular reconstitution.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

The lymphatic pathology of Brugia pahangi in nude (athymic) and thymic mice C3H/HeN.

The nude (congenitally athymic) mouse, C3H/HeN is highly susceptible to infection with Brugia pahangi (Nematoda: Filarioidea). Normal, hairy mice show a strong thymus-dependent resistance and usually terminate the infection in the larval stages. The present study examined chronological histopathologic changes in the lumbar lymph nodes and adjacent lymphatic vessels of both hosts. In thymic mice, lymphangitis and perilymphangitis reached a maximum 14 to 17 days PI, about the time of disappearance of live worms. The infiltrate showed characteristics of both acute and chronic inflammation: eosinophils, neutrophils, eosinophilic precipitates, and sometimes necrotizing lymphangitis, as well as macrophages and plasma cells. The cellular infiltrate in nude mice was weaker and developed more slowly. Inflammatory responses to identifiable dead worms were seen in both types of hosts but appeared more frequently in thymic mice. Although variable in both models, the granulomas of thymic mice generally showed more tendency to cavitation, greater macrophage or epithelioid cell infiltration, more granulocytes, and appeared to be more destructive than the foreign body responses of nude mice. Whereas lymphangiectasis was generally progressive in nude mice, it was arrested before the end of the third week in thymic mice. In thymic mice, at maximum lumbar lymph node size (17 days), there were large areas of lymphocyte hyperplasia and heavy infiltration of plasma cells. Most nodes returned to normal mean size by the end of the second month. Little or no reactivity was seen in athymic mouse nodes. Our results suggest that some lesions of lymphatic filariasis are potentially thymus-independent: lymphatic fibrosis, lymphangiectasis, accumulations of macrophages and giant cells around disintegrating worms, calcification of worms, intralymphatic thrombosis, and moderate vascular infiltrates including eosinophils.

Animals↗
PubMed1980

The lymphatic pathology of Brugia pahangi in the Mongolian jird.

We studied the sequence of histopathologic changes associated with Brugia pahangi (Nematoda: Filarioidea) infections in lymphatic vessels in the spermatic cord of the Mongolian jird (gerbil), Meriones unguiculatus. Intravascular granulomas caused mainly by disintegrating worms were seen in 67% of jirds necropsied on, or after, 35 days postinoculation, whereas none of 20 jirds examined before this day showed dying larvae. These granulomas usually evolved without vascular occlusion. Other granulomatous foci, often with a thrombuslike core, sometimes harbored microfilariae or microfilarialike materials. The perilymphatic cellular infiltrate consisted mostly of eosinophils, lymphocytes, and plasma cells. Large numbers of eosinophils were seen in the early weeks, but later declined, while lymphocytes increased to become the predominant cell in old infections. Irregular fibrosis of some valves and portions of the lymphatic walls were seen as early as the 2nd wk postinoculation. Lymphatic changes in the jird are similar to those described in other hosts infected with filariae, but remained moderate. Living worms appeared to be the stimulus for many observed changes. Most pathologic alterations were well established by 3 or 4 mo and showed little qualitative change during the remaining 4 mo of the study.

Animals↗