Reinfection of dogs with fish-borne zoonotic trematodes in northern Vietnam following a single treatment with praziquantel.

BACKGROUND: Fish-borne zoonotic trematodes (FZT) infections including liver- and minute intestinal flukes are common in Southeast Asia in both humans and domestic animals eating raw fish and since 2010, the liver flukes are recognised as neglected tropical diseases by WHO. Mass drug treatment with praziquantel is advised for humans, but no recommendations for control of the FZT in the reservoir hosts exist. METHODOLOGY/PRINCIPAL FINDINGS: A study was conducted to assess the ability of praziquantel treatment for control of FZT in farm dogs in an endemic area in Northern Vietnam. Initially, 101 dogs from 73 households were examined for small trematode eggs in their faeces. Forty seven copro-positive dogs were included in the study. Thirty eight dogs received treatment with a single dose of 40 mg/kg of praziquantel. A group of nine dogs were left untreated. Coprological examination for small trematode eggs was performed on day 0, 3, 10, 30, 60, 90 and 120 post treatment. Farmers were questioned about dog keeping practises. All dogs were copro-negative for small trematode eggs on both day 3 and 10 post treatment. From day 30 onwards previously negative dogs became positive again. The reinfection rates were 26.3% (day 30), 45.5% (day 60), 53.1% (day 90), 61.3% (day 120).The nine untreated dogs remained positive throughout the study period. There was no difference in the intensity of infection at day 0 and 120 neither in the treated or untreated group. CONCLUSION: Dogs had easy access to raw fish and did not receive treatment against flukes by their owner. More than 50% of the dogs were reinfected 3 months post treatment. We do not recommend controlling FZT infections in dogs by anthelmintic treatment alone since reinfection occurs fast under the existing farm management systems.

Evaluation of four coproscopic techniques for detection of small trematode eggs in dog faeces.

The study was conducted to evaluate copro-diagnostic techniques for detection of small trematode eggs in dogs. FLOTAC, a novel flotation technique, and DBL, a sieving and sedimentation technique developed at the former Danish Bilharziasis Laboratory (DBL), were compared using 53 subsamples from four copro-positive dogs. Moreover, a modified version of the DBL technique and the Kato-Katz (KK) thick smear were later compared using faecal samples from 21 dogs. The four techniques were pair-wise compared regarding sensitivity, infection intensity and practical applicability. For the former two techniques, egg recovery subsequent to storage and reproducibility were also compared. The DBL technique detected all 53 subsamples positive for small trematode eggs. Based on 17 subsamples, mean infection intensity of 47±49 eggs per gram of faeces (EPG) was detected by the technique. Due to large amount of sediment, examination of a single subsample required an average of 3 hours. The FLOTAC technique was found less sensitive (82%) than the DBL technique and recovered significantly less eggs (4±6 EPG). Both sensitivity and intensity were further reduced following storage. As the FLOTAC technique requires specialised equipment, safety disposal and personal protective equipment, it was found less suited than the DBL technique for a basic laboratory. Additionally, poor reproducibilities were found for both the DBL and FLOTAC techniques (30±15% and 38±33%, respectively). Based on the 21 faecal samples, the modified version of the DBL technique was found more sensitive (85%) than the KK technique (68%), whereas egg counts were significantly higher for the latter (23±26 EPG vs. 482±909 EPG). By modifying the DBL technique, it was possible to diminish the retained sediment and examination time to a maximum of an hour, which was also the time required by the KK technique, although the latter was faster and more easily processed. Based on the results obtained in this study, none of the techniques evaluated were found applicable in their current form for detection of small trematode eggs in faeces from dogs in Vietnam.

Population dynamics and host reactions in young foxes following experimental infection with the minute intestinal fluke, Haplorchis pumilio.

BACKGROUND: Infections with fish-borne zoonotic trematodes (FZT) including the minute intestinal fluke, Haplorchis pumilio, are highly prevalent in Southeast Asia. However, little is known about the infection dynamics and clinical symptoms in the final hosts which include a range of animal species and man. We aimed to generate such information using an experimental model with H. pumilio in foxes. METHOD: Eight commercially bred foxes were each orally infected with 2000 H. pumilio metacercariae. Another three foxes served as uninfected controls. Faecal examination for eggs was performed twice weekly. The body weight was measured, standard haematological and biochemical analysis were performed regularly. All foxes were euthanized at day 56 post infection (p.i.). Adult worms were quantified and location in the small intestine noted. RESULTS: Anorexia was observed in all infected foxes starting day 12 p.i. and lasting for approximately a week. A weight loss was noticed in the infected group in weeks 3-6 p.i. Five of eight infected foxes excreted H. pumilio eggs day 9 p.i. onwards, the remaining three started on day 13 p.i. Mean (± SD) faecal egg counts showed an initial peak at day 16-20 with a maximum of 1443 ± 1176 eggs per gram of faeces (epg), where after a stable egg output around 4-500 epg was seen. Worm burdens ranged between 116-2070 adult flukes with a mean (± SD) worm recovery of 948 ± 666. The majority of worms were found in the lower part of the jejunum. Total white blood cell and lymphocyte counts were significant lower in the infected group from first week p.i. onwards and throughout the study period. A significantly lower level of eosinophils was found in week 2 p.i. and transient anaemia was seen in week 2 and 4 p.i. CONCLUSION: This study showed a short prepatency period, an initial peak in egg excretion, establishment of infection in all animals with predilection site in the lower jejunum and a marked but transient clinical effect of the infection. The findings on egg output and prepatency should be taken into consideration when control programs targeting dogs and other reservoir hosts are to be established.

Experimental infection with the small intestinal trematode, Haplorchis pumilio, in young dogs.

Fishborne zoonotic trematodes (FZT) are highly prevalent in Southeast Asia. Recent studies on the role of domestic animals in the transmission of FZT in Northern Vietnam found that dogs, mainly infected with Haplorchis pumilio, contributed widely to the transmission of FZT. On this background, we conducted an experimental infection with H. pumilio to elucidate population dynamics and host reactions in dogs. Eight household-reared dogs (3-6 months old), were each orally infected with 500 H. pumilio metacercariae obtained by artificial digestion of naturally infected fish. Another eight dogs were included as uninfected controls. Faecal examination for eggs was performed twice weekly using a sieving and sedimentation technique. Body temperature and weight of the dogs were measured as was total white blood cells, blood eosinophils and packed cell volume. Subsets of dogs were examined post-mortem for presence of adult FZT at three different time points post infection by sectioning of the small intestine and caecum into four parts. Patent infections established in all eight infected dogs. The worm establishment ranged from 15 to 121 flukes (3-24%, mean 12%). Faecal egg excretion was measured in all eight infected dogs but no more than two eggs per g faeces (epg) were found at any time. Infections lasted for at least two months as documented by the presence of adult flukes in all three dogs necropsied on day 58 post infection. The predilection site of the flukes was identified as the lower part of jejunum (93% of total worm burden). The results of the haematological tests did not differ between the infected and uninfected group. Further, no clinical symptoms were observed in the infected group and no macroscopic pathological changes could be assigned to the trematode infections, neither did histopathological examination of the intestine reveal any differences between the infected and the control dogs. This study provides the first basic knowledge on the establishment, duration and location of H. pumilio infection in dogs. However, before any control measures can be recommended, knowledge regarding infection dynamics, epidemiology, health impact and control is needed.

Genetic analysis of Trichuris suis and Trichuris trichiura recovered from humans and pigs in a sympatric setting in Uganda.

The whipworms Trichuris trichiura and Trichuris suis in humans and pigs, respectively, are believed to be two different species yet closely related. Morphologically, adult worms, eggs and larvae of the two species are indistinguishable. The aim of this study was to examine the genetic variation of Trichuris sp. mainly recovered from natural infected pigs and humans. Worm material isolated from humans and pigs living in the same geographical region in Uganda were analyzed by PCR, cloning and sequencing. Measurements of morphometric characters were also performed. The analysis of the ITS-2 (internal transcribed spacer) region showed a high genetic variation in the human-derived worms with two sequence types, designated type 1 and type 2, differing with up to 45%, the type 2 being identical to the sequence found in pig-derived worms. A single human-derived worm showed exclusively the type 2-genotype (T. suis-type) and three cases of 'heterozygote' worms in humans were identified. However, the analysis showed that sympatric Trichuris primarily assorted with host origin. Sequence analysis of a part of the genetically conserved ß-tubulin gene confirmed two separate populations/species but also showed that the 'heterozygote' worms had a T. suis-like ß-tubulin gene. A PCR-RFLP on the ITS-2 region was developed, that could distinguish between worms of the pig, human and 'heterozygote' type. The data suggest that Trichuris in pigs and humans belong to two different populations (i.e. are two different species). However, the data presented also suggest that cross-infections of humans with T. suis takes place. Further studies on sympatric Trichuris populations are highly warranted in order to explore transmission dynamics and unravel the zoonotic potential of T. suis.

Prevalence of gastrointestinal nematodes in growing pigs in Kabale District in Uganda.

During the last 30 years, pig production in Uganda and neighbouring counties has increased markedly. Pigs are mainly kept as a source of income for small-scale farmers; however, the pig production is subject to several constraints, one of them being worm infections. A study was carried out in rural communities in Kabale District in the South Western part of Uganda in September and October 2007 in order to estimate the prevalence of gastrointestinal nematode parasites in pigs based on coprological examination. Fifty-six households were randomly selected and visited. Housing system and deworming history were recorded. Faeces was sampled from rectum of one to five pigs (age, 3-12 months) per household. A total of 106 pigs were examined coprologically of which 91% excreted nematode eggs. The following prevalences of nematode eggs were recorded: strongyles (89%), Ascaris suum (40%), Trichuris suis (17%) and spiruroid eggs (48%). On household level, rearing pigs on slatted floors in pens significantly reduced the faecal egg excretion of strongyle eggs with almost 80% (p=0.010) and a significant interaction between floor type and anthelmintic treatment was found for spiruroids (p=0.037). Fifteen T. suis egg positive pigs were selected for post-mortem examination of the gastrointestinal tract. The post-mortem examinations revealed that 93% pigs were infected with Oesophagostomum spp. (worm burden, min-max 10-2,180), 73% with A. suum (1-36), 67% with T. suis (6-58), and 20% with Hyostrongylus rubidus (worms not quantified). In general, nematode infections were widespread and polyparasitism common in pigs in Uganda. However, worm burdens were moderate which may be related to recent deworming or to the practice of rearing pigs on slatted floors in wooden elevated pens.