Experimental infection by Trypanosoma evansi in sheep: Occurrence of transplacental transmission and mice infection by parasite present in the colostrum and milk of infected ewes.

The aims of this study were to evaluate vertical transmission of Trypanosoma evansi in sheep experimentally infected, in addition to the mammary transmission by colostrum or milk of these infected sheep to mice. Three pregnant sheep were used: one uninfected, four months pregnant (Sheep A); and two (Sheep B and C) infected intravenously by T. evansi trypomastigotes (4.6×10(6) per animal) on the third (Sheep C) and fourth (Sheep B) month of pregnancy. Both infected sheep developed low and oscillating parasitemia measured by blood smears. Hemogram was performed at seven day intervals, showing anemia, leukocytosis, and lymphocytosis on sheep B and C. Three sheep had twins, where sheep A delivered healthy lambs and both infected sheep had delivered at least one stillborn. Additionally, lambs from sheep B and C died 24 and 72 h post-partum, respectively. Before colostrum intake, four lambs from infected sheep were positives for T. evansi according to blood smear evaluation, serology (CATT/T. evansi), and PCR. Sheep colostrum and milk samples collected from the first four days post-partum were positives for T. evansi on PCR, and these samples were able to infect seven mice (out of 10) orally (n=4/5) and intraperitoneally (n=3/5). Therefore, we conclude that the vertical transmission of T. evansi occurs in pregnant sheep, in addition to a strong possibility of the transmission by colostrum and milk.

Land-use change and emerging public health risks in New Zealand: assessing Giardia risks.

Agriculture is key to New Zealand's economy with land-use conversions in response to market forces occurring regularly, like that of recent dairy intensification throughout the country. However, land-use conversion can occasionally result in unexpected and significant consequences for public health that need to be accurately estimated and subsequently managed accordingly. For example, dairy cattle have high Giardia prevalence in New Zealand and identical strains from infected humans and cattle located in the same geographical region have recently been reported. Thus, the high rates of human infections in New Zealand compared to similar socioeconomic countries caused by the waterborne pathogen Giardia are particularly concerning given the increasing dairy cattle populations on the landscape. However, the ability of traditional, evidence-based, epidemiological approaches to detect such causal relationships between land-use and Giardia infections is limited given the many possible indirect links between the two, in turn highlighting the need to develop appropriate risk assessment techniques. As such, the general requirements for and development of risk assessment frameworks to evaluate the likelihood of public health risks from waterborne pathogens are introduced and explored using Giardia in New Zealand as an example. Specifically, the importance of recent advances in Giardia-based knowledge, the incorporation of such data into existing risk assessment frameworks and the influence of remaining research gaps are each discussed for expanding currently available risk assessment tools. Not surprisingly, the availability of appropriate risk assessment tools for agencies responsible for public health and environmental management would ensure the public health risks for Giardia resulting from land-use change could be quantified holistically and strategies subsequently developed through active agency communication to minimise such risks.

Humoral immune response of water buffalo monitored with three different antigens of Toxocara vitulorum.

Humoral immune response of water buffalo naturally infected with Toxocara vitulorum was monitored using three different antigens of this parasite in serum and colostrum of buffalo cows and calves. Soluble extract (Ex) and excretory/secretory (ES) larval antigens and perienteric fluid antigen (Pe) of adult T. vitulorum were used to measure the antibody levels by an indirect ELISA. Serum of 7-12 buffalo cows for the first 365 days and colostrum of the same number of buffalo cows for the first 60 days of parturition, and serum of 8-10 buffalo calves for the first 365 days after birth were assayed. The ELISA detected antibodies against all three T. vitulorum antigens in the colostrum and serum of 100% of buffalo cows and calves examined. The highest antibody levels against Ex, ES and Pe antigens were detected in the buffalo cow sera during the perinatal period and were maintained at high levels through 300 days after parturition. On the other hand, colostrum antibody concentrations of all three antigens were highest on the first day post-parturition, but decreased sharply during the first 15 days. Concomitantly to the monitoring of immune response, the parasitic status of the calves was also evaluated. In calves, antibodies passively acquired were at the highest concentrations 24 h after birth and remained at high levels until 45 days coincidentally with the peak of T. vitulorum infection. The rejection of the worms by the calves occurred simultaneously with the decline of antibody levels, which reached their lowest levels between 76 and 150 days. Thereafter, probably because of the presence of adults/larvae stimulation, the calves acquired active immunity and the antibodies started to increase slightly in the serum and plateaued between the days 211 and 365. All three antigens were detected by the serum antibodies of buffalo calves; however, the concentration of anti-Pe antibody was higher than anti-EX and anti-ES, particularly after 90 days of age. By conclusion, the buffalo cows develop immunity and keep high levels of antibodies against T. vitulorum-Ex, ES and Pe antigens and these antibodies are transferred to their calves through the colostrum. This passively acquired immunity does not protect the calves against the acquisition of the infection, but these antibodies, passively or actively acquired, may have an important role during worm rejection by the calves and prevention of intestinal reinfection.

Passive immunity and serological immune response in dairy calves associated with natural Giardia duodenalis infections.

In a previous study, Giardia infection patterns were studied in newborn dairy calves over a 4-month period. Chronic Giardia infections were observed in all calves with initial cyst excretion occurring at approximately 1 month of age. In the work presented here, the passive immunity and serological immune response associated with these Giardia infections were examined. Colostrum and milk samples were collected from the dams of these calves, and monthly serum samples were collected from each calf. The colostrum, milk and sera samples were analyzed by ELISA and Western blot for the presence of anti-Giardia IgG antibodies. In addition, the in vitro anti-Giardia activity of milk and colostrum was examined using a miniculture adherence assay. When examined by ELISA, mean anti-Giardia antibody titres were found to be significantly higher in colostrum compared to milk. The monthly mean serum antibody titres in the calves were not found to differ significantly at any time point during the study. Western blot analysis revealed that colostrum from the dams reacted strongly with many different Giardia antigens between 205 and 7.5kDa, while milk reacted with few antigens in the same size range. Sera collected from the calves when 30 and 60 days of age reacted with few Giardia antigens, but as the calves aged, IgG antibodies in their sera began to react with antigens of 21, 50, 65, 73 and 79kDa. The miniculture adherence assay demonstrated that colostrum had significantly more anti-Giardia activity in vitro compared to milk. These results suggest that the calves in this dairy did not mount a significant humoral immune response against Giardia following infection. However, colostrum contained a high level of anti-Giardia antibodies and exhibited anti-Giardia activity in vitro. Therefore, colostrum may have the potential to provide initial protection against Giardia infections in calves, but the lack of a strong, specific humoral immune response by these calves could account for the high prevalence and chronic duration of the infections.

Experimental studies on the transmission of Neospora caninum between cattle.

Three studies were conducted to investigate the transmission of Neospora caninum between cattle by the oral route. In the first study, six calves were dosed with 10(7)N caninum tachyzoites (NC LivB1) in colostrum and/or milk replacer on four occasions. In the second study, two calves and two cows were fed placental tissues from N caninum -infected cows, and, in the third study, seven uninfected calves were fostered onto N caninum -infected dams. In the first study, all six calves developed antibody responses and five calves developed antigen-specific lymphoproliferation responses, including two calves initially challenged at 1 week of age. No evidence of N caninum infection was found in the brain or heart of these calves by histology or polymerase chain reaction (PCR). In the second and third studies, there was no evidence of N caninum infection in any of the calves and cows. The results confirm that calves up to 1 week of age can be experimentally infected via the oral route, but suggest that this is not an important natural route of transmission for N caninum between cattle.

Efficacy of an in-feed formulation of ivermectin against somatic larvae of Strongyloides ransomi in pregnant swine.

OBJECTIVE: To confirm that ivermectin fed for 7 days to pregnant sows controls transmission of Strongyloides ransomi larvae to pigs via the colostrum or milk. ANIMALS: 24 mixed-breed sows. PROCEDURE: The sows were infected with 250,000 S ransomi larvae on 3 occasions (days 63, 64, or 65, days 71 or 73, and days 78, 79, or 80 of gestation). Eight sows received ivermectin at a dosage of 100 micrograms of ivermectin/kg of body weight/d from days 92 to 99 of gestation, and 8 sows were treated from days 103 to 110 of gestation; 8 remaining sows received unmedicated vehicle. Numbers of S ransomi larvae were counted in samples of colostrum or milk collected 1, 2, and 7 days after parturition. At 7 and 14 days after parturition, fecal samples were collected from each sow and from 4 pigs from each litter for determination of nematode egg counts; at the latter date, pigs were euthanatized and necropsied for worm counting. RESULTS: Pigs born to ivermectin-treated sows had significantly (P < 0.01) fewer adult S ransomi than did those born to control sows; efficacy was 100%. Treated sows had significantly (P < 0.05) fewer S ransomi larvae in colostrum/milk samples taken 1, 2, and 7 days after parturition than did control sows; efficacy was 100%, with the exception of 1 S ransomi larva found in a milk sample from 1 treated sow at 2 days after parturition. CONCLUSION AND CLINICAL RELEVANCE: Ivermectin fed to sows during the last third of gestation at a dosage of 100 micrograms/kg/d for 7 consecutive days is highly efficacious for control of transmission of infective S ransomi larvae to pigs via colostrum or milk.

Naturally occurring vertical transmission of Neospora caninum in dogs.

Vertical transmission of Neospora caninum was studied in naturally infected, privately owned dogs, using antibody detection by IFAT to identify infected individuals. Retrospective studies were undertaken in litters from six bitches of the Hamiltonstövare breed, and on litters from seven bitches of other breeds--in both cases following diagnosis of clinical disease in puppies--and prospective studies were carried out on 17 seropositive bitches of other breeds. Puppies were classified as infected if either pre-colostral sera, or serum taken at > or = 5 weeks, had a titre of > or = 1:50 in the IFAT. The frequency of putative congenital transmission was variable; three seropositive dams produced successive litters, each containing seropositive puppies; four other seropositive bitches, which each whelped twice, produced six litters in which all pups were seronegative. Bitches born to seropositive dams themselves produced litters containing seropositive pups. In the retrospective studies, 32/61 (52%) of pups tested born to 13 seropositive dams were themselves seropositive and 22/88 (25%) of all pups born developed clinical signs compatible with a diagnosis of neosporosis. However, in the prospective study, only 4/118 (3%) pups tested from 17 seropositive dams were seropositive and 4/122 (3%) of all pups born developed signs consistent with neosporosis. This difference reflected levels of IFAT titre in the two groups of bitches and overall the proportion of pups seropositive was strongly and positively correlated (r = 0.980, P < 0.05) with bitch IFAT titre. Overall, 80% of pups born to seropositive dams were not infected as determined serologically. This study shows that the frequency of vertical transmission of naturally acquired Neospora infection in dogs is variable, but much too low to sustain infection alone. Post-natal infection must occur to maintain infection at seroprevalence rates reported in dog populations.

Toxocara vitulorum in the milk of buffalo (Bubalus bubalis) cows.

The duration of excretion of Toxocara vitulorum larvae in the milk of buffalo cows determines the optimum time for treating calves. Studies on 10 cows showed that a few larvae occur in the colostrum of some cows before the calf has suckled, but most are present from the day after calving and for a further five days. From day 9 onwards, very few larvae were found in the milk. The total number of larvae found was comparable with the number of adult parasites collected from the calves of cows with similar histories. The larvae were 1254 +/- 60 microns long and 36 +/- 6.7 microns in diameter at the ventriculus, figures which are substantially different from some published results.

Toxocara vitulorum in beef calves kept on effluent-irrigated pastures in Zimbabwe.

Faeces from 20 calves aged 13 +/- 5 days were examined for Toxocara vitulorum eggs fortnightly for a period of 20 weeks. The age of calves when eggs were first detected varied from 24 to 110 days (mean 41 +/- 20 days). The mean egg count varied from 257 to 19,821 g-1 of faeces with a highest count of 68,400. The patency period of T. vitulorum lasted from 14 to 112 days (mean 65 +/- 30 days). None of the calves showed clinical signs of illness.

Strongyloides ransomi: prenatal and transmammary infection of pigs of sequential litters from dams experimentally exposed as weanlings.

Prenatal infection of pigs with Strongyloides ransomi occurred in 12% of 104 pigs and in 14% of 21 litters farrowed by 13 sows experimentally exposed to infective larvae as weanlings. Transmammary passage was observed in 38 of 39 litters studied. Milk samples obtained from 14 sows showed that larvae were usually shed in the colostrum within 24 hours after farrowing; however, larvae were recovered from samples of milk of sows up to 20 days after parturition. Larvae were recovered from milk samples obtained after each parturition up to the fourth. Prenatal infection in pigs was not detected after the 1st litter.