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At least 19 recordsLinked to original sources

Experimental infection/transmission of sculpins (Myoxocephalus scorpius) and cod (Gadus morhua) by sealworm (Pseudoterranova decipiens) larvae.

Five serial transmission experiments with sealworm larvae were carried out. Pseudoterranova decipiens third-stage larvae (L3) were transferred via a stomach tube from sculpin to cod, from cod to sculpin, from sculpin to sculpin, and from cod to cod. After a minimum of 37 days the recipient fish were killed and the numbers of surviving P. decipiens larvae were recorded. P. decipiens transferred to sculpins showed the greatest rate of survival.

Animals↗

The role of trade-off shapes in the evolution of parasites in spatial host populations: an approximate analytical approach.

Given the substantial changes in mixing in many populations, there is considerable interest in the role that spatial structure can play in the evolution of disease. Here we examine the role of different trade-off shapes in the evolution of parasites in a spatially structured host population where infection can occur locally or globally. We develop an approximate adaptive dynamic analytical approach, to examine how the evolutionarily stable (ES) virulence depends not only on the fraction of global infection/transmission but also on the shape of the trade-off between transmission and virulence. Our analysis can successfully predict the ES virulence found previously by simulation of the full system. The analysis confirms that when there is a linear trade-off between transmission and virulence spatial structure may lead to an ES virulence that increases as the proportion of global transmission increases. However, we also show that the ESS disappears above a threshold level of global infection, leading to maximization. In addition just below this threshold, there is the possibility of evolutionary bi-stabilities. When we assume the realistic trade-off between transmission and virulence that results in an ESS in the classical mixed model, we find that spatial structure can increase or decrease the ES virulence. A relatively high proportion of local infection reduces virulence but intermediate levels can select for higher virulence. Our work not only emphasizes the importance of spatial structure to the evolution of parasites, but also makes it clear that situations between the local and the global need to be considered. We also emphasize the key role that the shape of trade-offs plays in evolutionary outcomes.

Adaptation, Physiological↗

Neospora abortions in dairy cattle: diagnosis, mode of transmission and control.

AIM: To determine the contribution of Neospora caninum to abortions on a dairy farm in NSW (Australia), determine the mode of transmission and develop and trial a control option for infection. METHODS: Two whole herd bleeds were conducted 12 months apart and the association between serological status and abortion events were calculated for a number of bovine abortifacients. Family trees were constructed for N. caninum seropositive cattle in the herd. Some N. caninum seropositive cows were culled from the herd and no female offspring was retained from seropositive cows. RESULTS: At the first whole-herd bleed in December 2002 a seroprevalence of 10.2% for N. caninum infection was detected. Cows with N. caninum infection were 13 times more likely to abort than uninfected ones. Seventy-five percent of seropositive animals in the herd were related, suggesting a high degree of congenital infection/transmission. Only 15% of infections were likely to be postnatally acquired. Selective culling of seropositive cows and not breeding from them reduced the number of seropositive animals. Only one newly sero-converted cow was detected at the second whole-herd bleed 12 months later. CONCLUSIONS: Seroepidemiological approaches were able to establish a high degree of association between N. caninum infection and low-level abortion in the dairy herd. Vertical transmission of infection was the predominant mode of infection and hence control efforts aimed at selectively culling seropositive animals from the herd were highly successful in reducing the level of infection.

Abortion, Veterinary↗

Reaching and identifying the STD/HIV risk of sex workers in Beijing.

China's HIV cases are growing by more than 30% annually. Few researchers have been able to reach sex workers and examine their risk behavior patterns. Key informants in illegal prostitution connected with owners of establishments in Beijing to recruit the involvement of sex workers. A total of 69 were surveyed about their background and risk behaviors in spring, 2000 in four venues; hair salons, bathing centers, karaoke bars, and the street. The women were mostly young (in their 20s), of low socioeconomic status, and from small towns and villages. They worked about 3 to 4 days a week, averaged one to two clients per day, made the equivalent of about U.S. $135 a week, and averaged about 3 months at any one establishment. They lacked accurate knowledge of STDs/HIV, and although 61% reported consistent condom usage 93% associated usage with prevention of pregnancy and 72% perceived a low risk of HIV infection. Nearly all (98%) felt condoms were affordable, yet 37% reported they were not accessible; 74% had obtained a medical exam in the last year, but 29% were examined when sick; only 10% received prevention information during medical visits, and 55% did not know where to go for HIV testing. Based on venue, stratification among sex workers existed, impacting their risk. Sex workers are at high risk of HIV infection/transmission, especially as the virus becomes more established in Beijing. Although risk factors were consistent with those of sex workers in other countries, the variation by venue, the low perceived vulnerability to HIV, the highly illegal nature of prostitution, and high mobility of sex workers in Beijing calls for a tailored intervention approach. Prevention messages/strategies should be responsive to the differing background, knowledge,

AIDS Serodiagnosis↗