Case Report: Ocular Gnathostomiasis in Venezuela Most Likely Acquired in Texas.

A 69-year-old male dentist in Caracas, Venezuela, was referred to our Cornea Clinic with a history of pain, photophobia, and blurred vision on his left eye. Routine biomicroscopic examination with a slit lamp showed a worm in the corneal stroma of his left eye. The worm was surgically removed and was identified morphologically as Gnathostoma binucleatum.

Acanthamoeba keratitis challenges a case report.

Acanthamoeba keratitis is a rare, chronic, mainly contact lens-related infection caused by a free-living amoeba found ubiquitously in water and soil. A case of a 9-year-old child, who presented to our clinic with painful, red left eye, associated with photophobia, and decreased visual acuity, wais reported. The clinical examination revealed a discoid opacity inferiorly bounded by a dense, gray infiltrate. The progressive nature of the corneal infiltrate, the epithelial defect, and the lack of response to treatment was highly suggestive for Acanthamoeba keratitis. The distinctiveness of this case was the presence of Acanthamoeba keratitis in a child without a history of trauma or contact lens usage, the lack of an appropriate diagnosis and management of this vision-threatening infection.

The effects of parasite age and intensity on variability in acanthocephalan-induced behavioural manipulation.

Numerous parasites with complex life cycles are able to manipulate the behaviour of their intermediate host in a way that increases their trophic transmission to the definitive host. Pomphorhynchus laevis, an acanthocephalan parasite, is known to reverse the phototactic behaviour of its amphipod intermediate host, Gammarus pulex, leading to an increased predation by fish hosts. However, levels of behavioural manipulation exhibited by naturally-infected gammarids are extremely variable, with some individuals being strongly manipulated whilst others are almost not affected by infection. To investigate parasite age and parasite intensity as potential sources of this variation, we carried out controlled experimental infections on gammarids using parasites from two different populations. We first determined that parasite intensity increased with exposure dose, but found no relationship between infection and host mortality. Repeated measures confirmed that the parasite alters host behaviour only when it reaches the cystacanth stage which is infective for the definitive host. They also revealed, we believe for the first time, that the older the cystacanth, the more it manipulates its host. The age of the parasite is therefore a major source of variation in parasite manipulation. The number of parasites within a host was also a source of variation. Manipulation was higher in hosts infected by two parasites than in singly infected ones, but above this intensity, manipulation did not increase. Since the development time of the parasite was also different according to parasite intensity (it was longer in doubly infected hosts than in singly infected ones, but did not increase more in multi-infected hosts), individual parasite fitness could depend on the compromise between development time and manipulation efficiency. Finally, the two parasite populations tested induced slightly different degrees of behavioural manipulation.

Conflict between co-occurring manipulative parasites? An experimental study of the joint influence of two acanthocephalan parasites on the behaviour of Gammarus pulex.

When two parasite species are manipulators and have different definitive hosts, there is a potential for conflict between them. Selection may then exist for either avoiding hosts infected with conflicting parasites, or for hijacking, i.e. competitive processes to gain control of the intermediate host. The evidence for both phenomena depends largely on the study of the relative competitive abilities of parasites within their common intermediate host. We studied the effects of simultaneous infection by a fish acanthocephalan parasite, Pomphorhynchus laevis, and a bird acanthocephalan parasite, Polymorphus minutus, on the behaviour of their common intermediate host, the amphipod Gammarus pulex. We compared the reaction to light and vertical distribution of individuals infected with both parasites to those of individuals harbouring a single parasite species and uninfected ones under controlled conditions. Compared to uninfected gammarids that were photophobic and tended to remain at the bottom of the water column, P. laevis-infected gammarids were attracted to light, whereas P. minutus-infected individuals showed a modified vertical distribution and were swimming closer to the water surface. The effects of both P. laevis and P. minutus appeared to be dependent only on their presence, not on their intensity. Depending on the behavioural trait under study, however, the outcome of the antagonism between P. laevis and P. minutus differed. The vertical distribution of gammarids harbouring both parasites was half-way between those of P. laevis- and P. minutus-infected individuals, whereas P. laevis was able to induce altered reaction to light even in the presence of P. minutus. We discuss our results in relation to the occurrence of active avoidance or hijacking between conflicting manipulative parasites and provide some recommendations for future research.