Bilateral ocular toxoplasmosis in a returning traveller: age and route of infection as potential risk factors

We report the case of a 69-year-old man, who presented in the UK with a short history of deteriorating vision and clinical features of bilateral atypical retinochoroiditis, after travelling to South America. Vitreous samples demonstrated Toxoplasma gondii DNA by PCR. Serology tests demonstrated recent acquired Toxoplasma gondii infection with IgM antibodies. He responded well to treatment with trimethoprim-sulfamethoxazole, azithromycin and oral steroids.This case is a reminder of the global importance of Toxoplasma related eye disease, and its uncommon bilateral severe presentation in a returning traveller, where the risk factors were age and the route of infection likely to be a virulent parasite oocyst from vegetables or water rather than undercooked meat or direct contact with cats.

mSphere of Influence: the Dynamic Nature of the Nuclear Envelope during Mitosis of Malaria Parasites

ABSTRACT Sabrina Absalon works in the field of cellular and molecular biology of Plasmodium falciparum, the most virulent parasite causing malaria in humans. In this mSphere of Influence article, she reflects on how the paper “3D nuclear architecture reveals coupled cell cycle dynamics of chromatin and nuclear pores in the malaria parasite Plasmodium falciparum” by Allon Weiner et al. (A. Weiner, N. Dahan-Pasternak, E. Shimoni, V. Shinder, et al., Cell Microbiol 13:967–977, 2011, https://doi.org/10.1111/j.1462-5822.2011.01592.x) triggered her aspiration to study the molecular mechanisms governing nuclear envelope assembly and integrity of P. falciparum throughout the intraerythrocytic development cycle.

Interactions among bacterial strains and fluke genotypes shape virulence of co-infection

Most studies of virulence of infection focus on pairwise host–parasite interactions. However, hosts are almost universally co-infected by several parasite strains and/or genotypes of the same or different species. While theory predicts that co-infection favours more virulent parasite genotypes through intensified competition for host resources, knowledge of the effects of genotype by genotype (G × G) interactions between unrelated parasite species on virulence of co-infection is limited. Here, we tested such a relationship by challenging rainbow trout with replicated bacterial strains and fluke genotypes both singly and in all possible pairwise combinations. We found that virulence (host mortality) was higher in co-infections compared with single infections. Importantly, we also found that the overall virulence was dependent on the genetic identity of the co-infecting partners so that the outcome of co-infection could not be predicted from the respective virulence of single infections. Our results imply that G × G interactions among co-infecting parasites may significantly affect host health, add to variance in parasite fitness and thus influence evolutionary dynamics and ecology of disease in unexpected ways.

CK2 Secreted byLeishmania braziliensisMediates Macrophage Association Invasion: A Comparative Study between Virulent and Avirulent Promastigotes

CK2 is a protein kinase distributed in different compartments ofLeishmania braziliensis:an externally oriented ecto-CK2, an intracellular CK2, and a secreted CK2. This latter form is constitutively secreted from the parasite (CsCK2), but such secretion may be highly enhanced by the association of specific molecules, including enzyme substrates, which lead to a higher enzymatic activity, called inductively secreted CK2 (IsCK2). Here, we examined the influence of secreted CK2 (sCK2) activity on the infectivity of a virulentL. braziliensisstrain. The virulent strain presented 121-fold higher total CK2 activity than those found in an avirulent strain. The use of specific CK2 inhibitors (TBB, DRB, or heparin) inhibited virulent parasite growth, whereas no effect was observed in the avirulent parasites. When these inhibitors were added to the interaction assays between the virulentL. braziliensisstrain and macrophages, association index was drastically inhibited. Polyamines enhanced sCK2 activity and increased the association index between parasites and macrophages. Finally, sCK2 and the supernatant of the virulent strain increased the association index between the avirulent strain and macrophages, which was inhibited by TBB. Thus, the kinase enzyme CK2 seems to be important to invasion mechanisms ofL. braziliensis.

Combined treatment with benznidazole and allopurinol in mice infected with a virulentTrypanosoma cruziisolate from Nicaragua

SUMMARYWe evaluated the effect of chemotherapy with a sequential combined treatment of a low dose of benznidazole and allopurinol, in different schedules of administration, in experimental models of acute and chronicTrypanosoma cruziinfection. Mice were infected with NicaraguaT. cruziisolate, a virulent parasite from an endemic area of Nicaragua, genotyped asTcI (Grossoet al. 2010). We assessed survival rate, IgG levels, histopathological studies and quantified parasitaemia. A 15% survival rate was recorded in untreated mice during the acute phase ofT. cruziinfection. Allopurinol administered immediately after benznidazole treatment was able to reduce parasitaemia and attenuate tissue damage by reducing inflammation.Trypanosoma cruzi-specific antibodies also decreased in 40–50% of the treated mice. The addition of allopurinol during the chronic phase showed the highest beneficial effect, not only by reducing parasitaemia but also by lowering the degree of inflammation and fibrosis.

Transmission stage investment of malaria parasites in response to in-host competition

Conspecific competition occurs in a multitude of organisms, particularly in parasites, where several clones are commonly sharing limited resources inside their host. In theory, increased or decreased transmission investment might maximize parasite fitness in the face of competition, but, to our knowledge, this has not been tested experimentally. We developed and used a clone-specific, stage-specific, quantitative PCR protocol to quantify Plasmodium chabaudi replication and transmission stage densities in mixed-clone infections. We co-infected mice from two strains with an avirulent and virulent parasite clone and found competitive suppression of in-host (blood-stage) parasite densities and generally corresponding reductions in transmission stage production, with the virulent clone obtaining overall competitive superiority. In response to competitive suppression, there was little evidence of any alteration in transmission stage investment, apart from a small reduction by one of the two clones in one of the two host strains. This alteration did not result in a competitive advantage, although it might have reduced the disadvantage. This study supports much of the current literature, which predicts that conspecific in-host competition will result in a competitive advantage and positive selection for virulent clones and thus the evolution of higher virulence.

Defending against parasites: fungus-growing ants combine specialized behaviours and microbial symbionts to protect their fungus gardens

Parasites influence host biology and population structure, and thus shape the evolution of their hosts. Parasites often accelerate the evolution of host defences, including direct defences such as evasion and sanitation and indirect defences such as the management of beneficial microbes that aid in the suppression or removal of pathogens. Fungus-growing ants are doubly burdened by parasites, needing to protect their crops as well as themselves from infection. We show that parasite removal from fungus gardens is more complex than previously realized. In response to infection of their fungal gardens by a specialized virulent parasite, ants gather and compress parasitic spores and hyphae in their infrabuccal pockets, then deposit the resulting pellet in piles near their gardens. We reveal that the ants' infrabuccal pocket functions as a specialized sterilization device, killing spores of the garden parasite Escovopsis . This is apparently achieved through a symbiotic association with actinomycetous bacteria in the infrabuccal pocket that produce antibiotics which inhibit Escovopsis . The use of the infrabuccal pocket as a receptacle to sequester Escovopsis , and as a location for antibiotic administration by the ants' bacterial mutualist, illustrates how the combination of behaviour and microbial symbionts can be a successful defence strategy for hosts.