Prevention of Toxoplasmosis

Histopathology of active toxoplasmosis of myocardium.
Photo courtesy of  EP Ewing Jr. and CDC

Cara N. Wilder, Ph.D.

Toxoplasma gondii is a ubiquitous obligate, intracellular parasitic protozoan known to cause toxoplasmosis in a number of warm-blooded animals, including humans. This protist is transmitted to humans through the consumption of undercooked meat from infected animals, the ingestion of food or water contaminated with oocytes from infected cat feces, or by transplacental transmission. In healthy individuals, toxoplasmosis is relatively asymptomatic and self-limiting. However, this illness can silently affect pregnant women and result in severe consequences for the fetus including neurological impairment, chorioretinitis, or death. T. gondii can also affect immune-compromised individuals, resulting in cerebral or extra-cerebral toxoplasmosis.

Currently, the CDC considers toxoplasmosis to be one of the leading causes of death attributed to foodborne illness. Moreover, T. gondii infection in domestic animals represents a significant economic and public health threat due to the potential for foodborne outbreaks. Unfortunately, treatment of toxoplasmosis is difficult due to both the severe side-effects of the drug as well as the potential for re-infection. Thus, the development of effective preventative treatments is of great importance.

In recent study, Wang et al. analyzed the protective efficacy of recombinant T. gondii protein disulfide isomerase (PDI) as a potential target for the development of a novel vaccine. This particular antigen was chosen as a candidate vaccine target as it is soluble, demonstrates conserved homology among the three distinct clonal lineages of T. gondii strains, and is highly expressed on the outer surface of T. gondii tachyzoites. In this study, BALB/c mice were intranasally immunized with varying concentrations of recombinant T. gondii PDI (rTgPDI), and the resulting immunological response was evaluated by lymphoproliferative assays and by cytokine and antibody measurements. In addition to this analysis, immunized mice were also challenged with tachyzoites from T. gondii strain RH. Following this challenge, the survival time of the mice was assessed and the number of brain and liver tachyzoites enumerated.

From these analyses, the group discovered that immunization with 30 µg of rTgPDI demonstrated higher levels of anti-PDI antibody production, a strong lymphoproliferative response, and high levels of cytokine production as compare to the other doses tested. Further, mice immunized with rTgPDI demonstrated enhanced survival times and reduced levels of tachyzoites as compared to control mice. Overall, the results from the study demonstrated that immunization with rTgPDI elicited a protective immune response against T. gondii tachyzoites, thus suggesting that this recombinant protein may be a promising candidate for the development of a vaccine to prevent toxoplasmosis.

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Rapid diagnosis of typhoid from blood cultures

Image of Salmonella enterica, courtesy of the CDC

Cara N. Wilder, Ph.D.

Typhoid fever is a life-threatening illness caused by the Gram-negative bacterium, Salmonella enterica subsp. enterica serovar Typhi. This foodborne pathogen is commonly contracted though the consumption of food or water that has been handled by a person shedding S. Typhi, or through the contamination of these products with sewage. Once ingested, the bacteria will inhabit the intestinal tract and bloodstream, resulting in a variety of complications including high fever, stomach pains, septicemia, and death.

Typhoid fever is common throughout most of the developing world, particularly in parts of Asia, Africa, and Latin America. Unfortunately, a number of people within these countries do not have access to a reliable laboratory diagnosis as the appropriate clinical facilities and techniques are not available. Thus, there is an urgent need for an inexpensive, easy-to-use, portable technique that can rapidly and safely diagnose typhoid fever independent of a hospital setting.

In a recent study, Castonguay-Vanier et al. investigated the accuracy and efficacy of a technique combining blood culture amplification of S. Typhi with a S. Typhi antigen rapid diagnostic test (RDT) developed by Standard Diagnostics (Cat. No. 15FK12). When tested against 23 Gram-negative reference pathogens, this assay was able to detect S. Typhi, as well as Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Ndolo. The precision of this assay was further analyzed through the examination of 6,456 blood cultures from 3,028 patients. From this prospective study, the group found that the sensitivity, negative predictive value, specificity, and positive predictive value were 96.7%, 99.5%, 97.9%, and 87.9%, respectively, for patients with proven S. Typhi bacteremia. Overall, these results suggest that the combination of blood culture amplification of S. Typhi with an S. Typhi RDT is promising as an effective, sensitive, and inexpensive tool for the rapid diagnosis of typhoid fever.

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Characterization of Arcobacter species using multi-locus sequence typing

Cara N. Wilder, Ph.D.

Arcobacter is a genus of aerotolerant, Campylobacter-like bacteria first isolated from aborted bovine fetuses by Ellis et al. in 1977. Since then, Arcobacter species have been discovered in a variety of sources, including food, water, animals, and agricultural run-off. In recent years, the prevalence of Arcobacter butzleri and Arcobacter cryaerophilus in food, raw milk, and water has suggested the potential of these organisms to be spread by contaminated consumable products. This is particularly disconcerting as these species are considered to be pathogenic, causing a variety of symptoms such as abdominal pain, nausea, and septicemia.

To aid in the identification, characterization, and epidemiology of Arcobacter strains, Miller et al. developed a multi-locus sequence typing (MLST) scheme based on the analysis of partial, defined sequences from seven Arcobacter housekeeping genes (aspA, atpA(uncA), glnA, gltA, glyA, pgm, and tkt). In this study, a sample set of 374 strains comprising five known Arcobacter species was isolated from a diverse array of sources and geographical regions. The analysis of these strains yielded almost 300 sequence types and 1176 alleles across the seven loci. Overall, this extensive set of genomic sequence data may aid with strain discrimination as well as help track sporadic Arcobacter-related gastroenteritis and potential outbreaks.

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