Differential detection of Hammondia hammondi from Toxoplasma gondii using polymerase chain reaction

Sentinels in the shadows: Exploring Toxoplasma gondii and other Sarcocystidae parasites in synanthropic rodents and their public health implications

Synanthropic rodents play a crucial role in maintaining the life cycle of Toxoplasma gondii in anthropized regions and can serve as indicators of environmental oocyst contamination. This investigation aimed to explore the occurrence of T. gondii infection within synanthropic rodent populations using a molecular diagnostic technique targeting the 18S rDNA gene, which is generic for Coccidia, with subsequent specific PCR confirmation. We examined 97 brown rats (Rattus norvegicus), 67 black rats (R. rattus), 47 house mice (Mus musculus), and 1 common shrew (Sorex araneus). PCR tests were conducted on the brain, heart, and tongue tissues. PCR tested positive in at least one of the examined tissues in 26 R. norvegicus (26.8%), 13 R. rattus (19.4%), and 13 M. musculus (27.6%). Sequencing comparisons by BLAST allowed us to identify four different species of cyst-forming Apicomplexa. In particular, T. gondii DNA was detected in 13 (6.1%) rodents, Hammondia hammondi (including H. hammondi-like organisms) in 36 (17%) subjects, Besnoitia sp. (in two cases identified as B. besnoiti) in 8 (3.7%), and Sarcocystis gigantea in two (0.94%). Rodents from peri-urban and urban environments can act as indicators of environmental contamination by oocysts of apicomplexan parasites with cats as definitive hosts, such as T. gondii, H. hammondi, and S. gigantea, the latter of which has never been previously recorded in rodents. Moreover, the presence of B. besnoiti, a parasite with an unidentified definitive host in Europe, sheds light on the potential role of these hosts as infection sentinels.

Detection of Toxoplasma gondii and Sarcocystis sp. in the meat of common minke whale (Balaenoptera acutorostrata): A case of suspected food poisoning in Japan

A case of suspected food poisoning related to the consumption of raw meat from a common minke whale (Balaenoptera acutorostrata) was reported in Tokyo, Japan, in June 2020. Microscopic analysis revealed tissue cysts of Toxoplasma gondii and sarcocysts of Sarcocystis sp. in whale meat. The SAG2 and ITS1 region sequences of T. gondii were detected in the DNA extracted from the meat. Genotyping of the multilocus nested PCR-RFLP using the genetic markers SAG1, SAG2 (5'- SAG2, 3'-SAG2, and alt. SAG2), SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico revealed that the genotype of T. gondii was type II, with a type I pattern for the L358 locus. In the phylogenetic analyses of the six loci (GRA6, GRA7, SAG1, HP2, UPRT1, and UPRT7), these sequences clustered into haplogroup 2. Moreover, the sequences of the virulence-related genes ROP5 and ROP18 of T. gondii isolated from whale meat were similar to those of the type II ME49 reference strain. Sequence analyses of the mtDNA cox1 gene, 18S rRNA gene, and ITS1 region indicated the highest similarity of sarcocyst isolated from whale meat to Sarcocystis species that infect birds or carnivores as intermediate hosts; however, the species could not be identified. To our knowledge, this is the first report of T. gondii and Sarcocystis spp. being detected in same whale meat ingested by patients involved in a suspected food poisoning case in Japan.

A Field-Deployable Insulated Isothermal PCR (iiPCR) for the Global Surveillance of Toxoplasma gondii Infection in Cetaceans

Simple Summary

Since high trophic levels marine mammal species share the coastal environments and diets with humans, cetaceans provide an indication of contaminant bioaccumulation in humans and may serve as sentinels for public health problems. Parasite monitoring in marine sentinels can assist in evaluating the quality of the aquatic ecosystem’s health. T. gondii infection in cetaceans is an indicator of land-to-sea coastal pollution. Although T. gondii infection cases in cetaceans have been reported in several countries, an information gap still exists in some areas. The present study employs a portable insulated isothermal PCR (iiPCR) with an automatic extraction device as a rapid, affordable, user-friendly, and field-deployable platform to rapidly detect nucleic acid of T. gondii in stranded cetaceans. The platform utilizes duplex iiPCR designed to simultaneously detect T. gondii and a housekeeping gene of cetacean on the samples, which can prevent the false-negative results of pathogen detection and improve the accuracy of surveillance. This study would contribute to improving the environment through the warning of the sentinel animals and building new strategies by detecting the occurrence of land-based biological pollution.

Abstract

Toxoplasmosis is a zoonotic disease with veterinary and public health importance worldwide. Toxoplasma gondii infection in cetaceans is an indicator of land-to-sea oocyst pollution. However, there is a critical knowledge gap within the distribution of the T. gondii infection in cetaceans. To facilitate the global surveillance of this important zoonotic pathogen, we developed a field-deployable duplex insulated isothermal PCR (iiPCR) with automated magnetic bead-based DNA extraction for the on-site detection of T. gondii in stranded cetaceans. It targets the B1 gene of T. gondii combined with β2-microglobulin (B2M) gene of cetaceans as an internal control. Compared with the conventional qPCR assay, B1/B2M duplex iiPCR assay showed comparable sensitivity (21~86 bradyzoites in 25 mg of tissue) to detect spike-in standard of T. gondii DNA in cerebrum, cerebellum, skeletal muscle and myocardium tissues. Moreover, the overall agreement between the duplex iiPCR and qPCR was in almost perfect agreement (92%; 95% CI: 0.78–0.90; κ = 0.84) in detecting a synthetic spike-in standards. The B1/B2M iiPCR assay coupled with a field-deployable system provides a prompt (~1.5 h), feasible, highly sensitive and specific on-site diagnostic tool for T. gondii in stranded cetaceans. This platform provides one approach to evaluating aquatic ecosystem health and developing early warnings about negative impacts on humans and marine animals.

A real-time quantitative polymerase chain reaction for the specific detection of Hammondia hammondi and its differentiation from Toxoplasma gondii

Introduction

Hammondia hammondi and Toxoplasma gondii are closely related protozoan parasites, but only T. gondii is zoonotic. Both species use felids as definitive hosts and cannot be differentiated by oocyst morphology. In T. gondii, a 529-base pair (bp) repetitive element (TgREP-529) is of utmost diagnostic importance for polymerase chain reaction (PCR) diagnostic tests. We identified a similar repetitive region in the H. hammondi genome (HhamREP-529).

Methods

Based on reported sequences, primers and probes were selected in silico and optimal primer probe combinations were explored, also by including previously published primers. The analytical sensitivity was tested using serial dilutions of oocyst DNA. For testing analytical specificity, DNA isolated from several related species was used as controls. The newly established TaqMan PCR (Hham-qPCR1) was applied to tissues collected from H. hammondi-infected gamma-interferon gene knockout (GKO) mice at varying time points post-infection.

Results

Ten forward and six reverse primers were tested in varying combinations. Four potentially suitable dual-labelled probes were selected. One set based on the primer pair (Hham275F, Hham81R) and the probe (Hham222P) yielded optimal results. In addition to excellent analytic specificity, the assay revealed an analytical sensitivity of genome equivalents of less than one oocyst. Investigation of the tissue distribution in GKO mice revealed the presence of parasite DNA in all examined organs, but to a varying extent, suggesting 100- to 10,000-fold differences in parasitic loads between tissues in the chronic state of infection, 42 days post-infection.

Discussion

The use of the 529-bp repeat of H. hammondi is suitable for establishing a quantitative real-time PCR assay, because this repeat probably exists about 200 times in the genome of a single organism, like its counterpart in T. gondii. Although there were enough sequence data available, only a few of the primers predicted in silico revealed sufficient amplification; the identification of a suitable probe was also difficult. This is in accord with our previous observations on considerable variability in the 529-bp repetitive element of H. hammondi.

Conclusions

The H. hammondi real-time PCR represents an important novel diagnostic tool for epidemiological and cell biological studies on H. hammondi and related parasites.

Dissection of the in vitro developmental program of Hammondia hammondi reveals a link between stress sensitivity and life cycle flexibility in Toxoplasma gondii

Most eukaryotic parasites are obligately heteroxenous, requiring sequential infection of different host species in order to survive. Toxoplasma gondii is a rare exception to this rule, having a uniquely facultative heteroxenous life cycle. To understand the origins of this phenomenon, we compared development and stress responses in T. gondii to those of its its obligately heteroxenous relative, Hammondia hammondi and have identified multiple H. hammondi growth states that are distinct from those in T. gondii. Of these, the most dramatic difference was that H. hammondi was refractory to stressors that robustly induce cyst formation in T. gondii, and this was reflected most dramatically in its unchanging transcriptome after stress exposure. We also found that H. hammondi could be propagated in vitro for up to 8 days post-excystation, and we exploited this to generate the first ever transgenic H. hammondi line. Overall our data show that H. hammondi zoites grow as stringently regulated, unique life stages that are distinct from T. gondii tachyzoites, and implicate stress sensitivity as a potential developmental innovation that increased the flexibility of the T. gondii life cycle.

Cutaneous Toxoplasmosis in a Female Japanese Cat

A 16-year-old female Japanese cat was presented with a single mammary-gland nodule approximately 3 cm in diameter. Histologically, the nodule consisted of necrotizing granulomatous panniculitis, vasculitis, and mastitis, and contained free and clustered protozoal organisms. The organism was present in the cytoplasm of macrophages, fibroblasts, endothelial cells, and mammary-gland epithelia. The organism was positive for anti- Toxoplasma gondii and anti- Neospora caninum antibodies. Electron microscopy showed single and grouped tachyzoites, with morphologic features similar to those of T. gondii. Polymerase chain reaction and deoxyribonucleic acid sequence analysis was consistent with T. gondii infection. This is the first report of cutaneous toxoplasmosis in a Japanese cat.

Triplex PCR using new primers for the detection of Toxoplasma gondii

Molecular methods are used increasingly for the detection of Toxoplasma gondii infection. This study developed a rapid, sensitive, and specific conventional triplex PCR for the detection of the B1 gene and ITS1 region of T. gondii using newly designed primers and an internal control based on the Vibrio cholerae HemM gene. The annealing temperature and concentrations of the primers, MgCl(2), and dNTPs were optimized. Two sets of primers (set 1 and 2) were tested, which contained different segments of the T. gondii B1 gene, 529 repeat region and ITS1 region. A series of sensitivity tests were performed using parasite DNA, whole parasites, and spiked human body fluids. Specificity tests were performed using DNA from common protozoa and bacteria. The newly developed assay based on set 2 primers was found to be specific and sensitive. The test was capable of detecting as little as 10 pg T. gondii DNA, 10(4) tachyzoites in spiked body fluids, and T. gondii DNA in the organ tissues of experimentally infected mice. The assay developed in this study will be useful for the laboratory detection of T. gondii infection.

Detection of Toxoplasma gondii-like oocysts in cat feces and estimates of the environmental oocyst burden

OBJECTIVE

To estimate the analytic sensitivity of microscopic detection of Toxoplasma gondii oocysts and the environmental loading of T gondii oocysts on the basis of prevalence of shedding by owned and unowned cats.

DESIGN

Cross-sectional survey.

SAMPLE POPULATION

326 fecal samples from cats.

PROCEDURES

Fecal samples were collected from cat shelters, veterinary clinics, cat-owning households, and outdoor locations and tested via ZnSO(4) fecal flotation.

RESULTS

Only 3 (0.9%) samples of feces from 326 cats in the Morro Bay area of California contained T gondii-like oocysts. On the basis of the estimated tonnage of cat feces deposited outdoors in this area, the annual burden in the environment was estimated to be 94 to 4,671 oocysts/m(2) (9 to 434 oocysts/ft(2)).

CONCLUSIONS AND CLINICAL RELEVANCE

Despite the low prevalence and short duration of T gondii oocyst shedding by cats detected in the present and former surveys, the sheer numbers of oocysts shed by cats during initial infection could lead to substantial environmental contamination. Veterinarians may wish to make cat owners aware of the potential threats to human and wildlife health posed by cats permitted to defecate outdoors.

Fecal and serological survey of Neospora caninum in farm dogs in Costa Rica

To detect oocysts of Neospora caninum in dog feces and to determine the excretion pattern in dogs from specialized dairy farms in Costa Rica, a total of 265 fecal samples from 34 dogs were collected at intervals from February to August 2005. Fecal samples were examined for N. caninum-like oocysts microscopically, by DNA detection using the polymerase chain reaction (PCR), and by bioassay. N. caninum DNA was detected by PCR in four fecal samples, twice from one dog, but oocysts were not detected microscopically in these dogs. Sera of 31 of 34 dogs were tested for antibodies to N. caninum by a competitive-inhibition ELISA (VMRD). Fifteen (48.4%) of 31 dogs had antibodies to N. caninum by ELISA. Seroconversion was not found in 28 dogs that were bled twice, 4 months apart (March and July 2005). Only one dog tested positive to N. caninum by both ELISA and PCR. This is the first report of finding N. caninum DNA in feces of naturally infected dogs in Costa Rican dairy farms.

The development of a molecular approach for coprodiagnosis of Toxoplasma gondii

Copro-diagnostic methods for Toxoplasma gondii infected cats have been traditionally based on the identification of oocysts by light microscopy or by bioassays. The first method is not sensitive and also unable to differentiate between Toxoplasma oocysts from other coccidian parasites in cats, and the second is cumbersome, time consuming and expensive. We have adapted a polymerase chain reaction (PCR) method to detect T. gondii oocyst DNA in fecal samples. Oocysts were successfully disrupted by freeze thawing coupled with mechanical means, and DNA extraction was subsequently accomplished. The test, based on amplifying a 529 bp repeated sequence, proved sensitive for detecting 1-2 oocysts in 200 microg of stool sample. The test specificity was established by showing that DNA from other cat coccidia tested negative. Specificity was reconfirmed by Southern hybridization of the PCR products with a specific probe. Of 122 stool samples from Jerusalem cats surveyed for the presence of Toxoplasma oocysts, 11 were found positive by PCR while none was detected by microscopy.