Evaluation of a novel Tc-24 recombinant antigen ELISA for serologic testing for Trypanosoma cruzi in dogs.

Chagas disease is a parasitic infection caused by Trypanosoma cruzi. Diagnosis of chronic Chagas disease in dogs relies on limited serological test options. This study used a new Tc-24 recombinant antigen ELISA on an archival set of 70 dog serum samples from multi-dog kennel environments in Texas subjected to three existing Chagas serological tests. Tc-24 ELISA produced a quantitative result and could detect anti-T. cruzi antibodies in dogs with high sensitivity and specificity. Comparing individual tests to Tc-24 ELISA resulted in strong associations and correlations, which suggest that Tc-24 ELISA is a reliable and accurate diagnostic tool for dogs with a single test.

Validation of a multiplex microsphere immunoassay for detection of antibodies to Trypanosoma cruzi in dogs.

The vector-borne protozoan parasite Trypanosoma cruzi causes Chagas disease in humans, dogs, and many other mammalian hosts. Canine Chagas disease is increasingly diagnosed in dogs of the southern United States where triatomine insect vectors occur, and there are limited veterinary testing options; only the indirect fluorescent antibody (IFA) test is offered at a single accredited diagnostic laboratory. We evaluated a multiplex microsphere immunoassay (MIA) for the detection of antibodies against T. cruzi in dogs and compared it with existing serologic methods to establish cutoff values and relative sensitivity and specificity. We tested 135 canine sera that had been characterized using the IFA and off-label use of 2 commercial rapid assays with our multiplex MIA against 12 antigens: 9 T. cruzi antigens, a negative control recombinant protein (green fluorescent protein, GFP), a Leishmania antigen, and a canine parvovirus antigen (used as an antibody control given near-ubiquitous parvoviral vaccination). The median fluorescence intensity (MFI) ratio between each T. cruzi antigen and GFP was calculated for every sample. Samples with an antigen:GFP MFI ratio > 4 SDs above the mean of 25 known-negative sera were considered positive to that antigen. Samples testing positive to ≥ 2 antigens were considered positive for T. cruzi antibodies. Compared to the IFA, our multiplex MIA had a relative sensitivity of 100% and specificity of 97.0%. Given its precision, high-throughput format, potential for automation, and lack of subjective interpretation, our multiplex MIA should be considered a valid and improved assay for T. cruzi antibodies in dogs.

Canine Systemic Insecticides Fluralaner and Lotilaner Induce Acute Mortality of Triatoma gerstaeckeri, North American Vector of the Chagas Disease Parasite.

Chagas disease is a health concern for humans and animals across the Americas, and control options targeting the triatomine vectors of Trypanosoma cruzi, the causative agent of Chagas disease, are limited. Host-targeted interventions may be a useful and underused tool in controlling the spread of T. cruzi from vectors to hosts. Domestic dogs are known to be key bloodmeal hosts for triatomines as well as T. cruzi reservoirs and may be an effective and practical target for host-targeted insecticide deployment. We hypothesized that treating dogs with commercially available systemic insecticides (labeled for flea and tick control) would result in mortality of triatomines after consuming treated blood. We enrolled 16 privately owned dogs into five treatment groups to receive either fluralaner (Bravecto) or lotilaner (Credelio), alone or in combination with ivermectin. Blood from dogs before the initiation of treatment served as controls. Blood was collected 0, 7, 30, 45, and 90 days after the initial canine insecticide treatment and fed to 10 Triatoma gerstaeckeri nymphs through a membrane feeder, and survival was tracked daily for 7 days and weekly thereafter. All triatomines in the control and ivermectin groups survived the initial period, with no significant difference in long-term survival. In contrast, 99.7% of triatomines that fed on blood from dogs treated with either fluralaner or lotilaner died within 3 days. Although the impact of canine treatment on suppressing vector populations is unknown, fluralaner and lotilaner appear to be a compelling option for an integrated vector management approach to triatomine control.

A Scoping Review of Mathematical Models Used to Investigate the Role of Dogs in Chagas Disease Transmission.

Chagas disease is a zoonotic vector-borne disease caused by the parasite Trypanosoma cruzi, which affects a variety of mammalian species across the Americas, including humans and dogs. Mathematical modeling has been widely used to investigate the transmission dynamics and control of vector-borne diseases. We performed a scoping review of mathematical models that investigated the role of dogs in T. cruzi transmission. We identified ten peer-reviewed papers that have explicitly modeled the role of dogs in Chagas transmission dynamics. We discuss the different methods employed in these studies, the different transmission metrics, disease transmission routes, and disease control strategies that have been considered and evaluated. In general, mathematical modeling studies have shown that dogs are not only at high risk of T. cruzi infection but are also major contributors to T. cruzi transmission to humans. Moreover, eliminating infected dogs from households or frequent use of insecticide was shown to be effective for curtailing T. cruzi transmission in both humans and dogs. However, when insecticide spraying is discontinued, T. cruzi infections in dogs were shown to return to their pre-spraying levels. We discuss the challenges and opportunities for future modeling studies to improve our understanding of Chagas disease transmission dynamics and control.

Effectiveness of fluralaner treatment regimens for the control of canine Chagas disease: A mathematical modeling study.

BACKGROUND: Canine Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and transmitted by insect triatomine vectors known as kissing bugs. The agent can cause cardiac damage and long-term heart disease and death in humans, dogs, and other mammals. In laboratory settings, treatment of dogs with systemic insecticides has been shown to be highly efficacious at killing triatomines that feed on treated dogs. METHOD: We developed compartmental vector-host models of T. cruzi transmission between the triatomine and dog population accounting for the impact of seasonality and triatomine migration on disease transmission dynamics. We considered a single vector-host model without seasonality, and model with seasonality, and a spatially coupled model. We used the models to evaluate the effectiveness of the insecticide fluralaner with different durations of treatment regimens for reducing T. cruzi infection in different transmission settings. RESULTS: In low and medium transmission settings, our model showed a marginal difference between the 3-month and 6-month regimens for reducing T. cruzi infection among dogs. The difference increases in the presence of seasonality and triatomine migration from a sylvatic transmission setting. In high transmission settings, the 3-month regimen was substantially more effective in reducing T. cruzi infections in dogs than the other regimens. Our model showed that increased migration rate reduces fluralaner effectiveness in all treatment regimens, but the relative reduction in effectiveness is minimal during the first years of treatment. However, if an additional 10% or more of triatomines killed by dog treatment were eaten by dogs, treatment could increase T. cruzi infections in the dog population at least during the first year of treatment. CONCLUSION: Our analysis shows that treating all peridomestic dogs every three to six months for at least five years could be an effective measure to reduce T. cruzi infections in dogs and triatomines in peridomestic transmission settings. However, further studies at the local scale are needed to better understand the potential impact of routine use of fluralaner treatment on increasing dogs' consumption of dead triatomines.

Prophylactic low-dose, bi-weekly benznidazole treatment fails to prevent Trypanosoma cruzi infection in dogs under intense transmission pressure.

Trypanosoma cruzi naturally infects a wide variety of wild and domesticated mammals, in addition to humans. Depending on the infection dose and other factors, the acute infection can be life-threatening, and in all cases, the risk of chagasic heart disease is high in persistently infected hosts. Domestic, working, and semi-feral dogs in the Americas are at significant risk of T. cruzi infection and in certain settings in the southern United States, the risk of new infections can exceed 30% per year, even with the use of vector control protocols. In this study, we explored whether intermittent low-dose treatment with the trypanocidal compound benznidazole (BNZ) during the transmission season, could alter the number of new infections in dogs in an area of known, intense transmission pressure. Preliminary studies in mice suggested that twice-weekly administration of BNZ could prevent or truncate infections when parasites were delivered at the mid-point between BNZ doses. Pre-transmission season screening of 126 dogs identified 53 dogs (42.1%) as T. cruzi infection positive, based upon blood PCR and Luminex-based serology. Serial monitoring of the 67 uninfected dogs during the high transmission season (May to October) revealed 15 (22.4%) new infections, 6 in the untreated control group and 9 in the group receiving BNZ prophylaxis, indicating no impact of this prophylaxis regimen on the incidence of new infections. Although these studies suggest that rigorously timed and more potent dosing regimen may be needed to achieve an immediate benefit of prophylaxis, additional studies would be needed to determine if drug prophylaxis reduced disease severity despite this failure to prevent new infections.

Chagas Disease Ecology in the United States: Recent Advances in Understanding Trypanosoma cruzi Transmission Among Triatomines, Wildlife, and Domestic Animals and a Quantitative Synthesis of Vector-Host Interactions.

Chagas disease, a neglected tropical disease present in the Americas, is caused by the parasite Trypanosoma cruzi and is transmitted by triatomine kissing bug vectors. Hundreds of vertebrate host species are involved in the ecology of Chagas disease. The sylvatic nature of most triatomines found in the United States accounts for high levels of animal infections but few reports of human infections. This review focuses on triatomine distributions and animal infections in the southern United States. A quantitative synthesis of available US data from triatomine bloodmeal analysis studies shows that dogs, humans, and rodents are key taxa for feeding triatomines. Imperfect and unvalidated diagnostic tools for wildlife complicate the study of animal T. cruzi infections, and integrated vector management approaches are needed to reduce parasite transmission in nature. The diversity of animal species involved in Chagas disease ecology underscores the importance of a One Health approach for disease research and management.

SARS-CoV-2 B.1.1.7 variant of concern detected in a pet dog and cat after exposure to a person with COVID-19, USA.

As part of a longitudinal household transmission study of pets living with persons with COVID-19 in Texas, two pets were confirmed to be infected with the SARS-CoV-2 B.1.1.7 variant of concern (VOC). The pets were a dog and a cat from the same household, sampled two days after their owner tested positive for COVID-19. The oral, nasal and fur swabs for both pets tested positive for SARS-CoV-2 by qRT-PCR and consensus whole-genome sequences from the dog and cat were 100% identical and matched the B.1.1.7 VOC. Virus was isolated from the cat's nasal swab. One month after initial detection of infection, the pets were re-tested twice at which time only the fur swabs (both pets) and oral swab (dog only) remained positive, and neutralizing antibodies for SARS-CoV-2 were present in both animals. Sneezing by both pets was noted by the owner in the weeks between initial and follow-up testing. This study documents the first detection of B.1.1.7. in companion animals in the United States, and the first genome recovery and isolation of B.1.1.7 variant of concern globally in any animal.

High incidence of Trypanosoma cruzi infections in dogs directly detected through longitudinal tracking at 10 multi-dog kennels, Texas, USA.

Canine Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is increasingly recognized as a health concern for dogs in the USA, and infected dogs may signal geographic regions of risk for human disease. Dogs living in multi-dog kennel environments (kennels with more than one dog) where triatomine vectors are endemic may be at high risk for infection. We monitored a cohort of 64 T. cruzi-infected and uninfected dogs across 10 kennels in Texas, USA, to characterize changes in infection status over one year. We used robust diagnostic criteria in which reactivity on multiple independent platforms was required to be considered positive. Among the 30 dogs enrolled as serologically- and/or PCR-positive, all but one dog showed sustained positive T. cruzi diagnostic results over time. Among the 34 dogs enrolled as serologically- and PCR-negative, 10 new T. cruzi infections were recorded over a 12-month period. The resulting incidence rate for dogs initially enrolled as T. cruzi-negative was 30.7 T. cruzi infections per 100 dogs per year. This study highlights the risk of T. cruzi infection to dogs in kennel environments. To protect both dog and human health, there is an urgent need to develop more integrated vector control methods as well as prophylactic and curative antiparasitic treatment options for T. cruzi infection in dogs.

Host Bloodmeal Identification in Cave-Dwelling Ornithodoros turicata Dugès (Ixodida: Argasidae), Texas, USA.

Tick-host bloodmeal associations are important factors when characterizing risks of associated pathogen transmission and applying appropriate management strategies. Despite their biological importance, comparatively little is known about soft tick (Argasidae) host associations in the United States compared to hard ticks (Ixodidae). In this study, we evaluated a PCR and direct Sanger sequencing method for identifying the bloodmeal hosts of soft ticks. We collected 381 cave-associated Ornithodoros turicata near San Antonio, Texas, USA, and also utilized eight colony-reared specimens fed artificially on known host blood sources over 1.5 years ago. We correctly identified the vertebrate host bloodmeals of two colony-reared ticks (chicken and pig) up to 1,105 days post-feeding, and identified bloodmeal hosts from 19 out of 168 field-collected soft ticks, including raccoon (78.9%), black vulture (10.5%), Texas black rattlesnake (5.3%), and human (5.3%). Our results confirm the retention of vertebrate blood DNA in soft ticks and advance the knowledge of argasid host associations in cave-dwelling O. turicata.