Impact of the dog population and household environment for the maintenance of natural foci of Leishmania infantum transmission to human and animal hosts in endemic areas for visceral leishmaniasis in Sao Paulo state, Brazil

Comparative Study of a Novel Lateral Flow Rapid Test with Conventional Serological Test Systems for the Diagnosis of Canine Leishmaniosis in Croatia and Brazil

Control of canine infections with Leishmania infantum (L. infantum), a major zoonotic disease in Brazil and southern Europe, is becoming increasingly important due to its close proximity to humans, the increasing import of dogs from endemic regions and the impact of climate change on vector spreading. Simple, rapid and reliable diagnostic tests are therefore needed to detect infected dogs. Here, we re-evaluated different serological methods for the diagnosis of canine leishmaniosis (CanL) in Croatia and Brazil. The diagnostic performance of the indirect fluorescent antibody test (IFAT) and the VetLine® Leishmania ELISA (GSD Frankfurt, Germany) was compared with three rKLi8.3-based diagnostic test systems, the rKLi8.3 ELISA (GSD Frankfurt, Germany), the INgezim® Leishma CROM (GSD Madrid, Spain) lateral flow test (LFT) and the VetBlot®Leishmania LineBlot (GSD Frankfurt, Germany). CanL symptomatic dogs were efficiently diagnosed by all tests, except the VetLine® Leishmania ELISA, which is based on whole Leishmania antigens. The advantage of rKLi8.3 was also observed in oligo- and asymptomatic dogs from Brazil and Croatia, although with reduced diagnostic efficiency compared to symptomatic dogs. Similar to IFAT and rKLi8.3 ELISA, the LFT did not cross-react with other common canine pathogens; it showed very high specificity for healthy dogs from endemic regions in both countries and did not react with healthy, vaccinated dogs in Brazil. In conclusion, serodiagnostic tests based on the rKLi8.3 antigens are superior to whole parasite antigens, and the LFT has the advantage of providing a laboratory-independent, rapid and specific diagnosis of CanL.

Detecting Leishmania in dogs: A hierarchical-modeling approach to investigate the performance of parasitological and qPCR-based diagnostic procedures

BACKGROUND

Domestic dogs are primary reservoir hosts of Leishmania infantum, the agent of visceral leishmaniasis. Detecting dog infections is central to epidemiological inference, disease prevention, and veterinary practice. Error-free diagnostic procedures, however, are lacking, and the performance of those available is difficult to measure in the absence of fail-safe "reference standards". Here, we illustrate how a hierarchical-modeling approach can be used to formally account for false-negative and false-positive results when investigating the process of Leishmania detection in dogs.

METHODS/FINDINGS

We studied 294 field-sampled dogs of unknown infection status from a Leishmania-endemic region. We ran 350 parasitological tests (bone-marrow microscopy and culture) and 1,016 qPCR assays (blood, bone-marrow, and eye-swab samples with amplifiable DNA). Using replicate test results and site-occupancy models, we estimated (a) clinical sensitivity for each diagnostic procedure and (b) clinical specificity for qPCRs; parasitological tests were assumed 100% specific. Initial modeling revealed qPCR specificity < 94%; we tracked the source of this unexpected result to some qPCR plates having subtle signs of possible contamination. Using multi-model inference, we formally accounted for suspected plate contamination and estimated qPCR sensitivity at 49-53% across sample types and dog clinical conditions; qPCR specificity was high (95-96%), but fell to 81-82% for assays run in plates with suspected contamination. The sensitivity of parasitological procedures was low (~12-13%), but increased to ~33% (with substantial uncertainty) for bone-marrow culture in seriously-diseased dogs. Leishmania-infection frequency estimates (~49-50% across clinical conditions) were lower than observed (~60%).

CONCLUSIONS

We provide statistical estimates of key performance parameters for five diagnostic procedures used to detect Leishmania in dogs. Low clinical sensitivies likely reflect the absence of Leishmania parasites/DNA in perhaps ~50-70% of samples drawn from infected dogs. Although qPCR performance was similar across sample types, non-invasive eye-swabs were overall less likely to contain amplifiable DNA. Finally, modeling was instrumental to discovering (and formally accounting for) possible qPCR-plate contamination; even with stringent negative/blank-control scoring, ~4-5% of positive qPCRs were most likely false-positives. This work shows, in sum, how hierarchical site-occupancy models can sharpen our understanding of the problem of diagnosing host infections with hard-to-detect pathogens including Leishmania.

Isolation, typing, and drug susceptibility of Leishmania (Leishmania) infantum isolates from dogs of the municipality of Embu das Artes, an endemic region for canine leishmaniasis in Brazil

The parasitic protozoa Leishmania (Leishmania) infantum is the etiological agent of human visceral leishmaniasis and canine leishmaniasis in South America, where Brazil is the most affected country. This zoonotic disease is transmitted by the bite of an infected phlebotomine sand fly and dogs constitute the main domestic reservoir of the parasite. In this study, we screened 2348 dogs of the municipality of Embu das Artes, Brazil, for antibodies against the parasite. Prevalence for canine leishmaniasis seropositivity was 2.81%, as assessed using a Dual-Path Platform rapid test for canine leishmaniasis. Twenty-five seropositive dogs were euthanized for parasite isolation and 14 isolates were successful obtained. Nucleotide sequencing of the internal transcribed spacer confirmed the isolates to be L. (L.) infantum, and very low sequence variability was observed among them. The in vitro susceptibility to miltefosine and paromomycin was assessed and moderate variation in paromomycin susceptibility was found among the isolates in the promastigote and intracellular amastigote stages. On the other hand, in vitro susceptibility to miltefosine of these isolates was homogenous, particularly in the amastigote stage (EC₅₀ values from 0.69 to 2.07 μM). In addition, the miltefosine sensitivity locus was deleted in all the isolates, which does not corroborate the hypothesis that the absence of this locus is correlated with a low in vitro susceptibility. Our findings confirm that the municipality of Embu das Artes is endemic for canine leishmaniasis and that isolates from this region are susceptible to paromomycin and miltefosine, indicating the potential of these drugs to be clinically evaluated in the treatment of human visceral leishmaniasis in Brazil.

Efficacies of insecticide dog collars against visceral leishmaniasis in low and high-income areas and the effects for non-collared neighbor dogs

Previous studies demonstrated that insecticide collars are highly effective in reducing canine visceral leishmaniasis (CVL); however, it is unclear if the efficacy differs by socioeconomic conditions across diverse communities. This study aimed fourfold: (i) to evaluate the protection of 4% impregnated deltamethrin collared (DMC) dogs in different areas of an endemic city for visceral leishmaniasis (VL); (ii) to analyze socioeconomic variables with the seroconversion rates; (iii) to analyze the indirect effect of DMC on untreated dogs in areas of intervention; and, (iv) to evaluate the potential transmission to other dogs in the same household when one positive dog is present. The study employed the municipality of Bauru, São Paulo, Brazil, as the area of interest and used Geographic Information System tools to fit binary logistic regression models.  Dogs were divided into three cohort studies: intervention with DMC (I), indirect effect of DMC (IE), and control (C). Pre-intervention, lower mean income was associated with higher rates of CVL and a 142% increase in the odds of transmission (OR = 1.42, p-value = 0.001, CI 1.14,1.77). Post-intervention, lower-income areas depicted greater efficacy (76%) than higher-income areas (45%). The overall efficacy of DMC in preventing CVL was 63%; however, seroconversion rates were higher for IE (6.02%) than C (3.78%), revealing the failure of the indirect protection of DMC to manage the spread of the disease among the general non-wearing DMC canine population living in the same area. The protected dogs may repel the vectors, and non-protected dogs attract them, creating a higher transmission rate for non-protected dogs. Greater seroconversion was observed for living with an infected dog (10.20% in IE and 8.75% in C) than for the indirect effect of DMC, demonstrating the social burden of CVL. Overall, uncollared dogs have three times higher odds of being infected with CVL than DMC dogs (p < 0.005), and uncollared dogs living with (an) infected dog(s) in the same household can reach 3.5 times higher odds than those living with negative ones (p < 0.005). The results may assist in enhancing public policies and minimizing inequality in low and middle-income countries that suffer from neglected diseases such as VL.

Spatiotemporal analysis of highly pathogenic avian influenza (H5N1) outbreaks in poultry in Egypt (2006 to 2017)

Background

In Egypt, the highly pathogenic avian influenza (HPAI) subtype H5N1 is endemic and possesses a severe impact on the poultry. To provide a better understanding of the distributional characteristics of HPAI H5N1 outbreaks in Egypt, this study aimed to explore the spatiotemporal pattern and identify clusters of HPAI H5N1 outbreaks in Egypt from 2006 to 2017.

Results

The Epidemic curve (EC) was constructed through time series analysis; in which six epidemic waves (EWs) were revealed. Outbreaks mainly started in winter peaked in March and ended in summer. However, newly emerged thermostable clades (2.2.1.1 and 2.2.1.2) during the 4th EW enabled the virus to survive and cause infection in warmer months with a clear alteration in the seasonality of the epidemic cycle in the 5th EW. The endemic situation became more complicated by the emergence of new serotypes. As a result, the EC ended up without any specific pattern since the 6th EW to now. The spatial analysis showed that the highest outbreak density was recorded in the Nile Delta considering it as the ‘Hot spot’ region. By the 6th EW, the outbreak extended to include the Nile valley. From spatiotemporal cluster epidemics, clustering in the Delta was a common feature in all EWs with primary clusters consistently detected in the hot-spot region, but the location and size varied with each EW. The highest Relative Risk (RR) regions in an EW were noticed to contain the primary clusters of the next EW and were found to include stopover sites for migratory wild birds. They were in Fayoum, Dakahlia, Qalyobiya, Sharkia, Kafr_Elsheikh, Giza, Behera, Menia, and BeniSuef governorates. Transmission of HPAI H5N1 occurred from one location to another directly resulted in a series of outbreaks forming neighboring secondary clusters. The absence of geographical borders between the governorates in addition to non-restricted movements of poultry and low vaccination and surveillance coverage contributed to the wider spread of infection all over Egypt and to look like one epidemiological unit.

Conclusion

Our findings can help in better understanding of the characteristics of HPAI H5N1 outbreaks and the distribution of outbreak risk, which can be used for effective disease control strategies.

Graphical abstract