Current status of glanders in Brazil: recent advances and challenges

Comparison of immunogenicity of 17 Burkholderia mallei antigens and whole cell lysate using indirect ELISA

Glanders is a World Organization for Animal Health (WOAH)-notifiable equine disease caused by the infection of Burkholderia mallei, and is endemic in Mongolia, South Asia, Africa, and South America. While the complement fixation test (CFT) has been widely used for serodiagnosis of glanders and is considered a standard serological test, it has several limitations. These limitations include poor specificity, labor intensive techniques, variability in antigen and protocol. Consequently, indirect enzyme-linked immunosorbent assays (iELISAs) based on recombinant proteins have been developed as alternative serodiagnostic assays to address some of the challenges associated with the CFT. The accuracy of iELISA relies on the B. mallei proteins used as an antigen. Hence, to determine the best diagnostic candidate in iELISA, in terms of sensitivity and specificity, a comparison of 17 immunogenic B. mallei proteins and detergent-based whole cell lysate (WCL) was performed. According to the sensitivity and specificity on the sera from glanderous and non-glanderous Mongolian native horses, iELISA using Hcp1, GroEL, and detergent-based WCL represented the highest diagnostic accuracy. These three candidates did not have cross-reactivity to horse sera with several other equine diseases. WCL, Hcp1, and GroEL showed considerable potential as antigens for iELISA in the serodiagnosis of glanders in Mongolia. Detergent-based WCL extraction offers a consistent approach for the preparation of reliable B. mallei antigen. WCL-iELISA should be further validated in a large-scale study to meet WOAH demands.

Reassessing the distribution of Burkholderia pseudomallei outside known endemic areas using animal serological screening combined with environmental surveys: The case of Les Saintes (Guadeloupe) and French Guiana

BACKGROUND

Melioidosis, an emerging infectious disease that affects both humans and animals, is caused by the soil-dwelling bacterium Burkholderia pseudomallei. It is endemic in South and Southeast Asia, and northern Australia, causing an estimated 165,000 human cases annually worldwide. Human cases have been reported in the French West Indies (Martinique and Guadeloupe) since the 1990s. Conversely, no human cases have been reported in French Guiana, a French territory in South America. Our study aimed to investigate whether B. pseudomallei is locally established in Guadeloupe and French Guiana using animals as a proxy.

METHODOLOGY/PRINCIPAL FINDINGS

Blood samples were collected from different animals from 56 farms in French Guiana (n = 670) and from two goat farms in Les Saintes (n = 31), part of the Guadeloupe archipelago and tested by enzyme-linked immunosorbent assay (ELISA). In Les Saintes, a serological follow-up was performed, and soil, water and goat rectal swabs were collected and analyzed by culture and PCR. The highest seroprevalence rates (39%) were observed in goats in Les Saintes, followed by horses (24%) and cattle (16%) in French Guiana. In the two goat farms, supplementary analyses detected B. pseudomallei from one goat rectal swab, and a B. pseudomallei strain was isolated from the soil.

CONCLUSIONS/SIGNIFICANCE

Our animal serological data suggest the presence of B. pseudomallei in Les Saintes and French Guiana. In Les Saintes, environmental surveys confirmed the endemicity of the bacteria, which is consistent with documented human cases of melioidosis on the island. We did not conduct an environmental survey in French Guiana. Nevertheless, our serological results call for local environmental surveys and a retrospective reassessment of human infections with melioidosis-like symptoms.

First molecular characterization of Burkholderia mallei strains isolated from horses in Mongolia

Glanders, a highly contagious and often fatal disease affecting equids, is caused by Burkholderia mallei. Although sporadic cases of equine glanders have recently been documented in Mongolia, genome sequencing and molecular studies of the bacteria within this region are lacking. This study provided the first molecular characterization of B. mallei isolated from four native Mongolian horses from two different provinces in 2019 and 2022 by applying whole-genome sequencing with two SNP types (previously developed genotyping with 15 SNP markers that provide global coverage of the B. mallei population and the core genome coding SNP typing developed in this study). The Mongolian isolates were located within the L3B1 cluster, which was previously associated with the V-120 strain from Russia. Within the L3B1 cluster shared by neighboring countries, they were in a unique subbranch. In this study, specific SNP markers unique to the Mongolian strains were identified to track these strains using a high-resolution melting analysis (HRMA). This study revealed the unique phylogenetic background of Mongolian strains isolated from the eastern part of Mongolia. HRMA specific to the Mongolian subbranch may contribute to the molecular epidemiological monitoring of glanders in Mongolia and surrounding countries.

Spread analysis of glanders in the state of Piauí, northeastern Brazil

Brazil is strategic in controlling neglected zoonoses, such as glanders, in its territory. Among the Brazilian states, Piauí is a strategic state for the spread of the disease in the country. The present study aimed to evaluate the spatial and temporal distribution of official cases of glanders in Piauí between 2015 and 2022. The glanders cases were located in the municipalities of the north and central-north mesoregions, mainly in Campo Maior, Teresina and Altos. The highest incidence risk (IR) occurred in of Altos (IR = 257.9), Sussuapara (IR = 158.4), and Teresina (IR = 157.7). A primary cluster was formed with a relative risk of 14.88 between 2019 and 2022, encompassing 34 municipalities in the north and central-north regions. In Piauí, glanders is well localized, with the potential for spread across borders. This is the first study demonstrating the distribution of reported cases of glanders in the state of Piauí.

Assessment of the Virulence of the Burkholderia mallei Strain BAC 86/19 in BALB/c Mice

Burkholderia mallei is an aerobic, Gram-negative, non-motile bacillus. As an obligate mammalian pathogen, it primarily affects solipeds. Although rarely transmitted to humans, the disease it causes, glanders, is classified as a zoonosis. The bacterium was officially eradicated in Brazil in 1969; however, it reemerged after three decades. This study aims to assess the virulence of a specific B. mallei strain, isolated in Brazil, in BALB/c mice through intranasal infection. The strain, B. mallei BAC 86/19, was obtained from the tracheal secretion of a young mare displaying positive serology but no clinical signs of glanders. Post-mortem examinations revealed macroscopic lesions consistent with the disease, however. In mice, the LD50 was determined to be approximately 1.59 × 105 colony-forming units (CFU)/animal. Mice exposed to either 0.1 × LD50 or 1 × LD50 displayed transient weight loss, which resolved after three or five days, respectively. B. mallei persisted within the liver and lung for five days post-infection and in the spleen for seven days. These findings underscore the detectable virulence of the Brazilian B. mallei BAC 86/19 strain in mice, which are relatively resilient hosts. This research points to the importance of the continued investigation of the virulence mechanisms and potential countermeasures associated with B. mallei infections, including their Brazilian isolates.

Epidemiological Situation of Glanders in the State of Pará, Brazil

Glanders is an anthropozoonosis caused by the bacteria Burkholderia mallei, affecting mainly equids. It has been eradicated in North America, Australia, and Western Europe, but continues to occur sporadically in countries in Asia, Africa, the Middle East, and South America. Its notification is mandatory by the World Organization for Animal Health. After 30 years, the disease reappeared in Brazil in 1999 and, thereafter, 1,413 outbreaks have been reported. However, the epidemiological situation of the disease in the country is not adequately known. Thus, 2718 animals from 654 properties in the state of Pará were randomly selected by sampling and examined using a serial protocol with Complement Fixation and Western Blot serological tests. The prevalence of properties infected with glanders in the state was estimated at 1.68% [0.84; 3.33] and of seropositive animals at 0.50% [0.27; 0.94]. The introduction of animals was individualized as a risk factor for disease introduction in the properties (OR = 5.9 [1.4; 25.5]). Despite the low prevalence of infected properties and seropositive animals, the state must review actions to fight the disease, considering that the strategies implemented have not affected the endemic balance of the disease. This process must involve all public and private agents interested in the topic.