Dataset Information

How important are rats as vectors of leptospirosis in the Mekong Delta of Vietnam?

ABSTRACT: Leptospirosis is a zoonosis known to be endemic in the Mekong Delta of Vietnam, even though clinical reports are uncommon. We investigated leptospira infection in rats purchased in food markets during the rainy season (October) (n=150), as well as those trapped during the dry season (February-March) (n=125) in the region using RT-PCR for the lipL32 gene, confirmed by 16S rRNA, as well as by the microscopic agglutination test (MAT). Results were compared with the serovar distribution of human cases referred from Ho Chi Minh City hospitals (2004-2012) confirmed by MAT (n=45). The MAT seroprevalence among rats was 18.3%. The highest MAT seroprevalence corresponded, in decreasing order, to: Rattus norvegicus (33.0%), Bandicota indica (26.5%), Rattus tanezumi (24.6%), Rattus exulans (14.3%), and Rattus argentiventer (7.1%). The most prevalent serovars were, in descending order: Javanica (4.6% rats), Lousiana (4.2%), Copenageni (4.2%), Cynopterie (3.7%), Pomona (2.9%), and Icterohaemorrhagiae (2.5%). A total of 16 rats (5.8%) tested positive by RT-PCR. Overall, larger rats tended to have a higher prevalence of detection. There was considerable agreement between MAT and PCR (kappa=0.28 [0.07-0.49]), although significantly more rats were positive by MAT (McNemar 29.9 (p<0.001). MAT prevalence was higher among rats during the rainy season compared with rats in the dry season. There are no current available data on leptospira serovars in humans in the Mekong Delta, although existing studies suggest limited overlapping between human and rat serovars. Further studies should take into account a wider range of potential reservoirs (i.e., dogs, pigs) as well as perform geographically linked co-sampling of humans and animals to establish the main sources of leptospirosis in the region.

SUBMITTER: Loan HK

PROVIDER: S-EPMC4307199 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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How important are rats as vectors of leptospirosis in the Mekong Delta of Vietnam?

Loan Hoang Kim HK Van Cuong Nguyen N Takhampunya Ratree R Kiet Bach Tuan BT Campbell James J Them Lac Ngoc LN Bryant Juliet E JE Tippayachai Bousaraporn B Van Hoang Nguyen N Morand Serge S Hien Vo Be VB Carrique-Mas Juan J JJ

Vector borne and zoonotic diseases (Larchmont, N.Y.) 20150101 1

Leptospirosis is a zoonosis known to be endemic in the Mekong Delta of Vietnam, even though clinical reports are uncommon. We investigated leptospira infection in rats purchased in food markets during the rainy season (October) (n=150), as well as those trapped during the dry season (February-March) (n=125) in the region using RT-PCR for the lipL32 gene, confirmed by 16S rRNA, as well as by the microscopic agglutination test (MAT). Results were compared with the serovar distribution of human cas ...[more]

PMID: 25629781

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Project description:The Mekong Delta in Vietnam has seen a rapid development and intensification of aquaculture in the last decades, with a corresponding widespread use of antibiotics. This study provides information on current antibiotic use in freshwater aquaculture, as well as on resulting antibiotic concentrations in the aquatic environment of the Mekong Delta. Two major production steps, fish hatcheries and mature fish cultivation, were surveyed (50 fish farm interviews) for antibiotic use. Different water sources, including surface water, groundwater and piped water (164 water samples) were systematically screened for antibiotic residues. To better understand antibiotic fate under tropical conditions, the dissipation behavior of selected antibiotics in the aquatic environment was investigated for the first time in mesocosm experiments. None of the investigated antibiotics were detected in groundwater and piped water samples. Surface water, which is still often used for drinking and domestic purposes by local populations, contained median concentrations of 21 ng L-1 sulfamethoxazole (SMX), 4 ng L-1 sulfadiazine (SDZ), 17 ng L-1 trimethoprim (TRIM), and 12 ng L-1 enrofloxacin (ENRO). These concentrations were lower than the predicted no effect concentrations (PNECs) and minimum inhibitory concentrations (MICs), suggesting limited antibiotic-related risk to aquatic ecosystems in the monitored systems. The dissipation half-lives of the studied antibiotics ranged from <1 to 44 days, depending on the availability of sunlight and sediment. Among the studied antibiotics TRIM was the most persistent in water systems. TRIM was not susceptible to photodegradation, while the dissipation of ENRO and SDZ was influenced by photolysis. The recorded dissipation models gave good predictions of the occurrence and concentrations of TRIM, ENRO and SDZ in surface water. In summary, the currently measured concentrations of the investigated antibiotics are unlikely to cause immediate risks to the aquatic environment, yet the persistence of these antibiotics is of concern and might lead to chronic exposure of aquatic organisms as well as humans.

Project description:Small-scale farming of meat chicken flocks using local native breeds contributes to the economy of many rural livelihoods in Vietnam and many other low- and middle-income countries (LMICs). These systems are also the target of high levels of antimicrobial use (AMU); however, little is known about the profitability and sustainability of such systems. Since small-scale farms are commercial enterprises, this knowledge is essential to develop successful strategies to curb excessive AMU. Using longitudinal data from 203 small-scale (100-2,000 heads) native chicken flocks raised in 102 randomly selected farms in Dong Thap province (Mekong Delta, Vietnam), we investigated the financial and economic parameters of such systems and the main constraints to their sustainability. Feed accounted for the largest financial cost (flock median 49.5 % [Inter-quartile range (IQR) 41.5-61.8 %]) of total costs, followed by day-old-chicks (DOCs) (median 30.3 % [IQR 23.2-38.4 %]), non-antimicrobial health-supporting products (median 7.1 % [IQR 4.7-10.5 %]), vaccines (median 3.1 % [IQR 2.2-4.8 %]), equipment (median 1.9 % [IQR 0.0-4.9 %]) and antimicrobials (median 1.9 % [IQR 0.7-3.6 %]). Excluding labor costs, farmers achieved a positive return on investment (ROI) from 120 (59.1 %) flocks, the remainder generating a loss (median ROI 124 % [IQR 36-206 %]). Higher ROI was associated with higher flock size and low mortality. There was no statistical association between use of medicated feed and flock mortality or chicken bodyweight. The median daily income per person dedicated to raising chickens was 202,100 VND, lower than alternative rural labor activities in the Mekong Delta. In a large proportion of farms (33.4 %), farmers decided to stop raising chickens after completing one cycle. Farmers who dropped off chicken production purchased more expensive feed (in 1000 VND per kg): 11.1 [10.6-11.5] vs. 10.8 [10.4-11.3] for farms that continued production (p = 0.039), and experienced higher chicken mortality (28.5 % [12.0-79.0 %] vs. 16 [7.5-33.0 %]; p = 0.004). The rapid turnover of farmers raising chickens in such systems represents a challenge to the uptake of messages on appropriate AMU and chicken health. To ensure sustainability of small-scale commercial systems, advisory services need to be available to farmers as they initiate new flocks, and support them in the early stages to help overcome their limited experience and skills. This targeted approach would support profitability whilst reducing risk of emergence of AMR and infectious disease from these systems.

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How important are rats as vectors of leptospirosis in the Mekong Delta of Vietnam?

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How important are rats as vectors of leptospirosis in the Mekong Delta of Vietnam?

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