Seroprevalence of melioidosis in animals and environmental factors influencing presence of Burkholderia pseudomallei in small ruminant farms in peninsular Malaysia
Melioidosis results in chronic debilities that reduce productivity and causes condemnation of carcasses of affected animals. There have been anecdotal reports of increase in the disease in animals in Malaysia in recent times. However, there are limited scientific information on the distributio...
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| Format: | Thesis |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/70821/1/FPV%202014%2027%20IR.pdf |
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| Summary: | Melioidosis results in chronic debilities that reduce productivity and causes
condemnation of carcasses of affected animals. There have been anecdotal reports of
increase in the disease in animals in Malaysia in recent times. However, there are
limited scientific information on the distribution and risk factors of the disease in
animal populations as well as the factors in the environments of endemic areas that
influence presence of the disease agent. A study was carried out to determine the
distribution, risk factors and environmental factors that may influence the presence
of the disease agent in small ruminant farms in Peninsular Malaysia. Dataset on the
continuous surveillance of melioidosis in animals and another on rainfall and wind
speed were both obtained for a period of 10 years. The data were summarized
according to animal species, state, year and month of occurrence and relationships
between disease prevalence and rainfall and wind speed were examined. The overall
seroprevalence between the year 2000 and 2009 was 6.20% (95% CI; 6.02-6.37).
The seroprevalence according to animal species showed that buffalo had the highest
prevalence (28.18%, 95% CI; 19.04-39.54), followed by sheep (16.55%, 95% CI;
16.03 – 17.09), cattle (7.42%, 95% CI; 5.61-9.75), deer (6.45%, 95% CI; 4.50-9.17),
pigs (5.88%, 95% CI; 1.05–26.98), rabbits (3.90%, 95% CI 2.90-4.90) and goats
(2.19%, 95% CI; % 2.06-2.37). In terms of year of the study, the prevalence varied
from 3.14% (95% CI; 2.84-3.46) in 2008 to 11.79% (95%CI; 10.6-13.09) in 2003.
The prevalence for the year 2004 (7.46%, 95% CI; 6.73-8.26) was observed to be
significantly higher while those for the years 2008 (3.14%, 95% CI; 2.84-3.46) and
2009 (3.64%, 95% CI; 3.27-4.04) were significantly lower when compared to the
prevalence for the year 2000 (6.11%, 95% CI; 5.24-7.11). Correlation analysis
showed a moderate, positive and statistically significant correlation between
melioidosis prevalence and rainfall (r =0.58, 95% CI; 0.12-0.87, p=0.047) during the
period under review. The apparently low seroprevalence among pigs (5.88%) and
goats (2.19%) may partly be due to intensive farm management systems in which
animals had less contact with contaminated soil and water while the relatively high
seroprevalence in buffaloes may partly be due to the extensive management system in which animals are at higher risk of exposure to the disease agent. The higher
prevalence in 2000-2004 may be due to increased importations of animals and
unfavorable weather conditions during this period. The study however observed that
serosurveillance and data recording were not carried out consistently across states,
year and animal or livestock species.
To investigate the farm level risk factors of melioidosis seropositivity, questionnaires
were administered to the identified melioidosis negative and positive farms from four
selected states (Pahang, Perak, Negeri Sembilan and Selangor). The characteristics
and putative exposure to risk factors were compared between case and the control
farms using Chi-square test and logistic regression analysis. In the logistic regression
model, melioidosis–positive farms were significantly more likely to have; had bush
clearing around farms (odds ratio [OR]; 6.61, 95% confidence interval [CI]; 1.12-
38.84, p<0.037), B. pseudomallei present in the farm soil (OR; 6.23, 95% CI; 1.03-
37.68, p<0.046), other species raised on farm (OR; 7.96, 95% CI; 1.14-55.99,
p<0.037) and flooding or waterlogging condition (OR;11.95, 95% CI;1.39-102.6,
p=0.024) compared to negative farms. Farms that treated the soil with lime (OR;
0.028, 95% CI; 0.003-0.29, p=0.003) were protected from the infection. Bush
clearing may increase the risk of exposure to B. pseudomallei because it involves
dispersal of large amount of dust into the atmosphere, brings up agents located at
lower levels to the surface thereby increasing the risk of infection. Flood and or
waterlogging and presence of agent in farm soil may increase the risk of contact
between agent in soil and water with resident animals in the farm.
To investigate the physicochemical properties of soil and water that may influence
occurrence of the agent in the farm environment, soil and water samples collected
from small ruminant farms in the four states and cultured for B. pseudomallei. For
the soil properties, comparisons of the B. pseudomallei-positive and negative soil
samples using logistic regression model found that, when compared with B.
pseudomallei negative soil samples, a positive sample was found to be significantly
(p<0.05) more likely to have higher iron contents (OR; 1.009, 95% CI; 1.001-1.018,
p=0.034), higher water contents (OR; 1.28, 95% CI; 1.052-1.546, p=0.013) and
higher clay contents (OR; 1.54, 95% CI; 1.153-2.062, p=0.004). The significantly
higher iron, water and clay contents of the B. pseudomallei-positive soil is consistent
with the understanding that iron regulates expression of respiratory enzymes, soil
water is essential for soil ecology and agent’s biological processes and clay has
excellent water and nutrient retention capabilities due to its surface area and
chemical activity which favor survival of the agent in soil.
Investigation of the water properties found that, when compared with B.
pseudomallei negative water samples, positive water samples were found to be
significantly (p<0.05) more likely to have higher chemical oxygen demand (COD)
(OR; 1.002, 95% CI; 1.000-1.004, p=0.031) and higher pH value (OR; 12.69, 95%
CI; 2.67-60.34, p=0.001). This suggested that higher COD and higher water pH
supported the survival of the agent in water samples.
In conclusion, melioidosis is widely distributed in Peninsular Malaysia and affects all
livestock species regardless of the size, species, population size and breed. The
disease occurrence was associated with several factors such as events/activities
around farm such bush clearing, water logging/flooding and presence of other species of animal in the farm. The farm soil iron, water and clay content as well
chemical oxygen demand and pH of farm water supplies were the factors that
influence the presence of B. pseudomallei in farm environments. This information
may be of benefits when planning for control strategies against exposure to B.
pseudomallei from soil or water source. |
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