RISK FACTORS FOR PESTE DES PETITS RUMINANT (PPR) INFECTION IN GOAT
ABSTRACT
Importance of epidemiological information regarding the risk factors for peste des petits ruminant (PPR) infection led us to conduct a case-control study to measure the association between the PPR infection and possible risk factors. We used enzyme immuno slide assay (EISA) to check the status of the suspected clinical cases by antigen detection. Clinically suspected cases found positive by EISA were considered as case and negatives were considered as control. We compared 23 cases with 23 controls (1:1). We applied backward binary logistic regression to asses the association between the PPR cases and possible risk factors. Two risk factors remained statistically significant in the final model: Black Bengal breed (OR 5.048 [95 per cent CI 1.059 – 24.068]) and communal grazing (OR 7.802 [95 per cent CI 1.369 to 44.449]). The results of the study will be helpful for the planning of the prevention and control of PPR infection in goat in Bangladesh.
KEY WORDS: Peste des Petits Ruminant, Enzyme Immuno Slide Assay, Risk factor
CHAPTER-I
INTRODUCTION
Peste des petits ruminants(PPR), also known as goat plague, kata, or stomatitis- pneumoenteritis syndrome is a highly viral contagion of small ruminant particularly goat and sheep(Roeder et al. 1994; Amjad et al. 1996). The disease is characterized by the clinical signs including high fever (1060F), muco purulent discharges, profuse diarrhoea with fowl odour and death due to dehydration (Sil 2000). It is caused by the Morbillivirus a genus of the Paramyxoviridae family. The virus is antigenically, biologically, related and mimic to rinderpest. Antigenically, it is also related to canine distemper and measles virus (Kulkarni et al. 1996).
The PPR virus was first reported from west Africa in the early 40s(Gargadennec and Lalanne 1942) and was later found in Senegal(Gilbert and Monnier 1962) and subsequently recognized as being endemic in west and central Africa(Scott 1981). I has also been reported from Sudan(Taylor 1984),Kenya and Uganda(Wamwayi et al. 1995), Ethiopia(Roeder et al. 1994), Niger(Bloch and Diallo 1991), Egypt(Ismail and House 1990), India(Shaila et al. 1989), Pakistan(Amjad et al. 1996), Oman(Taylor et al. 1990), Saudi Arabia(Al-Naeem et al. 2000), Jordan(Al-Majali et al. 2008), Iran (Bazarghani et al. 2006), Turkey(Cam et al. 2005) and Tajikistan (Kwiatek et al. 2007). Increased number of the endemic county over the time period indicates that the disease is widely distributed and spreading in equatorial Africa, the Arabian peninsula, part of Indian
PPR is an exotic disease of goats in Bangladesh (Debnath 1995; Islam et al. 2001). In Bangladesh it was first recorded in 1993, and serious out break had been occurred in border belt of south-eastern districts of Bangladesh (Debnath 1995; Sil 2000). The outbreak of this Rinderpest like disease confirmed by reference virology laboratory of Pirbright, Surrey, UK to be PPR(Debnath 1995). The disease is in endemic status in Bangladesh. In a recent serological survey, sero prevalence in goat was 36% (Das et al.
2007).
The effect of PPR on goat population is certainly considerable. The outbreak of this disease every year causes heavy economical loss in the endemic countries. The morbidity and mortality rate vary but may reach up to 90-100% respectively (Sil 2000; Lefevre and Diallo 1990; Taylor et al. 1990). Besides, abortion and reduction of reproductive capacity in survived doe are also notable (Ezeibe and Wosu 1999).
Various techniques have been developed for the diagnosis of the PPR in sheep and goat.
These includes virus neutralization test (VNT)(Rossiter et al. 1985), Haemagglutination(HA)(Ezeibe et al. 2004), Haemagglutination inhibition(HI)(Wosu and Ezeibe 1992), agar gel precipitation test(Durojaiye 1987), indirect enzyme linked immunosorbent assay(ELISA)(Obi et al. 1990; Olaleye et al. 1989), monoclonal antibody based competitive enzyme linked immunosorbent assay (cELISA)(Choi et al. 2005), monoclonal antibody based blocking ELISA(bELISA)(Saliki et al. 1993), monoclonal antibody based enzyme immuno slide assay (EISA) (Sil et al. 2001) and polymerase
chain reaction(PCR)(Forsyth and Barrett 1995). Despite of this tests PPR cases still diagnosed based on clinical signs.
With the development of various diagnostic tools, demand for the in-depth epidemiological information increases, over the last few years. Considering the necessity and lack of information regarding the risk factors and their association with PPR infection, we aimed to explore the possible risk factors for PPR infection in Bangladesh.
CHAPTER-II
REVIEW OF LITERATURE
There are so many literatures about PPR diseases, from which some important research findings are listed below along with references.
The risk factors of PPR are presented below:
Hosts:
PPR is usually more severe in goats and is occasionally severe in sheep (Shaila et al., 1989). Black Bengal goats are more susceptible(67.24%) to PPR than Jamunapary (32.76%) (Samad, 2000).
Age:
The disease is rapidly fatal in young animals (60.87%) at 7-12 months of age (Blood et al., 1995).
Transmission:
There are several means of transmission between animals. These are close contact between infected and susceptible animals, direct contact with ocular , nasal or oral secretions (Taylor, 1979) , direct contact with feces, fomites such as bedding, water, feed troughs and inhalation of aerosols produced by sneezing and coughing of infected animals (Ozkul, 2002; OIE, 2000).
Epidemiological area:
PPR found in sub- Saharan Africa for several decades and in the Middle East and southern Asia since 1993 (Taylor, 2002). The disease remain endemic in Arabian Peninsula, the Middle East and in Indian subcontinent (Mornet et al., 1956). It also occurred in Bangladesh in the year of 1993 and 2003 (Dhar, 2002).
Other factors:
In both sheep and goat flocks, large flock size, visiting live animals market and inadequate veterinary services were identified as risk factors for PPR seropositivity.
Mixed (sheep and goats) raising was identified as a risk factor for PPR seropositivity in sheep flocks only (Ahmed , M. et al., 2008).
CHAPTER-III
MATERIALS AND METHODS
Study population and sampling:
The study was conducted over seven weeks in Jessore, Bangladesh. Study was conducted among the PPR infected goat of various age and sex that were bring to the veterinary hospital over the study period. The sampling procedure depended on the presence of sus- pected infection based on clinical signs of PPRV infection. These animals were examined clinically, and any animals with signs of disease were sampled by swabbing for antigen detection. A total number of 70 cases were recorded in Internship Case-Logs.
Clinical examination:
Clinical History of the cases were taken from the owner and carefully recorded in each case individually. Among clinical examinations close inspection were done carefully to observe the presenting signs and also recorded. Per rectal temperature were recorded with thermometer by indirect palpation method. Besides, indirect auscultation was performed to hear the lung sound and tracheal sound. Skin fold test were also performed to make the rough estimation of the degree of dehydration.
Test sample and EISA technique:
Animals with significant clinical signs were selected for taking samples for detecting PPRV antigen through EISA technique. EISA test was conducted in samples coated glass slides after acetone fixation. Smears were prepared using nasal discharge and oral
mucosa. Cotton swabbing of the infected samples were performed aseptically before smearing on slide or plate. The smear was air dried and fixed in ice cold acetone for 15 min, used immediately or kept at 4ºC for further use. Monoclonal antibodies against PPR virus (1:100 in PBS) was added at an amount of 50 μl/smear/well, while plate or negative control was kept using 50 μl/well blocking buffer solution. For every assay the PPR antigens (reference) were kept as positive control. Slide/plates were incubated at 37ºC for an hour and wash with PBS (1:5) and air dried. After drying, 50 μl of anti-mouse IgG conjugate (1:1000 in buffer solution) was added to all wells. The slide was then incubated at 37°C for 1 h. fifty microlitre of ortho-phenylendiamine (Sigma, UK) mixed with hydrogen peroxide (1:200) was added to each well and incubated for 15 min at room temperature. The reaction was stopped by the addition of 50 μl of sulphuric acid (6.8%) and examined by naked eyes. Golden yellow colour change were observed in positive cases (Sil et al. 2001).
Case Control study:
We defined our case and control based on EISA results. The samples were tested positive in EISA were considered as our case and all negative samples were potential candidates for control. We selected 23 cases randomly and took 23 control at 1:1 proportion for our study.
Risk factors:
We incorporate seven risk factors which, we consider, are important for understanding the causation of PPR infection ( Table 2)
Logistic regression:
We used binary Logistic regression to test association among case-control status and individual level risk factors. We estimated odds ratio (OR) and p value with 95%
confidence interval. For model building we used backward LR (p<.05 significant level) approach and forcefully included variable which were insignificant in X2 test with p>0.05. All the statistical analyses were performed in STATA 9.0 for windows (STATA corporation, USA).
CHAPTER-IV
RESULTS
The most frequent clinical findings in diseased animals were high temperature (up to 106–107 ◦F), necrotic stomatitis, respiratory distress, severe mucopurulent Ocular and nasal discharges, and diarrhoea was observed in suspected cases. The frequencies of the clinical findings were tabulated in table 1.
Table 1: Frequency and degree of severity of the clinical signs
Degree Fever Stomatitis Pneumonia Ocular and nasal discharge
Diarrhoea Dehydrartion
+ + + 63 4
1
29 60 59 58
+ + 7 46 34 7 11 11
+ 0 19 7 3 0 1
- 0 0 0 0 0 0
+ + + = severe, + + = moderate, + = mild, - = none
Stomatitis, ocular discharge and diarrhoea measured by inspection. For pneumonia, degree of consolidation was measured by auscultation. Dehydration was measured by skin fold test and capillary refill time.
Out of seventy in forty seven samples golden yellow colour changes were observed.
Form our suspected we confirmed sixty five percent of the animal truly possessing PPR antigen.
The results of the univariate analysis are shown in Table 2. The Black Bengal goats are at
Animals at communal grazing are more susceptible than the confined fed animals (OR 6.750 [95 per cent CI 1.265 to 36.029]).
Table 2: Results of the univariate analysis.
Risk factors Case
(% with RF)
Cont rol (% with RF)
X
2(p) OR(95%CI)n=23 n=23
Breed
Black Bengal 20(87.00%) 9(39.1) 4.059(0.044) 4.286(0.981,18.721) Others 3(13.00) 14(60.99)
Age group
Young(1<year) 6(26.1) 7(30.4) 0.107(0.743) 1.240(0.342 , 4.487)
≥1 year 17(73.9) 16(69.6) Sex
Male 6(26.1) 9(39.1) 0.890(0.345) 1.821(0.521 , 6.370)
Female 17(73.9) 14(60.9)
Communal grazing
Yes 21(95.7) 14(60.9) 5.855(0.016) 6.750(1.265 , 36.029)
No 2(4.3) 9(39.1)
Live market
Near 17(73.1) 15(65.2) 0.411(0.522) 1.511(0.426 , 5.359)
Far 6(26.9) 8 (34.8)
Recent introduction
Yes 5(21.7) 4(17.4) 0.138(0.710) 1.319(0.305 , 5.706)
No 18(78.3) 19(82.6)
All variables of the table 2 were included in the binary logistic regression model to estimate the independence of the effects. The final model identified two variables as independent risk factors for PPR infection in the goats (Table 3). They were Black Bengal breed (OR 5.048 [95 per cent CI 1.059 – 24.068]) and ‘communal grazing (OR 7.802 [95 per cent CI 1.369 to 44.449]).
Table 3: Results of multivariable analysis of potential risk factors for PPR infection
Risk factor OR 95%CI p value
Black Bengal breed 5.048 (1.059 – 24.068) 0.042
Communal grazing 7.802 (1.369- 44.449) 0.021
logistic regression; final model with two variable entered; X2 for likelihood ratio test
= 10.84 ; p>0.004; no. observations= 46.
CHAPTER-V
DISCUSSION
The majority of PPR outbreaks in the past have been diagnosed based on clinical signs.
infection had been difficult because the diagnostic tests that were available for the detection of PPRV were not commonly implemented. The development of EISA made it much easier to detect the antigen of the PPR virus. The implementation of this diagnostic test aided in tracking PPRV infection and studying the epidemiology of the disease in susceptible populations(Sil et al. 2001). Our definition of case and control is one example of the statement.
From our case-control study we found the black bangle goat breed is about five times more susceptible to PPR infection than the other exotic and cross bred goats. The higher prevalence (Mondal et al. 1996) of PPR infection noticed earlier was the clue for considering the Black Bengal breed as risk factor. Besides, the animals under the management of communal grazing found about eight times more vulnerable to PPR infection then those reared under confined stall feeding. The transmission of the virus is well documented. The direct contact between the susceptible and infected animals or by aerosol way is the common route of transmission (Scott 2000; Shankar et al. 1998). The communal grazing allows the susceptible animal to come in contact with the infected on and to acquire infection.
CHAPTER-VI
CONCLUTION
Black Bengal goats are very important economic animal for Bangladesh. Most of the goat owner are poor and mostly rear their goats by communal grazing. Based on the results of our study we suggest mass vaccination in black Bengal goats for preventing future outbreaks. We also suggest vaccine efficacy trail in Bangladesh to check which vaccine is the best in our field situation.
CHAPTER-VII
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