TABLE OF CONTENTS
TOC o “1-3” h z u LIST OF FIGURES PAGEREF _Toc515186505 h 2ABSTRACT PAGEREF _Toc515186506 h 31.0.INTRODUCTION PAGEREF _Toc515186507 h 32.0.OBJECTIVE PAGEREF _Toc515186508 h 42.1.Main Objective PAGEREF _Toc515186509 h 42.2.Specific Objectives PAGEREF _Toc515186510 h 43.0.QUANTITATIVE RISK ASSESSMENT (QRA) METHODOLOGY PAGEREF _Toc515186511 h 43.1.DATA SOURCES PAGEREF _Toc515186512 h 43.2.RISK QUESTION PAGEREF _Toc515186513 h 53.3.HAZARD IDENTIFICATION PAGEREF _Toc515186514 h 53.4.DEVELOPMENT OF A SCENARIO TREE PAGEREF _Toc515186515 h 53.5.INITIATING EVENT: DISEASE PATHWAY THROUGH LIVE ANIMAL MOVEMENT PAGEREF _Toc515186516 h 53.6.EVIDENCE GARTHERING AND PARAMETER ESTIMATION PAGEREF _Toc515186517 h 63.6.1.NODE 1: DOES FMD OCCUR AT THE FARM? PAGEREF _Toc515186518 h 63.6.2.NODE 2: WAS FMD DETECTED DURING QUARANTINE? PAGEREF _Toc515186519 h 73.6.3.NODE 3: IS THE VACCINE EFFICACY SATISFACTORY? PAGEREF _Toc515186520 h 73.6.4.NODE 4: IS FMD DETECTED AT ARRIVAL AT SLAUGHTERHOUSES? PAGEREF _Toc515186521 h 74.0.RESULTS AND DISCUSSION PAGEREF _Toc515186522 h 75.0.CONCLUSION AND RECOMMENDATIONS PAGEREF _Toc515186523 h 86.0.REFERENCES PAGEREF _Toc515186524 h 8
LIST OF FIGURES TOC h z c “Figure” Figure 1: Scenario pathway for determining the risk that an animal is infected with FMD PAGEREF _Toc515186525 h 6Figure 2: Probability density function (Cumulative Distribution) for the risk of introduction of FM to Central and North Malawi from Feedlot operations in Southern Malawi. PAGEREF _Toc515186526 h 8Figure 3: Sensitivity analysis for the likelihood of introduction of FMD into Central and Northern Malawi via live animal movement from feedlot operations from Southern Malawi. PAGEREF _Toc515186527 h 9Figure 4: Probability distribution for the number of infected animals that have to be transported from the Southern region to include one FMD infected animal PAGEREF _Toc515186528 h 9Figure 5: Number of years before a FMD-infected animal is introduced to the slaughterhouses in Central and Northern Malawi. PAGEREF _Toc515186529 h 10Figure 6: Probability distribution for at least one infected animal PAGEREF _Toc515186530 h 10
A QUANTITATIVE ASSESSMENT OF THE RISK OF INTRODUCTION OF FOOT AND MOUTH DISEASE (FMD) TO CENTRAL AND NORTHERN MALAWI THROUGH LIVE ANIMAL MOVEMENT FROM CATTLE FEEDLOT OPERATIONS IN SOUTHERN MALAWI. A CASE OF THE 2015 DISEASE OUTBREAK IN CHIKWAWA DISTRICT. (1)
James Greenwich Mponela (2)
This paper was presented at the 5th Pan African Conference on Sanitary/Phytosanitary (SPS) Regulations and Science based Risk Analysis, held in Dar es Salaam (Tanzania) from 4th June to 5th June, 2018.
Animal Health and Livestock Development Officer for Disease Investigation at the Mzuzu Regional Veterinary Laboratory, under the Department of Animal Health and Livestock Development of the Ministry of Agriculture, Irrigation and Water Development.
ABSTRACTThe Central region of Malawi is a self-declared foot-and-mouth disease (FMD) free region without vaccination while the Northern Region of the country bordering Tanzania has experienced 13 FMDV outbreaks the first occurring in 1957 and the last in 2001 and as such, is considered a low risk area. However, the country experiences FMD outbreaks mostly in the two Southern region districts of Nsanje and Chikwawa which lie under the Shire Valley Agricultural Development Division. Under such circumstances, a Quantitative Risk Assessment (QRA) could provide an objective, transparent, and internationally accepted means for evaluating the risk of introducing FMD into Central and Northern Malawi through live animal movements from feedlot operations in Southern Malawi (Nsanje and Chikwawa Districts).
Based on the knowledge base, a scenario tree was developed to determine conditions that could lead to the introduction of FMD through live animal movement. Parameters for the occurrence of the event at each node were estimated using published literature. Using @RISK software and setting Monte Carlo simulation at 10,000 iterations, the overall probability of introducing FMD was established as 8.47 × 10-5 (7.93 × 10-6 to 0.00039). The possible number of animals infected with FMD which would make it to the Slaughterhouses ranged from 0.01 to 1.35 (mean = 0.21) per year. The probability of at least one infected animal making it to the slaughterhouses was established to be 0.18 (0.01 to 0.73). Consequently, it would take up to 6.8 (0.88 to 67.1) years for FMD to be introduced into Central and Northern Malawi. Based on the knowledge base and the critical pathway analysis, the biological plausibility of introduction of FMD into Central and Northern Malawi through live animal movement is low.
Quantitative Risk Assessment (QRA); Monte Carlo Simulation; @Risk; Foot and Mouth Disease (FMD); Foot and Mouth Disease Virus (FMDV).
INTRODUCTIONFoot and mouth disease (FMD) is the most contagious disease of mammals and has a great potential for causing severe economic loss in susceptible cloven-hoofed animals. There are seven serotypes of FMD virus (FMDV), namely, O, A, C, SAT 1, SAT 2, SAT 3 and Asia 1. 1 FMD has been occurring sporadically in Malawi over the years, but only in the southern region areas in the Shire Valley where there is contact between cattle and buffaloes. Usually SAT 2 is implicated and the disease dies out quickly following ring vaccinations. The country is divided into three zones, the central zone is nationally self-proclaimed FMD free without vaccination while the northern part of the country bordering Tanzania is considered a low risk area.2
Shire Valley Agricultural Development Division (SVADD) was affected by a Foot and Mouth Disease outbreak around Mthumba Dipping area, Mitole EPA in Chikwawa District. The outbreak was first reported on 30th August, 2015 at Chinangwa Village where one cow showed clinical signs related to Foot and Mouth Disease and another report was from Mbenderana village, T.A. Kasisi in the same district where two cows and one heifer were infected. From the investigation, it was suspected that buffaloes from Lengwe National Park which are carriers of the FMDV were drinking water from water channels in the Sugar cane fields of Smallholders farmers around Chinangwa village. On the same note, cattle herds around Chinangwa village were also reported to be drinking water from the same water channels, and this scenario might be the possible genesis of the FMD outbreak. Mthumba area has a total cattle population of 2,512 which was at risk and three cattle were infected in Chinangwa and Mbenderana villages but no animal died. 3
OBJECTIVEMain ObjectiveThe main objective of this Quantitative Risk Assessment (QRA) is to provide an objective and defensible method for assessing the disease risks associated with the introduction of the FMDV to Central and North Malawi through movement of live animals from feedlot operations in the Southern region districts of Nsanje and Chikwawa.
Specific ObjectivesTo determine the effectiveness of quarantine procedures during a FMD outbreak.
To determine the FMD vaccine efficacy.
To determine the probability of transmission of FMD through live animal movements
To assess the effectiveness of mitigation measures used during a FMD outbreak
QUANTITATIVE RISK ASSESSMENT (QRA) METHODOLOGY
DATA SOURCESThe Method used in this QRA is the probabilistic Scenario Analysis (PSA) method. The following steps will be used;
Identifying the hazard
Stating the question to be investigated
Developing a scenario tree
Evidence gathering and parameter estimation
Linking the evidence generated by the scenario tree with empirical evidence
RISK QUESTIONThis quantitative assessment will specifically assess the risk of FMDV entry into Central and Northern Malawi, via live animal movement from Chikwawa District located in Southern Malawi under the Shire Valley Agricultural Development Division (SVADD). As such, the specific risk question is:
What is the risk of introduction of FMD to Central and Northern Malawi through live animal movement?
HAZARD IDENTIFICATIONThe hazard is identified as the Foot and Mouth Disease Virus (FMDV), which is currently endemic in the Southern Region districts in Malawi of Nsanje and Chikwawa.
Foot and mouth disease (FMD), caused by the FMD virus (FMDV), is one of the most contagious diseases of cloven-hoofed animals, including cattle, goats, pigs and sheep. It is endemic throughout much of Africa, Asia, the Middle East and South America.
Economic losses caused by FMD include reduction in production parameters such as decreases in milk production, weight gain, reproductive inefficiencies and death in young ruminants. The costs of prevention and control with restrictions in both local and international trade are high, thereby affecting food security and livelihoods along the production and marketing chain 4.
DEVELOPMENT OF A SCENARIO TREEAt each node along the scenario tree, a question was asked (and data collected) with the view of narrowing down the risk through specific mitigation. The accumulation of the answers to these questions determined the final risk. Quantitative estimates of the risk at each node were obtained from published literature. The ranges of the probabilities were determined by their source documents or their natural domain. The sum of the product of the probability distributions, E1 to E6 was considered the overall probability of introducing FMD to Central and Northern Malawi through live animal movement.
INITIATING EVENT: DISEASE PATHWAY THROUGH LIVE ANIMAL MOVEMENTFour events determine the probability of disease introduction by movement of live animals, as follows:
E1 – isolation of the animals at the farm of origin
E2 – quarantine
E3 – results of diagnostic tests during quarantine
E4 – detection of FMD on arrival of the animals at slaughterhouses
E1: DOES FMD OCCUR AT THE FARM? -1416050-30416500 NO RISK 1276985-16637000
E2: IS FMD DETECTED DURING QUARANTINE? -7810524574500
NO RISK 379095-46990NO (1-P2)
1273810-34480500 E3: IS THE VACCINE EFFICACY SATISFACTORY? -6350028638500
NO RISK 419100-104775NO (1-P3)
E4: IS FMD DETECTED AT ARRIVAL? -49530-20637500 NO RISK 1295400-14160500
PROBABILITY OF CONTAMINATED LIVE ANIMAL P=P1×(1-P2)×(1-P3)×(1-P4) Figure SEQ Figure * ARABIC 1: Scenario pathway for determining the risk that an animal is infected with FMDEVIDENCE GARTHERING AND PARAMETER ESTIMATIONNODE 1: DOES FMD OCCUR AT THE FARM?A FMD outbreak was reported around Mthumba Dipping area, Mitole EPA in Chikwawa District. The outbreak was first reported on the 30th August, 2015 at Chinangwa Village where one cow showed clinical signs related to Foot and Mouth Disease the last report was from Mbenderana village, T.A. Kasisi in the same district where two cows and one heifer were infected. From the investigation, it was suspected that buffaloes from Lengwe National Park which are carriers of SATFMD viruses were drinking water from water channels in the Sugar cane fields of Smallholders farmers around Chinangwa village. On the same note, cattle herds around Chinangwa village were also reported to be drinking water from the same water channels, and this scenario might be the possible genesis of the FMD outbreak. Mthumba area has a total cattle population of 2,512 which was at a risk. The prevalence of FMD in animals showing clinical signs of the FMDV was at 0.16%.
NODE 2: WAS FMD DETECTED DURING QUARANTINE?Initially 31 blood samples were collected by staff from the CVL, SVADD, and DAHLD. These tests were subjected to ELISA tests (Sensitivity 95%, expert opinion) where 21 were confirmed to be positive for the FMDV. And therefore, the quarantine efficiency was found to 68%. Based on the above evidence, it was estimated that the probability that quarantine fails to detect FMD was most likely 32%.
NODE 3: IS THE VACCINE EFFICACY SATISFACTORY?A post vaccination sero-surveillance exercise was conducted at Mthumba Dipping area on the 2nd of November, 2015. Surveillance was important to monitor titter levels of antibodies against FMD within the targeted cattle population after vaccination in Mthumba Dipping area. 57 blood samples were collected at Mthumba crush, and submitted to the CVL for diagnosis, results indicated that out of the 57 samples, 54 samples had sero-converted. This post vaccination Surveillance also revealed that effectiveness of vaccine to induce immunity (vaccine efficacy) was at 95% which meant that the objective of vaccination to build antibodies against FMD was achieved. The vaccine efficacy was estimated to be from 80% to 99% with the most likely scenario at 95%.
10,000 animals were targeted for vaccination in the affected area and 9,598 animals were vaccinated thus, vaccination coverage was established to be at 95.9%.
NODE 4: IS FMD DETECTED AT ARRIVAL AT SLAUGHTERHOUSES?Upon arrival at the slaughterhouse, all documentation is reviewed by a designated Government meat inspector before animals disembark. If everything is okay, the animals move to the reception pen for ante mortem inspection. Animals remain in these pens for at least 24 hours and not more than 72 hours. Since FMD has a short incubation period, infection of animals either at the farm of origin or in transit would probably be visible by then. In this case, the probability of failing to detect at least one animal with signs of FMD was estimated to be 0.01 – 0.10 while the most likely probability was estimated to be 0.05.
RESULTS AND DISCUSSIONThe probability of introducing the FMDV through movement of live animals from the southern region to the central and northern regions from feedlot operations in southern Malawi was run 10,000 times using a Monte Carlo approach implemented on a commercial software (@Risk version 7.5.2 and Precision Tree version 7.5, Industrial, Academic Edition©, Palisade Corporation, 1996–2015) on Microsoft Excel (Microsoft® Office Professional Plus, 2013).
The overall probability of introduction of FMD to Central and North Malawi through live animal movement was 8.47 × 10-5 (7.93 × 10-6 to 0.00039) as shown in figure 3 below. Under this circumstance, the number of infected animals per year was established to range from 0.01 to 1.3 with a mean of 0.2 according to figure 5. Figure 6 below show the number of years for infected animal to be imported and it would take 6.8 (0.8 to 67) years for an infected animal to make it to the slaughter houses. The probability of at least one infected animal being transported to the slaughterhouses was established to be 0.18 (0.01 to 0.73) as shown in figure 7.
With reference to the sensitivity analysis illustrated in figure 4; postmortem inspection efficiency and storage and transportation, were among the inputs with the highest variability/uncertainty. According to the sensitivity analysis, based on correlation coefficients using the spearman’s ranking system, if one of these inputs was changed by one standard deviation (SD), through for example acquisition of more data, the corresponding probability of the risk event would change by over 50%. The other input variable with the highest uncertainty was maturation and deboning; if there was a change of one SD, the probability of the risk would correspondingly change by 44%.
CONCLUSION AND RECOMMENDATIONSREFERENCESOIE Manual of Diagnostic tests and vaccines for terrestrial animals (mammals, birds and bees) 7th Edition, Vol. 1 (2012)
FAO/OIE Sub-Regional Seminar. (2011) “Progressing towards Foot and Mouth Disease (FMD) Control and OIE recognized status of SADC Member States”
DAHLD, SVADD FMD report 2015
Carly Lockhart, Keith Sumption, Julio Pinto ; Juan Lebroth. (2012) Foot-and-mouth disease caused by serotype SAT2 in Egypt and Libya, A Regional concern for animal health in North Africa and the Middle East.
Figure SEQ Figure * ARABIC 2: Probability density function (Cumulative Distribution) for the risk of introduction of FM to Central and North Malawi from Feedlot operations in Southern Malawi.
Figure SEQ Figure * ARABIC 3: Sensitivity analysis for the likelihood of introduction of FMD into Central and Northern Malawi via live animal movement from feedlot operations from Southern Malawi.
Figure SEQ Figure * ARABIC 4: Probability distribution for the number of infected animals that have to be transported from the Southern region to include one FMD infected animal
Figure SEQ Figure * ARABIC 5: Number of years before a FMD-infected animal is introduced to the slaughterhouses in Central and Northern Malawi.
Figure SEQ Figure * ARABIC 6: Probability distribution for at least one infected animal