Control Program of Cystic Hydatid Disease
Cystic hydatid disease (hereinafter referred as CHD) in man is caused principally by infection with the larval stage of the dog tapeworm Echinococcus granulosus. It is an important pathogenic zoonotic parasitic infection (acquired from animals) of humans, following ingestion of tapeworm eggs excreted in the faeces of infected dogs.
CHD represents a substantial disease burden. Worldwide, there may be in excess of three million people living with these diseases at any one time. Many of these people will be experiencing severe clinical syndromes which are life-threatening if left untreated. Even with treatment, people often face reduced quality of life.
The parasite is transmitted between the domestic dog and a number of domestic ungulate species. The dog/sheep cycle is most important. So this program focuses on sheep and dogs.
1. Control strategy
This control program is designed for controlling CHD in hyper endemic areas to prevent the release of E. granulosus eggs to the environment by monthly treatment of all dogs with praziquantel (hereinafter referred as PZQ), so that newborn domestic animals are free of infection with CHD. The whole biomass of CHD is decreased by vaccination of sheep in the endemic areas.
2. Targets and Work Indexes
2.1.1 By 2015 in every town, in epidemic region, the dog infection rate should be dropped below 10%, infection rate of sheep under 2 years old should be dropped below 15%, seropositive rate of children between 6 and 12 years old should be dropped below 8%.
2.1.2 By 2018, in every town, in epidemic region, the dog infection rate should be dropped below 5%, infection rate of sheep under 2 years old should be dropped below 10%, seropositive rate of children between 6 and 12 years old should be dropped below 5%.
2.2 Work Indexes
2.2.1. By 2015, the following indexes should be fulfilled:
188.8.131.52 Investigate the distribution and epidemic degree of CHD
Investigate and find out the dog infection rate, infection rate of sheep and rodent under 2 years old and seropositive rate of children between 6 and 12 years old in epidemic region
184.108.40.206 In epidemic region, home-dog registration rate should be no less than 80%, the coverage of dog treatment should be no less than 70%, the amount of stray dogs of each village should be less than 1.
220.127.116.11 In epidemic region, vaccination rate of sheep including the newborn should be no less than 85%.
18.104.22.168 In licensed slaughter houses, 100% of the sheep should be quarantined before slaughtering, and 100% of the organs of infected sheep should be disposed harmlessly.
22.214.171.124 In epidemic areas health education about CHD should cover more than 80% of cadre of each government level, clerical person and middle school and primary school students, and cover more than 70% of the farmers and herdsmen.
126.96.36.199 Staff Training
In epidemic areas, more the 90% of the staffs in disease control and prevention agency, medical treatment agency, veterinary disease control and prevention agency and veterinary surveillance agency should be educated about the relevant expertise and skills.
More the 85% of the cadre in the town and village, health care doctor, village doctor and veterinarian should be educated about the relevant expertise and skills.
2.2.2 By 2018, the following indexes should be fulfilled:
188.8.131.52 In epidemic region, home-dog registration rate should be no less than 90%, the coverage of dog treatment should be no less than 80%, the amount of stray dogs of each village should be less than 1.
184.108.40.206 In epidemic region, vaccination rate of sheep including the newborn should be no less than 85%.
220.127.116.11 In licensed slaughter houses, 100% of the livestock should be quarantined before slaughtering, and 100% of the organs of infected livestock should be disposed harmlessly.
2.2.2..4 In epidemic areas, health education about CHD should cover more than 90% of cadre of each level, clerical person and middle school and primary school students, and cover more than 80% of the farmers and herdsmen.
18.104.22.168 In epidemic region, registration rate of CHD patient should be no less than 90%, regular treatment should cover 80% of the patients.
22.214.171.124 Staff Training
In epidemic areas, more the 95% of the staff in disease control and prevention agency, medical treatment agency, veterinary disease control and prevention agency and veterinary surveillance agency should be educated about the relevant expertise and skills.
In epidemic areas, more the 90% of the cadre in the town and village, health care doctor, village doctor and veterinarian should be educated about the relevant expertise and skills.
126.96.36.199 Safe drinking water should reach all the pastoral, semi pastoral and agricultural residence.
3. Control measures
3.1. Structure of control authorities at the county level and their involvement.
The CHD control committee is established at the county level. The duties of the committee are to: (1) undertake leadership of the control program; (2) distribute control program tasks to the relevant departments; (3) monitor control program progress; and (4) reward those personnel who helps make the control program a success.
One officer is appointed for the control program at the community/township level in both counties. He/she plays a liaison role of linking villagers with the county control committee. Every village selects a responsible person as village hydatid disease control officer (hereinafter referred as VHDCO) who is responsible for implementing control measures in that village. He/she is highly respected by the villagers and is willing to take on the designated duties. Under the supervision of the head of the village, the role of the VHDCO is to: (1) explain the control program to all the villagers; (2) distribute educational materials to villagers; (3) register and dose all dogs in the village monthly with PZQ; (4) check and report stray and unwanted dogs in the village; (5) help police to capture stray/unwanted dogs.
The involvement of veterinary station staff in both counties includes: (1) consulting with the county hydatid control committees; (2) providing technical support as required, (3) purchasing and distributing PZQ tablets; (4) carrying out sheep vaccination; (5) monitoring VHDCO tasks; and (6) undertaking baseline and annual surveys of E. granulosus in dogs and slaughtered livestock, and annual census of dogs and livestock.
Involvement of Centre for Disease Control (CDC) staff at county level includes: (1) consulting with county hydatid control committees; (2) providing educational materials; (3) responsibility for recording and reporting human CHD cases; (4) using a questionnaire, prepared by CDC, with the support of the VHDCOs, as a cheap and effective way to obtain human prevalence (X-ray, ultrasound, and serological testing complemented the questionnaire survey in Hutubi County); (5) monitoring the VHDCOs’ tasks; (6) annual reporting of human incidence and changes in status of knowledge, attitudes, and practice with regard to CHD. Local hospitals are involved in human CHD case reporting and treatment.
3.2. Monthly treatment of all dogs with PZQ.
A dog bait tablet containing 100 mg PZQ, which is 100% effective in removing E. granulosus worms from the intestines of infected dogs at a dose of 2.1 mg/kg dog body-weight, is used for the control program. The bait is especially designed for treating dogs and is accepted by more than 90% of animals. If a dog rejects the tablet, the VHDCO wraps the tablet in food and fed the dog with the help of the dog owner. One tablet is used for monthly treatment of all dogs, 25 kg in body weight, while two tablets are used for dogs 25 kg.
3.3. Vaccination of sheep with EG95
Vaccination of sheep as an effective control method only requires the veterinarians to visit two times each year.
The control program team produces a booklet about the disease with cartoon pictures suitable for both students and adults. A booklet is distributed to every family. A colour poster is also designed for every village and is placed on the village notice board. Before the dog treatment day every month, two television programs are broadcast that presents general information on CHD and the control program, respectively.
3.5. Baseline survey and epidemiological monitoring.
Livers and lungs of sheep collected from county villages are monitored at the local county slaughterhouse to determine the prevalence of CHD. Small cysts, especially in sheep aged less than 1 year, that are unsuitable for macroscopic examination are fixed in formalin and sliced into 0.5 mm sections, and any cyst-like material checked microscopically. Any cyst containing both laminated and germinal layers is diagnosed as an E. granulosus hydatid cyst. Thirty sheep from each age group are also randomly purchased for examination for further monitoring of CHD prevalence, especially in newly born sheep after commencement of the control program. Three different types of communities are selected based on their village farming practices: mainly agricultural farming but with a small number of livestock, mainly sheep; 50% agricultural farming/50% farming of livestock on pasture; or farming of livestock on pasture only.
Arecoline purgation is used as the method for estimating dog parasite prevalence, as it has been used successfully to monitor control programmes in a number of different endemic settings. After dogs are successfully purged, about 30 g of dog feces are collected in a container and the worm burden classified macroscopically as: ‘‘2’’, negative; ‘‘+’’, 1–99 worms present; ‘‘++’’, 100–1,000 worms present; ‘‘+++’’, more than 1,000 worms present. The numbers of human CHD cases are obtained by questionnaire analysis of all residents of every village and confirmed by interview with the affected family or the patients themselves.
3.6. Dog registration and treatment with PZQ.
All dogs in each village are registered by the VHDCOs, who informs the villagers that the dogs should be dewormed using the special PZQ bait (described earlier) to remove the parasites causing CHD, and that treatment has to be given every month. The cost of treatment is partly paid for by the dog owners. The VHDCOs are then paid according to the numbers of dogs treated.
3.7. Elimination of stray and unwanted dogs.
A special team, supervised by local police officials, implemented regular elimination of stray and unwanted dogs in each village.
All leaders and staff in local governments, including those from each community/township/village involved in the control program, receive two hours of special training in workshops that included a 1 hour TV program about CHD and a 1 hour lecture when the details of the control program are explained. After training, a special contract is signed between the county, the community, and the village to clarify the duties. The VHDCOs receive 6 hours of training and attend specialized workshops every year of the control program.
why sheep and dogs
Although many species of domestic livestock and wildlife species are potential hosts for E. granulosus, sheep and dogs play a major role (accounting for around 90% of the total) in transmission of the parasite globally). The whole biomass of CHD will be decreased step by step by cutting sheep-dog life cycle of the parasite. Successful control of CHD between sheep and dog will finally result in elimination of CHD.
About EG95 Vaccine
Recently, a vaccine has been developed as a new tool to assist with control of CHD. The EG95 vaccine has been developed to prevent infection with E. granulosus in intermediate hosts. The vaccine contains a protein which occurs in the parasite egg and early developmental stages. Parasites attempting to establish an infection in a vaccinated host are killed by the immune responses induced by the vaccine. Immunization with the protein, termed EG95, has been shown to prevent hydatid infection in sheep.
A large scale trial has confirmed safety and efficacy of this vaccine. The characteristics of the immunity stimulated by the EG95 vaccine are summarized as: Two immunizations stimulate greater than 95% protection against hydatid infection in sheep. More than 50% of vaccinated animals have no viable hydatid cysts after challenge infection with E. granulosus. Immunity persists for at least a full year after two immunizations with the vaccine. Approximately 80% immunity is induced in sheep after a single injection. Solid immunity is transferred with colostral antibody from a vaccinated dam to neonatal offspring. The vaccine has been shown to be similarly effective in trials carried out in Argentina, Australia, China and New Zealand.
Recommendations for Practical Use of EG95 Vaccine
One visit by the vet should take place when animals return from Summer pastures, preferably after animals have been killed for Winter food, but before snow makes travel impossible.
In the Northern Hemisphere, November/December would be the months of choice, and this is also a good time to give the first vaccination(s) to animals born during the Summer, and to vaccinate older animals while they are well-fed and able to make a good immune response to the vaccine.
The other visit by the veterinarians should take place in early Spring, after the deaths from late Winter snow-falls. Animals born during the Winter should be vaccinated at this time (March/ April).
Although a single immunization has been shown to induce a useful degree of protection, where possible it is best to give two initial injections, one month apart. If it is possible for veterinarians to stay in the field for 2 months in November/ December and March/April, in order to give the two injections, a more rapid onset of full protective immunity will initially be achieved than if the injections are given 6 months apart.
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Post time: Nov-28-2019