| Angiostrongylus cantonensis(A. cantonensis), a rat lungworm, belonging to Order strongloidea, Family Mestatrongylidae, Genus Angiostrongylus, was discorvered in the pulmonary arteries and hearts of domestic rats in Guangzhou, China, by Chen in 1935. It was also a zoonotic pathogen.The life cycle of this nematode involves rats as the definitive host, and mollusks (snails and slugs) as intermediate host. Humans are accidental hosts for it, who become infected when raw or inadequately cooked snails or slugs, vegetables or freshwater contaminated with the larvae are ingested. These larvae mainly migrate to the brain and spinal cord, causing human eosinophilic meningitis or meningocephalitis.A. cantonensis is mainly epidemic in tropical and subtropical zone, such as in Southeast Asia, the Pacific islands, Australia, and the Caribbean islands. During the past few years, several outbreaks of human angiostrongyliasis and sporadic cases have been reported in these regions, especially in some Southeast Asia countries, mainland China and Japan. Angiostrongyliasis has been considered one of the emerging global threaten infectious diseases in the 21st century. In China, A. cantonensis mainly prevails in southeast provinces, namely, Guangdong, Fujian, Zhejiang, Guangxi, Hainan, Yunnan and Taiwan. Scine the first case of A. cantonensis in mainland China was reported in 1984, outbreaks and sporadic cases of human infection with A. cantonensis have been reported with increasing frequency in mainland China in recent years, and at the same time, the distribution range of A. cantonensis has also become more widespread. From 1997 to 2007, there were six various scale outbreaks of A. cantonensis in China. State Ministry of Health announced the angiostrongyliasis as"an Emerging infectious diseases"in 2003. Guangdong province was one of the major epidemic regions in our country. Besides sporadic cases, A small scale outbreak with 6 people occured in Guangning county in March 2007. The epidemiologic surveys has been done in some area of Guangdong province, but they had been finished long ago, and they were limited scope and unsystem. Meanwhile the information of human infection with A. cantonensis was lack.And at the present time, the date from these surveys can not adapt to the needs of the prevention and control of A. cantonensis. In order to grasp the the newest epidemic status of A. cantonensis in Guangdong province and to provide a scientific basis for prevention and control of it, our research team made an further epidemiological investigation of A. cantonensis in western part of Guangdong province (including Jiangmen,Panyu,Yangchun,Luoding,Zhaoqing,Lianjiang and Maoming)from 2006 to 2008 ,supported by a joint fund of the National Natural Science Foundation of China and the Guangdong Provincial Government.Objective To understand the infection condition and character of A. cantonensis in snails, rodents and human in western part of Guangdong province, and to provide a scientific basis for prevention and control of it.Methods First, adult of A. cantonensis was isolated from the heart and lung of rats caught in the area in the study. Secondly, third-stage larvae of A.cantonensis in snail Achatina fulica (A. fulica) and Ampullaria gigas (A. gigas) from the area were examined with the digestion method. Thirdly, 600 residents randomly selected from Yangchun and Jingmen of the zone were carried out the questionnaire survey concerned with infection of A. cantonensis, and their serums were detected for the specific IgG and IgM antibodies against A. cantonensis by an enzyme-linked immunosorbent assy (ELISA).Results1. 966 of rats were obtained in total. There were eight species of rats including Rattus norvegicus(R. norvegicus),Rattus flavipectus(R. flavipectus), Rattus sladeni(R. sladeni), Bandicata indica, Mus musculus, Rattus losea, S.murinus and Rattus confucianus. R. norvegicus was the most dominant species in number.The infection rate of rats with A. cantonensis was 9.01% (78/966), the mean worm burden was 7.45 worms per positive rat.2. There was a significant difference in the infection rate among the eight species of rats. The infection rate in R. flavipectus, R. norvegicus, Bandicata indica and R. sladeni were 15.62%, 9.61%, 7.23% and 3.85% respectively, but adult of A.cantonensis in other 4 species of rats caught from the aeras could not be isolated.3. There was also significant difference in the infection rates of rats among 5 different districts in westen regions of Guangdong province.The infection rate of rats in Lianjiang was highest (17.37%), the infection rate in Panyu was lowest (3.54%), the infection rate in Maoming, Jiangmen and Yangchun were 10.71%, 4.37% and 5.73% respectively.4. In westen part of Guangdong province, 2217 of A. fulica and 3723 of A. gigas were examined in total. Their infective rates of A cantonensis were 27.88% (618/2217) and 6.50% (242/3723), their infectiosity were 38.72 and 12.01 larvae per positive snail respectively. There was a statistical difference in the infection rate between A. fulica and A. gigas.5. The infective rates of Ac folica in the six districts were distinct, highest (45.00%) in Jiangmen and lowest (7.71%) in Yangchun, 38.41% in Maoming, 24.00%in Lianjiang, 18.58% in Luoding and 12.55% in Zhaoqing respectively. There was statistical difference in the infection rates of Ac folica among six districts.The infective rate of A. gigas were also different, highest(20.14%) in Maoming and lowest(0.86%) in Yangchun, 10.79% in Zhaoqing, 8.10% in Lianjiang, 5.13% in Jiangmen and 2.07% in Luoding. There was a statistical difference among these infection rates too.6. 1987 A. fulica and 2904 A. gigas from the region were diveded to big snail group and middle-small snail group according to the weights. The infection rates of big snail group(>31 gram) and middle-small snail group(≤31 gram) in A. fulica was 22.91% (151/659) and 26.28% (349/1328) respectively, the average infectiosity were 50.94 and 14.12 larvae per positive snail. However, The infection rates of big snail group(>21 gram) and middle-small snail group(≤21 gram) in A. gigas was 8.26%(65/787) and 5.24% (111/2117) respectively, their average infectiosity were 20.08 and 9.16 larvae per positive snail. There was a statistical difference in the infection rate between the two groups of A. gigas.7. The results of questionnaire survey indicated that 89.83% of subjects denied to have the history of eating raw or undercooked food, such as snails, fish, prawns, land crabs or frogs, that 4.17% of the subjects did not sure wether they had the history of eating these raw or undercooked food or not, that 6% of the subjects had the history of eating these raw or undercooked fish or prawns.Furthermore, 3.83% of subjects directly or indirectly touched the snails or slugs in routine life and work.However,66.33% of subjects did not use different kitchen gadgets when cut raw or cooked food.8. The positive rate of the specific IgG antibody for serum samples from the residents was about 9.83% (59/600). And 9 sera in the 59 IgG antibody positive samples had the specific IgM antibody against A.cantonensis (15.25%), and the proportion of IgM antibody positive samples was about 1.50% in 600 human sera.9. The results of ELISA test for the specific antibody against A.cantonensis were different between Jiangmen and Yangchun. The positive rates of the specific IgG and IgM antibody in Jiangmen were 14.0% and 1.67%, in Yangchun 5.67% and 1.33% respectively. Thus, the positive rate in Jiangmen was higher than in Yangchun, and there is a significant difference in the positive rate of IgG antibody between Jiangmen and Yangchun districts.ConclusionsIn comparison to investigation results from other regions of our country, the infection rate of rats with A. cantonensis in western part of Guangdong province is roughly on a middle level. There is a significant difference in the infection rate among the eight species of rats, R. norvegicus must be the most commom and most important definitive host for A. cantonensis in the areas. There is also a significant difference in the infection rates of rats among 5 different districts in western part of Guangdong province. In addition, the infection rate of rats varies with different natural habitats.Compared with the investigation results from other regions of our country, the infection rate of A. folica with A. cantonensis in western part of Guangdong province is high on moderate level, however, the rate of A. gigas is low on anerage level. The infection condition of A. folica is more serious than that of A. gigas. At the present, A. folica is still the most important intermediate host in the dispersal of A. cantonensis in western part of Guangdong province. Meanwhile, there is a significant difference in the infection rates of A. fulica and A. gigas among 6 different districts in western part of Guangdong province. The infection rate of A. cantonensis varies with difference of the snail weight. The bigger A. gigas are, the higher infection rate and infectiosity of them are, but there is no significant difference in the infection rate between big A. folica and middle-small A. fulica. Generally infective situation of the definitive host(rats) and the intermediate host(snails) is consistent in different districts within western part of Guangdong province.The results of epidemiological surveys indicate that the latitude, elevation, geomorphy and distance from the South China Sea are important natural factors related to the transmission of A. cantonensis in the area. The infective situation of the hosts of A. cantonensis is usually more serious in the districts of low latitudes and elevation , plain or low-hill and near the sea.There is a propotion of humans who are positive for specific IgG and/or IgM antibody against A.cantonensis in the western part of Guangdong province. It indicated that these people once or newly were infected with A. cantonensis. On the other hand, the positive rate of specific IgG antibody of serum samples in Jiangmen is higher than in Yangchun.And it showes that infection opportunity of the residents is different under the influence of some natural and social factors in the different districts of western part of Guangdong province.In general, the western part of Guangdong province is a natural foci of A. cantonensis, and human being of the area are at the risk of infection with A. cantonensis. Through the survey, we have got some basic information about the distribution and epidemiological features of A.cantonensis in western part of Guangdong province, and lay a good foundation for the scientific prevention and control of A. cantonensis.
|
PDF Full Text Request