森林発生ヒトマラリアと人獣共通感染症サルマラリアの生態研究 | JSPS アジア・アフリカ学術基盤形成事業

森林発生ヒトマラリアと人獣共通感染症サルマラリアの生態研究

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代表幹事	川合覚　獨協医科大学熱帯病寄生虫病教室
TEL	0282-87-2134
E-mail	tropmed@dokkyomed.ac.jp

一般演題抄録

ラオス・サバナケットにおける熱帯林の荒廃と感染症～マラリアベクターの生息場所～
Tropical forest degradation related with infectious diseases in Savannakeht, Laos-Habitats of Anopheles

Shigeo Kobayashi^*1, Bunpei Tojyo^*2, Kazuhiko Moji^*2, Toshihiko Sunahara^*3
*1: Graduate School of Asian and African Area Studies, Kyoto University,
*2: Research Institute for Humanity and Nature, 3 Nagasaki University

Introduction

Tropical monsoon Asia can be characterized by clear rainy and dry seasons. People were living in the tropical monsoon forest by doing slash and burn cultivation. Population increase, urbanization, deforestation by Vietnam War bombing and shifting cultivation, economic development, spread of wet rice cultivation changes in lifestyle are the factors changing the ecological relationships among human beings, pathogens, and vectors. Therefore, the purpose of our study is verified three hypothesizes such as (1) the degraded forest would offer diverse habitats for infectious diseases insect vectors, (2) the utilization of community forest by local community could contribute the conservation of the forest, (3) the community forest would be degraded caused by utilization.

Site and Methods

The study site is located at Lahanam District and Xepon District in Savannakhet province, Lao PDR. We applied several kinds of survey methods, such as (1) scaling up for determination of forest environmental changes using Tojyo’s pixel based classification approach, (2) tree census, (3) clarification of understory vegetation and natural regeneration by Brawn Blanquet’s method, (4) recording of understory biomass, litter, thickness and hardness of A horizon, (5) recording of forest coverage and sky factor using fish eye lens.

Results and Discussion

Vegetation recovery used to be occurred after seven to eight years fallow. But the fallow term is made shorten caused by economic reason. Area of Lahanum is flat and carried out paddy. Moreover, the community forest is well conserved. However, area of Xepon is mountainous and carried out swidden cultivation. Degraded secondary forests and fallow lands are distributed. Main factor of forest degradation is swidden cultivation and succession of fallow land was observed Eupatrium-bamboo-shrubs after fallow term from 1 year to 4 years. We have also found out another factor which is bombing holes during Vietnamese war. Bombing hole indicated circle figure which is av. 9.6m in diameter and av. 1.7m in depth. Bombing hole also showed its soil hardness as 15.4mm in bottom compared with 7.5mm at forest floor even about 40 years after termination of the war. There are no trees more than 10cm in DBH. In conclusion, we have verified hypothesis (1) it’s necessary to get ecological information about infectious diseases vectors, hypothesis (2) there are like natural forests with the highest of total basal area (64.6～98.1m2/ha), and they are conserved by village management, hypothesis (3) there are like bushes where offer the habitats infectious diseases vectors

森をめぐる静かな紛争～東南アジアにおける焼畑農耕民の暮らし～
Silent conflict over forestland: Livelihood of slash-and-burn peasant in Southeast Asia

SHINE Toshihiko
Assistant Professor – the International Center – Kyoto University

In the process of modernization, the new independent countries in Southeast Asia (include Vietnam) implemented the nationalization of natural resource, especially, forestland. In almost countries of Southeast Asia, the people in delta and mountainous area are belonging to different ethnic group. The mountain people are mainly ethnic minorities in each country. In Vietnam, at the stage of developmental dictatorship (or socialist dictatorship), conflicts over forestland between state owned forest enterprises and ethnic minority communities were invisible.

However, after the democratization and decentralization (market-oriented economy) started, the conflicts became visible although still silent. Forestlands in convenient location (near village) are already owned by enterprises and people cannot cultivate there. So, people must go deep forest far from village to cultivate because of shortage of forestland for slash-and-burn agriculture. They must take the risk of malaria infection to for their subsistence.

In the history of the Raglai and the Kaho (the T’Rin) residents in Khanh Phu Commune (Khanh Hoa Province, Vietnam), this is the 2nd time that mountain people (ethnic minority people) must take the risk of malaria infection (1st time is the stage of forced resettlement to build socialist dictatorship after 1975). Deferent from the cases after 1975, now (2000s), it is not difficult to get good quality anti-malaria medicine. Although people have indigenous knowledge about traditional anti-malaria medicine, they do not use more. Shortage of forestland, good quality of medical care may accelerate the people’s deep forest cultivation and also the monkey-human co-infection malaria parasites, too.

There are not yet happened the clash between enterprises and people. However, as “the art of not governed,” ethnic minority people (the Raglai and the Kaho) cultivate the buffer zone of state owned forest step by step. Silent conflict over forestland goes on.

サルマラリアの宿主となる東南アジアのマカク属を追って
In search of the south eastern Asian macaque hosts of monkey malaria

Michael A. Huffman
Primate Research Institute, Kyoto University

Conservation medicine is an emerging, interdisciplinary field that investigates the relationship between human and animal health and the environmental conditions affecting the emergence of infectious diseases. In collaboration with veterinarians, virologists, parasitologists and other experts in the bio-medical sciences, primatologists have begun to investigate the role of diseases in primates and as a tool for the conservation of endangered wild populations. A key role of primatologist in this multidisciplinary research is the collection of behavioral and ecological data necessary to elucidate the impact of disease on a group and to collect the relevant samples (urine, feces, hair, postmortem tissues) needed for laboratory identification and quantification of the disease in question. Many advances in the ability to identify parasite and viral infections from non-invasively collected samples have strengthened our ability to determine and monitor disease affecting wild primate populations. Recent work in Africa and Southeast Asia has begun to investigate the dynamics of malaria transmission in wild apes and their human primate counterparts. In Vietnam, an international collaborative research project is focusing on the transmission dynamics of malaria among the Raglai of south-central Vietnam. A component of this research is the study of the wild and captive macaque species in the area thought to be a reservoir host for Plasmodium knowlesi responsible for infections in people over-nighting in the forest for the purpose of subsistence activities. While the primate component of this project is still in the beginning states, these efforts and future directions will discussed.

人獣共通感染性サルマラリア
Zoonotic Simian Malaria

Satoru Kawai
Laboratory of Tropical Medicine and Parasitology,
Dokkyo University School of Medicine

At least 26 species of malaria parasite have been known to infect non-human primates in their natural habitats. Some of these species have been implicated as zoonoses in symptomatic human malaria. In fact, recent studies have shown that naturally occurring human cases infected with a macaque malaria parasite, Plasmodium knowlesi, are not rare and are widely distributed in Southeast Asia. Moreover, P. cynomolgi and P. inui can also be transmitted to humans either through the bite of a mosquito or by infected blood inoculation. Although an authenticated natural infection in human case caused by these parasites have not been found in previous epidemiological investigations, recent studies have warned that the parasites have a high risk of causing zoonoses as well as P. knowlesi. Since these simian malaria parasites have the same host species of macaque, and also grow well in anopheline species, which are well known as important vectors for human malaria within the same geographic range.

マレーシア・サラワク州における新型マラリアの現状
The situation of human Plasmodium knowlesi infection in Sarawak state, Malaysia and its ethnic peculiarity.

Gaku MASUDA
Center for the Southeast Asian Studies, Kyoto University.

The Sarawak state in Eastern Malaysia has created a database registering Malaria cases. It is mandatory for medical facilities, from village clinics to city hospitals, to record every single case statewide. Each case record file consists of more than 170 items. This system began around 1993 in Sarawak. This database’s purpose, however, is mostly limited to activity record and national census, and the data is seldom examined once the year passes. This epidemiological case data is little used for control purpose, but one exception is for some occasional outbreaks that require aggressive control such as ACD. From this database, I will describe the current situation of human P. knowlesi infection cases and some epidemiological characteristics, such as ethnic, seasonal, regional and age factors, by statistical processing of data. In this area, most recorded cases of P. malariae are wrong diagnosis and are in fact P. knowlesi. Interestingly, there are some ethnic peculiarities in Malaria species. P. knowlesi is strongly prevalent among the Iban people while P. vivax is observed very commonly among the Penan people. Where does this difference come from? I will present a hypothesis for this “mystery”.

ベトナム・カンホア省森林地域におけるマラリアの実態
The circumstances of forest malaria in Khan Phu commune, Khanh Vinh district, Khanh Hoa province, Vietnam

Yoshimasa Maeno
Department of Virology and Parasitology, Fujita Health University School of Medicine

Concerted control measures have considerably reduced the burden of malaria in Vietnam, and the parasites that cause it are now mostly restricted to forested rural areas. Forest Malaria became new situation because human cases of natural Plasmodium knowlesi infection were found in forested rural areas and transmission of P. knowlesi from monkeys to humans may form an additional complication in forest malaria. However, zoonotic malaria by P. knowlesi infection in those areas was still unclear. In order to determine whether P. knowlesi is infecting the human population of Khanh Phu commune, Khanh Vinh district, Khanh Hoa province, Vietnam, we collected mosquito and human blood samples in Khanh Phu, and analyzed these for the presence of malaria parasites using PCR. In analysis of sporozoites positive salivary glands, P. knowlesi was detected in 42 salivary glands, which was the same detection number as P. falciparum in the samples. Mixed infection with P. knowlesi and human malaria parasites was detected in 27 samples, 19 were mixed with P. vivax, one with P. falciparum, and 7 with P. vivax and P. falciparum. The results suggest that Anopheles dirus harbors P. knowlesi in a considerably high rate and bites monkeys as frequently as human being. In analysis of human blood samples, P. knowlesi was detected in 45 out of 170 blood samples with malaria parasites. All P. knowlesi parasites were found in mixed infection with other human malaria parasites. Gametocytes of P. falciparum and P. vivax, moreover, were detected by RT-PCR analysis but that of P. knowlesi was not detected. These results indicate that natural human infection of P. knowlesi is prevalent in this area. In this study, we were not able to determine whether P. knowlesi is being transmitted from human to human although transmitted it from monkey to human via mosquito.

ヒトや動物のマラリアを媒介する蚊の生態研究
Vector ecology of mosquitoes transmitting malaria parasite of human and wild animals.

Yoshio Tsuda
Department of Medical Entomology, National Institute of Infectious Diseases

Plasmodium parasites are transmitted by mosquitoes. Comparing to the directly transmitted disease systems in which the force of infection is determined simply, the force of infection in vector-borne disease systems varies greatly depending on vector species and the structure of vector populations. In general, the capacity of vector population to transmit pathogens, often called vectorial capacity, is determined by several ecological characters of vector populations, such as vector competence, host preference, survival rate/longevity and biting density.

The vector competence and host preference of vector mosquitoes are major ecological factors determining the combination of host animals and vector species of pathogens. It is likely that mosquito-borne pathogens are maintained between vector mosquitoes and their major blood-source animals. Human Plasmodium parasites are transmitted by only Anopheles mosquitoes which show feeding preference to humans and large mammals. Vectors of monkey malaria have been studied intensively in Malaysia during 1960’s and several Anopheles species were suggested to be the vector. Other than primate malaria parasite, only limited information is available for vector mosquitoes of mammalian Plasmodium parasite

About vector mosquitoes of avian Plasmodium, several entomological studies have been conducted recently in Japan, and a variety of avian Plasmodium lineages were detected from various mosquito species, such as Culex pipiens pallens, Culex quinquefasciatus, Culex nigropuntatus, Culex inatomii, Armigeres subalbatus, Mansonia sp. and Aedes albopictus. The feeding pattern of avian malaria vector, Culex pipiens pallens, observed in Tokyo is not fixed but changeable depending on availability of blood-source animals. The seasonal changes in feeding pattern of Culex pipiens pallens governed the transmission dynamics of avian Plasmodium in Japanese wild bird community.

Strategic meeting

July 8th Fri.

19:00	Perspective of the project, " The eco-epidemiology of forest and zoonotic malaria." Shusuke Nakazawa (Coordinator, JSPS AA Science Platform Program)
19:45	A break
20:00〜 21:00	Chairperson : Shusuke Nakazawa Monkey malaria parasites, past, present and future. Richard Culleton (Institute of Tropical Medicine, Nagasaki University) Malaria situation and its control in Savannakhet province, Lao PDR. Tiengkham Pongvongsa (Director, Savannakhet provincial malaria station) Plasmodium knowlesi frequently co-infecting with P. vivax than P. falciparum, and rarely manifesting symptoms in Khanh Phu, Vietnam, why? Shusuke Nakazawa (Institute of Tropical Medicine, Nagasaki University)

July 9th Sat.

9:00	Chairperson : Richard Culleton Epidemiological surveys of filariasis and malaria with urine. Makoto Ito (Aichi Medical University School of Medicine) Copro-DNA extraction of helminthes, Opisthorchis viverrini. Megumi Sato (School of Health Sciences, Faculty of Medicine, Niigata University) Prevalence and transmission cycle of avian malaria in Japan. Hiroko Ejiri, Yukita Sato (School of Veterinary Medicine, Nihon University, Japan) Monkey distribution surveys and possible malaria research in Sri Lanka. Michael A Huffman (Primate Research Institute, Kyoto University)
10:00	A break
10:10〜 10:30	General discussion (Chairperson Shusuke Nakazwa) (Participants: All the speakers and chairpersons in the seminar and the meeting and Andrew Macintosh, Osamu Kaneko, Jun Kobayashi, Fumie Kobayashi, Hiroyuki Matsuoka and Yukita Sato)