CHAPTER I GENERAL INTRODUCTION

Transcription

1 1 CHAPTER I GENERAL INTRODUCTION

2 2 CONTENT Chapter I. GENERAL INTRODUCTION 1.1 INTRODUCTION MEDICAL IMPORTANCE OF MOSQUITOES MOSQUITO BORNE DISEASES IN KERALA 7-14

3 3 1.1 INTRODUCTION The history of man is the history of his undaunted struggle against diseases. In fact, Haematophagous Arthropods and vector-borne diseases have proved to be a major deterrent in the progress of man towards a better life, particularly in tropical and subtropical countries. For the last 130 years since Arthropods were first shown to transmit human diseases, hundreds of virus, bacteria, protozoa, and helminths have been found to require a haematophagous Arthropod for transmission between vertebrate hosts (Gubler, 1991; Brown, 1970). Major Arthropod vectors include mosquitoes, fleas, flies and lice. They transmit parasites for more than a dozen of diseases such as Filariasis, Malaria, Dengue, Yellow Fever, Chikungunya, Plague, African Sleeping Sickness, Relapsing Fever, Chagas Disease, Sand Fly Fever, Louse-Borne Typhus, Japanese Encephalitis, Kyasanur Forest Disease (KFD), etc. Table 1.1 shows the major Arthropod vectors and human diseases caused by them. Arthropod-vectors took a heavier toll of human lives in the 17 th through the early 20 th centuries than all other causes put together. (Gubler,1991). Mosquitoes are one of the most important Arthropod vectors that affect the well being of humans and domestic animals world-wide. They are undeniably more detrimental to human health than any other group of Arthropod vectors. Mosquito vectors transmit parasites responsible for

4 4 diseases such as Malaria, Dengue Fever (DF), Chikungunya (CG), Filariasis, Yellow Fever and various forms of Encephalitis such as Japanese Encephalitis (JE), Eastern Equine Encephalitis, St Louis Encephalitis, Western Equine Encephalitis, Venezuelan Equine Encephalitis, etc. Table 1.1 Major Arthropod vectors and human diseases (Youdeowei and Service 1986; Rozendaal, 1997) Vectors Diseases Mosquitoes Anopheles Malaria, Lymphatic filariasis Culex Lymphatic filariasis, JE, Other viral diseases Aedes CG, YF, DF, Other viral Diseases, lymphatic Filariasis Mansonia Lymphatic filariasis Tsetse flies African sleeping sickness Black flies River blindness (Onchocerciasis) Sandflies Leishmaniasis, Sandfly fever Horse flies Loiasis Triatomine bugs Chagas disease Body lice Epidemic typhus, Epidemic relapsing fever Fleas Endemic typhus, Plague Ticks Endemic relapsing fever Mites Scrub-typhus During the 19 th and early part of 20 th century these diseases caused an appallingly terrific human mortality, dealt a severe blow to the economic growth and overall developments of many countries of the world. However, most of these important mosquito-borne public health problems were effectively tackled and brought under control by the middle of the 20 th

5 5 century. The discovery and effective use of residual insecticides contributed substantially to this signal success. Unfortunately, the benefits of mosquitoborne disease control programme were rather short-lived. A number of mosquito-borne diseases began to re-emerge in the different parts of the world in the 1970s. The resurgence has greatly intensified in the past 20 to 30 years (Gubler, 1996 (a & b), 1998; Krogstad, 1996). A similar pattern of resurgence of many mosquito borne-diseases occurred in different parts of India. The recent emergence and resurgence of various mosquito-borne diseases is a serious global health problem and has become more of a growing concern in India over the past few decades. 1.2 MEDICAL IMPORTANCE OF MOSQUITOES Mosquitoes are medically important as vectors of Malaria, various forms of Filariasis and numerous arboviruses. The most important vector species belong to the genera Anopheles, Aedes, Culex and Mansonia. Anopheles is the notorious vector of Malaria. An.culicifacies, An.stephensi, An.fluviatilis, An.dirus, An.sundaicus and An.minimus are the primary vectors of malaria in India while An.annularis, An.philippinesis, An.jeiporiensis and An.varuna are the secondary ones (Rao,1984). Certain Anopheles species transmit filarial worms of Wucheraria bancrofti, Brugia malayi and B. timori, which cause filariasis in man (Nagpal and Sharma, 1995). Cx.vishnui, Cx. pseudovishnui, Cx. tritaeniorhynchus and Cx. gelidus are the common vectors of JE in different parts of the country. Cx. whitmorei, Cx.

6 6 bitaeniorhynchus, Cx. fuscanus, Cx. infula and Cx. fuscocephala were also incriminated as vectors of JE (Samuel et al., 2000). Cx. quinquefasciatus is primary vector for bancroftian filariasis and suspected vector of JE (Mourya et al., 1989). Aedes species are the principal vectors of Yellow Fever Virus, Dengue Fever Virus, Encephalitis Virus, Chikungunya Virus and many other arboviruses, and in some areas they are also vectors of filarial worms such as Wucheraria bancrofti and Brugia malayi. Ae. aegypti was identified as primary vector and Ae. albopictus as secondary vector of DF and CG in different parts of the world, including India (WHO,1999; Jupp and McIntoch, 1988). In some parts of India, Ae.albopictus is recognized as the primary vector and plays a significant role in transmission of DF and CG (Kannan et al., 2009; Thenmozhi et al., 2007). Ae. niveus has been incriminated as a secondary vector of DF in some parts of the world (Huang, 1979). Ae. vittatus and Ae. aegypti were identified as the main vectors of Yellow Fever in many parts of the world (Bruce, 2005). Mansonia species acts as vectors of filariasis. Ma. annulifera, Ma. indiana and Ma. uniformis transmit Brugia malayi and Wucheraria bancrofti (Iyengar, 1938). They were also incriminated as vectors of JE. (Dhanda et al., 1997).

7 7 Many species such as Armigeres sabalbatus, although not carriers of any disease, can be troublesome because of the serious biting nuisance they cause (Service, 2004). 1.3 MOSQUITO BORNE DISEASES IN KERALA Kerala s health indicators are often said to be on a par with those of developed countries. Ironically, Kerala status of being the best health care system in India has received a mortal blow in the past two decades due to the recent emergence/re-emergence of various vector-borne diseases. The table 1.2 (a&b) gives the recent history of Mosquito-borne diseases in Kerala. Table 1.2 (a). Mosquito born diseases reported from Kerala ( ) (DHS Kerala, 2002, 2005, 2006) Disease DF Cases Death CG Cases Death Malaria Cases Death JE Cases Death Central Kerala can be considered as the epicentre of various vector-borne diseases. In fact, Arboviral diseases such as DF, CG and JE originated from Central Kerala which comprises Kottayam, Pathanamthitta, Alappuzha,

8 8 Ernakulam and Idukki districts. Table 1.3 and 1.4 gives the details of vectorborne diseases in Kottayam and Idukki districts (Districts randomly selected from Central Kerala for study). Table 1.2 (b). Mosquito born diseases reported from Kerala ( ) (DHS Kerala, 2007, 2010, 2011) Disease DF CG Malaria JE Cases Death Cases Death Cases Death Cases Death Table 1.3. Mosquito born diseases reported from Kottayam for the last six years (DHS Kerala, 2010, 2011). Disease Total DF CG Malaria JE Cases Death Cases Death Cases Death Cases Death

9 9 Table 1.4. Mosquito born diseases reported from Idukki district for the last six years (DHS Kerala, 2010, 2011). Disease Total DF Cases Death CG Cases Death Malaria Cases Death JE Cases Death The major mosquito borne diseases like Malaria, Filariasis, Dengue, Chikungunya, Japanese Encephalitis, etc. continue to cause serious health concern in Kerala. a. Malaria In Kerala Malaria was a vital public health issue during the past. The history of Malaria can be traced back to those periods earlier than the recorded history where it prevailed among tribal people in the hills and forests (DHS Kerala, 1964). From hilly terrains, Malaria had gradually spread to foothills and adjoining areas and paved the way to occasional outbreaks and deaths. Malaria was successfully eradicated from the state as early as 1965 through National Malaria Control Programme (NMCP) launched in 1953 and National Malaria Eradication Programme (NMEP) launched in But it got

10 10 re-established in the state after a few years following the importation of cases from other endemic states. The virtual reintroduction of malaria case was reported by around 1975 (DHS Kerala, 1978). Thereafter, from 1984 onwards the state showed that indigenous malaria cases in Kerala were on the increase. There has been a shift in the epidemiology of malaria in Kerala over the last decade. The highly malarious hill tracts of the state have now become almost free from the disease, but the urban areas especially those on the coastal regions which were impervious to malaria, have now become endemic for the disease. The shift is mainly due to the disappearance of Anopheles fluviatilis, which was the principal vector in the hills and foothills, and the appearance of Anopheles stephensi in the urban areas on the coastal belt. This species, in fact, contributed to the malaria outbreak during 1996 at Valiyathura of Thuruvananthapuram district, where over 100 cases of malaria were reported (DHS Kerala, 1997). This was followed by another outbreak in Kasargod during 1998 when 400 cases with few deaths reported (DHS Kerala, 1998, 1999). The present problem is, therefore, urban malaria through Anopheles stephensi, which has now become very much prevalent in the entire coastal areas and also in some inland pockets (NVDCP, 2010). b. Filariasis The first important official document of the incidence of filariasis in the Travancore appeared in the censes report of 1901 (Aiya, 1906). This revealed the maximum incidence in Cherthali taluk with persons afflicting one in every twenty seven of the population, followed by Ambalappuzha with one in 194

11 11 persons. Alappuzha and Trivandrum were recorded as highly filarial, with endemicity rates 20.5% and 13.6 % respectively (Iyengar,1938). Studies of National Filariasis Control Programme (NFCP) in Alappuzha and Kozhikode revealed the endemicity rates of 21.6% and 14.94% during 1975 and 1960 respectively. Later in early 1990s studies showed a diminishing trend of lymphatic filariasis in certain foci in Kerala (Arunachalam et al., 1996). Towards the end of 1990s, the endemicity rates were reduced to a lower level, being 2.6%, 1.7% and 1.58% during 1998, 1999 and 2000 period respectively (NFCP Kerala, 2001). These results show that filariasis still continues in the state though in low level. This observation resulted in the implementation of Mass Drug Administration (MDA) for the elimination of lymphatic filariasis in Alappuzha and Kozhikode in From 2004 onwards the programme is being implemented in eleven districts including Kottayam (NICD, 2012). c. Japanese Encephalitis Japanese Encephalitis (JE) is a mosquito borne viral disease of human and animals. Approximately 3 billion people (60 % of the world's population) live in JE endemic regions (Joshi et al., 2004). It has much public health importance due to its high epidemic potential, high case fatality rate (CFR) and sequelae among survivors. JE has been emerged as a serious threat in many parts of India (ICMR 1980; Geevarghese et al., 1994; Reuben and Gajanana 1997; Gajanana et al., 1997; Gajanana 1998). JE Virus is transmitted to man by the bite of infected mosquitoes, especially Culex species (Gajanana et al., 1997; Hiriyan et al., 2003). JE was first reported in Kerala in 1996, around the axis of

12 12 Kottayam, Alappuzha and Pathanamthitta districts. Twenty eight deaths were reported during that outbreak (DHS Kerala, 1997). Since then cases with deaths have been regularly reported from the state except in the years 1998, 2002, d. Dengue Fever In Kerala, Dengue Fever first appeared in 1997 when 14 suspected cases with 4 deaths were reported from Kottayam district. This was followed by an outbreak with 67 cases wherein 13 deaths were reported from the same district in The disease was virtually silent during By 2001, Dengue Fever which was confined to Kottayam district, spread to neighbouring districts like Ernakulum and Idukki. Sixty six cases were reported from these districts (DHS Kerala, 2005), followed by 219 cases in 2002 with few deaths here and there in the state. The year 2003 witnessed a severe epidemic yielding 3546 confirmed cases and a toll of 68 lives, spreading for the first time all over the Kerala s fourteen districts. (DHS Kerala, 2005). Since then, DF cases reports have become a routine affair in all the fourteen districts in Kerala. e. Chikungunya Chikungunya which appeared for the first time in 2006 added a new dimension to the entire scenario of vector-borne diseases in Kerala. It was first reported from some localities of Kozhikode, Trivandrum, Ernakulum and Alappuzha districts during May-June 2006 and then from the districts of Kottayam, Pathanamthitta and Idukki. By the end of 2006, all the 14 districts of state were affected. According to Directorate of Health Services Kerala, 70731

13 13 suspected cases were reported from Kerala in 2006 and in The districts of Kottayam, Pathanamthitta and Idukki experienced a high incidence of Chikungunya in outbreaks. In 2008 CG mainly affected the northern districts, mainly Kasargod, Kozhikode, Malapuram and Palakkad. A total of suspected Chikungunya cases were reported in (Table 1.2 b). High incidence of disease continued in the following years. The Studies have shown that vector-borne disease is a knotty problem in Kerala state, especially Central Kerala. The causes of resurgence or emergence of mosquito-borne diseases are rather complex and include interstate and international travel, inadequate environmental sanitation, urbanization, agricultural pattern and unscientific practices, climatic conditions, import of vectors from outside the state and the migration of huge labour force from other endemic states. As a result, there has been influx of parasitic carriers increasing the vulnerability of the state to mosquito-borne diseases. Another reason for the outbreak of diseases is the complete absence of vector monitoring and subsequent control measures. The emergence and resurgence various mosquito-borne diseases in Kerala, necessitated a detailed study of mosquito fauna. Ironically, the mosquito composition, diversity, distribution, ecology and population dynamics of many species of mosquitoes are not adequately known from Kerala. Therefore, it is highly relevant and appropriate to investigate the mosquito fauna, especially of central Kerala which is considered as the epicentre of various mosquito-borne

14 14 diseases. The present work has immense scope in the current scenario. A sound knowledge of mosquito vector is the foundation on which we can hope to control them and subsequently the mosquito-borne diseases Objectives The general objectives of present study were the following:- 1. To understand the diversity, composition, distribution and breeding ecology of the mosquito fauna of the Central Kerala. (Chapter II) 2. To study the breeding ecology and population dynamics of Aedes albopictus in rubber plantation belt of the Central Kerala. (Chapter III) 3. To understand Knowledge, Attitude and Practice (KAP) of people on Aedes albopictus and Aedes albopictus - borne diseases. (Chapter IV)