Outbreak Of Chikungunya Epidemic Biology Essay

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Reports of large-scale outbreaks of fever caused by CHIKV virus infection in several parts of the country especially in Southern India have confirmed the re-emergence of this virus. In 2006, Southern India states Andhra Pradesh, Karnataka, Tamil Nadu and Kerala together contributed more than 70% of the total country's incidence out which Karnataka state alone contributed nearly 55% of incidence. In 2008, Karnataka and Kerala together contributed more than 95% of the total suspected cases and in 2009 also 41,649 suspected CHIKV cases have been reported and 3,239 cases were confirmed for Karnataka. There is no specific treatment (therapies) or vaccines are available for CHIKV. But the Homoeopathic system of medicine claims to have medicines as well as preventive measures against this disease.

Key words: CHIKV, Aedes aegypti, dengue, incidence and outbreak.

1. Introduction

Chikungunya (CHIKV) virus has recently re-emerged as an important pathogen causing epidemics of the disease in several countries. Epidemic resurgence of CHIKV was recorded in 2000 in the Democratic Republic of Congo (DRC), in Indonesia during 2001-2003 and in India during 2005-2006, after a gap of 39, 20 and 32 years respectively. In December 2006, there were outbreaks of 3,500 confirmed cases in the Maldives, and over 60,000 suspected cases and over 80 deaths in Sri Lanka. The widespread outbreak of CHIKV in India is in the states of Maharashtra, Gujarat, Madhya Pradesh and mainly in southern states Andhra Pradesh, Tamil Nadu, Karnataka, and Kerala. In Kerala state, 43,138 suspected cases and 125 deaths were occurred due to this outbreak, with the majority of the casualties reported in the district of Alapuzha, mainly in Cherthala. In early 2007, CHIKV spread from Kerala and Tamil Nadu to Sri Lanka and many people were infected. CHIK outbreaks in east, south, west and central Africa have been documented (see Fig 1. for global distribution of CHIKV).

Fig 1.: Chikungunya (CHIKV) global distribution map (countries affected)

Source: WHO report, 2007

2. Spread of the Epidemic:

CHIKV virus is indigenous to tropical Africa and Asia, where it is transmitted to humans by the bite of infected mosquitoes, usually of the genus Aedes mosquito. Aedes albopictus is considered to be the vector in Reunion and other islands of the Indian Ocean. Although both Aedes aegypti and Aedes albopictus mosquitoes are prevalent in India, the former is the main responsible vector for the spread (Yergolkar et al., 2006). CHIKV fever is a relatively rare form of viral fever caused by an alphavirus that is spread by the bite of an infected "Aedes aegypti mosquito". The mosquito usually transmits the disease by biting an infected person and then biting someone else. An infected person cannot spread the infection directly to other persons (i.e. it is not a contagious disease) (see Fig 2). In Makonde language, CHIKV means "that which bends up". Although it may feed at any time, the peak biting periods of mosquitos are few hours after dawn and in the late afternoon until a few hours after dark. The mosquito's preferred breeding areas are in areas of stagnant water, such as flower vases, uncovered barrels, buckets, and discarded tires, but the most dangerous areas are wet shower floors and toilet bowls, as they allow the mosquitoes to breed right in the residence (www.cdc.org 2006). CHIKV virus is highly infective and disabling but is not transmissible between people. In India, the first CHIKV outbreak was recorded in 1963 in Kolkata (Calcutta) followed by epidemics in eastern coastal areas Chennai (nearly 4,00,000 cases), Pondicherry and Vellore of Tamil Nadu state in 1964, Visakhapatnam, Rajmundry and Kakinada of Andhra Pradesh state in 1965 (Rao, 1966), Nagpur and Barsi of Maharashtra state in 1965 and 1973 respectively (Padbidri and Gnaneswar, 1979). In view of the long absence of CHIKV epidemics, it was under the impression that CHIKV virus had disappeared from India and South-East Asia (Burke et al., 1985; Pavri, 1986). Serological surveys supported this view (Neogi et al., 1995), see also Vidya et al (2007). The outbreak of CHIKV fever that started in the Indian Ocean Islands in early 2005 spread through adjoining islands and appeared in peninsular India by late 2005. It has been estimated that over 1, 80,000 suspected cases of CHIKV fever have occurred in India since December 2005 (Ravi, 2006). Andhra Pradesh (AP) was the first state to report this disease in December 2005, and one of the worst affected states (over 80,000 suspected cases); it spread to Tamil Nadu in April 2006 and to Karnataka and Kerala in May. However, reports of large-scale outbreaks of fever caused by CHIKV virus infection in several parts of Southern India have confirmed the re-emergence of this virus (Enserink, 2006), see also Fig 3. and Fig 4. for the suspected cases of CHIKV during 2006-2009 and distribution in India particularly in south-India respectively.

Fig 2.: Transmission Cycle of CHIKV

Sources: Directorate of National Vector Borne Disease Control Programme

Fig .3: CHIKV suspected cases of South India during 2006-09

Fig 4.: Spreading of Chikungunya fever (shaded area- states affected) in India during 2006-2010.

Source: Krishnamoorthy et al. (2009)

3. Effects of the Epidemic:

CHIKV virus is an arbovirus, of the genus, Alphavirus, that is transmitted to humans by virus-carrying Aedes mosquitoes. There have been recent outbreaks of CHIKV associated with severe morbidity. CHIKV causes an illness with symptoms similar to dengue fever. CHIKV manifests itself with a prolonged arthralgic disease that affects the joints of the extremities. The acute febrile phase of the illness lasts only two to five days. The pain associated with CHIKV infection of the joints persists for weeks or months. All age groups were affected, including newborns. Recovery from the disease varies by age. Younger patients recover within 5 to 15 days and middle-agers recover in 1 to 2.5 months. Recovery is longer for the elderly. The severity of the disease as well as its duration is less in younger patients and pregnant women. In pregnant women, no untoward effects are noticed after the infection.

4. Epidemic Status of Karnataka state:

Karnataka was the worst affected state during 2006 CHIKV outbreak, 27 districts of the state reported over 7, 62,026 (54.74% of the total) suspected cases. Several districts of the state such as Gulbarga, Tumkur, Bidar, Raichur, Dharwad, Bellary, Chitradurga, Davangere, Kolar and Bijapur have recorded large number of CHIKV virus related fever cases in 2006, Bijapur (over 80,00 cases) and Gulbarga (more than 52,353 cases) are the worst affected districts during the epidemic outbreak. In 2007, only 1705 suspected CHIKV cases were reported and whereas in 2008, the state reported 45,618 cases, more than 64 percent of the entire suspected cases in India in 2008, the Mangalore (over 27,408 reported cases) was the worst affected district of the state. Unofficial reports suggested that more number of individuals were suffered from symptoms of CHIKV. In 2009, 41,649 suspected CHIKV cases have been reported and 3,239 cases were confirmed for CHIKV (Table 1, 2 and 3). There has also been a marked decrease in CHIKV cases in 2010 in the state with 5,244 cases reported and 528 cases were confirmed (by the end of august 2010). There is no statistical relationship between CHIKV and Dengue cases (though CHIKV causes an illness with symptoms similar to dengue fever), refer Table 2 and 3.

Table1: Chikungunya (CHIKV) Fever Situation in the Country during 2006 (Prov.).

State

No. of districts affected

Total fever cases/Suspected CHIKV fever cases

(percentage values)

No. of samples sent to NIV/NICD

No. of confirmed cases

Andhra Pradesh

23

77535 (5.57)

1,224

248

Karnataka

27

762026 (54.74)

5,000

298

Maharashtra

34

268333 (19.28)

5,421

786

Tamil Nadu*

35

64802 (4.66)

648

116

Madhya Pradesh

21

60132 (4.32)

892

106

Gujarat

25

76012 (5.46)

1,155

225

Kerala

14

70731(5.08)

235

43

A &Nicobar

2

4469 (0.32)

0

0

GNCT of Delhi

12

560(0.04)

560

67

Rajasthan

1

102 (0.01)

44

24

Pondicherry

1

542 (0.04)

52

9

Goa

2

287(0.02)

75

2

Orissa

13

6461(0.46)

171

34

West Bengal

1

-

21

21

Lakshadweep

2

35(0.003)

6

6

Total

213

13,92,027

15,504

1,985

Sources: Directorate of National Vector Borne Disease Control Programme

Table 2: As on 19-9-2008, the total of 70740 suspected cases of CHIKV have been reported from 8 States in the India. The State-wise suspected cases of CHIKV are as follows

State

CHIKV cases

(percentage values)

Dengue cases

(percentage values)

Andhra Pradesh

5 (0.01)

24 (1.15)

Goa

16 (0.02)

18 (0.86)

Gujarat

168 (0.24)

250 (11.94)

Haryana

20 (0.03)

739 (35.29)

Karnataka

45618 (64.49)

221 (10.55)

Kerala

24505 (34.64)

308 (14.71)

Maharashtra

398 (0.56)

252 (12.03)

Tamil Nadu

10 (0.01)

282(13.47)

Total

70740 (100.0)

2094(100.0)

Sources: Directorate of National Vector Borne Disease Control Programme

Table 3: As on 30-04-2009, the total of 2717 suspected cases of CHIKV have been reported from 7 States in the India. The State-wise suspected cases CHIKV are as follows

State

CHIKV cases

(percentage values)

Dengue cases

(percentage values)

Andhra Pradesh

549 (20.21)

20 (2.45)

Goa

64 (2.36)

6 (0.73)

Karnataka

1913 (70.41)

45 (5.51)

Kerala

38 (1.40)

485 (59.36)

Maharashtra

102 (3.75)

75 (9.18)

Tamil Nadu

16 (0.59)

113 (13.83)

West Bengal

35 (1.29)

73 ( 8.94)

Total

2717 (100.0)

817 (100.0)

Sources: Directorate of National Vector Borne Disease Control Programme

A Case of Mangalore District (Karnataka State) during 2008:

As on 05-07-2008, the total 27408 suspected cases of CHIKV have been reported from all the Taluks of Mangalore district. The Taluk-wise suspected cases are as follows

Table 4: The District-wise suspected cases of CHIKV of Karnataka State in 2008.

District

Suspected Cases

Blood sample collected

Number of positives

Dengue cases

D.K.

27,408

396

122

24

Kodagu

1,074

85

20

0

Shimoga

454

41

8

0

Udupi

357

165

40

0

Mysore

343

53

23

0

Dharwad

325

19

18

0

Belgaum

267

20

10

1

Hassan

171

36

10

0

Bangalore

30

30

12

1

U.K.

23

23

0

0

Tumkur

21

21

11

1

Gadag

24

4

3

18

Table 5: The Taluk-wise suspected cases of CHIKV in 2008

Taluk

Suspected Cases

Number of positives

Dengue cases

Mangalore

2426

32

7

Beltangadi

3252

17

2

Bantwal

9628

20

4

Puttur

9419

13

5

Sulya

2683

22

6

Total

27,408

104

24

In some areas of Mangalore district about 50% of the population is affected by this disease. Also a large number of infections are unreported or are misdiagnosed (Table 4 and 5).

5. Conclusion:

There is no specific treatment (therapies) or vaccines are available for chikungunya. But the Homoeopathic system of medicine claims to have medicines as well as preventives against this disease. The effects of these medicines are not scientifically proved. They claim to have used these effectively in recent outbreaks in Kerala State of India. The most effective means of prevention are those that protect against any contact with the disease carrying mosquitoes.

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