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PUBLIC HEALTH
Virulent outbreak
R. RAMACHANDRAN
in New Delhi
Chikungunya is spreading fast across the country in an epidemic form presenting a big challenge on the public health front.
K.R. DEEPAK
AT A FREE medical camp, organised by the Visakhapatnam Municipal Corporation.
FOR India, 2006 is likely to go down as one of the worst years in terms of public health in recent times. The country is witnessing not just a high incidence of familiar diseases such as malaria, polio, Japanese encephalitis and dengue; chikungunya, practically unknown to a whole generation, has emerged after a gap of 32 years. The disease seems to have resurfaced in October 2005. It reached outbreak proportions by March 2006 in the States of Maharashtra, Karnataka and Andhra Pradesh and has spread since then across the southern States, coastal areas in particular, and to other parts of the country.
As of October 4, nearly 1.3 million suspected cases of the disease from 152 districts in 10 States have been reported (see table on page 118). Karnataka, Maharashtra and Andhra Pradesh, where the disease surfaced initially, are the worst affected States. What may, however, be of significance from a public health point of view is that all ages and both sexes have been affected. Unlike what has been observed in the past, the current outbreak seems to have affected the adult population (over 15 years of age) more. Also, in contrast to earlier chikungunya outbreaks, when only urban and semi-urban populations were affected, cases in the current outbreak have been predominantly reported from rural areas.
The Indian outbreak seems to have followed the chikungunya outbreak on the Indian Ocean islands of Madagascar, Mayotte, Mauritius, Reunion (territory of France) and the Seychelles, which began in 2005 and waned early this year. Whether the two outbreaks are in any way linked is a subject of ongoing epidemiological study in the country and elsewhere. It is pertinent to note that there is a great deal of tourist traffic between India and the Indian Ocean islands. Initial studies have, however, revealed that the causative viruses in the Indian Ocean and the Indian outbreaks are genetically linked and both belong to the African genotype of the virus.
Chikungunya, pronounced as chik-en-gun-yah, which incidentally has no relation to chicken or bird flu, is a debilitating but non-fatal, self-limiting illness caused by the bite of mosquitoes belonging to the Aedes species that infect humans with the chikungunya virus (CHIKV). CHIKV belongs to the virus family Togaviridae, genus Alphavirus. It is geographically distributed in Africa, India and South-East Asia. In India, the dominant carrier of the virus is Aedes aegypti, which breeds in stored fresh water in urban and semi-urban environments and bites during the day. The virus is maintained in the human population by a human-mosquito-human transmission cycle. This is somewhat different from the transmission cycle on the African continent where the virus is transmitted through a sylvatic transmission cycle between wild primates and mosquitoes of the types A. luteocephalus, A. furcifer and A. taylori.
The disease, in fact, was first reported in 1952 in Tanzania when the virus too was isolated. Since then, CHIKV outbreaks have occurred all over Africa, the most recent one being during 1999-2000 in Kinshasa in the Democratic Republic of the Congo, where an estimated 50,000 people were infected. The first Asian outbreak was in Thailand in 1958. Since then outbreaks have repeatedly occurred in various South-East and East Asian countries. Prior to the current outbreak, the most recent re-emergence in the Asian region was in Java in Indonesia in 2001-2003, which occurred after a 20-year gap.
According to a group of French scientists, led by Isabelle Schuffenecker of the Pasteur Institute, who investigated the genetic characteristics of the virus implicated in the current Indian Ocean outbreak, the reemergence of CHIKV in both Africa and Asia has been unpredictable, with intervals of seven to 20 years between epidemics. This observation has led them to study the microevolution of the virus, which has thrown up some interesting findings with regard to the changing virulence of the virus.
Chikungunya usually starts suddenly with fever, chills, headache, nausea, vomiting, joint pain and rashes. Many of the clinical symptoms resemble a non-severe form of dengue whose causative virus is also transmitted by A. aegypti. There is thus a likelihood of confusion between the two diseases at the level of initial clinical symptoms presented by a patient.
But there are distinct features of chikungunya, which are severely arthritic in nature, that serve to distinguish clinically the Chikungunya cases. In fact, the disease derives its name from the language of the tribes in the Makonde plateau of Tanzania. Literally meaning "that which contorts or bends up", the term is descriptive of the stooped posture of patients who are afflicted with severe pain and inflammation in the joints - referred to in medical parlance as poly-arthralgia - which is the typical clinical symptom of the disease. While the disease itself is self-limiting and lasts for 10-15 days, arthralgia or joint pains could persist for months or even years, requiring long-term pain medication. The infection itself has been found to confer long-term immunity.
The severe arthritis itself is considered sufficient diagnosis for official classification of "suspected chikungunya cases" and the guidelines apparently require that virological confirmation be done on only a fraction of suspected cases, according to P.L. Joshi, Director of the National Vector Borne Disease Control Programme (NVBDCP) of the Union Health Ministry (see table). However, from the figures it would seem that there is gross misdiagnosis at the State level, which is the primary source for the data. "Often dengue or even other infections like influenza that cause high fever get mistakenly classified as suspected chikungunya," points out P.K. Das, Director of the Vector Control Research Centre (VCRC), Puducheri (formerly Pondicherry). This is apparent from the fact that, of the samples sent by the States to the National Institute of Virology (NIV), Pune, or the National Institute for Communicable Diseases (NICD) for laboratory confirmation (which for some reason constitutes only about 1 per cent of the suspected cases), only about 10 per cent were found to be positive for the chikungunya virus (see table). How this translates into the actual incidence of the disease is not very clear.
As for patient care, this does not matter because clinical management for chikungunya and non-severe forms in the initial phase of dengue, which are basically self-limiting and do not have any curative medicine, is the same involving control of fever and pain through paracetemol and non-aspirin-based pain relievers. It is also possible that both infections are simultaneously present in a patient. Of course, if any case progresses into features that characterise severe forms of Dengue with Haemorrhagic Fever (DHF) or Shock Syndrome (DSS), the clinical management and the course of treatment are entirely different.
So, while the detailed data may not be important for the management of chikungunya patients, for epidemiological studies they are important. Even from a public health perspective, since the carrier of both the viruses is the same, namely the A. aegypti mosquito, prevention strategies in terms of vector control also would be the same. Unfortunately, given the weak district-level public health system and disease monitoring, the true burden of the disease may not be known at all. A na?ve extrapolation to the total number of cases would suggest that there would be about 0.13 million cases, which is not a small number.
http://www.lettera22.it/showart.php?id=5820&rubrica=177
Virulent outbreak
R. RAMACHANDRAN
in New Delhi
Chikungunya is spreading fast across the country in an epidemic form presenting a big challenge on the public health front.
K.R. DEEPAK
AT A FREE medical camp, organised by the Visakhapatnam Municipal Corporation.
FOR India, 2006 is likely to go down as one of the worst years in terms of public health in recent times. The country is witnessing not just a high incidence of familiar diseases such as malaria, polio, Japanese encephalitis and dengue; chikungunya, practically unknown to a whole generation, has emerged after a gap of 32 years. The disease seems to have resurfaced in October 2005. It reached outbreak proportions by March 2006 in the States of Maharashtra, Karnataka and Andhra Pradesh and has spread since then across the southern States, coastal areas in particular, and to other parts of the country.
As of October 4, nearly 1.3 million suspected cases of the disease from 152 districts in 10 States have been reported (see table on page 118). Karnataka, Maharashtra and Andhra Pradesh, where the disease surfaced initially, are the worst affected States. What may, however, be of significance from a public health point of view is that all ages and both sexes have been affected. Unlike what has been observed in the past, the current outbreak seems to have affected the adult population (over 15 years of age) more. Also, in contrast to earlier chikungunya outbreaks, when only urban and semi-urban populations were affected, cases in the current outbreak have been predominantly reported from rural areas.
The Indian outbreak seems to have followed the chikungunya outbreak on the Indian Ocean islands of Madagascar, Mayotte, Mauritius, Reunion (territory of France) and the Seychelles, which began in 2005 and waned early this year. Whether the two outbreaks are in any way linked is a subject of ongoing epidemiological study in the country and elsewhere. It is pertinent to note that there is a great deal of tourist traffic between India and the Indian Ocean islands. Initial studies have, however, revealed that the causative viruses in the Indian Ocean and the Indian outbreaks are genetically linked and both belong to the African genotype of the virus.
Chikungunya, pronounced as chik-en-gun-yah, which incidentally has no relation to chicken or bird flu, is a debilitating but non-fatal, self-limiting illness caused by the bite of mosquitoes belonging to the Aedes species that infect humans with the chikungunya virus (CHIKV). CHIKV belongs to the virus family Togaviridae, genus Alphavirus. It is geographically distributed in Africa, India and South-East Asia. In India, the dominant carrier of the virus is Aedes aegypti, which breeds in stored fresh water in urban and semi-urban environments and bites during the day. The virus is maintained in the human population by a human-mosquito-human transmission cycle. This is somewhat different from the transmission cycle on the African continent where the virus is transmitted through a sylvatic transmission cycle between wild primates and mosquitoes of the types A. luteocephalus, A. furcifer and A. taylori.
The disease, in fact, was first reported in 1952 in Tanzania when the virus too was isolated. Since then, CHIKV outbreaks have occurred all over Africa, the most recent one being during 1999-2000 in Kinshasa in the Democratic Republic of the Congo, where an estimated 50,000 people were infected. The first Asian outbreak was in Thailand in 1958. Since then outbreaks have repeatedly occurred in various South-East and East Asian countries. Prior to the current outbreak, the most recent re-emergence in the Asian region was in Java in Indonesia in 2001-2003, which occurred after a 20-year gap.
According to a group of French scientists, led by Isabelle Schuffenecker of the Pasteur Institute, who investigated the genetic characteristics of the virus implicated in the current Indian Ocean outbreak, the reemergence of CHIKV in both Africa and Asia has been unpredictable, with intervals of seven to 20 years between epidemics. This observation has led them to study the microevolution of the virus, which has thrown up some interesting findings with regard to the changing virulence of the virus.
Chikungunya usually starts suddenly with fever, chills, headache, nausea, vomiting, joint pain and rashes. Many of the clinical symptoms resemble a non-severe form of dengue whose causative virus is also transmitted by A. aegypti. There is thus a likelihood of confusion between the two diseases at the level of initial clinical symptoms presented by a patient.
But there are distinct features of chikungunya, which are severely arthritic in nature, that serve to distinguish clinically the Chikungunya cases. In fact, the disease derives its name from the language of the tribes in the Makonde plateau of Tanzania. Literally meaning "that which contorts or bends up", the term is descriptive of the stooped posture of patients who are afflicted with severe pain and inflammation in the joints - referred to in medical parlance as poly-arthralgia - which is the typical clinical symptom of the disease. While the disease itself is self-limiting and lasts for 10-15 days, arthralgia or joint pains could persist for months or even years, requiring long-term pain medication. The infection itself has been found to confer long-term immunity.
The severe arthritis itself is considered sufficient diagnosis for official classification of "suspected chikungunya cases" and the guidelines apparently require that virological confirmation be done on only a fraction of suspected cases, according to P.L. Joshi, Director of the National Vector Borne Disease Control Programme (NVBDCP) of the Union Health Ministry (see table). However, from the figures it would seem that there is gross misdiagnosis at the State level, which is the primary source for the data. "Often dengue or even other infections like influenza that cause high fever get mistakenly classified as suspected chikungunya," points out P.K. Das, Director of the Vector Control Research Centre (VCRC), Puducheri (formerly Pondicherry). This is apparent from the fact that, of the samples sent by the States to the National Institute of Virology (NIV), Pune, or the National Institute for Communicable Diseases (NICD) for laboratory confirmation (which for some reason constitutes only about 1 per cent of the suspected cases), only about 10 per cent were found to be positive for the chikungunya virus (see table). How this translates into the actual incidence of the disease is not very clear.
As for patient care, this does not matter because clinical management for chikungunya and non-severe forms in the initial phase of dengue, which are basically self-limiting and do not have any curative medicine, is the same involving control of fever and pain through paracetemol and non-aspirin-based pain relievers. It is also possible that both infections are simultaneously present in a patient. Of course, if any case progresses into features that characterise severe forms of Dengue with Haemorrhagic Fever (DHF) or Shock Syndrome (DSS), the clinical management and the course of treatment are entirely different.
So, while the detailed data may not be important for the management of chikungunya patients, for epidemiological studies they are important. Even from a public health perspective, since the carrier of both the viruses is the same, namely the A. aegypti mosquito, prevention strategies in terms of vector control also would be the same. Unfortunately, given the weak district-level public health system and disease monitoring, the true burden of the disease may not be known at all. A na?ve extrapolation to the total number of cases would suggest that there would be about 0.13 million cases, which is not a small number.
http://www.lettera22.it/showart.php?id=5820&rubrica=177