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I was just doing some reading in 'Tropical Infectious Diseases', Principles, Pathogens, and Practice 2nd edition 2006 and thought I'd post a few things I found interesting...
Japanese Encephalitis
JE virus is enzootic in rural agricultural areas throughout much of eastern and southern Asia and the Pacific Islands. Domestic swine and ardeid birds, such as herons and other waterfowl are the most impoortant virus-amplifying hosts. However, the most important source
of human infections is linked to trhe mosquito-swine transmission cycle.
JE virus is a leading cause of viral encephalitis in tropical Asia, where it causes an estimated 35,000 to 50,000 clinical cases and 15,000 deaths annually.
Over the past four decades, the incidence of JE has increased dramatically in central and northen India, Nepal, and the northern region of Southeast Asia,. JE virus has also expanded its range into other areas of Southeast Asia and eastward to the Australasian zoogeographic region. The expanding distribution of JE is not fully understood, but may be associated with changes in agricultural practices that provide suitable breeding habitat for mosquitoes or an increase in swine production.
In endemic areas, the annual infection rate is about 10% among the susceptible populations, with about 85% of the cases occurring among children under 15 years of age. Most JE virus infections are silent: the ratio of symptomatic to asymptomatic infections varies from about
one in 25 to one in 1000.
In contrast to the situation in endemic regions, all age groups are affected during epidemics in nonimmune populations. Similarly, when nonimmune individuals (travelers, or military personnel) visit endemic areas they too are at risk.
Patients typically present with a history of 1 to 3 days of fever, headache, stupor, and, especially in children, generalized motor seizures. The case-fatality rate can be as high as 30%.
The etiologic diagnosis of a flaviviral infection (ie JE) cannot be determined clinically.
Dengue
In 2005, dengue viruses and Ae. aegypti mosquitoes have a worldwide distribution in the trppics with over 2.5 billion people living in dengue-endemic areas. Currently, dengue fever causes more illness and death than any other arboviral disease of humans. Each year, an estimated 50 to 100 million dengue infections and several hundred
thousand cases of DHF (Dengue hemorrhagic fever) occur, depending on epidemic activity. DHF is a leading cause of hospitalization and death among children in many Southeast Asian countries.
The emergence of epidemic dengue and DHF as a global public health problem in the past 25 years is closely associated with demographic and societal changes that have occurred over the past 50 years. A major factor has been the unprecedented population growth and, with that, unplanned, and uncontrolled urbanization, especially in tropical developing countries. The substandard housing and the deterioration in water, sewer, and waste management systems associated with unplanned urbanization have created ideal conditions for increased
transmission of mosquito-borne diseases in tropical urban centers.
DHF is primarily a disease of children under the age of 15 years, although it may also occur in adults. It is characterized by sudden onset of fever, usually of 2 to 7 days duration, and a variety of nonspecific signs and symptoms. During the acute phase of illness it is difficult to distinguish DHF from dengue fever and other illnesses
found in tropical areas. The differential diagnosis during the acute phase of illness should include measles, rubella, influenza, typhoid, leptospirosis, malaria, viral hemmorrhagic fevers, and any other disease that may present in the acute phase as nonspecific viral syndrome. Children frequently have concurrent infections with other
viruses and bacteria causing upper respiratiory symptoms. There is no pathognomonic sign of symptom for DHF.
A definitive diagnosis of dengue infection can be made only in the laboratory and depends on isolating the virus, detecting dengue virus specific RNA sequences by nucleotide amplification test, of detecting specific antibodies in the patient's serum.
Chickungunya
This viral disease is only very briefly discussed reflecting how fast these diseases can change in incidence and virulence. This 'out of date' 2006 book states that CHIK is generally an acute, self-limited infection with no deaths reported but has a useful discussion of symptoms.
CHIKV infection is characterized by the sudden onset of fever, chills, headache, photophobia, backache, nausea, vomiting, arthralgia, and rash. Patients are quite sick although the acute illness only lasts about 3 to 5 days, with recovery usually in 5 to 7 days. The incubation period is about 2 to 4 days, and the most common complaint
is the severe arthralgia, which is seen in 70% of cases. Febrile convulsions sometimes occur in children, and hemorrhagic manifestations (petechiae, purpura, epistaxis, bleeding gums, hematemesis, and melena) also have been reported.
This is a very limited summary of the differential diagnosis of tropical diseases that can be confused with H5N1. Although some of these diseases can be strongly suggested by time of year, geographic area, and cluster of symptoms there is a lot of overlap. It would appear easy for H5N1 (both typical and atypical cases) to hide in this
background of disease. With the limited if any medical care available in some of these areas and the complexities of good laboratory diagnosis I'm sure many of these cases are not properly diagnosed as to etiologic agent yet alone being followed for genetic changes in the agents that may lead to increased virulence. We'll be able to tell if a raging H5N1 or other influenza pandemic emerges out of this but if we want to catch it early or get a better idea of the smoldering nature of the problem we have our work cut out for us.
Japanese Encephalitis
JE virus is enzootic in rural agricultural areas throughout much of eastern and southern Asia and the Pacific Islands. Domestic swine and ardeid birds, such as herons and other waterfowl are the most impoortant virus-amplifying hosts. However, the most important source
of human infections is linked to trhe mosquito-swine transmission cycle.
JE virus is a leading cause of viral encephalitis in tropical Asia, where it causes an estimated 35,000 to 50,000 clinical cases and 15,000 deaths annually.
Over the past four decades, the incidence of JE has increased dramatically in central and northen India, Nepal, and the northern region of Southeast Asia,. JE virus has also expanded its range into other areas of Southeast Asia and eastward to the Australasian zoogeographic region. The expanding distribution of JE is not fully understood, but may be associated with changes in agricultural practices that provide suitable breeding habitat for mosquitoes or an increase in swine production.
In endemic areas, the annual infection rate is about 10% among the susceptible populations, with about 85% of the cases occurring among children under 15 years of age. Most JE virus infections are silent: the ratio of symptomatic to asymptomatic infections varies from about
one in 25 to one in 1000.
In contrast to the situation in endemic regions, all age groups are affected during epidemics in nonimmune populations. Similarly, when nonimmune individuals (travelers, or military personnel) visit endemic areas they too are at risk.
Patients typically present with a history of 1 to 3 days of fever, headache, stupor, and, especially in children, generalized motor seizures. The case-fatality rate can be as high as 30%.
The etiologic diagnosis of a flaviviral infection (ie JE) cannot be determined clinically.
Dengue
In 2005, dengue viruses and Ae. aegypti mosquitoes have a worldwide distribution in the trppics with over 2.5 billion people living in dengue-endemic areas. Currently, dengue fever causes more illness and death than any other arboviral disease of humans. Each year, an estimated 50 to 100 million dengue infections and several hundred
thousand cases of DHF (Dengue hemorrhagic fever) occur, depending on epidemic activity. DHF is a leading cause of hospitalization and death among children in many Southeast Asian countries.
The emergence of epidemic dengue and DHF as a global public health problem in the past 25 years is closely associated with demographic and societal changes that have occurred over the past 50 years. A major factor has been the unprecedented population growth and, with that, unplanned, and uncontrolled urbanization, especially in tropical developing countries. The substandard housing and the deterioration in water, sewer, and waste management systems associated with unplanned urbanization have created ideal conditions for increased
transmission of mosquito-borne diseases in tropical urban centers.
DHF is primarily a disease of children under the age of 15 years, although it may also occur in adults. It is characterized by sudden onset of fever, usually of 2 to 7 days duration, and a variety of nonspecific signs and symptoms. During the acute phase of illness it is difficult to distinguish DHF from dengue fever and other illnesses
found in tropical areas. The differential diagnosis during the acute phase of illness should include measles, rubella, influenza, typhoid, leptospirosis, malaria, viral hemmorrhagic fevers, and any other disease that may present in the acute phase as nonspecific viral syndrome. Children frequently have concurrent infections with other
viruses and bacteria causing upper respiratiory symptoms. There is no pathognomonic sign of symptom for DHF.
A definitive diagnosis of dengue infection can be made only in the laboratory and depends on isolating the virus, detecting dengue virus specific RNA sequences by nucleotide amplification test, of detecting specific antibodies in the patient's serum.
Chickungunya
This viral disease is only very briefly discussed reflecting how fast these diseases can change in incidence and virulence. This 'out of date' 2006 book states that CHIK is generally an acute, self-limited infection with no deaths reported but has a useful discussion of symptoms.
CHIKV infection is characterized by the sudden onset of fever, chills, headache, photophobia, backache, nausea, vomiting, arthralgia, and rash. Patients are quite sick although the acute illness only lasts about 3 to 5 days, with recovery usually in 5 to 7 days. The incubation period is about 2 to 4 days, and the most common complaint
is the severe arthralgia, which is seen in 70% of cases. Febrile convulsions sometimes occur in children, and hemorrhagic manifestations (petechiae, purpura, epistaxis, bleeding gums, hematemesis, and melena) also have been reported.
This is a very limited summary of the differential diagnosis of tropical diseases that can be confused with H5N1. Although some of these diseases can be strongly suggested by time of year, geographic area, and cluster of symptoms there is a lot of overlap. It would appear easy for H5N1 (both typical and atypical cases) to hide in this
background of disease. With the limited if any medical care available in some of these areas and the complexities of good laboratory diagnosis I'm sure many of these cases are not properly diagnosed as to etiologic agent yet alone being followed for genetic changes in the agents that may lead to increased virulence. We'll be able to tell if a raging H5N1 or other influenza pandemic emerges out of this but if we want to catch it early or get a better idea of the smoldering nature of the problem we have our work cut out for us.
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