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BALTIMORE – Two imported mosquito-borne illnesses continue to push into the United States, threatening to take up residence in areas with a favorable environment.
Neither dengue fever nor West Nile virus are naturally endemic to any part of the United States, Dr. Larry Davis said at the annual meeting of the American Neurological Association. But both diseases show some indications of establishing a local infective reservoir.
Dengue remains a rare disease here, with about 650 cases reported in 2013. The majority of those occurred in patients who had just returned from endemic countries. But since 2009, local transmission appears to be occurring in three hot spots: Hawaii, Texas, and south Florida, including Key West and Miami, said Dr. Davis, a professor of neurology at the University of New Mexico, Albuquerque.
Locally acquired disease first popped up during 2009-2010 in Key West, Fla. During that time, 29 residents developed clinical dengue. Many more probably carried the virus, however, since a robust immune response usually tamps down about 80% of first infections. But those asymptomatic carriers provide a potent reservoir for hungry mosquitoes, and dengue is one virus that doesn’t need an intermediate host. Instead, Dr. Davis said, any mosquito that bites an infected person passes the agent directly into the bloodstream of his next meal.
During the Key West outbreak, the Centers for Disease Control and Prevention (CDC) estimated that about 5% of those living on the small island had been infected at some point.
Last year, 53 clinical cases were identified in south Texas. About half of these were locally acquired, which is another sign that the virus may be taking up residence, Dr. Davis said. And, so far this year, four residents of Miami-Dade County, Fla. have been diagnosed with locally acquired disease. The outbreak recently prompted local health officials to issue an alert for mosquito-borne disease, and remind residents to take precautions against being bitten.
In addition to its direct transmissibility, dengue has another neat infective trick, Dr. Davis noted. There are four serotypes, each with their own unique immunogenic profile. Thus, infection with any one confers no protection against any of the others. Any vaccine, therefore, would have to protect against all four serotypes.
In fact, such a tetravalent vaccine is in clinical trials, he said. Last month, Sanofi-Pasteur reported that its candidate vaccine, tested in almost 21,000 children in Latin America and the Caribbean, reduced the risk of disease by more than 60%, and the risk of dengue-related hospitalization by 80%. The results mirror those seen in an earlier Asian trial, the drug company noted.There has been no such progress on a human vaccine against West Nile virus, Dr. Davis said. So far this year, 1,585 cases in 47 states have been reported to the CDC, with the majority occurring in California (563), Colorado (108), and Texas (207). Of these, 917 (58%) were classified as neuroinvasive disease (such as meningitis or encephalitis). Thus far, 54 patients have died; 20 of these in California alone.
The California Department of Public Health has identified 3,282 positive mosquito samples as of Oct. 27. Director Dr. Ron Chapman said in a press statement that the state has never experienced such a severe outbreak.
“The proportion of mosquitoes infected with West Nile virus is at the highest level ever detected in California,” Dr. Chapman said. “We expect to see more people become infected as this is the time of year when the risk of infection is the highest.”
Like dengue, the majority of West Nile cases are asymptomatic, Dr. Davis noted. But in the absence of a robust immune response, the virus can cross the blood-brain barrier and initiate a devastating neuroinvasive illness than can cause a flaccid paralysis, seizures, and death.
Neuroinvasive West Nile carries many clinical and diagnostic similarities to polio, he said. Like polio, the limb weakness has a sudden onset and can be accompanied by pain, although the sensory neurons aren’t apparently involved. Imaging studies show the virus attacking at the anterior horns of the spinal cord; nerve conduction studies show a motor axonopathy, but without much demyelination. Survivors have a variable course of recovery; some may regain full strength of the affected limbs, but many retain persistent weakness.
There is no vaccine against the disease, although several are in early-stage development, including a live, attenuated chimeric vaccine that did well in a phase II, placebo-controlled trial. Within 28 days of vaccination, 98% of subjects experienced seroconversion.
Dr. Davis had no relevant conflicts of interest.
On Twitter @alz_gal
BALTIMORE – Two imported mosquito-borne illnesses continue to push into the United States, threatening to take up residence in areas with a favorable environment.
Neither dengue fever nor West Nile virus are naturally endemic to any part of the United States, Dr. Larry Davis said at the annual meeting of the American Neurological Association. But both diseases show some indications of establishing a local infective reservoir.
Dengue remains a rare disease here, with about 650 cases reported in 2013. The majority of those occurred in patients who had just returned from endemic countries. But since 2009, local transmission appears to be occurring in three hot spots: Hawaii, Texas, and south Florida, including Key West and Miami, said Dr. Davis, a professor of neurology at the University of New Mexico, Albuquerque.
Locally acquired disease first popped up during 2009-2010 in Key West, Fla. During that time, 29 residents developed clinical dengue. Many more probably carried the virus, however, since a robust immune response usually tamps down about 80% of first infections. But those asymptomatic carriers provide a potent reservoir for hungry mosquitoes, and dengue is one virus that doesn’t need an intermediate host. Instead, Dr. Davis said, any mosquito that bites an infected person passes the agent directly into the bloodstream of his next meal.
During the Key West outbreak, the Centers for Disease Control and Prevention (CDC) estimated that about 5% of those living on the small island had been infected at some point.
Last year, 53 clinical cases were identified in south Texas. About half of these were locally acquired, which is another sign that the virus may be taking up residence, Dr. Davis said. And, so far this year, four residents of Miami-Dade County, Fla. have been diagnosed with locally acquired disease. The outbreak recently prompted local health officials to issue an alert for mosquito-borne disease, and remind residents to take precautions against being bitten.
In addition to its direct transmissibility, dengue has another neat infective trick, Dr. Davis noted. There are four serotypes, each with their own unique immunogenic profile. Thus, infection with any one confers no protection against any of the others. Any vaccine, therefore, would have to protect against all four serotypes.
In fact, such a tetravalent vaccine is in clinical trials, he said. Last month, Sanofi-Pasteur reported that its candidate vaccine, tested in almost 21,000 children in Latin America and the Caribbean, reduced the risk of disease by more than 60%, and the risk of dengue-related hospitalization by 80%. The results mirror those seen in an earlier Asian trial, the drug company noted.There has been no such progress on a human vaccine against West Nile virus, Dr. Davis said. So far this year, 1,585 cases in 47 states have been reported to the CDC, with the majority occurring in California (563), Colorado (108), and Texas (207). Of these, 917 (58%) were classified as neuroinvasive disease (such as meningitis or encephalitis). Thus far, 54 patients have died; 20 of these in California alone.
The California Department of Public Health has identified 3,282 positive mosquito samples as of Oct. 27. Director Dr. Ron Chapman said in a press statement that the state has never experienced such a severe outbreak.
“The proportion of mosquitoes infected with West Nile virus is at the highest level ever detected in California,” Dr. Chapman said. “We expect to see more people become infected as this is the time of year when the risk of infection is the highest.”
Like dengue, the majority of West Nile cases are asymptomatic, Dr. Davis noted. But in the absence of a robust immune response, the virus can cross the blood-brain barrier and initiate a devastating neuroinvasive illness than can cause a flaccid paralysis, seizures, and death.
Neuroinvasive West Nile carries many clinical and diagnostic similarities to polio, he said. Like polio, the limb weakness has a sudden onset and can be accompanied by pain, although the sensory neurons aren’t apparently involved. Imaging studies show the virus attacking at the anterior horns of the spinal cord; nerve conduction studies show a motor axonopathy, but without much demyelination. Survivors have a variable course of recovery; some may regain full strength of the affected limbs, but many retain persistent weakness.
There is no vaccine against the disease, although several are in early-stage development, including a live, attenuated chimeric vaccine that did well in a phase II, placebo-controlled trial. Within 28 days of vaccination, 98% of subjects experienced seroconversion.
Dr. Davis had no relevant conflicts of interest.
On Twitter @alz_gal
BALTIMORE – Two imported mosquito-borne illnesses continue to push into the United States, threatening to take up residence in areas with a favorable environment.
Neither dengue fever nor West Nile virus are naturally endemic to any part of the United States, Dr. Larry Davis said at the annual meeting of the American Neurological Association. But both diseases show some indications of establishing a local infective reservoir.
Dengue remains a rare disease here, with about 650 cases reported in 2013. The majority of those occurred in patients who had just returned from endemic countries. But since 2009, local transmission appears to be occurring in three hot spots: Hawaii, Texas, and south Florida, including Key West and Miami, said Dr. Davis, a professor of neurology at the University of New Mexico, Albuquerque.
Locally acquired disease first popped up during 2009-2010 in Key West, Fla. During that time, 29 residents developed clinical dengue. Many more probably carried the virus, however, since a robust immune response usually tamps down about 80% of first infections. But those asymptomatic carriers provide a potent reservoir for hungry mosquitoes, and dengue is one virus that doesn’t need an intermediate host. Instead, Dr. Davis said, any mosquito that bites an infected person passes the agent directly into the bloodstream of his next meal.
During the Key West outbreak, the Centers for Disease Control and Prevention (CDC) estimated that about 5% of those living on the small island had been infected at some point.
Last year, 53 clinical cases were identified in south Texas. About half of these were locally acquired, which is another sign that the virus may be taking up residence, Dr. Davis said. And, so far this year, four residents of Miami-Dade County, Fla. have been diagnosed with locally acquired disease. The outbreak recently prompted local health officials to issue an alert for mosquito-borne disease, and remind residents to take precautions against being bitten.
In addition to its direct transmissibility, dengue has another neat infective trick, Dr. Davis noted. There are four serotypes, each with their own unique immunogenic profile. Thus, infection with any one confers no protection against any of the others. Any vaccine, therefore, would have to protect against all four serotypes.
In fact, such a tetravalent vaccine is in clinical trials, he said. Last month, Sanofi-Pasteur reported that its candidate vaccine, tested in almost 21,000 children in Latin America and the Caribbean, reduced the risk of disease by more than 60%, and the risk of dengue-related hospitalization by 80%. The results mirror those seen in an earlier Asian trial, the drug company noted.There has been no such progress on a human vaccine against West Nile virus, Dr. Davis said. So far this year, 1,585 cases in 47 states have been reported to the CDC, with the majority occurring in California (563), Colorado (108), and Texas (207). Of these, 917 (58%) were classified as neuroinvasive disease (such as meningitis or encephalitis). Thus far, 54 patients have died; 20 of these in California alone.
The California Department of Public Health has identified 3,282 positive mosquito samples as of Oct. 27. Director Dr. Ron Chapman said in a press statement that the state has never experienced such a severe outbreak.
“The proportion of mosquitoes infected with West Nile virus is at the highest level ever detected in California,” Dr. Chapman said. “We expect to see more people become infected as this is the time of year when the risk of infection is the highest.”
Like dengue, the majority of West Nile cases are asymptomatic, Dr. Davis noted. But in the absence of a robust immune response, the virus can cross the blood-brain barrier and initiate a devastating neuroinvasive illness than can cause a flaccid paralysis, seizures, and death.
Neuroinvasive West Nile carries many clinical and diagnostic similarities to polio, he said. Like polio, the limb weakness has a sudden onset and can be accompanied by pain, although the sensory neurons aren’t apparently involved. Imaging studies show the virus attacking at the anterior horns of the spinal cord; nerve conduction studies show a motor axonopathy, but without much demyelination. Survivors have a variable course of recovery; some may regain full strength of the affected limbs, but many retain persistent weakness.
There is no vaccine against the disease, although several are in early-stage development, including a live, attenuated chimeric vaccine that did well in a phase II, placebo-controlled trial. Within 28 days of vaccination, 98% of subjects experienced seroconversion.
Dr. Davis had no relevant conflicts of interest.
On Twitter @alz_gal
EXPERT ANALYSIS AT ANA 2014
