•U.S. govt issues health alert as malaria cases in over 20 years resurface in two states
•New mosquito species found in Florida, Finland, three other countries for first time
Nigeria and the rest of the world have been put on the alert as the United States (US) is seeing some locally acquired cases of malaria – the first spread of the mosquito-transmitted disease inside the country in 20 years.
The United States Centres for Disease Control and Prevention (CDC) said its is continuing active surveillance for more cases is continuing. It, however, said the risk of catching malaria in the US remains extremely low and that all five patients – four in Florida, one in Texas – have now had treatment.
Malaria is caused by being bitten by an infected mosquito. People cannot catch it from each other. But the insects catch it from infected people – and the cycle continues.
Until now, malaria is common in large areas of Africa, Asia and Central and South America but not the US.
According to the CDC, however, Anopheles mosquitoes, found throughout many parts of the US, can transmit malaria, if they have fed on an infected person.
It said the risk is higher in areas where: the climate means insects survive during most of the year; and travellers from malaria-endemic areas are found.
Infected people can suffer fever, sweats and chills. Malaria is an emergency and must be treated quickly with drugs to kill the parasite that causes the infection. Using insect repellent and covering up can help protect against mosquito bites.
The CDC said it is working with the Florida and Texas health departments and those recently diagnosed and treated “are improving”.
US doctors are being advised to consider malaria in any person with an unexplained fever, regardless of international travel history, particularly if they have visited or live in the affected areas of Florida or Texas.
Florida has issued a mosquito-borne illness alert after cases were discovered in Sarasota County and Manatee County, warning residents to drain standing water where mosquitoes can breed and wear long-sleeved shirts and pants.
Meanwhile, scientists had, two months ago, in March 2023, reported another new mosquito species, which has made its way across the tropics into Florida, making a permanent home in at least three counties. Scientists are concerned because of the rate of new mosquitoes arriving in Florida and the potential for them to transmit mosquito-borne diseases.
According to a new study published in the Journal of Medical Entomology by faculty at the UF/IFAS Florida Medical Entomology Laboratory (UF/IFAS FMEL), a mosquito known only by its scientific name, Culex lactator, is the latest to establish in the Sunshine State.
This species was first discovered in Miami-Dade County in 2018 by UF/IFAS faculty while they hunted for other nonnative mosquitoes. Since then, thriving populations have been recorded in Miami-Dade, Collier and Lee counties. Scientists are concerned there hasn’t been enough research on the species and their potential disease risk.
Also, scientists have reported rebound of malaria in several countries. According to a study published in the April edition of The Lancet Regional Health Americas, malaria control programmes in Amazonian Peru helped reduce the incidence of the deadly parasitic disease by 78 percent. That is, until the programmes ceased to operate. Within four years of the programmes being de-funded, malaria rates where right back where they started. The rebound was driven not only by the removal of prevention programmes, but also by climate change. Average temperatures in Peru have risen a half-degree Centigrade in the last 20 years.
Indeed, nearly half of the world’s population was at risk of malaria — an acute febrile illness transmitted by mosquito bites — and approximately 619,000 people died from it in 2021, the most recent year for which the World Health Organisation (WHO) provides such statistics. Its burden falls hardest on people living in poverty-impoverished communities in Africa, where children under five accounted for about 80 per cent of all malaria deaths in 2021.
A new study integrates climate, land use, and socioeconomic data to explain and predict malaria dynamics at the village level. The approach could inform health care practitioners and make control strategies more efficient and cost-effective.
As with COVID, public health agencies around the world have struggled to predict which communities will be hit the hardest with malaria, a life-threatening disease that infected an estimated 247 million people in 2021. A new Stanford-led study done in collaboration with local scientists and health care experts in Madagascar paves the way to using easily obtainable data to accurately predict malaria outbreaks in communities. The analysis, published February 22 in PLOS Global Public Health, is the first such study to show these relationships in fine detail and could inform efforts to combat malaria more efficiently and affordably.
Meanwhile, a species of mosquito not previously recorded from Finland has been discovered in the coastal municipality of Pori. Culex modestus has become the 44th mosquito species found in Finland, and the northernmost record of the species in Europe. The previous findings closest to Finland, but further south, have been made in the Leningrad Province in Russia and in Skåne in Sweden.
The discovery was made by researcher Lorna Culverwell from the Department of Virology at the University of Helsinki. The new species was found amongst mosquito samples collected by Culverwell in summer 2022 in the coastal areas of Finland. One male specimen was identified after examining the genitalia and performing a Deoxy ribonucleic Acid (DNA) analysis.
“Only one specimen of this species was found, but I believe it to be unlikely that it would be the only one of its species in Finland,” says Culverwell.
According to Culverwell, this discovery is an important addition to the mosquitoes recorded from Finland. Up-to-date knowledge about the different mosquito species and their distributions increases our understanding of which, if any, potential pathogens (example viruses or parasites), the mosquitoes could spread now or in the future.
Culex modestus is known to spread West Nile virus, a flavivirus, in southern Europe, between birds and humans or birds and horses. In most human cases West Nile virus causes a mild infection with symptoms such as fever, headache and muscle pain. In some cases the virus may cause neurological disease. For now, West Nile virus has not been discovered in Finland.
“Finns shouldn’t be concerned about this mosquito discovery at this point. To date, no infections acquired in Finland have been discovered in humans or horses, but this finding is a reminder that we should be aware of which mosquito species are here. Knowing potential mosquito-borne diseases that these species are linked to elsewhere in the world helps us to better investigate how likely it would be for these infections to occur in the future,” says Culverwell.
Several mosquitoes in genus Culex maintain West Nile virus in bird populations, including Culex pipiens and Culex modestus. For transmission to humans to occur, usually a mosquito would first have to bite a bird carrying the virus, wait several days for the virus to enter their saliva, and then bite a human when they are infected. Sometimes the virus is inherited from female mosquitoes via their eggs.
“At present it is very unlikely for transmission of the virus to humans or horses as several species are required for a disease transmission cycle to occur. Firstly, there would need to be West Nile virus already present in the local or migratory birds in Finland. No virus has so far been reported, despite small scale screening of birds at some sites in Finland. Secondly, only one specimen of Culex modestus is so far known from one location in Finland. For transmission to occur, larger numbers of mosquitoes would be needed for the possibility of some of them to meet any infected birds, and then survive to bite any humans or horses several days afterwards,” says Culverwell.
Culverwell has collected more than 111,000 mosquito samples in Finland since 2012. According to her, it is uncertain how long Culex modestus has potentially occurred in Finland. It is also still unknown whether the area of discovery has a more established population of Culex modestus mosquitoes.
According to Culverwell, further research is now required on both bird and mosquito populations to assess both the short-term and long-term impacts of the discovery.
“A solid foundation of mosquito research in Finland is important because climate change will likely alter the number of mosquito species in the longer-term. Some may die out, but the chance of species from further south invading Finland will increase if the climate warms and winters become milder. Several species from southern Europe are able to transmit other disease-causing pathogens which are not yet found in Finland, so research should be kept up to maintain an understanding of which pathogens are found where, and whether they are a real or potential risk to human or animal health.”
The study was published online ahead of print in the scientific Journal of the European Mosquito Control Association on June 25, 2023.
