With the number of deaths due to the Chandipura virus rising to 25 in Gujarat in just about five weeks, public health specialists have found no trace yet of the virus in any of the known carriers screened so far, the most common being sandflies found in the crevices of mud houses or livestock.Results from a massive screening exercise taken up after the outbreak since June 30, covering thousands of sandflies, and later extended to mosquitoes and ticks suspected to be carriers of the virus, returned negative. The question of where exactly the virus is breeding continues to haunt researchers who were clueless after similar screenings even during the 2024 outbreak, when 28 children died out of the 78 that had shown its symptoms. In the current outbreak, the Gujarat government has confirmed 39 children infected with the Chandipura virus, apart from the 25 that died.The Chandipura Vesiculovirus (CHPV) largely impacts children below 15 years old, manifesting as Acute Encephalitis Syndrome (AES) and has so far caused fatalities in Gujarat and Rajasthan.The more disquieting detail is that sandflies are endemic to eastern Gujarat, but patients infected with the CHPV, some fatally, have been found in Saurashtra as well, which is in the west.Also read | What is the Chandipura virus and who is susceptible to it?This has given rise to the preliminary conjecture that there could be more than one vector (insect) transmitting the disease to humans.Researchers from Gujarat and five national institutes currently in the state as part of the National Joint Outbreak Response Team (NJORT) have not been able to find any trace of the virus in any of the more than a thousand samples of sandflies and other vectors, collected during both the 2024 and current 2026 outbreaks in Gujarat and Rajasthan.Those confirmed as infected by CHPV in the current outbreak are distributed over 12 districts of Gujarat and 3 districts of Rajasthan, with the Patan district having the highest at 5, followed by 4 from Sabarkantha district. An animal husbandry official told The Indian Express, “There are no clusters of human cases, just single cases from every area. We are not even finding multiple cases from the same locality. So the number of carriers (vectors) will also be less, is what we assume. Usually, the more the number of victims in any vector-borne disease, the greater the chance of finding the vector.”Story continues below this adSandflies were established as vectors of CHPV in a 2018 outbreak. In the paper “Molecular Evidence of Chandipura Virus from Sergentomyia species of Sandflies in Gujarat”, researchers from ICMR-NIV stated, “In the present study, a highly zoophilic species of the sandfly Sergentomyia was found to be a potential vector of CHPV in Gujarat. This is probably the first report from India of male sandflies testing positive for CHPV in RT-PCR analysis…”The disease was first identified and catalogued in the small village of Chandipura in Nagpur, Maharashtra in 1965.A senior scientist from a national institute studying vector-borne diseases, told the paper, “We have collected several hundred samples of sandflies and are currently carrying out Reverse Transcription – Polymerase Chain Reaction (RT-PCR) to amplify and check if they were infected with Chandipura Vesiculovirus. Unfortunately, we haven’t found any positives yet. This is similar to the outbreak in 2024 when we also did not find any infected Sandflies. However, we are also looking at Aedis aegypti and Culex genus of mosquitoes to see if they have acted as vectors for CHPV but there are no positive results there so far.” Researchers have not been able to find any trace of the virus in the samples of sandflies and other vectors, collected during both the 2024 and current 2026 outbreaks in Gujarat and Rajasthan.According to a mid-level scientist who has worked on these entomological samples “After entomologists collect samples at the outbreak sites, they are sent to the laboratory where they are frozen at -20 degrees celsius. They are then crushed, the nucleic acid extracted, and is then run on RT-PCR to check whether it contains CHPV.”Story continues below this adTesting of samples from cattle in the vicinity of the human cases have also not yielded any clues as to the animal host reservoirs of the virus.Expanding screening to ticks and mitesResponding to a questionnaire sent by the Indian Express to the Union Ministry of Health and Family Welfare (MoH&FW), the PIB said in a statement, “A key focus of the investigation is to unravel the virus transmission cycle. While sandflies are the established vectors of Chandipura virus, scientists are also examining whether other arthropods – including mosquitoes, ticks and mites—may have a role in transmission. Large numbers of vector samples collected from affected areas are currently undergoing laboratory analysis. Officials have emphasised that it is premature to identify the vector responsible for the current outbreak until scientific investigations are completed.” The statement added that even in the investigations into the 2024 outbreak “no specific vector could be conclusively implicated”.The government statement added that the animal surveillance had also been expanded to determine whether the virus was circulating among domestic animals that could potentially act as reservoirs. “Blood samples from cattle, buffaloes and goats, along with milk samples, have been collected for testing. Around 70 animal blood samples have been collected so far and are being analysed for Chandipura virus and other relevant pathogens. Authorities have clarified that no conclusions can be drawn until laboratory investigations are completed”, the statement said.Expert flags surveillance shortfallsDr Sujatha Sunil, Group Leader of Vector-borne Diseases at the International Centre for Genetic Engineering and Biotechnology (ICGEB), an inter-governmental organisation in Delhi flagged that researchers could be missing the “timing of the surveillance and the depth of the surveillance during non-transmitting time”. Though not involved in the current investigation Dr Sujatha has been working on Chandipura with other researchers in Maharashtra where the disease was first identified, for several years now.Story continues below this adAlso read | Why Chandipura virus returns every monsoon and why children face the highest risk“During the 2005 Chikungunya outbreak, the virus was able to jump from its classical Aedes Aegypti (mosquito) vector to the non-classical Aedes Albopictus mosquito species on the basis of a single mutation in the virus, which enabled it to change its vector between two species of mosquitoes”, Dr Sujatha tells The Indian Express.On the need for constant and stringent entomological surveillance, especially in hotspot areas, Dr Sujatha said, “We need to be looking for all possible vectors, not just sandflies as well as animal reservoirs that maintain the virus between human outbreaks. And since it is an India-specific problem, we need proper vector surveillance especially in these hotspots that leave no stone unturned. The collection of (vector) samples too has to be denser. We cannot use dengue or malaria as examples to say we will pick up sandflies and mosquitoes in hundreds and check for the virus. You have to sample several times more, which is the depth of surveillance required in this case because of the difference in population numbers between mosquitoes and sandflies, and low CHPV infection rates. Additionally, surveillance should not be limited to outbreaks but in the time of the year starting from June till August regardless of whether there is an outbreak. That will be conducive to finding the vector.”