Pune witness decline in Zika infections; rise of chikungunya, dengue cases

PUNE The Pune Municipal Corporation (PMC) health officials have witnessed a declining trend in the number of new Zika virus infections in the city, however, the number of dengue and chikungunya cases are on the rise as per health department data.

The city reported its first Zika virus case this year on June 20 and to date, as many as 100 cases of Zika virus infection have been reported. Of which 5 cases were reported in June, followed by 54 cases in July, 39 cases in August and 2 cases in September respectively.

However, PMC reported 34 dengue cases in July, followed by 82 cases in August and 168 cases in September respectively. Similarly, 24 chikungunya cases were reported in July, followed by 52 cases in August and 225 cases in September.

As per officials, PMC health department under the guidance and help of experts from the National Institute of Virology (NIV), Pune, National Centre for Vector Borne Diseases Control, ministry of health and family welfare and public health department in September succeeded in ending the Zika virus transmission chain in the city.

The scientist from the ICMR-NIV in July had found virus presence in the adult mosquitoes and larvae samples collected from the Erandwane and Dhanukar Colony. These two areas had a cluster of cases. Besides, out of 100 Zika-infected cases, 45 were expecting mothers, said the officials.

Dr Rajesh Dighe, assistant health officer of PMC, said, the containment measures helped to break the Zika virus transmission chain in the city.

“The entomological survey and containment activities were conducted to eliminate horizontal transmission of virus from adult mosquitoes and vertical transmission in the larvae. The breeding spots were destroyed and larva control measures with fumigation and spraying insecticides helped reduce the transmission of the Zika virus,” he said.

“Also, none of the 45 Zika-infected women have reported any complications and their anomaly scan reports are normal,” he said.

Dr Rajesh Karyakarte, head of microbiology department at B J Medical College and Sassoon General Hospital, said, that due to containment activities, the population of the infected mosquitoes have declined. Also, the vector mosquitoes have a life span depending on the environmental conditions.

“If the infected mosquitoes are not there eventually the incidents will decline. The vector for dengue, chikungunya and Zika and even the host remains the same. Such outbreaks are seasonal and reported during monsoon,” he said.

Dr Amitav Banerjee, professor emeritus, epidemiology department, DY Patil Medical College, said the presence of CHIKV or dengue may or may not have a role in the decline of Zika.

“There is some evidence that Zika and chikungunya infections may induce cross-protective immunity against dengue. However, more research is needed to confirm this and to determine if the protection is long-lasting,” he said.

Dr Banerjee, said, “The intense Zika virus transmission in Pune seems to have occurred from mid-June to mid-Sept 2024. One should note that 80% of Zika virus infections are asymptomatic. Most likely while only 100 cases of Zika were confirmed it is possible that the actual infections may be many times more and due to lack of symptoms the infected may not have sought treatment or tested.”

“The declining trend in Zika may be due to a state of herd immunity as well due to large swathes of the population having acquired natural immunity through subclinical infection. A serosurvey among the population can reveal the true picture,” he added.