Asian-West African strain of Congo fever in humans found in Gujarat

Of the 34 cases recorded in 2019 in Gujarat — a majority of it from Bhavnagar and Surendranagar, 17 died, pegging the case fatality rate at 50 per cent, which is higher than the WHO defined CFR of upto 40 per cent.

The Asian-West African reassortment variant of Crimean Congo hemorrhagic fever (CCHF) in humans was recorded for the first time in the country in a recent study of 34 cases in Gujarat reported in 2019. Human genomic sequences reported from Indian samples so far belonged to Asian lineages, as per the study.

Gujarat had seen a high case fatality rate (CFR) of the virus with half of those infected dying of it in 2019. The study has also detected viral load upto 76 days after the onset of the disease.

CCHF is caused by a tick-borne virus and is transmitted to humans either through tick bites or contact with infected animal blood or tissues during and immediately after slaughter. According to World Health Organisation (WHO) outlines, human-to-human transmission can also occur on close contact with the blood, secretions, organs or other bodily fluids of infected persons.

Of the 34 cases recorded in 2019 in Gujarat — a majority of it from Bhavnagar and Surendranagar, 17 died, pegging the case fatality rate at 50 per cent, which is higher than the WHO defined CFR of upto 40 per cent. The study published in the PLOS Neglected Tropical Diseases journal on August 30 notes that “all the fatalities happened during hospital admission within one to three days”.

The study has also found a correlation of higher viral load and higher mortality among primary cases with either history of known tick bites or through livestock contacts compared to secondary cases — those who contracted the infection on contact with infected humans or animals.

The study notes that while a majority of the CCHF virus sequences from Gujarat clustered with Asia 2 subgroup in the Asian clade (clade is the broader family, which splits into sub-groups with a common ancestral connection), and a “small subset of the sequences had proximity with Matin (Pakistan) and Iran sequences that formed a part of Asia 1 subgroup”, a particular ‘M gene segment’ clustered with the West Africa-1 clade Senegal sequences.

So far from India, the human sequences obtained from previous studies clustered with the Asian lineage. While the presence of reassortment of Asian-West African strains was reported in in tick pools in Rajasthan, the presence of the same in human samples in Gujarat “emphasise the movement of ticks through animal trade and tick bites to human spreading the infection in both the states”, the study notes.

Though the genomic variation has not been linked to any specific geographical location or increased virulence, the study notes that it requires to be studied better to understand the “importation and mixing of two different lineages” of the virus.

The study was authored by officials of the ICMR-NIV in Pune, RR Gangakhedkar of ICMR’s epidemiology division and Gujarat health department officials, including those affiliated to government medical college and Sir T Hospital in Bhavnagar, BJ Medical College, Morbi district panchayat, and animal husbandry department in Gujarat.

Citing a case where viral load remained as long as 76 days, the study sounds caution on public health. “Persistence of the CCHF viral RNA without any symptom or sign of active disease in survivors up to 76th POD (post-onset of disease) as noticed in our study has not been reported earlier. This finding of an extended persistence of CCHF viral RNA has a significant implication for public health implying that CCHF cases can remain infective and standard contact precautions needs to be taken during patient care activity,” the study notes while observing that the infective potential needs to be corroborated with more clinical samples.

In 2019 study to identify CCHF seropositivity in Gujarat, ICMR-NIV along with Gujarat health department and Dr Kamlesh Upadhyay of medicine department at BJ Medical College in Ahmedabad, screened 4,978 human serum samples from 91 villages in 33 districts during 2015, 2016 and 2017.

The study, published in BMC Infectious Diseases journal, had seen 25 samples positive, with Amreli reporting the highest seropositivity where 11 samples tested positive for antibodies of the 196 collected. The study marked Amreli as a “high-risk area” of Gujarat and also observed that “the risk for seropositivity increased sevenfold when a person was in contact or neighbor with a CCHF case”. It also noted that seropositivity in “comparatively naïve areas like Panchmahal and Devbhoomi Dwarka suggests under-diagnosed CCHF disease”.

Gujarat first reported a CCHF case in 2011 and since then, a large number of cases were reported only from the state, as the 2019 study notes. In India, CCHF cases were confirmed from 2011 to 2019 in Gujarat and in 2014, 2015 and 2019 from Rajasthan. In Gujarat, numbers were high during August, September, October and November.

There was no notification of an outbreak of the disease in 2021, as per a portal of Integrated Disease Surveillance Programme. In 2020, till October, Gujarat reported four cases of CCHF and one death. of which three were from Botad and one from Kutch.

Source: Read Full Article