A creeping menace

The number of deaths on account of Scrub typhus in Indira Gandhi Medical College and Hospital has reached ten. Many states in this season are bearing witness to the worst Scrub typhus outbreak. This vector born disease which was endemic in the past and was considered to be of less importance has again shown an upsurge in recent years. The global re-emergence of Scrub typhus has dealt a deadly blow to the public health professionals and medical fraternity alike surpassing even malaria and dengue by its sheer magnitude in terms of geographical expanse, morbidity and mortality in areas endemic for both. This vector-borne disease has been known to mankind since antiquity. Scrub typhus, also known as bush typhus, is a mite-borne rickettsial zoonosis caused by the organism Orientia tsutsugamushi. It is the leading cause for treatable and yet, unidentifiable febrile illnesses in Southeast Asia.

Humans occasionally become infected after being bitten by an infected chigger (the larval stage of a mite). Both rodents and mites are the natural reservoir hosts. The chigger (larvae of trvombiculid mite) borne disease which is caused by intracellular obligate bacterium Orientia tsutsugamushi, has finally expanded its area of influence from the famous 'tsutsugamushi triangle', which covers more than 8 million square kms, from the Russian Far East in the north to Pakistan in the west, Australia in the south and Japan in the east.

The earliest published record of Scrub typhus can be traced to the 3rd century AD from the Ming Dynasty in China. It was in China in 313 AD that symptoms associated with Scrub typhus were first described in Chinese "Material Medica". During the same time, the vector of Scrub typhus was also mentioned in Chinese literature as red insects found along river banks referring probably to the chiggers of trombiculid mites. However, the description of Scrub typhus in recent times is from Japan in the year 1899. The study of Scrub typhus is indebted to the Japanese and British researchers who did pioneering work prior to World War II on characterising Scrub typhus and the epoch-making discovery of the etiological agent of Scrub typhus by Nagayo.

Scrub typhus, nevertheless, shot into prominence during the Second World War, afflicting millions in the China- Burma- India corridor of military action. The impact of Scrub typhus on the military was so enormous that commanders were forced to withdraw troops from the affected areas, changing the course of the war itself. Scrub typhus, thereafter, came to be established as a disease of significance to the military but by the end of the war, it had lost its prominence and was nearly forgotten barring its mention in the medical textbooks as a disease of historical importance.

The changing paradigms of human behaviour, coupled with globalisation, industrialisation, climate change, urbanisation, changing agricultural patterns, deforestation and expansion of humans into previously uninhabited areas has led to the resurgence of Scrub typhus and other

rickettsial diseases globally. Population explosion and increased urbanisation has changed land use and land cover including huge garbage accumulation on the land. This has provided a favourable environment for the chiggers of trombiculid mite.

Urbanisation without any attention to proper sanitation and solid waste management causes an increase in the rodent population, which are reservoirs of the infection. This also contributes to a rise in rat associated zoonoses, such as rickettsiosis. Chiggers might indicate the connection between climate change and the incidence of Scrub typhus. Chiggers are mainly located in grassy fields, gardens, parks, forests, bush and moist areas around lakes or rivers. Their distribution is influenced by humidity, temperature, and sunshine.

Now, Scrub typhus has emerged as a leading cause of public health concern in known areas of endemicity. The disease is currently estimated to impact close to a billion people globally with around a million casualties as the outcome. Today, regrettably, the world stands as a mute witness to its increasing sphere of activity and the day is not far when Scrub typhus will likely emerge as a major global vector-borne disease. Thereby, it is imperative to appreciate the necessity and urgency of efforts to control its expanses with reference to anthropogenic activities. In this context, it is pertinent to mention the quotation of Hans Zinsser, Rats Lice and History 1934 - "Typhus is not dead. It will live on for centuries and it will continue to break into the open whenever human stupidity and brutality give it a chance, as most likely they occasionally will." Man has indeed made brutal assaults on nature and transgressed into ecological niches of mites called the 'mite islands' to influence and amplify opportunities of enhanced man-vector contact.

One of the reasons postulated for the repeated outbreaks of Scrub typhus is the antigenic heterogeneity of Orientia species coupled with the fact that exposure to one strain does not confer long-lasting heterologous immunity in exposed individuals leading to repeated episodes. Increasing awareness and high index of suspicion in endemic areas has also contributed to greater reporting of outbreaks. It is astonishing that despite stupendous advances in epidemiology of Scrub typhus, we are still struggling to contain Scrub typhus and its associated morbidity and mortality.

During the months of August to November, there is a growth of secondary scrub vegetation which is the habitat of tormiculid mites. During this period, a high index of suspicion, rapid diagnosis and early onset of appropriate therapy can considerably decrease the case fatality rate. The clinical spectrum varies from mild fever to multi-organ dysfunction. It was considered as a lethal disease in the pre-antibiotic era and is militarily important, causing enormous losses during World War II and the Vietnam War. Early diagnosis and the timely use of antibiotics is quite important to counter the onset. The median untreatable mortality is 6 per cent, with a range of 0 per cent–70 per cent.

India's poor surveillance network possibly leads to huge under-reporting of cases. India's response to these acute public health emergencies is a health-care system which is chronically underfunded, unregulated and has inadequate infrastructure. Successive governments have promised health reform but at the same time funding for many health ministry programs is not adequate. Despite some gains in health care, India only spends little over 1 per cent of its gross domestic product on health, which is among the lowest in the world. In 2011, a Lancet Series called for the implementation of a universal Indian health service. The recent debate arguing for greater dependence on the private sector for health care is deeply troubling and reflects an ideological split within the government. Differences in laboratory diagnostic methods and test results have further aggravated the problem of under-reporting in India. Many laboratories in India do not have stringent quality control regulations to ensure the reliability of these tests as done in the WHO-approved laboratories under the global network of laboratories program. Thereby, all laboratories should strictly follow the CDC (Centre for Disease Control and Prevention) testing algorithm for diagnosis and reporting of Scrub typhus disease cases in India at specialised referral laboratories.

As an emerging and re-emerging disease with unspecific clinical manifestations, Scrub typhus has been neglected and often misdiagnosed. Of course, advances in diagnostics have made the detection of agents responsible for such diseases easier in recent times. At present, no Scrub typhus vaccine is available. Deratisation and mite control can stop the transmission fundamentally but it is usually impossible. Prevention strategies include avoiding unnecessary exposure and aggressive efforts to eliminate chigger breeding areas by weeding. Also, public awareness campaigns are needed with an emphasis on good sanitation (both general and personal), use of protective clothing and insect repellents to help reduce disease transmission. Healthcare workers, including medical doctors, also need to be educated so that Scrub typhus is considered as a differential for all individuals that show acute febrile illness, even when the characteristic eschar is absent. All the above measures not only have the potential to reduce disease burden but have also been found to prevent morbidity and mortality. Prospective long term studies are needed to further understand the disease dynamics so that focussed interventions can be designed and implemented for Scrub typhus surveillance and control in India. An emergent need is to improve disease surveillance in Scrub typhus risk areas that may prevent the growing threat of this infection spreading across the country. The number of incidences and their correlation to seasonal variability must be critically evaluated to support and guide health policies of the decision-makers.

Dr Debapriya Mukherjee is a former Senior Scientist, Central Pollution Control Board. Views expressed are strictly personal