Kyasanur Forest Disease and Alkhurma Hemorrhagic Fever Viruses

Kyasanur Forest Disease (KFD)

KFD (monkey fever) was first noted during die-offs of nonhuman primates, the black-faced langur ( Presbytis entellus ) and the red-faced bonnet monkey ( Macaca radiata ), and a human outbreak in the Kyasanur forest region of the Karnataka State of southwest India in 1957. Monkeys are very susceptible to severe illness and death. Upon the animal’s death, infected ticks drop to the forest floor, creating viral hotspots in which humans may become infected. KFDV resides in evergreen, semievergreen, and neighboring, moist, deciduous forests. Several outbreaks in humans and sporadic cases have led to 400–500 reported cases yearly during the past five decades. Disease was restricted to five districts in a region of the Western Ghats, Karnataka State until 2011, when it emerged in other areas of Karnataka and into Tamil Nadu and Kerala States, which run parallel to the western coast of peninsular India, as well as Goa and Maharashtra between 2012 and 2017. The disease is continuing to move into new areas of these states as well as Gujarat State and parts of West Bengal State. Serological evidence of KFDV infection is also present in the Andaman Islands. KFDV was isolated from a febrile patient in Yunnan, China, as well and was named “Nanjianyin virus.” This isolate, however, most likely represented a laboratory artifact since it is virtually identical at the nucleoside level with the 1957 reference strain from India, which is often used in other reference laboratories, including those in China.

In an outbreak of KFD in humans and monkeys in the Kerala State in 2015, 91% of the people were older than 15 years. Most of the patients belonged to two tribes, both of which depended on the forest for their livelihood. Many members of these groups engage in trench digging and fire line work or trap monkeys for game meat. The major vectors of KFDV, Haemaphysalis spinigera and Haemaphysalis turturis ticks, are abundant in the affected areas. Monkeys are infected by the bite of infected ticks, leading to enzootic die-offs. A substantial increase in numbers and proportions of infected monkeys has occurred over the course of the past few decades.

A large outbreak of KFD occurred in the Sindhudurg district of the Maharashtra State of India in 2016, with 130 human cases of laboratory confirmed disease using either PCR or IgM ELISA, in addition to an infected monkey and tick pool. Females comprised 59% of the confirmed cases, and the greatest proportion of the patients was 14–50 years old. The fatality rate among these cases was 2.3%. Almost all of the cases (93.1%) had visited Western Ghats forest, a hotspot of disease, including migrant workers in cashew nut or coconut farms and people who collect firewood, dry leaves, and grass. The former group of migrant workers is believed to have spread the virus into new locales in the Goa State. Anti-KFDV IgG antibodies were also detected among the healthy population of the region, indicative of prior KFDV infection. Seroprevalance rates of 9.7% ( n = 745) and 9.1% ( n = 165) were recorded in the affected area and two neighboring villages, respectively. A clinical to subclinical ratio of 6:1 was found in the KFD-affected areas. Not surprisingly, the Kattunayakan community, which is completely dependent on the forest for their livelihood, was the most affected during this outbreak. None of the area’s Paniyas, landless farm laborers who rarely visit the forest, were affected.

Changes in the forest ecosystem may play a large role in the spread of KFDV, as forests are converted to agricultural land, with accompanying timber extraction and road development. KFDV is found naturally in the wild in an enzootic cycle that involves ticks; small mammals, such as rodents and shrews; ground birds; and monkeys in these forested areas. Humans are dead-end hosts. Trees are being replaced by shrubs, providing suitable environments for small mammals, especially rodents, and birds. These serve as hosts for tick larvae and nymphs, which occupy the microclimate under the leaves and within the bushes. Wildlife, including nonhuman primates in the remaining forest patches, uses the new agricultural crops as a food source, bringing them into closer contact with humans. Regions containing waterlogged crops, such as rice paddies, have increased humidity, which helps to maintain a year-long tick life cycle.

Alkhurma Hemorrhagic Fever (AHF)

AHF was first detected in 1995 in western Saudi Arabia along the coast of the Red Sea. It led to the death of a 32-year-old butcher exposed to sheep surmised to having been infected with AHFV. Five other butchers were also infected in late 1995. In 2001–2003, the disease reemerged and spread to other areas of the country, including Mecca, and southward to the border of Yemen. It is also present in Djibouti and southern Egypt, bordering the Red Sea, and in Sudan. Visitors to Egypt who had contact with healthy camels brought the virus into Europe, causing a number of imported cases in Italy. A study conducted between 2012 and 2016 found a lower incidence rate in Saudi citizens than in foreigners or expatriate workers, suggesting that Saudis may be partially immune, perhaps due to a prior, asymptomatic, or mild infection. Less than 100 human AHFV infections are typically reported annually.

Massive movements of people and animals that occur during the yearly Hajj (pilgrimage) play a role in the acquisition and, perhaps, dispersal of AHFV. During this time, 2–3 million people from all over the world meet in the holy city of Mecca in western Saudi Arabia to perform Hajj, which involves the slaughter of hundreds of thousands of livestock.

Different patterns have been noted between the 2001–2003 AHFV outbreak in Mecca and disease in southern Saudi Arabia from 2003 to 2009. In the latter, the proportion of infected females was higher than that during the Mecca outbreak, disease was reported in children under the age of 10 years, infection occurred more commonly in family units, and the mortality was much lower (1.3% and 25%, respectively). Some of these differences may be due to the rural nature of life in the southern area of Saudi Arabia, where closely related families and extended family members often live together in large houses with sheep and goats kept in the backyards, where they are cared for by all family members. Milking and butchering of infected, but asymptomatic, animals are important means of acquiring disease from livestock.