Introduction
The disease condition “Scrub typhus” takes its name from the causative organism “Orientia tsutsugamushi,” which scientists find in chigger mites. These mites are vectors, and scientists find them in certain types of woody vegetation. Scrub typhus does not spread from human to human.
Physicians diagnose about a million annual cases of this condition. Cases are more prevalent in countries like Korea, Japan, Australia, Pakistan, India, and other regions between these nations. The disease has no gender or racial predilection, and it equally affects people of all ages.
However, older people have a greater tendency to suffer from a more severe form of the disease.
Etiology
As written above, the gram-negative bacteria Orientia tsutsugamushi is the causative pathogen for scrub typhus. Orientia tsutsugamushi is an intracellular pathogen with three primary strains Karp, Kato, and Gilliam. Many antigenic strains have been identified from the original three strains over the years. Scrub typhus passes to other people through the bites of chigger (infected larval form) of the trombiculid mite, particularly Leptotrombidium delicense. Trombiculid mites are small (0.2–0.4 mm) and have a four-stage life cycle: egg, larva (chigger), nymph, and adult.
Other diseases in the typhus category are the epidemic and murine typhus, which are also rickettsial diseases. There’s also a considerable similarity between the causative organism of scrub typhus and the genus Rickettsia. However, “O. tsutsugamushi” has several serotypes that can lead to various degrees of debilitating illness.
How does scrub typhus present?
Since it mimics several other infectious diseases, it has no typical presentation except that patients usually have a fever and a small painless papule. However, the physician might confuse this condition with dengue fever due to their similarity in symptoms and complete blood count results.
After the bite from a chigger mite and a ten-day incubation period, most patients usually develop symptoms such as chills, anorexia, malaise, myalgia, and headache. Also, shortly after the bite, many patients develop swelling at the infection site. This painless swelling can form an eschar in the long run.
The eschar coupled with the coinciding fever makes many people seek immediate medical attention. First, however, the physician must rule out other acute febrile illnesses by asking for a recent travel history to endemic regions.
Scrub typhus also has several systemic manifestations that affect various body regions. However, the prevalence of these manifestations varies from patient to patient. For instance, some people have involvement of the central nervous system, such as deafness, slurred speech, and nuchal rigidity. Common respiratory manifestations include cough and tachypnea. Cardiac involvement is rare.
On physical examination, the eschar is a classical sign of this condition. Approximately fifty percent of people who visit physicians with primary infection and signs of eschar confirm scrub typhus. In addition, many adults have the presence of eschar on any part of their trunk and other less common sites like the perineum.
Apart from the pathognomonic lesion that a physician sees in more than fifty percent of people, they can also perform a complete physical examination. On some occasions, this general examination might show significant lymphadenopathy.
Thus, to summarize, here are the signs and symptoms of scrub typhus:
- Fever accompanied by chills
- Headache
- Muscle and Body pain
- Presence of Eschar
- Enlarged lymph nodes
- Rashes and swelling
- Confusion, delirium, and other mental problems
Diagnosis of Scrub Typhus
The choice of diagnosis for scrub typhus is the antibody tests. Standard guidelines recommend these tests for all strains of the organism. A four-fold rise in antibody titers confirms the infection. The physician must suspect the disease if there’s just a single high titer with classical clinical features.
Other laboratory studies for this condition include complete blood counts and liver function tests. The total blood count and differentials might reveal early shortage and late excessive numbers of lymphocytes. The physician can also order a chest x-ray that might show signs of pneumonitis.
What are the risk factors?
Practices that might predispose you to this disease include:
- Travel to areas with a high prevalence of scrub typhus
- Sleeping on the grass, vegetation areas where mites might bite you
- Wearing short sleeves while working in an area with a high prevalence of scrub typhus
- Not applying EPA registered insect repellent cream on the skin in scrub typhus endemic regions.
- Not keeping your surroundings clean.
- People who work with bare hands without any protective gearing during high-risk seasons are also predisposed to this condition. Other practices that might predispose you to this disease are squatting while defecating or urinating in an area with a high prevalence of scrub typhus.
How to treat scrub typhus?
Typically, scrub typhus disease responds well to antibiotics. However, doxycycline, a tetracycline derivative, remains the drug of choice for scrub typhus. In addition, chloramphenicol and Macrolides such as Telithromycin are beneficial in this condition. Therefore, the patient must take the antibiotics for seven days, while some studies state that a five-day regimen is sufficient.
However, relapse is expected when the patient stops the drugs abruptly. In a case of typical relapse, the patient must use the drug for additional days. Recently, there have been growing concerns for resistant and severe forms of the condition.
Usually, this treatment should be on an outpatient basis. However, people with severe cases might need admission, activity, and diet management to prevent complications such as disseminated intravascular coagulopathy.
Complications
Depending on the strain and endemicity, the mortality rate of this condition could be between one and sixty percent. Early treatment prevents complications such as encephalitis and disseminated intravascular coagulopathy. Late treatment could lead to death, mostly by the second week of illness. Besides, people that are elderly or anyone that doesn’t develop eschar are at higher risk of fulminant disease.
Preventive measures
At present, there are no licensed vaccines to treat scrub typhus. However, research is still ongoing to prepare a vaccine that fights all three strains of scrub typhus. However, standard preventive measures that people staying within endemic areas should imbibe:
- Donning long-sleeved clothes.
- Staying off bushy grounds as much as possible.
- Defecating and urinating in a modern facility.
- Chemical vector control.
In addition to these measures, people exposed or planning to travel to risky areas can take prophylactic antibiotics after consulting with a physician. The standard regimen is a weekly doxycycline dose. You can take this medicine before you travel, and you must continue the regimen for six weeks after exposure. An alternative to a weekly dose of doxycycline is a dose of chloramphenicol. You can take this every five days for five weeks. However, any medication or insect repellent should only be used after consulting with a physician.
References
- “Scrub typhus”, Wikipedia, 22 October 2021, Available from:
https://en.m.wikipedia.org/wiki/Scrub_typhus. - David J Cennimo, Scrub Typhus [Medscape]. 19 April 2018, Available from:
https://emedicine.medscape.com/article/971797-clinical#b1 - Elizabeth Svoboda, Typhus [ WebMD], 18 September 2018, Available from:
https://www.webmd.com/a-to-z-guides/what-is-typhus - Centers for disease control and prevention, Scrub Typhus, ²CDC website, 13 November 2020 Available from:
https://www.cdc.gov/typhus/scrub/index.html#:~:text=Scrub%20typhus%2C%20also%20known%20as,body%20aches%2C%20and%20sometimes%20rash.
