Scrub Typhus

Note: This is a paper I wrote on a Infectious Disease here in India. This is part of my grade and may not be so enjoyable for those not interested. Just a forewarning.

During my time here at CMC (Christian Medical College) Hospital in Vellore, India, the doctors have talked about a new sort of epidemic over the past couple years of Rickettsial infections. Over the three weeks here, I have seen 4-5 cases of Scrub Typhus in all age groups.
So what is this Scrub Typhus, was my question and may be yours.
Scrub Typhus is caused by a gram negative bacteria, Orientia tsutsugamushi. The name was recently changed from Rickettsia tsutsugamushi, for very important “microbiology” reasons, I’m sure.
How do we get it?
The bacteria’s host is chiggers, which are baby mites. The bacteria are in increased numbers in the chiggers’ salivary glands. Usually the chiggers pass the bacteria on to rodents as the secondary reservoir when the chigger/mite feasts on rodents. However, humans are exposed when bitten by an infected chigger.
The certain type of mite that carries this bacteria populate scrub vegetation, hence the name. However, they have also been found to populate sandy beaches, deserts, and rain forests. People are at risk at getting Scrub Typhus in areas of East and Southeast Asia, India, Japan, and Northern Australia and adjacent islands. These mites prefer rainy seasons and cooler weather, and thus India has seen an increased number of infections during the winter (also the rainy season).
How does a person present?
People can present with many different combinations of symptoms that may cause a rather confusing picture. They may have headache, shaking chills, lymphadenopathy, high fever usually in the 104-105 F range, apathy, anorexia, GI symptoms and conjunctival injection. Without treatment, in 5-8 days a person can start to get a maculopapular rash. The rash starts on the trunk and spreads to the extremities (centrifugal). This rash also helps narrow the differential due to the soles of the feet and palms of the hand being involved, which only occurs with a handful of diagnosis. This rash may also have a petechial look to it, due to the perivasculitis of small blood vessels that occurs causing endothelial injury – resulting in small hemorrhages under the skin or petechiae.
In this same time period of 5-8 days since the start of symptoms, the person may present with an enlarged spleen, cough, and delirium. If not treated, people can die from this infection usually from complications of the infection such as hepatitis, renal failure, shock, or pneumonitis.
The bacteria incubate for 10-12 days prior to a person’s symptoms starting, so a person may remember having been bitten by chiggers 2-3 weeks prior or may still have a bite mark present.
What does a chigger bite look like?
The bite of a chigger or mite goes through different phases as it heals. First the area of skin is red and endurated and enlarges to 8-12mm. It turns into a vesicle before rupturing. Next it becomes dark and necrotic in the center and in called an eschar. This is usually the stage the doctor will see it as and will look for an eschar during the physical exam. How do you diagnose Scrub Typhus?
The Weil-Felix test is a widely used test, due it availability, and being cheap fast; although it will not be positive till the second week of infection and it is not specific for Scrub Typhus. The test causes the antibody to the bacteria in the patient’s blood to react with strains of Proteus bacteria and agglutinate when positive. Another test, the Fluorescent Antibody test, or IFA, is the gold standard test. It identifies the antibody is present in the patients’ blood to Orientia tsutsugamushi. ELISA is another test method that has greater than 90% sensitivity and specificity.
Here at CMC, they use the Weil-Felix test first to narrow and than if positive use the IFA test. However, usually the patient has been treated and responded before this time.
SO, what is the treatment?
Doxycycline 100mg bid for 7-10 days or chloramphenicol is also effective.
Doxycycline can be given if the diagnosis is suspected due to symptoms (often done in Vellore) and the patient’s fever will reside within 36 hours if the diagnosis of Scrub Typhus is correct.
Some History…
Scrub Typhus first made history in the United States during World War II, killing more American troops than any other infectious disease in the China-Burma-India theatre.
It has also recently made the news due to its return to Maldives, which is a popular island resort off southern coast of India. Research was undertaken here due to the bizarre return of this disease. There was no recorded cases in humans on the island since the 1940’s, than in 2002 there was almost 70 people that contracted the disease and 3 people died. People thought it may be due to an influx of rats, the reservoir. So, much money was put in place to correct this problem and guests warned to protect themselves from chiggers. Also, it was seen that in Japan, another common place for the infection, numbers of humans infected would cycle through the years, at times, going 5-10 years without having one case. Maybe a similar cycling also happened in the Maldives.

Resources from
- "Rictkettsial Spotted Fever in Kerala." National Medical Journal of India. Volume 17 #1, Jan 2004.
- "Scrub Typhus." Aracelis, Fernandez. eMedicine. July 14, 2006.
- "Scrub Typhus Reemergence in Maldives." Lewis, Michael; Emergent Infectious Disease. December 2003.