Conditions related to mosquito exposure are known as arthropod-borne infections. Flaviviral infections are the most common type worldwide. Patients will typically present with a diffuse rash and conjunctivitis. This unique combination can help narrow your differential to this exposure source. Let’s review three common flaviviral infections: dengue fever, Zika virus, and chikungunya, which are also reviewed in Table 2.
- Dengue fever – The one aspect of clinical history that should increase your suspicion for dengue fever is the amount of pain patients will be in. There’s a reason why it is also known as “breakbone” fever. It is endemic to 100 countries in total, including North America. A rash described as “islands of white in a sea of red” occurs in 50%-80% of patients and appears on the palms and soles 3-4 days after the initial infection. Given its association with vascular dysfunction, hemorrhagic bleeding may also occur in mucosal sites. Treatment is self limiting and supportive.
- Zika virus – This gained prominence in headlines around 2013 and spread to over 84 countries before reaching pandemic status in 2015. There is heightened suspicion in those returning from the Caribbean, Asia, and South America. While approximately 80% of patients are asymptomatic, those who do experience symptoms complain of conjunctivitis with an intensely pruritic, micropapular, descending erythema of the trunk and extremities with relative sparing of the palms and soles. As with dengue fever, no specific therapy exists, and management revolves around supportive care.
- Chikungunya – A trademark of this condition is a patient presenting with significant joint pains with an associated maculopapular rash of the trunk and extremities (with sparing of the face) that commonly presents 48 hours after fever develops. If the rash does involve the face, then look for a melisma-like presentation with hyperpigmentation involving the nasal central face. Chikungunya has been reported in all 5 continents, with the most infections localized to Africa and Asia. Polymerase chain reaction (PCR) testing can help diagnose; biopsies of the rash are rarely of benefit. No antiviral treatments exist.
Lyme disease is the most common vector-borne disease in the United States. Prevalent in areas inhabited by the Ixodes scapularis tick (which harbors Borrelia burgdorferi), most will associate risk with those traveling to the Connecticut region, as it was first discovered in the city of Lyme, CT, after an abnormal cluster of “juvenile rheumatoid arthritis” cases sprouted. The classic appearance is the “bull’s-eye” rash, termed erythema migrans, with erythema and central clearing only occurring with prolonged infection. It is imperative, however, to understand that in the acute phase of the infection, simple erythema without central clearing is the most common presentation. Diagnosis requires multiple factors to increase pre-test probability of infection (eg, risk, presence of engorged tick, duration of tick attachment, location). PCR testing of tissue or fluid is helpful. Treatment is essential to prevent neurological complications that can occur in up to 12% of patients.
The beach is notoriously home to helminths (aka worms). In general, look for recent travel to a tropical or subtropical environment as well as to developing countries. In the developed world, however, poor hand hygiene can still lead to transmission.
What type of worms are we talking about? Think nematodes (roundworms), with trematodes (flukes) and cestodes (tapeworms) collectively known as flatworms. See Table 1 for a brief list of those associated with skin manifestations. Infections do not always lead to clinical manifestations if the worm burden is low. In general, look for complaints of a migratory, serpiginous lesion that is palpable (can produce subcutaneous nodules) with urticaria and pruritus. These can present anywhere in the body, including the sclera, but think of the areas likely to be exposed directly to the ground (eg, soles, buttocks). This may be misdiagnosed as a fungal infection when presenting on the skin; therefore, lack of response to antifungal therapy should increase suspicion for an underlying helminthic infection. Let’s dive into the major ones to know about:
This is one of the most common infections encountered worldwide (most common in the tropics), encompassing 25% of all helminthic-related diseases. It is seen in patients whose skin has direct contact with sand surfaces (walking barefoot or wearing open-toed shoes) or soil that has been contaminated with the hookworm larvae (Ancyclostoma) of dogs, cats, and other mammals. Diagnosis is clinically based; biopsies are not advised. Look for a slowly advancing (few millimeters per day) serpiginous rash. The larvae remain localized to the dermal tissue and rarely will be found deeper. While the infection can be self limiting, treatment with oral ivermectin or albendazole or, as an alternative, topical thiabendazole is curative and can decrease the duration of symptoms.
An infection from the bite of the silent and small sandfly (one-third the size of a mosquito), leishmaniasis is commonly found in tropical countries and can lead to multisystem organ failure if not identified and treated early. There are four known forms of the infection, but we will focus on the localized cutaneous form. It is mostly associated with Leishmania braziliensis and L mexicana and presents with painless papulonodules with ulceration defined by a well-circumscribed border. Mucocutaneous involvement is common in infections acquired from South America. Biopsies are required for diagnosis and should occur at the edge of the ulcer. Treatment requires infectious disease consultation to initiate liposomal amphotericin.
American Trypanosomiasis or Chagas
Caused by Trypanosoma cruzi and found primarily in Latin America, this infection is transmitted by the “kissing bug,” which is known to bite humans primarily in the evening. After the bite, the bug then sheds feces, and the host (human) itching the area further deposits the feces into the wound. The inflammatory reaction that develops creates a furuncle known as a chagoma, which may take weeks to develop after the initial bite and may last months. Treatment involves systemic therapy with nifurtimox and benznidazole.
Scabies is caused by a mite (Sarcoptes scabiei) and typically occurs through direct contact with the skin. While it is more common in tropical countries, cases do occur consistently within the United States. Patients who have not traveled internationally may also be susceptible if they reside in a nursing home, long-term care facility, or prison. Patients will complain of intense pruritus that is worse at night with overlying erythema, pustules, papules, and even vesicles. The itching can eventually lead to hyperkeratosis in areas with the highest concentration of infection. Look primarily at the web spaces of the hands and for evidence of burrowing. The classic three-papule finding of “breakfast, lunch, and dinner” can help increase suspicion for this infection; otherwise, direct identification of mites on the skin is the best way to diagnose. Topical preparations of permethrin 5% are essential for treatment as well as thoroughly cleaning all clothing in hot water (or placing it in a closed bag for 3 days, as mites cannot survive that long without being on human skin).
What should my patient carry in their “go bag”?
As an homage to my time in the US Army, your “go bag” is another name for your go-to bag that has all essential supplies for a mission. In preparing for travel, consider advising your patient to carry antihistamines (eg, Benadryl), a mosquito net, DEET-containing insect repellant, and plenty of long-sleeved clothing. If camping, smoke can help repel mosquitos; therefore, campfires are beneficial. I recommend clipping the fingernails prior to travel to prevent significant excoriations if pruritic eruptions do develop. If a travel clinic is not available, then ensure the patient follows up with you to review their vaccines. The US Centers for Disease Control and Prevention (CDC) has a plethora of information for travelers as well as information for the healthcare provider to consider.
What should I tell my patient before they travel to prevent these conditions?
- Use DEET-related products (or any insect repellant) to mitigate the risk of acquiring an arthropod-related disease.
- Wear appropriate footwear when on beaches (and ideally walking along the shoreline).
- Avoid sustained contact with freshwater sources.
- Cover exposed skin as much as possible. If sleeping outside, utilize mosquito nets.
- See a physician prior to travel to ensure all necessary vaccinations (tetanus, rabies if exposure is likely) are up to date.
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