Week 27: Infectious Disease

This patient is exhibiting signs and symptoms of Lyme disease. Lyme disease is the most common vector-borne disease in the United States. It is endemic to New England, the mid-Atlantic states, and the upper Midwest. It is caused by the spirochete Borrelia burgdorferi and transmitted by the Ixodes dammini tick, more commonly known as the deer tick. The tick must be attached for more than 48 hours for transmission to occur. There are three stages of clinical Lyme disease. Early Lyme disease is characterized by erythema migrans, an erythematous blanching patch that may have central clearing and classically has a “bull’s eye” appearance. Hematogenous spread leads to diffuse erythema migrans, which spares the palms and soles. Acute disseminated Lyme disease occurs approximately 4 weeks after initial infection and can include meningoencephalitis, Bell’s palsy (which may be bilateral), or carditis which often manifests with variable AV block. This AV blockade may be high-grade and require temporary transcutaneous or transvenous pacing; however, it nearly universally resolves gradually with IV antibiotics and has a favorable prognosis with no need for permanent pacemaker placement. Late Lyme disease develops greater than 1 year after initial infection and includes chronic arthritis with or without chronic subtle encephalopathy. Only 50% of patients remember a tick bite; thus, diagnosis may be difficult. Erythema migrans is diagnostic; however, not all patients present with this finding. Initial screening involves ELISA testing with Western Blot and PCR to confirm the diagnosis. If the diagnosis is suspected, empiric treatment should be administered. Treatment for early Lyme disease and mild acute disseminated Lyme disease is doxycycline for 3-4 weeks. In pregnant women or children under the age of 8 years, amoxicillin should be substituted. Patients with neurologic or cardiac manifestations should be admitted and treated with IV ceftriaxone.

Rocky Mountain spotted fever (RMSF) is a tick-borne illness caused by Rickettsia rickettsii and transmitted to humans through the dog tick or Rocky Mountain wood tick. The disease is endemic in all 48 states, but most commonly occurs in the southeastern United States. After infection, the organism invades and replicates inside of vascular endothelial cells. The most common victims of RMSF are children. After a mean incubation period of 7 days, patients develop classic symptoms including fever, headache, myalgias, nausea and vomiting. Fever is usually the first symptom and may be the only symptom for up to one week. The rash is classically small red macules that are sometimes pruritic. The rash begins only on the ankles and feet and then spreads to the palms and soles. Thereafter, it moves centrally to the rest of the arms, legs and torso. After several days, the rash becomes papular and deeper red. In the early stage the rash blanches with direct palpation and enhances with warm compresses. In later stages, the rash becomes petechial and application of proximal pressure causes additional lesions to appear distally (Rumpel-Leede phenomenon). The cardiovascular system is affected with myocarditis and an impaired ejection fraction in some patients. Neurologically, the most common symptom is headache but may include seizures and an eosinophilic meningitis. Diagnosis is made through the identification of serum antibodies present 5 to 7 days after the infection begins. Treatment is with doxycycline

Babesiosis (A) is a tick-borne illnesses transmitted by the Ixodes tick in the northeastern part of the United States. The clinical symptoms are similar to malaria as the organism infects red blood cells causing fevers, myalgias headache and significant sweats. Approximately 20% of patients with babesiosis are co-infected with Lyme disease. Leptospirosis (B)is most commonly transmitted to humans through the urine of rodents. In most cases, patients have a flu-like illness with fever, myalgia and severe headache. Ten percent of patients develop severe leptospirosis with liver and renal failure.Lyme disease (C) is the most common vector-borne disease in the United States. The Ixodes ticks transmit the organism Borrelia burgdorferi. The initial manifestation of Lyme disease is the classic rash erythema migrans described as an erythematous macule with central clearing. With time patients develop fever, arthralgias, adenopathy and ultimately arthritis. Neurologically patients may develop unilateral or bilateral Bell’s palsy, aseptic meningitis and a neuritis causing similar pain symptoms to post-herpetic neuralgia.

Isospora and coccidial organisms may cause an almost cholera-like diarrheal illness. Eradication is very difficult.

Malaria and invasive amebiasis are not considered opportunistic infections.

AIDS patients have much more severe allergic manifestations to the antiparasitics.

Schistosomiasis enhances HIV pathogenesis.

The fish tapeworm is associated with pernicious anemia. Hookworm and whipworm are associated with gastrointestinal iron loss and microcytic anemia. Malaria causes hemolytic anemia.

Onchocerciasis is a major cause of blindness worldwide. Ninety-five percent of cases occur in Africa. The biting flies are found near rivers, and humans are the only host for the parasite. It occupies the skin, resulting in pruritus, edema, and later atrophy with redundant skin folds. The following are other causes of parasite-induced visual loss: Toxoplasma can cause retinal hemorrhages, Toxocara can cause inflammatory retinal granulomas, and Acanthamoeba may cause a keratitis in contact lens wearers.

This patient has clinical and radiographic evidence for pneumonia. Community-acquired pneumonia caused by Streptococcus pneumoniae is the most common cause of pneumonia in HIV-infected patients. Therefore, he should receive ceftriaxone and azithromycin. Additionally, his low CD4 count puts him at risk of opportunistic infections, such as Pneumocystis jiroveci pneumonia (PJP), formerly known as Pneumocystis carinii pneumonia (PCP). PJP is the most common opportunistic infection among AIDS patients. Signs and symptoms of PJP pneumonia include fatigue, fever, cough, and hypoxia. Chest radiographs typically show diffuse interstitial infiltrates, though negative radiographs are not unusual in PJP. Serum lactate dehydrogenase levels are often elevated. Initial therapy for PJP includes trimethoprim/sulfamethoxazole. In severe cases, corticosteroids are also given. The indications for corticosteroid use include an arterial oxygen partial pressure of < 70 mm Hg (equivalent to an oxygen saturation of <~93%) and an alveolar-arterial gradient > 35 mm Hg. Prophylaxis with oral trimethoprim-sulfamethoxazole is recommended for all HIV-positive patients with CD4 counts less than 200 cells/mm3 to prevent PJP pneumonia.

Amphotericin B (A) is used in the treatment of disseminated fungal infections, such as Aspergillus fumigatus and Cryptococcus neoformans. These infections are typically seen at a higher degree of immunosuppression. Azithromycin and ceftriaxone (B) treat most community-acquired pathogens, but do not cover opportunistic infections like PJP. Trimethoprim/sulfamethoxazole and prednisone (D) is incorrect because the patient should also receive treatment for community-acquired pneumonia.

In the United States, an estimated 1.2 million individuals are HIV positive, with approximately 50,000 people newly diagnosed each year. The clinical presentation of acute HIV infection, also known as acute retroviral syndrome, is variable both in type and severity of symptoms. The classic presentation is abrupt onset of a viral-like illness, which develops 10–14 days following exposure to the virus. Symptoms may include fever, malaise, sore throat, headache, arthralgias, anorexia, nausea, vomiting, and rash. Physical examination findings vary and may include generalized lymphadenopathy, nonexudative pharyngitis, mild hepatosplenomegaly, mucocutaneous ulcers, and oral thrush. A maculopapular rash on the thorax, face, and limbs may also be present. Due to the nonspecific and self-limited nature of symptoms, many affected individuals do not seek care and thus the true incidence of acute HIV is unknown. However, experts estimate that 60–90% of individuals who contract HIV develop an acute illness. Identification of acute HIV has tremendous public health implications, as acute infection represents the peak infectivity of the disease, characterized by high levels of viral shedding. Routine HIV tests used in most emergency departments measure anti-HIV antibodies, which are often falsely negative during acute infection. Therefore, when acute HIV is suspected, nucleic acid amplification tests, which directly measure viral RNA in the patient’s blood, should be utilized.

The tongue lesions seen in the image are characteristic for oral hairy leukoplakia (OHL). This is a disease of the lingual squamous epithelium and is thought to be caused by the Epstein-Barr virus (EBV). It is highly specific for concomitant HIV infection and rarely seen in other immunocompromised states. OHL is often confused with oral candidiasis (thrush). However, unlike the lesions of thrush, OHL cannot be scraped off the tongue.

OHL most commonly develops on the lateral portions of the tongue, not the posterior oropharynx (A). The disease is caused by the Epstein-Barr virus, unlike oral thrush, which is caused by the yeast (C) Candida albicans. The plaques are painless (D), and most patients are asymptomatic.

Aplastic crisis is defined as having a reticulocyte count of less than 1%. Patients with sickle cell disease who are infected with Parvovirus B19 are at risk for developing an aplastic crisis. Parvovirus B19 is the causative agent of Fifth disease and can lead to an aplastic crisis by causing a temporary arrest of red blood cell production. This is characterized by a sudden decrease in hemoglobin production by bone marrow resulting in severe anemia. Patients may present with pallor, lethargy, and shock. Treatment includes hemodynamic support and blood transfusion.

Labs that should be sent include type and cross, CBC, and reticulocyte count.  This is usually self-limited disease and resolves once the viral syndrome resolves.  Blood transfusions to support the patient through the anemia is the treatment along with other supportive measures.

Infectious mononucleosis is caused by the Epstein-Barr virus. While young children with the disease typically have minimal, if any, symptoms related to the infection, adolescents and young adults usually have a more pronounced course. It is uncommonly seen in adults as most are immune due to a previous exposure. Patients may have a prodrome of low-grade fever, headache, and malaise. There is pharyngeal erythema and tonsillar exudates that may appear white, gray-green, or necrotic. Palatal petechiae can also be seen, but may be present in streptococcal pharyngitis as well. Severe fatigue is common and often the symptom that persists the longest. The lymphadenopathy is usually mildly tender, symmetric and involves the posterior cervical chain. Hepatosplenomegaly can be noted on examination. A generalized maculopapular rash almost always occurs following administration of amoxicillin or ampicillin although the mechanism of this is unclear. Diagnosis is made based on history and physical and can be confirmed with a positive heterophile antibody test (monospot test). Treatment is supportive. Symptoms generally resolve in 1-3 weeks although the fatigue may persist for months. Patients should refrain from contact sports for four weeks post-infection.