This study will evaluate subjects with fever and/or rash to determine the percentage of those infected by the Zika, Chikungunya, or Dengue virus. The study will also compare the clinical signs, symptoms, and lab abnormalities related to each virus, to better specify each virus's characteristics.

The study will enroll subjects in several different cohorts including a febrile rash cohort (attempting to capture acute Zika/Chikungunya/Dengue infection), a household cohort (attempting to capture asymptomatic or minimally symptomatic subjects), and a cohort of those with Guillain Barré). Additionally, two subpopulations of the febrile rash cohort that have special follow up. This includes the pregnant population, who will be followed through delivery to determine pregnancy outcomes, and those subjects with neurologic or cognitive manifestations who will be evaluated to determine the spectrum of neurologic disease seen with these diseases.

Subjects with Guillain Barré with potential exposure to Zika virus are of special interest given the severity of disease. Subjects with Guillian Barré do not need to have a preceding illness suggestive of Zika or other viruses. As there are few subjects with Guillain Barré, subjects will be enrolled in two ways - a prospective cohort for subjects with acute Guillain Barré, and a cohort for subjects that had Guillain Barré in the last several years. Data collected systematically from these cohorts will improve the understanding of Zika/Chikungunya/Dengue virus infections.

There are many uncertainties about the number of subjects that meet this case definition. There are limits to the ability to enroll based on staffing and other resources. If there are many cases, an emphasis will be placed on enrolling pregnant subjects and adults with neurologic complications that meet the case definition, as this is the area of highest clinical need. If there are few pregnant women or subjects with neurologic problems that can be enrolled, then any adults or children meeting the criteria can be enrolled. Not all cohorts will be active at all sites, based on the type of facility and type of patients typically seen. If sufficient numbers of certain populations are enrolled (i.e. children born to women infected with Zika), the protocol may be amended to study those populations in more detail.

Febrile Rash Cohort Inclusion Criteria:

Subjects with fever and/or rash will be included if they are 1 year of age or older, and meet one of the following criteria (1 or 2):

1. Meeting the WHO/PAHO case definition, as defined as (a and b and c):

   1. One or both of the following primary signs:

      • Rash
      • Elevated body temperature (> 37.2 °C) AND

   2. One or more of the following symptoms (not explained by other medical conditions):

      • Arthralgia
      • Myalgia
      • Non-purulent conjunctivitis or conjunctival hyperemia
      • Headache
      • Malaise AND

   3. Onset of illness in the last 7 days

2. Modified case definition (a and b):

   1. Any two of the following:

      • Rash
      • Elevated body temperature (> 37.2 °C)
      • Arthralgia
      • Myalgia
      • Non-purulent conjunctivitis or conjunctival hyperemia
      • Headache
      • Malaise AND

   2. Onset of illness in the last 7 days

Household Cohort Inclusion Criteria:

1. 1 year of age and older, and
2. Either live in the same household as a subject enrolled into the febrile rash cohort OR live in the same household as a subject who is experiencing an illness similar to Zika (fever and rash as previously described), regardless if said subject is enrolled in the study.

Guillain-Barré Prospective Cohort Inclusion Criteria:

Either confirmed or suspected Guillain-Barré (areflexic flaccid paralysis) as defined either of the following:

1. Confirmed Guillain-Barré

   1. Acute onset of weakness or paralysis (from baseline to full weakness in 20 days)
   2. Weakness is symmetrical
   3. Areflexic (reflexes are 0/4)

2. Suspected Guillain-Barré

   1. Acute onset of illness
   2. Areflexic flaccid paralysis

Prior Guillain-Barré Cohort Inclusion Criteria:

1. Confirmed Guillain-Barré

   1. Acute onset of weakness or paralysis (from baseline to full weakness in 7 days)
   2. Weakness is symmetrical
   3. Areflexic (reflexes are 0/4)
   4. Diagnosis since January 2014

2. Suspected Guillain-Barré

   1. Acute onset of illness
   2. Areflexic flaccid paralysis
   3. Clinical diagnosis of Guillain-Barré
   4. Diagnosis since January 2014

The study will recruit male and female individuals of one year of age or older from southeastern Mexico and neighboring areas who exhibit signs of rash and/or fever that may be indicative Zika, Dengue, or Chikungunya. In addition, family members of these individuals will asked to be participate whether they have symptoms or not. Pregnant women will be included. Also, all individuals with a prior diagnosis of Guillain-Barré or history suggestive of Guillain-Barré will be asked to enroll.