Friday, March 03, 2023

CDC HAN: Increased Chikungunya Virus Activity in Paraguay and Associated Risk to Travelers

Feb 13th PAHO Alert


Just over two weeks ago, in PAHO Epidemiological Alert: Chikungunya In The Americas, we looked at reports of greatly increased CHKV activity in Southern half of South America (see updated PAHO surveillance report). 

Until 2004, Chikungunya was an obscure mosquito-borne virus that was limited to Eastern and Central Africa. That is, until a new mutation appeared that allowed it to be carried by the Aedes Albopictus `Asian tiger’ mosquito (see A Single Mutation in Chikungunya Virus Affects Vector Specificity and Epidemic Potential).

In short order it jumped to Reunion Island in the Indian Ocean, where it reportedly infected about 1/3rd of that island’s population (266,000 cases out of  pop.770,000) in a matter of a few months. From there it began its world tour, establishing itself in the Caribbean in 2013, and quickly spreading throughout Central and South America. 

Puerto Rico saw a significant Chikungunya epidemic in 2014-15 (see EID Journal High Incidence of Chikungunya Virus and Frequency of Viremic Blood Donations during Epidemic, Puerto Rico, USA, 2014)but the virus has never really established itself in the lower 48 states. 

Between continuing climate change and increasing reports of insecticide resistant mosquitoes (see Science Advances: A Widespread Super–Insecticide-Resistant Aedes aegypti Mosquito in Asia), however, status quo may not last.

Every year, hundreds (perhaps thousands) of infected travelers arrive in this country, who have the potential to `seed' the virus in local mosquitoes.  Most of the time that doesn't happen, but occasionally we've seen small outbreaks of CHKV (along with Dengue, Zika, and Malaria). 

Yesterday, in light of the recent increase in CHKV in parts of South America, the CDC issued a HAN (Health Alert Network) advisory for clinicians to be on the lookout for potential cases, particularly among those with recent travel in the region.

Due to its length, I've only posted excerpts from the CDC's announcement.  Follow the link to read it in its entirety.  I'll have a postscript when you return. 

Increased Chikungunya Virus Activity in Paraguay and Associated Risk to Travelers 

Distributed via the CDC Health Alert Network
March 2, 2023, 12:15 PM ET


The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Advisory to notify clinicians and public health authorities of an increase in the number of cases of chikungunya reported in Paraguay. Most cases have been reported in the capital district of Asunción and the neighboring Central department. As of February 24, 2023, the Ministry of Health in Paraguay reported a total of 71,478 suspect chikungunya cases in Paraguay, with 29,362 of those being probable or confirmed cases since the outbreak began in October 2022 [1]. Further spread of the outbreak in Paraguay and to surrounding countries is possible.

This Health Advisory provides information on the current status of the chikungunya outbreak in Paraguay and advises on evaluating and testing travelers returning from Paraguay with signs and symptoms consistent with chikungunya virus infection. It also highlights those at increased risk for severe disease and prevention measures to mitigate additional spread of the virus and potential importation into unaffected areas, including the United States.


Chikungunya virus is a mosquito-borne alphavirus transmitted by infected mosquitoes, primarily Aedes aegypti and Aedes Albopictus [2]. Humans are the primary reservoir during epidemics. Before 2013, outbreaks had been described in Africa, Southern Europe, Asia, and islands in the Indian and Pacific Oceans [3]. In late 2013, local transmission of chikungunya virus was first detected in Caribbean countries and then quickly spread, causing large outbreaks throughout the Americas over the next several years [4-5]. Following these large outbreaks, cases continued to be reported from countries in the Americas at lower levels [6-7].

In 2022, the number of chikungunya cases (n=273,685) reported to the Pan American Health Organization more than doubled the average annual number of cases reported during 2018-2021 [7]. Beginning in late 2022, Paraguay reported an increasing number of chikungunya cases, with more than 70,000 suspect and confirmed cases reported as of February 24, 2023 [1]. Most cases are currently being reported from the capital district of Asunción and neighboring Central department. Further increases in case counts are expected, including from other areas in Paraguay and surrounding countries (e.g., Brazil, Argentina, and Bolivia).

Most people infected with chikungunya virus become symptomatic. The incubation period is typically 3–7 days (range 1–12 days). The most common clinical findings are acute onset of fever and polyarthralgia. Joint pains are usually bilateral, symmetric, and often severe and debilitating [8-9]. Other symptoms can include headache, myalgia, arthritis, conjunctivitis, nausea, vomiting, or maculopapular rash. Clinical laboratory findings can include lymphopenia, thrombocytopenia, and elevated creatinine. Rare complications include uveitis, retinitis, myocarditis, hepatitis, nephritis, bullous skin lesions, hemorrhage, meningoencephalitis, myelitis, Guillain-Barré syndrome, and cranial nerve palsies. People at risk for more severe disease include neonates exposed intrapartum, older adults (e.g. age > 65 years), and people with underlying medical conditions (e.g., hypertension, diabetes, or cardiovascular disease) [9].

As we've discussed previously (see EID Journal: Hx of Mosquitoborne Diseases In the U.S. & Implications For The Future), the United States is not immune to imported exotic mosquito-borne diseases establishing themselves.   

In 1999, a virus previously unseen in North American birds - West Nile Virus - began to spread from New York, and in a few short years it had established itself across much of the United States.


Today, WNV is reported in every state in the lower 48, and across much of Canada.  According to a 2021 PLoS study (A 20-year historical review of West Nile virus), this virus has exacted a heavy toll on public health:

In the 20 years since West Nile virus (WNV) first emerged in the United States, more than 51,000 clinical cases have been reported, including more than 2,300 deaths, while an estimated 7 million people have been infected.

Early detection of infected travelers, and limiting their opportunities to `seed' the virus into local mosquitoes, are our best defenses against seeing a repeat performance by another vector-borne virus.