International authorities are issuing warnings about “sloth fever”. Despite the name, it’s not contracted via contact with sloths. Rather, you should avoid contact with mosquitoes and biting midges.

So how can Aus­tralians pro­tect them­selves from sloth fever when trav­el­ling to South and Cen­tral Amer­i­ca? And how does “sloth fever” com­pare with oth­er mos­qui­to-borne dis­eases, such as Zika?

Sloth fever is caused by Oropouche virus and is for­mal­ly known as Oropouche virus dis­ease or Oropouche fever.

The virus is an orthobun­yavirus. So it’s from a dif­fer­ent fam­i­ly of virus­es to the fla­vivirus­es (which includes dengue, Japan­ese encephali­tis and Mur­ray Val­ley encephali­tis virus­es) and alphavirus­es (chikun­gun­ya, Ross Riv­er and Barmah For­est viruses).

Oropouche virus was first iden­ti­fied in 1955. It takes its name from a vil­lage in Trinidad and Toba­go, where the per­son who it was first iso­lat­ed from lived.

Symp­toms include fever, severe headache, chills, mus­cle aches, joint pain, nau­sea, vom­it­ing and a rash. This makes it dif­fi­cult to dis­tin­guish it from oth­er viral infec­tions. Around 60% of peo­ple infect­ed with the virus become ill.

There is no spe­cif­ic treat­ment and most peo­ple recov­er in less than one month.

How­ev­er, seri­ous symp­toms, includ­ing encephali­tis and menin­gi­tis (inflam­ma­tion of the brain and mem­branes sur­round­ing the brain and spinal cord) have occa­sion­al­ly been reported.

What’s happening with this latest outbreak?

In July, the Pan Amer­i­can Health Orga­ni­za­tion issued a warn­ing after two women from north­east­ern Brazil died fol­low­ing infec­tion with Oropouche virus, the first fatal­i­ties linked to this virus.

There has also been one fetal death, one mis­car­riage and four cas­es of new­borns with micro­cephaly, a con­di­tion char­ac­terised by an abnor­mal­ly small head, where infec­tion dur­ing preg­nan­cy occurred. The sit­u­a­tion is rem­i­nis­cent of the Zika out­break in 2015–16.

Oropouche had his­tor­i­cal­ly been a sig­nif­i­cant con­cern in the Amer­i­c­as. How­ev­er, the ill­ness had slipped in impor­tance fol­low­ing suc­ces­sive out­breaks of chikun­gun­ya and Zika from 2013 to 2016, and more recent­ly, dengue.

How is Oropouche virus spread?

Oropouche virus has not been well stud­ied com­pared to oth­er insect-borne pathogens. We still don’t ful­ly under­stand how the virus spreads.

The virus is pri­mar­i­ly trans­mit­ted by blood-feed­ing insects, par­tic­u­lar­ly bit­ing midges (espe­cial­ly Culi­coides paraen­sis) and mos­qui­toes (poten­tial­ly a num­ber of Aedes, Coquil­let­tidia, and Culex species).

We think the virus cir­cu­lates in forest­ed areas with non-human pri­mates, sloths and birds as the main sus­pect­ed hosts. Dur­ing urban out­breaks, humans are car­ry­ing the virus and blood-feed­ing insects then go on to infect oth­er people.

The involve­ment of bit­ing midges (blood suck­ing insects mis­tak­en­ly known as “sand­flies” in Aus­tralia) makes the trans­mis­sion cycle of Oropouche virus a lit­tle dif­fer­ent to those only spread by mos­qui­toes. The types of insects spread­ing the virus may also dif­fer between forest­ed and urban areas.

Why is Oropouche virus on the rise?

The Unit­ed States Cen­tres for Dis­ease Con­trol and Pre­ven­tion (CDC) recent­ly issued a warn­ing about ris­ing cas­es of Oropouche in the Amer­i­c­as. Cas­es are ris­ing out­side areas where it was pre­vi­ous­ly found, such as the Ama­zon basin, which has author­i­ties concerned.

More than 8,000 cas­es of dis­ease have been report­ed from coun­tries includ­ing Brazil, Bolivia, Peru, Colom­bia and Cuba.

Cas­es of trav­ellers acquir­ing infec­tion in Cuba and Brazil have been report­ed on return to Europe and North Amer­i­ca, respec­tive­ly.

While a chang­ing cli­mate, defor­esta­tion and increased move­ment of peo­ple may part­ly explain the increase and geo­graph­ic spread of the virus, some­thing more may be at play.

Oropouche virus appears to have a greater poten­tial for genom­ic reas­sort­ment. This means the evo­lu­tion of the virus may hap­pen faster than oth­er virus­es, poten­tial­ly lead­ing to more sig­nif­i­cant dis­ease or increased transmissibility.

Oth­er types of orthobun­yavirus­es have been shown to under­go genet­ic changes to result in more severe dis­ease.

Should Australia be concerned?

With­out more defin­i­tive infor­ma­tion about the role of local bit­ing midges and mos­qui­toes in Oropouche virus spread, it is dif­fi­cult to assess how great the risk is to Australia.

The risk of an infect­ed trav­eller bring­ing the virus to Aus­tralia is low. Very few cas­es of Zika were report­ed in trav­ellers from South or Cen­tral Amer­i­ca return­ing to Aus­tralia. Dengue is rarely report­ed from those trav­ellers either.

The bit­ing midges most impor­tant to the spread of the virus in the Amer­i­c­as are not present in Australia.

While the risks are low, author­i­ties need to be aware of poten­tial­ly infect­ed trav­ellers return­ing from South and Cen­tral Amer­i­ca and to have appro­pri­ate test­ing pro­to­cols to iden­ti­fy infection.

Aus­tralia has its own local orthobun­yavirus­es and while these are known to infect peo­ple, the health risks are con­sid­ered low.

What can travellers do to protect themselves?

There are no vac­cines or spe­cif­ic treat­ments avail­able for Oropouche virus.

If you’re trav­el­ling to coun­tries in South and Cen­tral Amer­i­ca, take steps to avoid mos­qui­to and bit­ing midge bites.

Mos­qui­to repel­lents con­tain­ing diethy­tolu­amide (DEET), picaridin and oil of lemon euca­lyp­tus have been shown to be effec­tive in reduc­ing mos­qui­to bites, and are expect­ed to work against bit­ing midge bites too.

Wear­ing long-sleeved shirts, long pants and cov­ered shoes will fur­ther reduce the risk.

Sleep­ing and rest­ing under insec­ti­cide-treat­ed mos­qui­to bed nets will help, but much fin­er mesh nets are required as bit­ing midges are much small­er than mosquitoes.

Although no spe­cif­ic warn­ings have been issued by Aus­tralian author­i­ties, the CDC and Euro­pean Cen­tre for Dis­ease Pre­ven­tion and Con­trol have warned that preg­nant trav­ellers should dis­cuss trav­el plans and poten­tial risks with their health-care professional.

Cameron Webb, Clin­i­cal Asso­ciate Pro­fes­sor and Prin­ci­pal Hos­pi­tal Sci­en­tist, Uni­ver­si­ty of Syd­ney and Andrew van den Hurk, Med­ical Ento­mol­o­gist, The Uni­ver­si­ty of Queensland

This arti­cle is repub­lished from The Con­ver­sa­tion under a Cre­ative Com­mons license. Read the orig­i­nal arti­cle.