Date: Sun 30 Mar 2019
Source: Tribuna do Norte [in Portuguese trans. ProMED Mod.TY, edited]
Infectious disease physicians in the state health network of the Rio Grande do Sul Federal University UFRN) did not confirm that the disease, having symptoms similar to chikungunya [virus infection], observed this past week in 140 residents of 2 neighborhoods of Tirol and Petropolis in Natal [state] is in fact chikungunya. Blood tests done on Sat 23 Mar 2019 on samples from 6 individuals detected the presence of that virus, but the specialist physicians do not discard other hypotheses. Occurrence of this number of cases in less than one month is considered an outbreak.
Investigations were done on 73 cases in order to identify whether there is a mutation of that virus or a new virus in circulation in Natal. "The fact of a confirmation of chikungunya [virus infection] in some of the cases does not close the case [outbreak]," stated Kleber Luz, an infectious disease physician at the Federal University of Rio Grande do Norte.
In a meeting of infectious disease physicians convened for studies in order to identify the virus [responsible for the cases], 4 hypotheses were presented:
- 1st that this could be an arbovirus called "Ross River" that is present in Australia,
- 2nd an arbovirus call Barmah Forest, also in Australia,
- 3rd Mayaro virus present in other states of Brazil since 2016,
- Last, it could be a modification [mutant] of chikungunya [virus] caused by the circulation of another virus [another type of chikungunya virus? - ProMED Mod.TY]
All are transmitted by the _Aedes aegypti_ mosquito [not correct. See comment below. - ProMED Mod.TY].
The profile of the ill individuals:
The majority are women with a median age of 58 years. No children were identified with the disease. The majority are residents and workers in the Tirol neighborhood, a locality in which the numbers of _Aedes aegypti_ mosquitoes increased according to the municipal surveillance team. The most frequent symptoms are pain in the joints, fever and rash.
It is the unusual nature of the symptoms that impede the diagnosis as chikungunya [virus infection], Zika [virus infection] or dengue. For example: the majority of the patients examined present with arthralgia, sores in the mouth and fever, which are common in chikungunya cases, but also have a rash which is common in Zika cases, but with strong itching; a symptom that the new patients have is itching, but not to the point of troubling them as in Zika [virus infections].
The symptoms of the new cases are less intense than the known diseases and appear more rapidly. Most of the patients feel pain in the soles of their feet on the 1st day [of illness]; when this pain happens in known chikungunya cases, generally it appears during the 2nd week.
"A patient told me, 'Doctor, when I decelerate (step on the clutch) of the car, it hurts a lot.' This pain of the soles of the feet only appears at the end of [chikungunya] disease," said Kleber.
This difference does not mean that this could be a new virus. During the meeting, the infectious disease physician Andre Prudente called attention to the "spectrum" of symptoms that arboviruses produce. "The big problems with arbovirus diseases is that the spectrum of symptoms is very wide. Some patients have intense pain, and others do not. And this can be with the same disease [virus]," he explained.
"Some symptoms seem to be a milder chikungunya," a caveat offered by infectious disease physician Kleber Luz. He accredits this to the hypothesis of a modified virus but will not discard the others [hypotheses] until the end of the investigation. "That is to say, laboratory tests, and until then, we will continue to work with all the hypotheses. I believe that it is chikungunya, but not only that."
The specialists discussed the progress of the studies.
Hypotheses raised up to now:
- A modified chikungunya or other virus is circulating or present in the people.
This hypothesis takes into consideration that the chikungunya virus could have had a modification from another [chikungunya] virus in circulation. This could explain why patients had chikungunya [virus] present in their blood but with symptoms different from the disease.
Ross River arbovirus, for its similarity of symptoms
Transmitted by _Aedes aegypti_, Ross River [virus] causes joint pains,rash, but unlike the symptoms identified in Natal, the rash appears just 10 days after illness. [In Australia, the recognized vectors for Ross River virus are _Aedes vigilax_, _Ae. camptorhynchus_, and _Culex. annulirostris_. _Aedes aegypti_ is not considered a significant vector. - ProMED Mod.TY]
Barmah Forest arbovirus is also present in Australia
Barmah Forest virus also causes similar symptoms, mainly a red rash. They are similar to those of Ross River [virus infections] but the symptoms last longer. Another similarity is that Barmah [Forest virus] is found in possums. According to some of the physicians present in the meeting, there are species of possums in Dunas Park near Tirol, a place most related to the cases. [The recognized vectors of Barmah Forest virus in Australia are: _Ochlerotatus vigilax_, _Culex annulirostris_, _Aedes (Oc.) camptorhynchus_, _Ae. normanensis_, and _Coquillettidia spp._. _Aedes notoscriptus_ is considered an additional potential vector (see ProMED-mail archive Barmah Forest virus - Australia: (TS) http://promedmail.org/post/20190309.6359062)
. _Aedes aegypti_ is not considered a significant vector of this virus. - ProMED Mod.TY]
Mayaro arbovirus, present in Brazil but never identified in Ro Grande do Norte Cases of Mayaro, an arbovirus similar to those in Natal, are related to Goiania. The symptoms are similar and [the virus occurs] near cities with forests [as is the case with Goiania and wetlands; in Natal Dunas Park) which is a common factor.
[Mayaro virus was 1st isolated by Charles Anderson and his colleagues during the 1950s from humans with febrile illnesses in Trinidad. Mayaro virus has since been identified in the Amazon and other tropical regions (Trinidad, Suriname, French Guyana, Brazil, Peru, Bolivia, and Venezuela) and more recently in Haiti. In South America, it has been shown mostly to be transmitted by _Haemogogus_ mosquitoes. However, the urban mosquito _Aedes aegypti_ has now been also shown to be an experimental vector of the virus and was recovered from this mosquito captured in Mato Grosso state.
[There follows a summary of the observations, discussion and points covered in the above text. - ProMED Mod.TY]
[Occurrence of Ross River or Barma Forest viruses in Natal state, Brazil, is very unlikely. Mayaro virus is a much more likely possibility. The laboratory tests that were done identified chikungunya virus (CHIKV), but apparently, differences in the clinical picture caused the infectious-disease physicians to doubt that diagnosis or instead postulate a variant of that virus that causes milder disease. The type of test that was done that detected the virus (or RNA?) in the blood of affected patients is not specified. There is no mention of whether mosquitoes, especially _Aedes aegypti_, were collected in the area where the cases occurred and were tested for the presence of viruses. Until further laboratory tests are completed, the only laboratory-based evidence points to CHIKV infections. ProMED would appreciate receiving additional information as it becomes available. - ProMED Mod.TY]
[Regarding unidentified febrile disease in Rio Grande do Norte, 23 of 34 samples examined suggested CHIKV infection (there is no information about if the tests performed were serological and/or biomolecular tests). On 25 Mar , it was informed by local public health authorities that there is the circulation of all DENV serotypes, ZIKAV, and CHIKV. The director of the Natal Health Surveillance Department said, "I do not consider that [the disease] is any mystery. We have 6 types of arboviruses circulating in the [Tirol] municipality: dengue types 1, 2, 3, and 4; Zika virus; and chikungunya [virus]." ([in Portuguese]).
Despite the lack of more qualified clinical, epidemiological, and laboratorial clues, it should be considered that the current circulating arboviruses are the most probable agent of this apparent cluster. - ProMED Mod.RNA]