Reproductive seasonality, sex ratio and philopatry in Argentina's common vampire bats.

Common vampire bats (Desmodus rotundus) are a key rabies vector in South America. Improved management of this species requires long-term, region-specific information. To investigate patterns of demography and dispersal, we analysed 13 642 captures of common vampire bats in Northern Argentina from the period 1969-2004. In contrast with findings from more tropical regions, we found reproductive seasonality with peak pregnancy in September and peak lactation in February. Curiously, sex ratios were consistently male-biased both in maternity roosts and at foraging sites. Males comprised 57% of 9509 adults caught at night, 57% of 1078 juveniles caught at night, 57% of 603 juveniles caught in roosts during the day, and 55% of 103 newborns and mature fetuses. Most observed roosts were in man-made structures. Movements of 1.5-54 km were most frequent in adult males, followed by young males, adult females and young females. At night, males visited maternity roosts, and non-pregnant, non-lactating females visited bachelor roosts. Males fed earlier in the night. Finally, we report new longevity records for free-ranging vampire bats: 16 and 17 years of age for a female and male, respectively. Our results are consistent with model predictions that sex-biased movements might play a key role in rabies transmission between vampire bat populations.

Observations of sylvatic rabies in Northern Argentina during outbreaks of paralytic cattle rabies transmitted by vampire bats (Desmodus rotundus).

During rabies outbreaks in cattle (paralytic rabies) in Argentina associated with the common vampire bat Desmodus rotundus, rabies was observed in marsh deer (Blastocerus dichotomus), red brocket deer (Mazama americana), capybara (Hydrochoerus hydrochaeris), savanna fox (Cerdocyon thous), and great fruit-eating bat (Artibeus lituratus). Rabies could constitute a threat to the survival of marsh deer in places where they live in small groups, and infection of both great fruit-eating bats and savanna fox represent a risk for humans; both species exhibit aggressiveness and fury when infected.

Virus isolation from saliva and salivary glands of cattle naturally infected with paralytic rabies.

The infectivity of saliva, salivary and mammary glands, muscle, lung, kidney and liver of 87 cattle infected with paralytic rabies (positive viral isolation from brains) was studied. Fifty percent dilutions of saliva and tissue samples were inoculated intracerebrally into 10- to 15-day-old mice. Viral isolation in mice was confirmed by direct rabies fluorescent-antibody test and the antigenic variant of the isolates characterized by monoclonal antibodies. Rabies virus was isolated from 4.6% of salivary glands and from 1.6% of saliva samples. The rest of the peripheral tissues were negative. Cerebral and peripheral isolates belonged to vampire-bat antigenic variants. These results indicate that cattle infected by vampire bats may be a source of infection for man. The infection risk would depend on the type of contact between rabid cattle and man.

Monoclonal antibody characterization of rabies virus strains isolated in the River Plate Basin.

In this study, 91 strains isolated in the River Plate Basin, South America, were examined from the epidemiological standpoint and with monoclonal antibodies (MAbs) to the nucleocapsid of rabies virus. Such strains reacted to MAbs in accordance with nine different patterns (antigenic variants). Rabies virus was isolated from 49 cattle, 21 dogs, 11 non-haematophagous bats, four vampire bats, two foxes, two horses, one buffalo, and one human. Five of the variants had not been described previously. It was also found that two cases of rabies in wild foxes (Cerdocyon thous) which had attacked persons in the Province of Chaco, Argentina, had been caused by variants from dog and vampire bat, while two cases in frugivorous bats (Artibeus lituratus) from Argentina and Brazil, had been infected by vampire bat variants. In addition, symptoms shown by cattle infected with strains which reacted as originating in canine vectors, differed from those observed in bovines from which the variants isolated corresponded to vampire bats.

[Ecological and epidemiologic aspects of the attacks by vampire bats and paralytic rabies in Argentina and analysis of the proposals carried out for their control]. / Aspectos ecológicos y epidemiológicos de la agresión del vampiro y de la rabia paralítica en la Argentina y análisis de las propuestas efectuadas para su control.

The authors describe the ecology of attacks by vampire bats and the epidemiology of rabies (paralytic rabies) transmitted by these bats in Argentina, based on data obtained from an epidemiological vigilance programme conducted between 1984 and 1993. It was found that rabies spread rapidly among vampire bats, causing high mortality (over 50%); subsequently, the population recovered slowly due to the low reproductive rate. This explains the features of paralytic rabies, such as high mortality among affected populations, brief duration and subsequent recurrence. Paralytic rabies occurs throughout the year without evidence of seasonal occurrence and with no relationship to rainfall. This is because vampire bats remain active within their habitat, neither hibernating nor migrating. The problem created by vampire bats depends on the ecosystem of their habitat. In the livestock ecosystem, the bats are synanthropic and their population is abundant. They feed almost exclusively on livestock and attacks on human beings are sporadic. In this ecosystem, paralytic rabies is a serious economic problem because of its frequency and readiness to spread (41 separate outbreaks were recorded in addition to an epidemic). On the contrary, in the scarcely populated livestock ecosystem, the vampire but population is much smaller; they feed on various species of animals, and attacks on human beings are more common, but paralytic rabies occurs only sporadically (one isolated outbreak). For overall control of paralytic rabies, the authors recommend reduction of the vampire bat population to a safe level, in order to break the chain of rabies transmission and diminish attacks by bats.

Transmission de rabia a roedores por la ingestion de tejidos extraidos de animales naturalmente infectados / Rabies transmission to rodents after ingestion of naturally infected tissues

Se describen 7 ensayos en los que calomys musculinus y Mus musculus alimentados con tejido extraídos de perros, bovinos y vampiros naturalmente infectados de rabia. Los tejidos no fueron sometidos a ningún tipo de manipulación previa en el laboratorio. Se administraron directamente y los roedores los consumieron en forma voluntaria. Sobre 132 animales que ingirieron los distintos tejidos infectados, 3 contrajeron rabia (2,3%) y hubo seroconversión en 22 de los 128 sobrevivientes (17,2%). La possibilidad de contraer rabia por el consumo de tejido naturalmente infectados indicaría que los roedores pueden actuar como reservorios del virus, dado que la ingestión de cadáveres es una fuente de alimentación normal para muchas especies. Además, puede constituir un puente para el pasaje del virus rábico entre los carnívoros, ya que en muchos ecosistemas son la principal presa de estos animales. Es decir, que se trata de dos situaciones en las que aumenta el riesgo de infección al hombre por modedura de roedores

Transmission de rabia a roedores por la ingestion de tejidos extraidos de animales naturalmente infectados / Rabies transmission to rodents after ingestion of naturally infected tissues

Se describen 7 ensayos en los que calomys musculinus y Mus musculus alimentados con tejido extraídos de perros, bovinos y vampiros naturalmente infectados de rabia. Los tejidos no fueron sometidos a ningún tipo de manipulación previa en el laboratorio. Se administraron directamente y los roedores los consumieron en forma voluntaria. Sobre 132 animales que ingirieron los distintos tejidos infectados, 3 contrajeron rabia (2,3%) y hubo seroconversión en 22 de los 128 sobrevivientes (17,2%). La possibilidad de contraer rabia por el consumo de tejido naturalmente infectados indicaría que los roedores pueden actuar como reservorios del virus, dado que la ingestión de cadáveres es una fuente de alimentación normal para muchas especies. Además, puede constituir un puente para el pasaje del virus rábico entre los carnívoros, ya que en muchos ecosistemas son la principal presa de estos animales. Es decir, que se trata de dos situaciones en las que aumenta el riesgo de infección al hombre por modedura de roedores (AU)

[Rabies transmission to rodents after ingestion of naturally infected tissues]. / Transmisión de rabia a roedores por la ingestión de tejidos extraídos de animales naturalmente infectados.

We describe seven trials in which Calomys musculinus and Mus Musculus were fed with naturally rabies-infected tissues extracted from vampire bats, dogs, and bovines. The tissues were not subjected to any kind of previous laboratory handling and were administered directly in Petri dishes; rodents ate them voluntarily. The only infectious tissues were bovine brains taken from outbreaks transmitted by vampire bats (Table 1). It was possible to infect the two species of tested rodents, and there was no relationship between infection and amount of virus ingested. From the total number of 132 animals that ingested different kinds of rabies-infected tissues, 3 died of rabies infection. From 128 survivors of all the exposed mice, 22 presented seroconversion to rabies. In the infected Calomys musculinus there was evident nervous symptomatology consisting in excitability, aggressiveness, paralysis and isolation of rabies virus from their salivary glands. The possibility that rodents become rabies infected by the ingestion of naturally infected tissues would indicate that they may constitute a reservoir for rabies because cadaver ingestion is a natural feeding source for many species. Furthermore they may permit the passage of rabies virus in carnivorous, animals since they are an important prey for them. The present observations indicate two situations which may increase rabies risks to man through rodent bites.

Transmisión de rabia a roedores por la ingestión de tejidos extraídos de animales naturalmente infectados. / [Rabies transmission to rodents after ingestion of naturally infected tissues]

We describe seven trials in which Calomys musculinus and Mus Musculus were fed with naturally rabies-infected tissues extracted from vampire bats, dogs, and bovines. The tissues were not subjected to any kind of previous laboratory handling and were administered directly in Petri dishes; rodents ate them voluntarily. The only infectious tissues were bovine brains taken from outbreaks transmitted by vampire bats (Table 1). It was possible to infect the two species of tested rodents, and there was no relationship between infection and amount of virus ingested. From the total number of 132 animals that ingested different kinds of rabies-infected tissues, 3 died of rabies infection. From 128 survivors of all the exposed mice, 22 presented seroconversion to rabies. In the infected Calomys musculinus there was evident nervous symptomatology consisting in excitability, aggressiveness, paralysis and isolation of rabies virus from their salivary glands. The possibility that rodents become rabies infected by the ingestion of naturally infected tissues would indicate that they may constitute a reservoir for rabies because cadaver ingestion is a natural feeding source for many species. Furthermore they may permit the passage of rabies virus in carnivorous, animals since they are an important prey for them. The present observations indicate two situations which may increase rabies risks to man through rodent bites.

Presence of rabies neutralizing antibodies in wild carnivores following an outbreak of bovine rabies.

In an outbreak of bovine rabies in Argentina, a study was made of vampire bats (Desmodus rotundus) and wild carnivores. Rabies antibody rates of high prevalence were found in the bats, foxes (Dusicyon gymnocercus) and skunks (Conepatus chinga). The outbreak was part of an extensive continuing epizootic of vampire transmitted bovine rabies which may have also involved other vectors in the area of this study. Consumption of dead and dying bats by the carnivores is the suggested means of passage of rabies virus from vampire bats to foxes and skunks. Given optimum conditions it is conceivable that some outbreaks in carnivores may begin in this way.

Observations on the epizootiology of vampire bat rabies.

Vampire bat populations were opportunely sampled before, during, and at varying intervals after outbreaks of bovine rabies. The captured bats were examined for rabies neutralizing antibody and virus. In all, sera from 1,024 vampire bats were tested for antibody, and tissues from these bats plus 83 others were tested for virus. Neutralizing antibody only rarely appeared in vampire serum samples taken before bovine rabies outbreaks, and only low percentages of samples positive for rabies antibody were obtained from bats captured during bovine outbreaks. In contrast, varying percentages of positive samples (including some high percentages) were taken from bats captured at various intervals after bovine outbreaks. Only eleven rabies virus isolations were obtained in the course of this study. In each case the virus came from a bat captured just before or during a bovine outbreak. The authors suggest that rabies virus behaves in vampire populations the way diverse infectious agents typically behave in other hosts. That is, the virus infects many individuals; some die and others survive to demonstrate their exposure through the appearance of anitbody. The disease disappears from the bat population in time and does not return until a sufficient number of susceptible bats have re-entered the population.